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      A Few Simple Rules   05/22/2017

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fsylvestre

LiFePO4 batteries

26 posts in this topic

Are LiFePO4 batteries made for motorcycles a good option for sailboats? From what I can read they could do the job and they are really light.

 

I want 12v on my sailboat for instruments and I have no engine to crank or to recharge...

 

Thanks

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You don't say much about your boat or your charging system. LFP batteries are significantly lighter than lead-acid (flooded, gel or AGM) batteries and they are far, far safer than other forms of Lithium-based battery technology.

 

LFP batteries are a fine choice, but they do require careful attention when charging. It's usually the case that a Battery Management System is used to balance the charge on each individual cell of the battery and to disconnect the battery from loads should the voltage drop too low and to disconnect from charge sources should the voltage get too high. For small installations, the cost of the BMS is often not worthwhile and LFP batteries might not make sense as a result.

 

Do you have a link to the batteries to which you refer? What's your boat? What's your charge source?

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For small installations, the cost of the BMS is often not worthwhile and LFP batteries might not make sense as a result.

 

Not true.

http://minibms.mybigcommerce.com/products/HousePower-BMS.html

You need a balancer module per cell, plus a relay for the unit to control. So min 120 bucks for a 12V system, 200 if you want a very low power draw solid state relay.

I fully intend to use one of these for as a 75-100ah house battery on my 7m trimaran.

 

For even simpler usage such as what the OP is talking about, one of these would probably be adequate.

http://www.ev-power.eu/SBM-CBM-1-1/Simple-Battery-Management-Board-4-cells-12V-10A.html

Put together a 4 cell bank of these

http://www.ev-power.eu/WINA-30Ah-100Ah/WINA-LiFePO4-Power-3-2V-15Ah-aluminium-case.html

And you have a 15Ah lithium battery with basic management for 100 bucks at a weight of 2kg.

 

To OP, whether you go with shore power or solar cells for charging, make sure that the charger/controller is set up for lithium batteries, the charge and cutoff voltages are slightly higher than with conventional batteries. And regardless of how cheap or fancy you go with the BMS, make absolutely sure you have appropriate inline fuses to protect against short circuits. Lithium batteries suffer very little voltage sag under high discharge rates and so even small batteries can pose quite a significant fire risk if a short occurs, without proper protection.

Also be aware that when a lithium battery is run down, the voltage plummets very quickly over the last 5-10% of the discharge curve so relying on voltage as warning for low battery condition is not a very good idea unless running out of power is not a significant hazard. Without a BMS, like the ones linked to above, or extremely diligent manual monitoring, running your lithium battery down to completely 0% charge even just once can destroy your battery. Likewise a single major overcharging event can destroy your battery.

See discharge curve for a single cell in the image below - the drop from 80-90% is 0.1 volts, below 80% discharge the curve is essentially flat.

SEdischargecurve.jpg

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Are LiFePO4 batteries made for motorcycles a good option for sailboats? From what I can read they could do the job and they are really light.

 

I want 12v on my sailboat for instruments and I have no engine to crank or to recharge...

 

Thanks

I would just go with a small AGM - way cheaper than LFP's - http://www.atbatt.com/batteries/agm-battery.asp

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Diggler,

 

I think we're in complete agreement. One needs a BMS. A BMS adds quite a bit of cost. LFP is always expensive per AH. The result is that LFP is often not the right solution.

 

The biggest cost savings with an LFP battery is extended engine life and reduced diesel cost - so if there's no engine, LFP probably doesn't make sense at all, financially. And with a small LFP, there won't be much weight advantage, either.

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It's true. We don't sell very many 100Ah GLi batteries (the smallest made by Genasun). For anything smaller you'd have to DIY like Diggler suggests. There just isn't much demand on boats where the battery bank is already small.

 

So most of the market is for boats that have high enough loads and to require large/heavy house battery banks, and the desire to recharge quickly and efficiently. In many cases the reduced charging times and fuel savings are significant. Li can actually be less expensive per kWh of energy used over the life of the system, as the cycle life is extraordinarlly high.

