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Removing second battery


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Currently have two batteries in 35' boat for racing I want to remove one of them when racing.  If I disconnect and remove the second battery temporarily for racing and cover the main wires that connect to the battery terminals and turn my Perko to battery 1, is that all i need to do? Or by removing the second battery will the boat not have power and I need to take additional steps? 

Obviously wiring is not my strong suit so I apologize for the stupid question in advance. 

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Sounds good. Take extra care insulating and securing the unused battery cables. They could easily start a fire (either + or -) by flopping around during pro-level racing ...like a broach.

On many boats the batteries have owner-added junk connected directly to the terminals. I assume you do not. 

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really not enough information. If you have two batteries in a boat your size, typically one is dedicated to starting the motor and the other to your "house" loads. So before you remove a battery, you need to trace the leads to see what it's actually powering. The last boat I was on with a 2 position switch, there was this idea of starting the engine on battery 2, switching to "both" to charge, and then when the engine went off to switch to battery 1. Terrible battery management (since inevitably you forget to switch to 1 and run both batteries down), but if that's the way your boat is wired - that both batteries can do everything - then disconnecting the one and taking it out should have no effect. just make sure you cover the ends completely so you don't have loose wires that could potentially contact something they ought not.

To Borracho's point, some of that 'owner-added junk' may be a bilge pump, which is typically wired directly to the battery.

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19 minutes ago, usa1136 said:

I want to remove one of them when racing. 

what rating are you racing under ?

was the boat weighed / measured with two batteries ?

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16 minutes ago, Mid said:

what rating are you racing under ?

was the boat weighed / measured with two batteries ?

OD class allows one or two.  Thinking of making the change prior to weighing the boat. 

All owner junk (bilge pump only) is attached to Bat 1 that will stay. 

Both are AGMs and the same size Cranking amps

 

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Be careful when starting engine - many electronics will shut down due to the voltage drop when spinning the starter. Easiest work around is do not turn on electronics until engine is running

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21 minutes ago, Grande Mastere Dreade said:

35' boat and you want to remove  50-60lbs... ok...        how about a diet instead?

I don't need to go on a diet.  The body weight of movable crew members is not quite the same as a battery.   If an owner's goal is to win, why would they not want to optimize their boat by following the rules and guidelines of the class they sail?  If you don't want to attempt to optimize your boat, that's cool, but sorry to break it to you, but trying to balance a boat's weight and focus weight in more preferred and allowed areas of the boat is not a foreign concept for competitive boats.   

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How about wiring in these between boat and battery:

https://www.mcmaster.com/7043K8/

They make caps as well.

I agree with the more trouble then its worth though.  I kept the 2 battery setup and just went with smaller, lighter batteries.

--Matt

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3 minutes ago, Salona said:

What is the smallest AGM battery that can reliably start a diesel engine?

(On a previous boat) we had single bank, but yes,  starting the engine created a voltage drop that sometimes reset the electronics. 

 

The engine datasheet will tell. My 38 HP engine specs at 100 A. So any battery with a CCA of 100 should work. A quite small battery, even a motorcycle battery (300-400 CCA), will start a happy engine. The problem is if the engine is reluctant or the battery old. Just like an automobile, the batteries age without warning until one cold morning...nothing. My diesel tractor has a shockingly small battery but starts easily....while cruising yachties believe a 100 pound battery is required...same engine.

Yes, starting the engine will often reset some (all too typically) poorly designed electronics. Shouldn't be an issue for racers though, right?

One can measure the resistance across the starter motor and solenoid terminals. Divide 12 V by that those Ohms to get the maximum possible current draw while starting. About 1 Ohm, apparently...

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4 hours ago, Salona said:

What is the smallest AGM battery that can reliably start a diesel engine?

(On a previous boat) we had single bank, but yes,  starting the engine created a voltage drop that sometimes reset the electronics. 

 

I used a Lifeline U1 battery (motorcycle sized) on a Yanmar 2GM for ~18 months.  It worked fine except for when the temp was near freezing, then it just didn't have the oompf.  I'd call that borderline.

Odyssey makes a similar sized AGM battery that has higher CCA and a reputation with working for this purpose.  I think it is the PC925.  I have no personal experience with it.

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23 hours ago, Grande Mastere Dreade said:

35' boat and you want to remove  50-60lbs... ok...        how about a diet instead?

my first thought .... couple of the crew eat salads for a week or two and bob's your uncle, plus you're not removing good ballast from way down low where it actually does ya some good. 

I wouldn't want to be caught without my "backup" battery in the event I had to use anything electrical on the boat like radio, chartplotter with a big screen that sucks down a lot of juice, or an autohelm... 

how much does said boat weigh- ballparkish?

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We know from experiance that 1 battery can give you trouble after a long day racing to get in the harbour. Running the electronics a full day without recharging is using a lot.

Ok old battery now, but we have sailed more our slip than we would like.

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23 hours ago, Borracho said:

Yes, starting the engine will often reset some (all too typically) poorly designed electronics. Shouldn't be an issue for racers though, right?

IDK - I'd argue its an important safety issue for offshore racing.  If you have an MOB and start the engine to get back to him, and it resets the electronics, you could lose your MOB position on the plotter.  Now you're really screwed.

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@gewoon ik and @Salona raise good points. Two right-sized batteries could be the right choice in some cases. Especially with longer offshore races or where an engine is required for returning. Like I wrote above, the right size for starting an engine could be a quite small battery.

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I was shocked -- figuratively -- to discover that many boost packs are three series cell lithium-cobalt batteries. 3S li-ion is not a good match with lead-acid. If I was considering a lithium backup or starting battery I'd look at a 4 cell lifepo4. Safety aside, lifepo4 is a better match with lead acid.

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On 5/4/2021 at 5:54 PM, egon said:

How about wiring in these between boat and battery:

https://www.mcmaster.com/7043K8/

They make caps as well.

I agree with the more trouble then its worth though.  I kept the 2 battery setup and just went with smaller, lighter batteries.

--Matt

I don't race but I do use that type of connector between batteries and boat.  Great for maintenance and winter storage.

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On 5/4/2021 at 4:31 PM, longy said:

Be careful when starting engine - many electronics will shut down due to the voltage drop when spinning the starter. Easiest work around is do not turn on electronics until engine is running

Not necessarily. 
I've a 120ah lead carbon single battery that I use for engine & domestic. 

I can start my Penta 2001 single without shutting down the electrics. Probably helps that I have a large fuse block with separate take offs for engine & domestic loads, all with good spec wiring. 


That said I'm refitting a starter battery for peace of mind. 

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3 hours ago, longy said:

That's why I said "many". IE, not 'all"

My mind must have glossed over that part when I was reading it. Sorry. 

My old boat everything used to reset as you described, I think this ones resilience is probably more down to the battery & installation quality rather than the electronics themselves. 

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When I disconnect a potentially live heavy cable with a ring terminal, I slide a 12" length of rubber hose over the end and tape THAT in place. Could use a hose clamp or two instead of tape if your hose is sized well. With the terminal end isolated mid way up the hose you can relax about most imaginable misadventures.

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18 hours ago, MiddayGun said:

That said I'm refitting a starter battery for peace of mind. 

that was my choice too. wiring or not, our electronics would reset when we started the engine, and even when you tried to be careful inevitably you'd forget, and I blew up a Zeus 2 that way. I went with a single position battery switch and an ACR and it works exactly as advertised - no more start spikes, and for the really long overnight races I've got a little extra if I need it.

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