cpt_757

Having dedicated starting battery, pros and cons.

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I am considering to install a dedicated starting battery now, any input please.

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What kind of boat?  Do you race or cruise?  Do you do coastal or off-shore sailing?  How do you charge your current battery (ies)?  What battery(ies) do you currently have?  

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Yes. A dedicated start battery. Or a hand crank, heh. Such a battery can be quite small. Mine is a 51R...I think...like in a small tractor...bcuz weight is an issue for me. The charging gizmo is a bit of a pain. I now just use the battery switch. But that is a pretty depressing revelation of my memory skills.

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19 minutes ago, bugger said:

What kind of boat?  Do you race or cruise?  Do you do coastal or off-shore sailing?  How do you charge your current battery (ies)?  What battery(ies) do you currently have?  

33 ft. racer/cruiser, mainly day sailing and 2-3 days off shore sailing.  Now, other than running engine or shore power to charging batteries.

2 optima blue top AMG batteries, total about 110 amps.  Using autopilot and 5 sailing instruments mainly for day sailing.

Do not have any issue for now after 4-5 hrs sailing and starting up diesel but having a dedicated one may make worry less.

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You might be surprised 

- how small the starter battery needs to be, don't overdo it and save on weight.

- how much wiring is needed. Look for your alternator output and starter power wire possibly being shared (run another, you want your alternator output to go to the house battery), the need for a new battery switch (give yourself the ability to start your engine from the house or starter battery), you must design fuses into the additional wiring you include.

- many options on how to charge your 2nd battery.  Consider using an automatic starting relay from Blue Sea (along with their battery switch and fuses), that will cover topping off your starter battery either from alternator (connected to house battery) or shore power. When doing so, keep in mind if you use different battery chemistries they have different charging voltages.

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I've got one.

If on shorepower, charging 2 separate banks is trivial.

Engine charging, you need a way to charge the 2 banks.  There are various manual or automatic options - I chose to go automatic with this. No vested interest, I just like the product.

 

Pro Split R - Alternator 0.0V drop splitting system 1-in,  2-out 120A 12V

0.0V drop alternator split charging system - 14V at alternator = 14V at battery

  • Rated at 12V / 180A - alternator must be 180A or smaller
  • 2 output
  • Suitable for all alternators and all battery types - simple B+ plug and play
  • IP66 fully waterproof

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Other than a little extra weight I can't think of a very good reason to not have a separate start battery. Having 2 separate battery banks is a nice insurance policy if one battery bank goes dead. 

Lots of good products available to make the wiring and isolating circuit work but I personally like the one Blue Sea makes.  I've installed it on a couple of my past boats and it's fantastic. Once it's installed you never have to touch it again.  Leave it on and both batteries always get charged but are also always isolated when drawing power from the batteries.  If one battery bank runs dead you can combine them to get the engine started or whatever else you need.  Plenty of other options out there that probably do the same thing such as the one Raz'r mentioned.  I just happen to have experience and really like the blue sea version.

https://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A

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So, this blue sea system can separate an engine battery and my 2 house bank batteries, to preventing drains from an engine battery but still be able to charging both an engine battery and house bank batteries.

how about installation?

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19 minutes ago, cpt_757 said:

So, this blue sea system can separate an engine battery and my 2 house bank batteries, to preventing drains from an engine battery but still be able to charging both an engine battery and house bank batteries.

how about installation?

Yes, exactly.  Leave the switch at the "on" position and that's it, never have to touch it or think about it again.   Both banks always get charged but engine bank only gets used when starting the engine and the house bank is only used for everything else.  There's a "combine" position to use for example if your start battery is dead so you can combine both the house and start bank and get the engine started.  Vice versa if the house bank is dead and you have one more pina colada to make with the DC blender you can combine both banks and get that last blended drink thoroughly blended with the start battery.  Not too hard to install if you're a reasonably competent DIY'er and have just a basic understanding of electrical circuits.  Certainly don't need any advanced skills or knowledge, just a good general understanding of how electrical circuits work.

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I need to get an automatic dual charger box too. Manual switching is just too unreliable because of the weak link: me. One would think flipping a switch after 30 minutes would be easy to remember.

However, I once had a West Marine dual charge box. It once went bang! and leaked all its smoke out when the battery was dead while hitting the starter. Apparently it forgot to open its relays and tried to pass the starting current from the house bank. Looks like the Pro Split R (above) might be the same idea. Maybe it works better. Then I had a fancy-schmancy electronic gizmo (Echo Charge?) that simply died a too-soon natural death like all fragile marine electronic gizmos with tiny wires and blinky lights. Been on the memory system ever since. Hasn't yet failed completely, but not without coming close to disaster. 

From your boat use description I would think you need a dedicated start battery.

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Thank you so much,

I would go this Blue sea system rather than have an Echo charge which was recommended by one of the electric place who makes one.

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In most all applications, a separate start battery is not a good choice when weighing the costs and benefits. Instead, a simple low-voltage cutout solution that shuts off the house loads at, say, 11.5V, is a far simpler and statistically more reliable solution. No extra battery, no extra cabling, no dual charging dilemma, no dual monitoring. Instead, invest those dollars in what you want, which is a larger house bank.

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8 minutes ago, Moonduster said:

In most all applications, a separate start battery is not a good choice when weighing the costs and benefits. Instead, a simple low-voltage cutout solution that shuts off the house loads at, say, 11.5V, is a far simpler and statistically more reliable solution. No extra battery, no extra cabling, no dual charging dilemma, no dual monitoring. Instead, invest those dollars in what you want, which is a larger house bank.

You have a point, but...

$150 is a cost?

12 kilos?

Don't need a monitor on the dedicated start battery.

Shut off the bilge pumps at 11.5V?

Not so sure a 11.5V resting house bank will reliably start some engines.

Statistically reliable means what?

Can argue that a large house bank that is not allowed below 11.5V is a huge waste of money and weight budgets.

Waiting for the solar panels to charge the batteries for a start is not a happy fallback position.

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It's not $150. The dual charging solution is probably 3x that, so all up with switches and cabling, closer to $1000.

No monitoring is a choice, but if you don't know the state of your emergency battery, then are you really prepared for an emergency? This is exactly the slippery slope of foolish economies and lousy design decisions. Hell, if you choose to add a battery in case your battery goes dead - when do you stop?

Yes, shut off the bilge pumps at 11.5V. Again, this kind of thinking is pretty suspect. It's far better to shut off the bilge pumps when the boat is unattended and simply have a loud high water alarm 100% of the time.

This isn't a resting house battery. This is a house battery that's in use and has fallen below 11.5V. That happened because someone is on board using the boat. The low voltage alarm kicks in and they start the engine just as they would with a separate start battery.

Statistically reliability is about endlessly adding complexity in a effort to improve reliability but actually reducing reliability due to the increased complexity and associated statistical increase in failure modes and, therefore, failures.