 

All that said, a 100Ah Li batt can often replace 200Ah or more of Pb, due to the deeper cycling, lack of voltage drop, and about a 15% gain in discharge/recharge efficiency over Pb (adding even more effective capacity). Expensive, yes. But also safe, lighter, more efficient, much longer lasting, etc.

 

Something to note about Pb batts is that most need to be replaced long before their expected retirement date, due to improper charging. It is very hard to properly recharge Pb at sea (or on a mooring) with diesel without wasting fuel and adding undesirable engine hours. However, on a small boat with low loads, you can often meet those loads with some solar power. Which gives Pb the long, slow soak recharge that it needs to have a better life. So, solar can be a Pb batt's best friend. And is usually less $ than going Li on a smaller boat.

 

Sad to say, the biggest clients for GLi battery systems are 45-60 high-perf but comfortable powerboats. The weight savings are irressistible if you need to go 36kts on a boat that also has air conditioning...;-)

 

My 2 cents.

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Bruce, I'm one of the few that will be interested when my current battery is done- my logic is more usable energy for the same weight, and more tolerance for using a greater percentage of the available energy without damage. My 31 foot tri, with an outboard that can be hand started if necessary, but the main charging is solar. Does an Li battery charge well from solar, meaning slow and steady (in Maine.)

 

Jesse

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Bruce, I'm one of the few that will be interested when my current battery is done- my logic is more usable energy for the same weight, and more tolerance for using a greater percentage of the available energy without damage. My 31 foot tri, with an outboard that can be hand started if necessary, but the main charging is solar. Does an Li battery charge well from solar, meaning slow and steady (in Maine.)

 

Jesse

Yes, Li charges perfectly fine from solar, and is about 15% more efficient on "energy returned" than Pb. The solar charge controllers usually need to be speficially for Li, as you don't want temp compensation (which some Pb controllers have) and usually have different max and float voltage requirements. The voltage specifics can vary from one brand of Li to another.

 

Regarding outboard alternators (if you have one), some are virtually unregulated, so although the output is rather low, they may have a rather high max voltage. So, if after a long period of motoring and/if the Li batts are fully charged, the alternator output may try to charge too high. Which would then trigger a HVC (High Voltage Cutoff) from most Li systems, to prevent overcharging (which could damage or shorten the life of Li batts). So no damage happens to the batts...however it is possible there could be damage to the outboard's alternator recifier diodes if disconnected from a load (batteries). One way around this is to have an automatic load dump relay that connects the batts to a resistive load to keep the batts from overcharging and disconnecting from the outboard alt. This doesn't come up very often, however is something to think about.with certain outboards.

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After 13 years of serviceable life from 4-group 27 gel cells it was time for something else. I was never a fan of AGM technology and I wanted to loose the weight.

I've just completed a 4-100ah LiFePo4, cpu and BMS by Elite Power in Tempe AZ system. The installation is on a '78 Morgan 382. Not cheap but if I live another 20 years it may be worth it.

I imported a programable 160 amp relay sold only in Australia. The relay is in series with a legacy Freedom 10 to keep it from floating the system charge when plugged in

at the dock. (12.8v lv cut off 13.3v hv cut off.)

The alternator is a 106 amp Ample Power externally regulated and has a "zap" stop diode. My thought to keep the alternator safe was to turn the inverter on before starting and whenever motoring so that when the hv relay cuts off there will still be a load.

I hope I haven't strayed too far.

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For even simpler usage such as what the OP is talking about, one of these would probably be adequate.

http://www.ev-power.eu/SBM-CBM-1-1/Simple-Battery-Management-Board-4-cells-12V-10A.html

Put together a 4 cell bank of these

http://www.ev-power.eu/WINA-30Ah-100Ah/WINA-LiFePO4-Power-3-2V-15Ah-aluminium-case.html

And you have a 15Ah lithium battery with basic management for 100 bucks at a weight of 2kg.

 

.

