Any use in having two banked engine start batteries?

[Davidhoy]

I currently have a seemingly odd configuration - two engine start batteries banked in parallel under the companionway ladder, and a separate generator start battery in the bottom on a locker next to that compartment. The generator battery needs replacement, and I'm considering not getting another instead splitting the engine bank so that one battery goes to the engine, and the other goes to the generator. With an appropriate switch I can still bank the two batteries to start either motor.

Any thoughts on this? Any good reason to have three batteries when two may suffice? One less battery to maintain seems like a good thing, as long as I'm not overlooking something important...

Regards,
David

[Navi2016]

Might simply be a of Amp output required to start the engine, 2 small batteries in parallel instead of 1 larger capacity battery. Less weight to move when installing.

My 2c

[Davidhoy]

Originally Posted by Navi2016

Might simply be a of Amp output required to start the engine, 2 small batteries in parallel instead of 1 larger capacity battery. Less weight to move when installing.

My 2c

Perhaps I should have clarified that all three batteries are group 27 12v marine starting batteries. I would imagine that one of these alone should be able to start either the engine or generator...

[roverhi]

Know that one of the larger Perkins engines, 4-236 maybe, required more than a group 27 to start the engine. To little amperage eats starters and they are expensive to rebuild and grossly expensive new. Check with engine Mfg. for minimum starter battery amperage.

[Davidhoy]

Originally Posted by roverhi

Know that one of the larger Perkins engines, 4-236 maybe, required more than a group 27 to start the engine. To little amperage eats starters and they are expensive to rebuild and grossly expensive new. Check with engine Mfg. for minimum starter battery amperage.

I have a Westerbeke 82B, and its specs call for 250-300 CCA - a typical group 27 starting battery provides way more than this, generally 600 CCA and up. Good food for thought, though...

[Privilege]

Don't forget your charging requirements for the batteries that are now separated. Many gen sets don't have a charging system so if you don't want to be constantly playing with the switch you may need a voltage sensitive relay to connect the batteries.

[Davidhoy]

Originally Posted by Privilege

Don't forget your charging requirements for the batteries that are now separated. Many gen sets don't have a charging system so if you don't want to be constantly playing with the switch you may need a voltage sensitive relay to connect the batteries.

Good point! I checked on this and I already have charging systems for both the engine bank and the generator battery, so if I split the bank I can still use the original systems for the resulting independent batteries. Fortunately all batteries are the same type, flooded lead acid, no need to worry about different charging parameters. I would anticipate that any switch to bank the batteries together would only be for emergency purposes, in the event that one of the batteries cannot start its respective motor, effectively the same as jumper cables. As such a manual switch would probably suffice.

[accomplice]

We have 2 start battery banks, one for the Yanmar auxiliary, the other for the genset. The Yanmar has a 4D. When we replaced the genset battery, we upgraded to a 4D. Tbis way if one battery dies, the other can be connected. Each of genset and yanmar has a small alternator for charging their starting battery.

If you can afford the space and weight, having redundancy is great.

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[Davidhoy]

Originally Posted by accomplice

We have 2 start battery banks, one for the Yanmar auxiliary, the other for the genset. The Yanmar has a 4D. When we replaced the genset battery, we upgraded to a 4D. Tbis way if one battery dies, the other can be connected. Each of genset and yanmar has a small alternator for charging their starting battery.

If you can afford the space and weight, having redundancy is great.

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What size engine and genset are you starting, that need something as big as a 4D? I can see using 4Ds for your house bank, but they seem a bit much for starting purposes. Your point about redundancy is very valid, and I'd still have two independent systems, that can be banked in an emergency.

I may try disconnecting one of the engine batteries, and see how well a single battery does in cranking it. If that goes well I can install a switch to bank them, and connect the other battery to the genset.

[leftbrainstuff]

You cant have too many start batteries. We have two optimas for starting and windlass use. Our generator also uses these batteries for starting.

We then have the house bank and two jump start batteries for additional redundancy.

Our two start batteries are on seperate circuits. Our house bank is seperated into 3 pairs.

You could retire the extra generator start battery and still have redundancy.

[Davidhoy]

Originally Posted by leftbrainstuff

You cant have too many start batteries. We have two optimas for starting and windlass use. Our generator also uses these batteries for starting.

We then have the house bank and two jump start batteries for additional redundancy.

Our two start batteries are on seperate circuits. Our house bank is seperated into 3 pairs.

You could retire the extra generator start battery and still have redundancy.

I appreciate your thoughts :-). In addition to the start batteries, I also have a totally separate house bank of 4 batteries totaling about 440 amp-hours, plus an independent battery up front for the windlass, bow thruster and Electroscan head. Worst case scenario I can pull the bow battery and use it to start the engine...

[accomplice]

Originally Posted by Davidhoy

What size engine and genset are you starting, that need something as big as a 4D? I can see using 4Ds for your house bank, but they seem a bit much for starting purposes. Your point about redundancy is very valid, and I'd still have two independent systems, that can be banked in an emergency.

We have a Yanmar 4LHA. Yanmar recommends a minimum 660CCA/780MCA. Available group 31's were marginal to this spec (650CCA/800MCA).

BTW, We use 4x4D for house, and another 4xgroup31 for windlass/thruster. Plus separate 12V system for comms.



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[Kiwi.]

Originally Posted by Davidhoy

........plus an independent battery up front for the windlass, bow thruster and Electroscan head. Worst case scenario I can pull the bow battery and use it to start the engine...

I had the same setup on a large launch that I owned when I went to the dark side for a few years. It worked very well and saved the cost of some really fat wires to the anchor winch. It was a standard truck battery with a plastic handle that I thought would be great if I had to lift it and take it back to start my 3208 Cats.
One morning, anchored in Drunks Bay Auckland, a neighbouring yacht skipper rowed his dilapidated plywood pram dingy over to ask if I he could borrow a battery to start his engine as he had run his batteries dead flat over night. His teenage kids and friends had kept us awake playing loud music all night and had connected the starter battery link to keep the music going. After taking a deep breath (and not informing him of my opinion of his children) I went forward and disconnected the winch battery and carried it back aft to lower it into his dingy (I was a bit younger and stronger then). As a game fisher my launch didn't have a boarding platform so the battery was at least six feet above the dingy when the plastic handle broke. Straight through the dingy which immediately sank to the waterline. The verbal exchange that followed gave me some understanding of where his children had got their bad attitude from. As he was swimming I simply suggested that he send a couple of the strong teenage men on his yacht over to pull up my 60lb CQR and 100ft of chain by hand; the reply wasn't polite. So I ended up moving an engine battery up to the anchor winch after starting the engines.

[Davidhoy]

Originally Posted by accomplice

We have a Yanmar 4LHA. Yanmar recommends a minimum 660CCA/780MCA. Available group 31's were marginal to this spec (650CCA/800MCA).

BTW, We use 4x4D for house, and another 4xgroup31 for windlass/thruster. Plus separate 12V system for comms

That's a monster engine, at least compared to mine, about 3x the horsepower. Now I see why you might need a 4d. Also 4x group 31 for the thruster all adds up to a pretty big boat. My needs are a little more modest :-). I do like your separate 12v system for comms - I'll have to give that some thought when I install my SSB.

[SV Bacchus]

Originally Posted by Kiwi.

The verbal exchange that followed gave me some understanding of where his children had got their bad attitude from. As he was swimming I simply suggested that he send a couple of the strong teenage men on his yacht over to pull up my 60lb CQR and 100ft of chain by hand; the reply wasn't polite. So I ended up moving an engine battery up to the anchor winch after starting the engines.

No good deed goes unpunished!!!