If you're hung up on 11.5V, then choose 11V. Nonetheless, you'll get more total AH for your house by increase the house battery size and maintaining a small reserve within it for starting than you will be adding a start battery.

There's no need to wait for solar. The house cuts out and you start the diesel.

 

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So lemme get this straight you already have 2 batteries and want a 3rd?   Well i have done weekend trips with 2 group 24s and no issues.  You probably have a “1/2/all” switch now.  If you dont get one.  Simply start with battery 1.  Then switch to battery 2 for everything else.  Then u will never have a problem starting.  You can always start with battery 1 and switch to battery 2 to charge it if its low.  If you are at a slip AC will charge both batteries.  Putting it on “all” will allow you to combine both batteries to charge.  It will charge both batteries from the alternator but it will stop charging both batteries when either show a full charge. So if one is more depleted that one wont fully charge unless you switch to that battery.  Im not seeing the need for a third battery. I would use the boat the way it is.  If your house battery goes dead all the time then yes get a third but you will probably find that 2 batteries are just fine for those uses.  

 

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The bluesea acr is a simple and genius bit of kit.

If you want something even easier then consider a lithium powered jump starter like the NOCO Boost. They're available on amazon for ~100.

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Definitely agree with Longhorn that if you've got a hard-on for a start battery then a low-cost, long-life booster pack is the best way to go.

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6 hours ago, longhorn said:

The bluesea acr is a simple and genius bit of kit.

If you want something even easier then consider a lithium powered jump starter like the NOCO Boost. They're available on amazon for ~100.

Thinking about replacing my old school “1/2/all” switch with one.  Although it will just do automatically what i do manually.  I read that in order to charge 2 batteries at the same time it requires some other hardware? Charging relay?   Maybe i read that wrong.  

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31 minutes ago, cuajota said:

Thinking about replacing my old school “1/2/all” switch with one.  Although it will just do automatically what i do manually.  I read that in order to charge 2 batteries at the same time it requires some other hardware? Charging relay?   Maybe i read that wrong.  

Your description isn't very clear, as it stands now you need to select Both to charge both batteries. If you change the setup and get rid of the combiner switch then you will need another way of combining them, i.e. relay or diode. 

Moonduster is spot on though, the last two boats I went to the trouble of a dedicated engine start battery, extra wiring, extra fuses, the relay, its just a needless fuck about. Save the weight or put it to use as more battery capacity. Loud low voltage alarm and you're set. 
And if you're worried keep a mini car jump starter pack onboard. 
 

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Simpler the better. I'm with Moonduster also. Here is my emergency backup. It's lithium-ion so less safe than LiFePO4 though. If you really want LiFePO4 they also sell the Crankenstein, but the price was hard for me to swallow.

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I have a separate engine starting battery. I suppose its applicability depends on one's sailing style. It is not complicated. It is a smallish battery. Cabled to an on/off switch and then to the engine just like in my tractor. Three little short battery cables. Being a starting type battery is works great and cost next to nothing. Two more little cables lead over to the house bank battery switch area. I know how many sailors make everything complicated. It doesn't need to be so. Start battery monitoring  in this setup is with the Voltage Gauge and Charge Warning lamp on the engine panel. That is free. What could be simpler? Plus I don't use the crazy oversized paranoid sailor cables. That is just a silly waste. It all works great. Although occasionally I forget to put the house battery switch on BOTH while motoring and I suppose after a many many hours of motoring the instrument panel draw would kill the starting battery as the alternator leads to the house bank. And occasionally I forget to put the switch back to isolated after motoring. That is the worse error as the start battery gets run down with the house bank. 

When I had the two (kinda pricey and failure prone) combiners they were simply connected across the battery switch. Simple. Lightweight. Cheap. No 'statistical reliability' conundrum. No additional $ booster battery. And I leave my bilge pumps on when away...shocking.

Yeah, I guess I'm nuts. Sorry to interrupt.

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If you do forego the separate starting battery in favor of a small emergency jumpstart pack, there are a couple things to keep in mind.

First, don't buy an "emergency charger", which is designed just to partially recharge a flat car battery enough to turn over the engine. What you want is a true jump starter that can turn the engine over all by itself even if there is no battery. Those emergency chargers can't get enough juice into a big, flat house bank to make a difference. 

Second, you still want a 1/2/both make-before-break switch wired the same as you'd use for a separate start battery but instead of leading to a start battery, it will lead to a positive power post that you can clamp the jump starter connector to. Make sure the post is close to a good ground (ideally another post wired to the ground bus), as those jump starter cables are pretty short. Just set the switch to 1 for normal use and 2 for emergency jump starting. After starting, switch back to 1 to have the alternator start charging the house bank. 

Works great, but if you're starting from scratch you'll need about $100 in infrastructure. If you already have a start battery and want to get rid of it, it's really easy as you already have the switch and all the associated wiring. Just terminate the start battery cables on two posts and you're good to go.

 

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5 hours ago, MiddayGun said:

Your description isn't very clear, as it stands now you need to select Both to charge both batteries. If you change the setup and get rid of the combiner switch then you will need another way of combining them, i.e. relay or diode. 

Moonduster is spot on though, the last two boats I went to the trouble of a dedicated engine start battery, extra wiring, extra fuses, the relay, its just a needless fuck about. Save the weight or put it to use as more battery capacity. Loud low voltage alarm and you're set. 
And if you're worried keep a mini car jump starter pack onboard. 
 

I was talking about the BlueSea Battery switch that just has on/off/combine instead of my current switch which is 1/2/all/off.  The BlueSea switch is wires one battery to the starter automatically and the other for the house battery so you just turn it on and it uses the appropriate battery for starting and the other for house.  If you need to combine both you can.  The way I have it now is I have to manually select which battery to start and then which is house then it will charge whichever battery is selected, or both but the alternator will read the charge of the strongest battery and stop charging BOTH when the strongest battery is full so one battery MIGHT now ever get a full charge.  I did this inadvertently and thought something was wrong with my wiring.  Always used ALL and thought Bothe batteries were charging but battery 2 never got a charge because battery 1was always full.  Thats when I was at a mooring so no shore power.  Shore power charges both fully.  

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14 minutes ago, cuajota said:

I was talking about the BlueSea Battery switch that just has on/off/combine instead of my current switch which is 1/2/all/off.  The BlueSea switch is wires one battery to the starter automatically and the other for the house battery so you just turn it on and it uses the appropriate battery for starting and the other for house.  If you need to combine both you can.  The way I have it now is I have to manually select which battery to start and then which is house then it will charge whichever battery is selected, or both but the alternator will read the charge of the strongest battery and stop charging BOTH when the strongest battery is full so one battery MIGHT now ever get a full charge.  I did this inadvertently and thought something was wrong with my wiring.  Always used ALL and thought Bothe batteries were charging but battery 2 never got a charge because battery 1was always full.  Thats when I was at a mooring so no shore power.  Shore power charges both fully.  

Do you have a multi stage 'smart' regulator on your alternator?