Thanks for the links Diggler

 

Regarding outboard alternators (if you have one), some are virtually unregulated, so although the output is rather low, they may have a rather high max voltage. So, if after a long period of motoring and/if the Li batts are fully charged, the alternator output may try to charge too high. Which would then trigger a HVC (High Voltage Cutoff) from most Li systems, to prevent overcharging (which could damage or shorten the life of Li batts). So no damage happens to the batts...however it is possible there could be damage to the outboard's alternator recifier diodes if disconnected from a load (batteries). One way around this is to have an automatic load dump relay that connects the batts to a resistive load to keep the batts from overcharging and disconnecting from the outboard alt. This doesn't come up very often, however is something to think about.with certain outboards.

 

Do you know which brand or type?

 

For the trimaran that I'm building I'm planning a simple electric system. The idea is to use a 50Wp solar panel for charging, but to enable the 6 or 10 Amp outboard alternator to charge the batteries as well. Anything that I'm missing here?

 

elecsystem.jpg

 

Regards

Nico

www.nyker.nl/index2.html

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Nyker,

 

You should put a charge controller in there to avoid the risk of the alternator or solar panel overcharging the lifep04.

Something like this should isolate it OK http://ev-power.com.au/webstore/index.php/ev-power-bms/12v-lifepo4-battery-control-unit.html

But email him and ask the question.

 

We've been running a small lifep04 for 4 years and it works fine. We use one of these that's been modified to suit the Lifep04 charge profile and it manages all our charging for us.

http://www.redarc.com.au/products/product/in-vehicle-battery-charger-40a/

 

And we're running a simple 100ahr lifep04 battery - https://www.ev-power.com.au/-EV-Powerpak-Custom-LFP-Batteries-.html

The slim line epoxy coated BMS cell modules are good for a marine environment.

 

I'd also suggest you put in a amp hour meter so you can monitor what is going in and out of your battery.

 

Such as this type of unit - http://ev-power.com.au/webstore/index.php/battery-power-meter.html


Our biggest benefits to date are:

Single charge per day when racing - Takes less than 20 minutes to put in what we have taken out over a 24 hour period

Space and weight savings. (Space not so much an issue as we used our previous 100ahr AGM battery box - so same box with more room inside it ;)

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The Genasun GV-10 is an MPPT solar charge controller.

 

Interesting idea to also use it to regulate the DC from the outboard. I assume the outboard charging "circuit" would deal with being abruptly switched off when the batteries got full.

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I'd also suggest you put in a amp hour meter so you can monitor what is going in and out of your battery.

 

Such as this type of unit - http://ev-power.com.au/webstore/index.php/battery-power-meter.html

That is an interesting idea. The discharge graphic is very flat, so the voltage will not really show how much 'juice' the system has left. As far as I understand, this one only works one way though. You need something that will take charging current and load current to calculate the state of the battery.

Interesting idea to also use it to regulate the DC from the outboard. I assume the outboard charging "circuit" would deal with being abruptly switched off when the batteries got full.

I plan to use the outboard charging option only when the batteries are low, thus avoiding any problems with charging cutoff. As far as I understand, it is not advisable to switch off the power while the engine is running as it might damage the alternator electronics.

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The wiring diagram in the description shows the meter sitting between the battery and the load. I don't understand how it can tell you the state of charge of the battery as it will not be seeing any charge current unless the charge sources are on the load side of the meter as well?

 

I'm more familiar with meters like the following with an external shunt being used to track the state of charge of a battery by integrating the inputs and outputs: http://www.defender.com/product3.jsp?path=-1|328|2289954|2289950&id=1130625 or http://www.solar-electric.com/tr20mosy.html . However they are expensive.

 

With any of the battery monitors, you'd want to check that they could be set for LiFePO4 batteries. I believe the voltages and charge efficiencies are different.

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To understand how to properly install a battery monitor, read this:

 

www.pbase.com/mainecruising/battery_monitor

 

Also note that you guys are talking about a small, simple system. However, even on those you should consider a dual-buss configuration so that you don't lose power if any source tries to overcharge. That is, the positive bus is separated into a charge bus, and a load bus, with a relay for each controlled by the BMS.

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For instance, here are some system diagrams, all with dual-bus configurations. Most relevant here is the first one; note that although it's a single bank, the charge and load busses are separated.