Because if you don't the alternator tries to achieve 14.0 -- 14.4 volts regardless of if either battery is full or not, so if you have the switch set to both its still putting out enough voltage to charge  the other battery even if one of them is full. 

 

 

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9 hours ago, cuajota said:

Thinking about replacing my old school “1/2/all” switch with one.  Although it will just do automatically what i do manually.  I read that in order to charge 2 batteries at the same time it requires some other hardware? Charging relay?   Maybe i read that wrong.  

 I think what you're looking for is the Blue Sea add a battery kit.  It comes with the switch and the relay.  Just the switch alone won't do what you want, you'll need the relay which comes with this kit. https://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A

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I'm a fan of starter batteries, and the blue sea add a battery kits.

Dual 12v house batteries on small boats.  Gist is that if you lose a cell in a single 4d or 8d 12v battery you are dead in the water without the voltage potential to do anything about it. 

If you have two 12v in parallel and you lose one cell, you still have the voltage potential to start the engine by disconnecting the bad battery from the house bank.  If you've got oversized cable ends on a screw post battery, you can be mean to the starter and rewire for series if you just have a low charge voltage, sometimes you can get a clicking relay to make with a screwdriver or knife blade to the solenoid, and once started pull the cable.  Gist is wire it as a single, and add the jumper to the other battery.  Rather than taking from the ends of the bank, temporarily move it to one battery with the helper giving to the ground.  Once you've got one battery up to charge, shut her down and reconnect the house as it should be.  A single 12v battery as house/start doesn't have the potential to self-help, if either a bad cell, or a low voltage charge. 

A lightening strike may not get your starting battery if you get hit, and the switch has an air gap.  I'm a fan of having a spare VHF, with an emergency antenna coiled up in a pelican case, in light of a lightening strike.  Have had a few commercial fishing friends have everything fried on board, and the few that carry spares have had a lot less rough go of getting back running.  I'm a fan of seeing a 12v optima or gel cell by or in the nav station that isn't in use or connected, but kept charged just for that reason, preferably up out of the bilge well above the waterline.  Friend had a trawler lose power, and grounded out on a shoal in a squall at the bottom of each trough and had the masthead lights wiped off.  Said that when the cabin house windows stove in, he was glad  to have a battery around to get on the vhf being otherwise dead ship.     

Big difference between "dead ship" and having spent the time to put yourself in the path of getting lucky to jury rig things back alive.  No big deal at all if you've got an around the can racer, or buddy boat port to port...  but doing near shore hops I like to see the hundred bucks every 5 years stored as insurance as a seldom used gel cell.

Last failure method I've had is having an terminal on a 1/2/both switch go bad.  If you've got low voltage alarms, and battery monitoring you can be aware of it as it happens. 

If you've got a simple boat with a single volt meter that lights up off the alt terminal, then you can be unaware that you've got a stone dead battery either start or house, because you aren't using the stone dead battery.  If the battery switch feeds both the main panel, and the volt meter.  Turn to both, and you've got what amounts to a dead short between the battery that has a charge and the stone dead one... so in the time it takes to debug why the engine still won't start on both, you've got the charge being equalized between the good battery and the flat one.  The Blue Sea charging relay can help prevent that...  In that I'm not entirely sure that my burned out 1/2/both switch didn't burn up while figuring out what was going on as I lost #2 contact on a switch and could start the engine with it still on both, once the switch contact burned up. The ACR relay separates things, and a separate battery switch to involve the emergency starting battery allows the failure method not to include rapidly discharging your get out of jail card...   

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On 6/7/2019 at 9:31 PM, Moonduster said:

It's not $150. The dual charging solution is probably 3x that, so all up with switches and cabling, closer to $1000..

It's really not that complicated and especially not that expensive. Basically all sailboats are required to have a separate starting battery around here. Also Offshore Special Regulations require a separate starting battery for OSR 3 and above. I don't recall seeing any new build without a starting battery when it has a diesel engine.

Starting battery is basically always full, since it is only used for starting,  which doesn't consume much. Charging system doesn't need to be that complicated. If the engine is run a few hours every month or two, there isn't much need for a shore power charging the starting battery. However almost all shore power chargers have two or three separate outputs anyway.

Some way charging the starting battery from the alternator is needed. The simplest option are to use 1-2-both main switch or putting a single diode from domestic battery plus to starting battery plus. Also a relay could be used. These simple systems cost only 50-60 Ah battery (50-100 €/$) + main switch (50 €/$) + diode or relay (if 1-2-both is not used 20 $/€). With some cabling maybe 200 $/€, if DIY.

A bit more expensive way is to have a battery separator. Diode based cost less than 100 €/$ and solid state ones maybe 150 €/$. Still well under 400 $/€.

There is not much point monitoring the starting battery with more than just a voltage meter. Many boats have that as standard in their switch panel and a simple LCD voltage display doesn't cost much.

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You propose two different plans. One is to not charge the start battery, which begs the question of why should it be installed as it decreases rather than increases reliability. The second suggests using a switch, a solenoid or a diode isolator, neither of which are capable of correctly charging two different batteries of either the same or different technologies that are of different capacities and different states of charge. Both these schemes are ill advised.

Few boats do Cat 3 or above races. Most of those that do Cat 2 and above have lithium batteries that should never be connected to switches or solenoids that combine them with other batteries at different states of charge as the currents that flow can be very, very high - this is a serious safety issue.

The OSR says there must be a "dedicated starter battery", however, it does not say that's the only battery that can be used for starting. The most cost effective way to be OSR compliant is to carry a booster pack and have a mechanism for isolating the starter. It is also often the lightest way to be OSR compliant.

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34 minutes ago, Moonduster said:

You propose two different plans. One is to not charge the start battery, which begs the question of why should it be installed. The second suggests using a switch, a solenoid or a diode isolator, neither of which are capable of correctly charging two different batteries of either the same or different technologies that are of different capacities and different states of charge. Both these schemes are, frankly, dumb.

That is not true at all. I suggested many different options, all of which are known to work fine in thousands of boats around here. All of them included charging from alternator. For that 1-2-Both option is the worse, since it needs user action to get charged and to separate the batteries (connect to Both when engine is running, choose 1 or 2 when not).

Typically alternators charge at 14-14.8 V depending on temperature, alternator and possible sense wire connection. This is good for rapid charging of domestic battery. Starting battery is always full and doesn't need that high voltage. It is charged enough even through a diode from domestic battery. If that is a high current Schottky diode, there is only 0.3-0.4 V voltage drop. Even charging at 13.2-13.5 V is enough to fully charge a lead acid battery, but it just takes longer. It will be rapid up to 60-70% SOC and then quite slow.

All lead acid batteries are charged at the same voltage, when using an alternator. It doesn't matter, if it's AGM, GEL, sealed, open etc. All are fine with 14-14.8 V. The actual voltage is always a compromise between fast charging and battery life.

In my boats I have had a system that connects batteries together with a relay while engine is charging and a system with diode based battery isolator. They both have worked excellently and my current batteries are from 2010 or older (from previous owner) and they are not expensive. Still running fine.

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That depends very much on one's sailing area. Here at the Baltic Sea we don't have a single Cat 2 or above race, but most offshore races are Cat 3. Everybody racing more than just evening beer can races, will race Cat 3 races.

Everybody has a separate starting battery, even the ones who never race. Some boats are starting to have LiFePO4 batteries, but that's a very small minority.

I just raced a 160 M DH race with my friends boat. It has LiFePO4 batteries. I was quite disappointed with their performance. We had to run the engine 2 hours to get the batteries from 40% to 80% SOC. I can do the same with my cheap lead acid.

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maybe on your planet.

No, on your planet, too. Remember, the comment was in the context of the OSR requirements for separate starter batteries and my comment was that this affects nearly no boats. Few boats race, so by definition, few boats do Cat 3 or above races.

That is not true at all. I suggested many different options

No, you listed two - mechanical or electrical operated battery combining switches and diode isolation. You go on to state that these work perfectly in 1000s of installations and I'd counter that most have no idea whether they work or not, which is exactly the problem with the extra-jiz-that's-rarely-if-ever-used approach.

It has LiFePO4 batteries. I was quite disappointed with their performance

This is precious - you were disappointed with the batteries whereas it looks as if you should be questioning the charging solution, which is entirely separate from the batteries. This could be a regulator, alternator or wiring problem - or it might be a cell problem - it certainly has nothing to do with the capabilities of the battery chemistry.

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I just did this on my Columbia 32. We do enough long distance racing that we were in danger of running down the single Group 27 AGM on an overnight race. Plus, we had to turn off all the electronics to start the engine or risk a spike or a drop that reset all of the electronics. I decided to go with the Blue Sea "Add a Battery" system, which has a single battery switch and an ACR. The start battery is a group 24, the engine is a 1gm10, the alternator is a powermax 85 amp with a balmar 614 regulator.

I ended up not putting in the battery switch this year because of time constraints, so what have is a 75 amp breaker on each battery. The ACR left side has the start battery and the starter fused through a 100 amp ANL and grounded directly to the ground post on the engine, the right side is also fused through a 100 amp ANL (Blue sea recommendation) and has the alternator and the house bank. Next year, when I have more time, I'll add the battery switch itself.

This system has been essentially flawless. The house and start are fully separated when starting the engine and combine as expected when the alternator kicks in above 13.1 (I think, from memory) volts. They uncombine as expected when the engine is shut off as well. I had to figure out which wire on the 1gm10 harness was for the key switch which provides added security during starting, but it's all good now.

The only issue is the same issue I've always had, which is driving an 85 amp alternator on a small engine. I have the belt program set to 4, and I have the small motor switch installed, and I use premium NAPA belts to minimize slippage during bulk charging and 99% of the time it works fine. The plus is that if the belt breaks, I just can't charge but the water pump still runs.

There are a bunch of other solutions out there of course, but this one was relatively inexpensive, works as advertised, and was easy to self-install, as long as you have a good battery terminal crimper. Adding the actual battery switch next year will just make it one step easier (only one switch instead of two breakers).

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The problem with relay-based charging solutions is that when the house is quite low and the engine is started, the start battery tends to discharge into the house, leaving both the start and house low on charge. Start the engine for a short period of time when the house is low and you could easily wind up with two relatively flat batteries. I have seen several installations where the engine could not be started for exactly this reason.

The usual solution is to raise the house voltage at which you choose to charge, in which case there was no reason to have added a start battery.

Another solution is to add a diode to prevent the start from charging the house. One really needs to add two diodes to ensure the batteries see the same voltages.

In addition, the current flow from start to house can quite large - large enough to blow that 100A fuse you use. This gets worse if the start battery is a super capacitor or LFP cell, like a Super-B as these cells have little internal resistance and can source very, very large currents. Generally speaking, it's difficult to size that fuse and, by extension, the cables between the batteries.

Finally, the combiner strategy is one that says the start battery is not fully charged until the house is fully charged, and that the start sits in absorption far, far longer than necessary because the larger house dictates the absorption cycle's timing. So the start battery is subject to considerable abuse - often left undercharged and then significantly overcharged. Not a great way to treat one's "emergency" battery.

The weekend sailor sees none of these problems, but that does not mean they don't exist. On an extended cruise, they conspire to provide a false sense of security in one's starting solution. In no case do they provide a superior solution to using a simple low-voltage cut out for the house or carrying a booster pack for emergency starting.

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There is no meaningfull current from starting battery to house battery when the engine is running no matter how flat the house battery is. The voltage would need to be well below 12.5 V for more than 1 A to flow out from the fully charged starting battery longer tha a few minutes. Even at 25% SOC house battery will have about 12 V open voltage and only a few A is needed to lift it to 12.5. 11.5 V is basically 0% SOC and even then not much current is needed to get the voltage to 12.5 V.

When engine is running a modern alternator will provide >10 A even at idle, which is certainly enough to bring the charging voltage close to 13 V.

Having a separate staring battery is really not complicated at all. You know it's working OK, when you see that starting battery always has 12.6 V or more when you come to boat (shore power not connected).

Yes I know LiFePO4 should be able to charge much faster than it did in my friends boat. I don't know why it didn't.

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2 hours ago, Moonduster said:

The problem with relay-based charging solutions is that when the house is quite low and the engine is started, the start battery tends to discharge into the house, leaving both the start and house low on charge. Start the engine for a short period of time when the house is low and you could easily wind up with two relatively flat batteries. I have seen several installations where the engine could not be started for exactly this reason.

The usual solution is to raise the house voltage at which you choose to charge, in which case there was no reason to have added a start battery.

Another solution is to add a diode to prevent the start from charging the house. One really needs to add two diodes to ensure the batteries see the same voltages.

In addition, the current flow from start to house can quite large - large enough to blow that 100A fuse you use. This gets worse if the start battery is a super capacitor or LFP cell, like a Super-B as these cells have little internal resistance and can source very, very large currents. Generally speaking, it's difficult to size that fuse and, by extension, the cables between the batteries.

Finally, the combiner strategy is one that says the start battery is not fully charged until the house is fully charged, and that the start sits in absorption far, far longer than necessary because the larger house dictates the absorption cycle's timing. So the start battery is subject to considerable abuse - often left undercharged and then significantly overcharged. Not a great way to treat one's "emergency" battery.

The weekend sailor sees none of these problems, but that does not mean they don't exist. On an extended cruise, they conspire to provide a false sense of security in one's starting solution. In no case do they provide a superior solution to using a simple low-voltage cut out for the house or carrying a booster pack for emergency starting.

This is all BS, sorry.

I already replied to your claim about discharging starter battery.