Genasun System Configurations.pdf

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I know this is drifting from the original question, but Haji, why would you go with a two bank system rather than a one bank system? Is there any advantage to 2 banks over 1 with lithium?

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Simple redundancy mostly...for instance, one bank can operate even if the other is off-line. Another advantage is if you push them to a LVC (Low Voltage Cutoff) then one tends to cut out a touch before the other, and they sort of bounce back & forth for a bit. So you don't get as abrupt of a system cutoff, and more time to deal with it (start charging).

 

However this would only be if you have ignored your battery monitor warnings (loud music? heavy weather, etc.) and kept on loading the banks until the cutoff. Not something that should happen very often.

 

For small, light, simpler systems we are doing more single banks now than we used to. On the bigger systems using multiple paralleled banks is the way to go.

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I guess I'm not quite getting it. Lots of us used to have 2 banks of batteries that we switched between, and then slowly migrated to one big house bank of batteries and a small engine starting battery. I know this is not quite the same, but it feels like we are drifting back in that direction.

 

Or maybe I'm not understanding this correctly, and tripping over the use of the term "bank". Would it be OK to look on the two banks as just two smart batteries in parallel making up one house "bank"? We get redundancy in the electronics for managing the batteries (a good thing), but from a normal operation perspective we just have one big "house" bank (another good thing)?

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I can understand the redundancy for more complex systems. However, for a small system ( like mine ) I prefer the KISS principle.

 

The tutorial about battery monitoring systems confirms my idea to place the shunt directly next to the battery, so that all load and charge current runs through the shunt.. Thanks for that Haji. Great info in this thread!

 

regards

Nico

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I guess I'm not quite getting it. Lots of us used to have 2 banks of batteries that we switched between, and then slowly migrated to one big house bank of batteries and a small engine starting battery. I know this is not quite the same, but it feels like we are drifting back in that direction.

 

Or maybe I'm not understanding this correctly, and tripping over the use of the term "bank". Would it be OK to look on the two banks as just two smart batteries in parallel making up one house "bank"? We get redundancy in the electronics for managing the batteries (a good thing), but from a normal operation perspective we just have one big "house" bank (another good thing)?

Yes...they are running in parallel, effectively as one bank. However you could turn one off (or if one had any sort of problem), then the other would continue to operate. So all would be as before only with less capacity..

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Before getting too fancy have you done the AH calculations and determined what you need?

 

A simple sealed lead acid battery with a dockside charger may get it done to run your instruments for 6 hours.

 

battery and charger $40-80 total.

 

keep it simple and cheap

 

http://www.amazon.com/UB645-Sealed-Lead-Acid-Batteries/dp/B0006N61RW/ref=sr_1_5?ie=UTF8&qid=1394569107&sr=8-5&keywords=sealed+lead+acid+battery

 

http://www.amazon.com/Battery-Tender-021-0123-Junior-Charger/dp/B000CITK8S/ref=sr_1_1?ie=UTF8&qid=1394569160&sr=8-1&keywords=12v+battery+charger

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There are a LOT of advantages to LiFeYPO4 batteries, so many in fact I would never use AGM's again.

 

Why I'm no longer a fan of AGM's: Typically voltage drop after 50% discharge will put you below 12v so right there you can half the capacity in terms of actual usability. Then there's the low charge acceptance rate (which drops further after 85-90% charge).

 

LiFeYPO4 batteries have a truly mental charge acceptance rate. You can push 200A into them and they won't even blink.

 

They are also 25% the weight of AGM's and typically the size is far, far smaller.


Our new 300Ah batteries are

  • Operating Voltage: Min 2.5V Max 4.2V
  • Weight (kg): 9.6
  • Height (mm): 305.7
  • Width (mm): 55.5
  • Depth (mm): 363

We couldn't even dream of fitting that capacity with AGM's. The whole bank can charge off the alternator in less than 2 hours. Go price out a bank of Rolls batteries with an actual 300Ah of usable 12v capacity and measure their footprint and weight. That usually settles it for most people.

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