It is good practice to charge the house battery well before it is even close to flat, since most lead acid batteries suffer a lot from deep discharges. But there is no need for that when considering the starting battery. In any case the house battery can become flat by forgetting some load on or just not monitoring it closely enough. Sooner or later it will also fail by old age. Starting battery will also fail some day, but it is very unlikely to happen simultaneously with the house battery, thus you can use house battery for starting.

There is no need for starting battery to see the same voltage as the house battery. You want to have rather high charging voltage for the house battery, since it has been likely used a lot and thus needs to be charged a lot. Starting battery is only used for starting and that doesn't lower the SOC even 1% per start. Thus it is fine to charge the starting battery at trickle charge voltage level, which is enough to charge back the <<1 Ah used while starting in a few minutes.

If both batteries are lead acid, there will never be large currents between them. Nowhere near 100 A. The only exception would be one battery having cells in short circuit. Even one battery being LifePO4 and the other lead acid is unlikely to show high currents, especially if the starting battery is lead acid. Anyway mixing LiFePO4 and lead acid is a bad idea they should be kept totally separated (separate alternators and chargers).

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Joakim,

You take a nearly fully-charged start battery and connect it to a house battery at a lower state of charge. Say 12.5 and 11.5V. There is massive current flow from one battery to the other.. It is limited only by the internal resistance of the two batteries. Depending on the size of the batteries, it can easily exceed 100A. What is your basis for saying the electrons won't flow quickly from the more-charged to the less-charged battery?

The you go on to say that the start and house have no need to see the same voltage - I just don't follow. The combining relay shorts them together - they are at the same voltage by definition. A diode isolator is a different story and the start battery will not begin to charge until the house voltage rises to the level of the start. Then the start will charge at the rate of acceptance of the house, which can easily overcharge the start once the house reaches acceptance voltage. The only solution that fixes this dilemma is to use a battery-to-battery charger, which is not a solution that's been brought up.

These are not new problems and they are not controversial. You claiming they don't exist is the BS here.

 

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There is more to lead acid battery I vs. V behaviour than internal resistance. It's not linear. When discharging the voltage will drop a few tenth's with much smaller current than using just internal resistance would predict. 

Eg. my 180 Ah house battery (super heavy duty truck starting battery with high CCA) drops 0.2-0.3 V just from compressor starting to take 5 A while it can provide a huge current at 11 V (300 A?).

While charging the difference is even bigger. Even my 50 W solar panel can lift the voltage by about 0.5-1 V with only 1-2 A current. But still I get the full 60 A charging from my alternator at 13.5-14.5 V depending on SOC (up to about 70% where the current starts to drop).

Connecting two lead acid batteries together there will never be big enough voltage difference to get high currents. A fully charged battery will have about 12.7 V and 11.5 V is totally flat. That 1.2 V is just not enough. A recently charged battery may have some ghost charge showing over 13 V voltage and providing a bit higher current for a few minutes, but that's all. After just providing 100+ A for starting that ghost voltage is gone anyway.

My 180 Ah should provide 1000 A at 7.2 V. Calculating from that the internal resistance should be about 5 mohm. That should give just 0.05 V difference at 10 A, but in real life it's about 0.5 V discharging and more charging.

You can also take a look at charging charts provided by battery manufacturers. The one I just looked at showed more than 13 V for a 0% SOC battery charged at 0.25 C. That's 1.5 V and 45 A for a 180 Ah giving 30 mohm internal resistance. Order of magnitude higher than for discharging at a huge current.

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Even a totally flat house battery will have about 13 V while charged with a decently sized alternator. Now there is full alternator current in the cabling and in the possible diode between the alternator and the house battery. There will certainly be a few tenth's voltage drop in cabling and probably about 1 V in the diode. Thus the voltage at the alternator will be more than 14 V in the case of diode based battery isolator even with a flat battery.

Usually the isolator is installed near the alternator. The current to the starting battery will be very small, since it is always almost fully charged. There will be no voltage drop in it's cabling and at a small current the voltage drop of a Schottky diode is only 0.3 V. So it will see almost 14 V and charge happily.

If only one diode is used, the starting battery will see a bit lower voltage than the house battery. But that's not really a problem, since there is no need to charge the starting battery all the time. It will be easily enough to charge it when the house battery voltage reaches about 14 V.

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Indeed, Joakim is correct that almost all boats around here are equipped with dual batteries. Nevertheless, an increasing amount of boats at least in Sweden seem to be shifting towards a one-battery system with LifePO4 and a battery protection switch at ~12V to leave enough to start the motor in the case of discharge.  

The experiences in Sweden seem to be the opposite to what you had with your friend and rather people are experiencing extremely quick charging of their one-battery lifepo4 solutions. Perhaps your friend has a double battery solution and some voltage drop due to diode or similar? The alternator will of course matter as well with Volvo D1-series using 115A vs smaller for Yanmar afaik. Considering that at least theoretically a lifepo4 should be able to take 1C of charge, so for example 90A to a 90Ah battery this requires different cables than a 90A lead battery which will only take ~30A charge.

 

In principle I agree that having a separate starting battery is not a big hazzle, but I would prefer going with one battery(with a protect relay) due to less weight, space freed up and less cables and components(like diodes, switches e.g.). 

 

 

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I just took a 80 Ah car starting battery, which haven't been used nor charged for a year. The open voltage was 11.98 V (measured with a top of the line Fluke). I connected it to my lab power supply providing 5 A and within a minute the voltage at the battery terminals was more than 12.5 V. Now after three minutes it's already 13.17 V.  After 10 minutes it's 13.23 V so seems to stabilize there. How much current would you think a fully charged starting battery would be putting into this battery?

To give you more hints I reduced the charging current to 1 A. Now the voltage stabilizes to 12.58 V.

Nubben I see one possible hazard in the common one LifePO4 battery setup in Sweden and Finland. It uses a voltage cut off for house usage, but no cut off for stating use. That's fine as long as you don't forget the ignition on or have any other consumers connected in the cut off bypass. My Volvo Penta takes almost 1 A, if I forget to turn off the start panel switch. Have done that a few times and the remaining 10% of LifePO4 doesn't last that long with 1 A. And on top of that LiFePO4 is permanently dead from one single over discharge.

Also OSR doesn't allow that system. It very clearly requires a separate starting battery.

For most sailboats weight where the batteries are is just positive. E.g. my friend put some lead into bilge to replace the weight saved from going into LiFePO4. I don't think your boat is sporty enough to differ from that.

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16 minutes ago, Joakim said:

Nubben I see one possible hazard in the common one LifePO4 battery setup in Sweden and Finland. It uses a voltage cut off for house usage, but no cut off for stating use. That's fine as long as you don't forget the ignition on or have any other consumers connected in the cut off bypass. My Volvo Penta takes almost 1 A, if I forget to turn off the start panel switch. Have done that a few times and the remaining 10% of LifePO4 doesn't last that long with 1 A. And on top of that LiFePO4 is permanently dead from one single over discharge.

 

I'm pretty sure the voltage protection switch will be in addition to a BMS system that monitors the battery at cell level. (Which any safe LifePO4 should have)
Otherwise the battery would have no protection from overcharging either.  Most of the 'drop in solutions' have this stuff built into the case. 

So the low voltage switch stops you from depleting the battery and the BMS will still protect from under and over voltage events. 

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I feel there is a very good reason for the OSR requirement of a separate starting battery. With just one things can escalate when you get a bit of engine problems as well. Say you forget to monitor your only battery and just notice your instruments stop working. Now you have a navigational problem. If you have a voltage cut off, you can still start the engine, but you have very limited power left to do so. If you have some water or air in fuel lines, you may need to crank much more than normally. You don't have VHF, AIS etc. anymore. Hopefully you do have paper charts and maybe a handheld GPS with fresh batteries.

Without any cut off you don't even need to have an engine problem. Once the instruments die you have no changes of starting the engine. Modern electronics work to at least 10 V.

Another friend of mine had this kind of problem when he was delivering his new second hand boat to home. I guess he was not that familiar with the battery system the boat had (it did have a separate starting battery) and he ended up needing to call coast guard with a cell phone to give them a jump start. I think he had connected the batteries parallel and both were flat when they noticed that.

 

Just now, MiddayGun said:

I'm pretty sure the voltage protection switch will be in addition to a BMS system that monitors the battery at cell level. (Which any safe LifePO4 should have)
Otherwise the battery would have no protection from overcharging either. 

So the low voltage switch stops you from depleting the battery and the BMS will still protect from under and over voltage events. 

I don't think that's the case for the LiFePO4 system marketed around here which I think Nubben is referring to. AFAIK the starting system current is bypassed directly from the battery and house usage + charging goes through the BMS. I don't also know which is worse. Protecting the battery from being killed, but at the same time not letting you to start the engine anymore.

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9 hours ago, Moonduster said:

Joakim,

You take a nearly fully-charged start battery and connect it to a house battery at a lower state of charge. Say 12.5 and 11.5V. There is massive current flow from one battery to the other.. It is limited only by the internal resistance of the two batteries. Depending on the size of the batteries, it can easily exceed 100A.

 

Moonduster, Joakim,

 

There are two things to consider when shorting two batteries together at different starting charge states:

1/  the voltage drop at a given load current for the charged battery

2/ the voltage rise at the same charge current for the discharged battery.

They will meet at a voltage in the middle of the two initial open-circuit voltages.

here's a paper that has some typical curves: http://www.arttec.net/Solar_Mower/4_Electrical/Battery Charging.pdf

 

In particular, look at the last page, which has the charge and discharge curves overlapped.

curves.thumb.jpg.b1e95af1092c0ab4d7000d4e6251e144.jpg

Let's take, for example, a fully charged battery (open circuit voltage ~ 12.7V), and connect it to one of the same capacity at 30% charge (o/c ~ 12.3V)

 

Even at C/20 (1/20th of the battery capacity in Ah) charge rate, the terminals of the 70% flat battery are at ~ 12.7V, while a charged battery is pulled down a 100mV or so.

 

So for a typical pair of 120Ah batteries, we're only talking 6A.

 

(ps: I'd take those particular curves with a grain of salt -- they don't look right at very low levels of battery charge state., for example they overlap at C/40 and 15%)

 

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say you forget to monitor your only battery and just notice your instruments stop working.

The purpose of the low voltage cut-off is not to forget this...

 

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You don't have VHF, AIS etc. anymore.

Handheld VHF according to OSR cat 3?

 

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30 minutes ago, Joakim said:

Without any cut off you don't even need to have an engine problem. Once the instruments die you have no changes of starting the engine. Modern electronics work to at least 10 V.

agree, stupid not to have a cut-off

 

31 minutes ago, Joakim said:

I think he had connected the batteries parallel and both were flat when they noticed that.

I think this proves that having two batteries is not always a perfect solution either and there is some added value from the simplicity of a one-battery system.

 

32 minutes ago, Joakim said:

I don't think that's the case for the LiFePO4 system marketed around here which I think Nubben is referring to. AFAIK the starting system current is bypassed directly from the battery and house usage + charging goes through the BMS

What I refer to seems to be the benchmark installation in our westernly neighbour country. 12V winston with internal pre-balanced cells without an external BMS messing things up. Monitored with for example victron BMV-700 which alarms at 12.5V and low voltage cut-off at ~12V.

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With cut off, you will just notice, that the house power is gone (of course you could have an alarm well before). Then you have very limited power left. With handheld VHF you can communicate only with vessels quite near to you, maybe up to 10 M masthead antennas in good conditions.

The Winston system is the one I was talking about. The standard system the Swedish company provides is a cut off for house and direct bypass for engine.

Yes it's of course true that you can have a stupid two bank system and you can use most systems stupidly. With a battery isolator or an automatic relay, it's not that easy to flatten your starting battery.

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Based on open voltage the car battery I'm know charging was at ~20% SOC. At 5 A (C/16) it first stabilized at 13.2 V and is know after about two hours 13.38 V and SOC should be a bit above 30%. 0.6-0.7 V higher than Duncan's chart shows.

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Now after almost 6 hours of 5 A charging the voltage has risen up to 14.4 V and I need to reduce the current. The SOC should be about 60% so more than 1 V above Duncan's curve. Maybe this battery doesn't have 80 Ah anymore and it is already at 80% SOC or even more?

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 I was quite disappointed with their performance. We had to run the engine 2 hours to get the batteries from 40% to 80% SOC. I can do the same with my cheap lead acid.

You missed the whole point of LFP vs flooded.    Yes, your cheap lead acid can charge that 40% range in the same time, it's when you try to go above 80% SOC that LFP kick the shit out of lead.  First this mean your charging system doesn't output much as an LFP pack can sustain usual 3x of the packs capacity (3C) vs. the lead that can handle up to .5C so unless your charging system can output above that rate the lead can handle the full charge amperage.   Now the real benefit from LFP vs. flooded (besides weight, lifespan, etc) is that the charge acceptance rate doesn't drop off above (85-90%) and you DON'T HAVE TO live in the 50% - 85% charge range AND you can discharge down further.

Some rough examples:  

Charging with a 100A alternator to a 200A house bank with lead.   You started with a 100% full charge battery.   You consume 100A to reach the max 50% discharge of a flooded pack.   You charge @ 100A for 30-40 minutes and the charge controller drops down output.   No sense running the alternator for another 1-2 hours to top off the pack at the greatly reduced charging rate.    Now you only have and 85-90% charged pack.   You discharge down again to 50% but you are basically now only using 35-40% of your packs capacity which is all you will get after the first top off charge to 100%.  Basically you have a 70Ah useable pack.

Charging with a 100A alternator to a 200A house bank with LFP.   You started with a 100% full charge battery.   You consume 140A to reach the recommended 30% discharge of a flooded pack (max 80%).   You charge @ 100A for 1+ hours and the charge controller doesn't drop down output until the packs are nearly full.   Now you only have and 90%+ charged pack.   You discharge down again to 30%, repeat.   Basically you have a 140Ah pack.....   twice the capacity @ 30% the weight.

Bottom line is you get to use a whole lot more of the amps you are carrying around with LFP which charge at a much higher acceptance rate to a much higher level in a shorter time.

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16 hours ago, solosailor said:

You missed the whole point of LFP vs flooded.    Yes, your cheap lead acid can charge that 40% range in the same time, it's when you try to go above 80% SOC that LFP kick the shit out of lead.  First this mean your charging system doesn't output much as an LFP pack can sustain usual 3x of the packs capacity (3C) vs. the lead that can handle up to .5C so unless your charging system can output above that rate the lead can handle the full charge amperage.   Now the real benefit from LFP vs. flooded (besides weight, lifespan, etc) is that the charge acceptance rate doesn't drop off above (85-90%) and you DON'T HAVE TO live in the 50% - 85% charge range AND you can discharge down further.

Some rough examples:  

Charging with a 100A alternator to a 200A house bank with lead.   You started with a 100% full charge battery.   You consume 100A to reach the max 50% discharge of a flooded pack.   You charge @ 100A for 30-40 minutes and the charge controller drops down output.   No sense running the alternator for another 1-2 hours to top off the pack at the greatly reduced charging rate.    Now you only have and 85-90% charged pack.   You discharge down again to 50% but you are basically now only using 35-40% of your packs capacity which is all you will get after the first top off charge to 100%.  Basically you have a 70Ah useable pack.

Charging with a 100A alternator to a 200A house bank with LFP.   You started with a 100% full charge battery.   You consume 140A to reach the recommended 30% discharge of a flooded pack (max 80%).   You charge @ 100A for 1+ hours and the charge controller doesn't drop down output until the packs are nearly full.   Now you only have and 90%+ charged pack.   You discharge down again to 30%, repeat.   Basically you have a 140Ah pack.....   twice the capacity @ 30% the weight.

Bottom line is you get to use a whole lot more of the amps you are carrying around with LFP which charge at a much higher acceptance rate to a much higher level in a shorter time.

I didn't miss any point, I just told what happened while racing with my friends boat. I'm well aware about the differences between battery chemistries.

My friends boat has 2009 YM30. Probably it has only 60 A alternator. He didn't know nor did he remember the capacity of his LiFePO4 bank. 57 A was probably the max the alternator could provide. I don't know why the current then dropped below 30 A.

At a lower price than LiFePO4 you can buy lead acid batteries that have the same or even better cycle life than LiFePO4 and do tolerate 80% or even deeper DOD.

But who even needs 2000 cycles? Most get way less than 100 cycles in a year. Probably 10-30 is typical. I don't think LiFePO4 will last 100 years with 20 cycles per year. Will it even last 10 or 20 years remsins to be seen.

My cheap lead acid batteries are from 2010 or earlier and still work fine. I sail quite a lot 2-6 weeks sailing holiday + some weekends + some racing. I don't use motor a lot and I haven't started motor for charging even every year. I can sail 30 hours before needing to consider charging. House battery is 180 Ah and it very seldom drops below 60% SOC. Quite often I don't bother connecting shore power when it's available at the harbour we are overnighting. I never leave the shore power connected at our home harbour unless I'm sleeping in the boat.

I see no point switching to LiFePO4 in my use.

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But who even needs 2000 cycles? Most get way less than 100 cycles in a year. Probably 10-30 is typical. I don't think LiFePO4 will last 100 years with 20 cycles per year. Will it even last 10 or 20 years remsins to be seen.

Most LFP info I've seen says 10 year service life, never seen anything about a super long life cycle, let alone a gross exaggeration of 100 years.   I know several packs out there in use longer than 10 years, including mine.      

So you were "disappointed" in the LFP performance but it was the 30A alternator output that was the problem, not the battery.  As to your friends setup, it sounds like his alternator regulator isn't setup correct and he need a larger alternator to take advantage of the packs.    It's like getting a Tesla and complaining about large charge times but you are charging it from a 10A, 110V plug......   and then blaming the batteries for the long charge time.

No, LFP isn't for you.

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At a lower price than LiFePO4 you can buy lead acid batteries that have the same or even better cycle life than LiFePO4 and do tolerate 80% or even deeper DOD.

Carbon foam batteries are great but don't even come close in life cycle let alone "better" than LFP.  Carbon/foam is rated at 1000 cycles at 80%DOD, not the 2000-5000+ of LFP,  are twice as heavy, and can not be charge at as high of rate.   A great choice for many though.

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5 hours ago, solosailor said:

Carbon foam batteries are great but don't even come close in life cycle let alone "better" than LFP.  Carbon/foam is rated at 1000 cycles at 80%DOD, not the 2000-5000+ of LFP,  are twice as heavy, and can not be charge at as high of rate.   A great choice for many though.

And impossible to get hold of in most countries. 

I was quoted 250$ per battery shipping to the UK. Add on import duty, VAT at 20% (which is payable on shipping as well) and its basically cheaper to get Winston Cells from an EU supplier. 

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You can get e.g. a pair Trojan T-105 (2 x 6 V, 225 Ah) for 313 € in UK. Those are not top of the line, but are still rated for about 800 80% DOD cycles. Winston LiFePO4 2x90 Ah 12 V cost 980 € and you have to buy some BMS system on top of that. They are rated for 2000-2200 70-80% DOD cycles depending on source.

800 cycles is already 40/year for 20 and 80/year for 10 years. I wouldn't know will Winston or Trojan last longer in real life. It's clear that Winston would outlast Trojan, if you have 100 or more 80% cycles in a year, but who would have that in a sailboat. You would need to sail almost every day and have no wind, water or solar power source.

While Trojan would charge rather slowly the last 20%, it would charge just as fast from 20 to 80 % SOC. But you do get 25% higher Ah rate to compensate that.

There are lead acid batteries rated for 2000 80% DOD cycles and even higher, but I don't really see the point paying extra for something you are very unlikely to really need. Also very high cycle lead acid batteries become even larger and heavier (T-105 is not).

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T-105 is almost equal in size to 12 V 90 Ah Winston. You do save some weight. With two of both 56 kg vs. 30 kg, 26 kg saved. Really nothing on a 3-7 tonne boat and the weight is below center of gravity in most boats increasing stability. Even if not lower than CG it will increase righting moment at normal sailing heel angles making the boat faster whenever full RM is needed.

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They are rated for 2000-2200 70-80% DOD cycles depending on source.

Well your information is far from correct when going TO THE SOURCE that manufactures them.  When Winston (ex-Thundersky) started shipping batteries they were rated at 2000-3000 cycles (70-80% DOD).   Over the years they increased those numbers as the lifetime stats were proven in the field.   Last time I checked 5 years ago they were at 3000-5000 cycles.   Now those same cells are spec'd as 5000-7000 cycles.   

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 I wouldn't know will Winston or Trojan last longer in real life.

You might not but the rest of the world knows it's no competition.   

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15 minutes ago, solosailor said:

Well your information is far from correct when going TO THE SOURCE that manufactures them.  When Winston (ex-Thundersky) started shipping batteries they were rated at 2000-3000 cycles (70-80% DOD).   Over the years they increased those numbers as the lifetime stats were proven in the field.   Last time I checked 5 years ago they were at 3000-5000 cycles.   Now those same cells are spec'd as 5000-7000 cycles.   

So this is false information given by major EU distributor? https://www.ev-power.eu/blog/The-Cycle-life-of-Winston-Batttery-cells-versus-lead-acid.html

They do have quite low values for lead acid, but I wouldn't have thought they give too low for their own product.

Anyway for most of us it doesn't matter at all if it's 1000 or 10 000 80% cycles. The whole system will be updated or the boat sold before such a huge number of cycles is reached. It's the calender life that's more important and it remains to be seen which chemistry is better in that.

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This is approaching mythical "What's the best anchor" status.

I will say I understand the passion, as eventually, you have to choose, and it's neither cheap nor easy to change the decision.

Good news is, that most of the solutions work just fine for what you want.  You just have to pick one and get on with it.

 

Mines the Carbon foam house batt from Bruce, with a basic high CCA starter battery, 2 bank shore power, and an external 2 bank regulator hanging off a 90 amp alternator.

Monitor with the Victron.

Works fine.

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4 minutes ago, solosailor said:

You might not but the rest of the world knows it's no competition.   

Why would it be no competition? Plenty of 10+ years old lead acid batteries still working fine. Or do you really think people use more than 800 80% DOD cycles in say 15-20 years and the better cycle life is the key. It may be for lower quality lead acid not really intended for deep cycly use (may still be marketed as deep cycle).

I would not count on BMS and charging systems working 100% for say 20 years, especially when LiFePO4 is used by people not well informed about them. They can be spoiled just as easily as some people manage to spoil their lead acid batteries in quite short time. And then the cost to replace them is 3-4 times higher than lead acid.

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I don't understand all the hatred for BMS installations on LFP banks. The whole point of a BMS is that it increases safety, allows you to use a broader charge/discharge range, and extends the life of the system. People seem to be afraid of them. Maybe it's just because they add some complexity to the installation but no more so than a programmable battery charger and shunt/monitor which everyone seems to accept in the lead acid world.

Anyway, I've got an LFP bank and love it but I'll be the first to say it's not necessarily the best battery tech for every boat. FLA has its place, though I'd argue that if you're going the AGM route then Firefly is a no-brainer, assuming they've gotten their quality issues behind them.

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11 hours ago, Joakim said:

You can get e.g. a pair Trojan T-105 (2 x 6 V, 225 Ah) for 313 € in UK. Those are not top of the line, but are still rated for about 800 80% DOD cycles. Winston LiFePO4 2x90 Ah 12 V cost 980 € and you have to buy some BMS system on top of that. They are rated for 2000-2200 70-80% DOD cycles depending on source.

That cycle life is pretty good to be fair, I hadn't realised there was one available here that did so well, 800 cycles at 80% DOD is good, however I'd never get that last 20% apart from extended motoring and shore power.. 
Also I notice on the data sheet that you only get the full capacity at nearly 30 degrees C. Which doesn't happen to often in England in the battery area of my boat anyway. 

You're a bit off with your weight calculations as well. 
90ah Winston cells are 3kg each. Total of 12kg for a 90ah battery. Versus 2x 28kg = 56kg for the T105. 
Maybe you meant the 200ah one which is much closer. 

Either way its incididental I was really responding to the Firefly suggestion, for my usage I generally just have a 70AH leisure battery onboard which is fine for most of the years sailing. I have a couple of 100AH's that I drop in when we're cruising, but that only adds up to 2-3 weeks of the year. The rest is racing and day sails. Not worth spending much for the type of sailing we do. 

If we were going to do anything longer than the normal 36 hour passages we do to get to the Netherlands then I'd think of upgrading. 

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Winston 12 V 90 Ah battery is 15 kg each so two of them to reach 12 V 180 Ah is 30 kg: http://en.winston-battery.com/index.php/products/power-battery/item/wb-lp12v90ah?category_id=176

Maybe you can save a few kg more by using 8 3.2 V 90 Ah cells at 3 kg each, but you need some cabling and some balancing, since the individual cells probably are not similar enough. Or you can use 4 3.2 V 200 Ah cells, but that's 32 kg just for the cells.

Interesting that for 12 V 90 Ah pack Winston site shows cycle life as 5-10 years and for individual cell it shows >5000 80% DOD. Why? Does the cells inside the 12 V package get out of balance? AFAIK they do not use any active balancing for 12 V packages, but you could use one for 4*3.2 V system.

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The Winston batteries have no electronics whatsoever. I certainly wouldn't consider using them on a boat. 
https://www.ev-power.eu/LiFeYPO4-batteries-12V-1-1/Lithium-Battery-12V-90Ah-WB-LP12V90AH.html

I'd use 4 cells & a bms to disconnect them in case of under / over volt events.

I suspect in real world usage they would outperform the 6v Trojans listed more than the numbers show, however as I said for my particular usage I have no need of either. No point overcomplicating matters. 

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One of the things we've learned over the years is that "owner fears" are real whether we agree with them or not. When an owner feels more comfortable about their systems, and understands the system, it leads to better enjoyment on the water. If adding a starting bank gives an owner a level of comfort, by all means go for it. It is an easy upgrade and rather inexpensive, as boat expenses go.

Also you don't really need to treat it as a "dedicated" start battery, although it is never a bad idea. A small reserve/emergency battery on a 1/2/B switch charged by an ACR, Echo Charger, Duo Charger etc. can work just fine for many, many years. We've had cheap (sub $80.00) starting batteries last in excess of 10+ years on 24/7/365 cruising boats that have been charged via a combiner/VSR/ACR from solar, wind & alternator the entire time. On the flip side, our advice to some customers with an existing start bank, would be to consider at least a dual-purpose or deep-cycle battery that could also be used in an emergency for both house and and starting duties, should the house bank go tits up. This can happen..

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While the owner above had to hand steer the rest of the crossing, and lost fridge contents, they still had navigation and communication. A jump-pack or small cranking battery would not have worked as a suitable "reserve" duty battery for the situation above.. On a small AUX diesel a deep-cycle battery can easily do both starting and cycling when or if an emergency situation arises. Of course when your electrician tells you the house bank is toast, and needs to be replaced, it may be best to listen to that advice first and avoid the above situation altogether.

Sadly the myth & lore surrounding Combiner/VSR/ACR's is rather wide spread. The link below will help explain how an ACR works and how to correctly install one on a cruising boat.
Making Sense of Automatic Combining Relays

 

 

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