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Old 13-08-2019, 20:43   #1
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Too many batteries

I'm sure this subject must have been discussed on this forum but I can find no mention of it.
I have a bank of house batteries and a start battery, that means I have dual output on the mains charger, a switching function on the engine alternator and manual switches from the solar and wind generator.

Wouldn't it be so much simpler to start the engine with the house battery? (that's the only function the start battery has) Then I could do away with these switches and complications.

What do members think, is this practical?
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Old 13-08-2019, 20:47   #2
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Re: Too many batteries

I have one large battery bank that does everything including starting the motors. I do have a separate battery that starts the generator... just in case
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Old 13-08-2019, 23:11   #3
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Re: Too many batteries

Yes, just make sure you really care properly for House, do not allow surprises, and

have at least one layer of redundancy
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Old 13-08-2019, 23:14   #4
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Re: Too many batteries

Sure you can start the main engine with the house bank. Many people do it.


The main reason for a separate start battery is redundancy. The case you really want to avoid is sitting at anchor for a long time and letting the house bank run down, and then you can't start the main engine. A secondary reason is that deep cycle batteries don't provide a lot of starting amps -- starting batteries have thinner plates, and do. But if you have a house bank with many deep cycle batteries wired together, this will not really be a problem for most engines (if you have a giant Detroit Diesel this might be different ).


My boat has not only a separate start battery but an entirely separate electrical system for starting the main engine including separate alternator. So no electrical failure whatsoever in the house bank and general boat systems can affect main engine starting.


However, since a few years ago it has been possible to buy very compact lithium emergency engine start devices. I know some people who carry those for backup starting, and possibly that is an entirely adequate approach.


So you'll have to think about it, weigh the risks, and make up your own mind!
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Old 13-08-2019, 23:57   #5
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Re: Too many batteries

You have 2 banks. The min amount any boat should have. That is not to many.

Solar, wind, alt should all go to the house bank. Why would you send wind or solar to a start bank?

Charge start bank with acr or echo charger.

No need to ever switch anything. As long as battery switching is ok. (Ie not a 1-2-all switch)
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Old 14-08-2019, 00:32   #6
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Re: Too many batteries

Quote:
Originally Posted by smac999 View Post
You have 2 banks. The min amount any boat should have. That is not to many.

Solar, wind, alt should all go to the house bank. Why would you send wind or solar to a start bank?

Charge start bank with acr or echo charger.

No need to ever switch anything. As long as battery switching is ok. (Ie not a 1-2-all switch)

To the OP: If you do stay with two banks, then the above is good advice about the right architecture.


I hate 1-2-Both switches. Use an echo charger to charge the start batt, as SMac suggests, or better a B2B charger to charge the house bank. In either case, don't worry about emergency switching, and toss out that infernal 1-2-Both switch -- jumper cables are all you need for that -- KISS.
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Old 14-08-2019, 03:48   #7
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Re: Too many batteries

We had 4 banks (sb engine, port engine, generator, house bank) , now reduced to 3. We keep the engines start AGMs, the generator is started now by the port engine battery, house bank is completely separated.

I think, it is a good design, the engine start batteries can be combined when necessary by a switch.

I guess, the electronics can be run by the charge current of the alternators without the house battery in an emergency situation, have not tried it yet.
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Old 14-08-2019, 04:38   #8
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Re: Too many batteries

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Originally Posted by Dockhead View Post
To the OP: If you do stay with two banks, then the above is good advice about the right architecture.


I hate 1-2-Both switches. Use an echo charger to charge the start batt, as SMac suggests, or better a B2B charger to charge the house bank. In either case, don't worry about emergency switching, and toss out that infernal 1-2-Both switch -- jumper cables are all you need for that -- KISS.
Agree with what you suggest.
With 1 possible differences.

I have a B2B charging my Start batt, not House bank.

Alts, Solar and AC charger all charge my House bank. Then my B2B charges the Start batt via an ACR.

The B2Bs are only 60A which is plenty for the Start bank, but less than I want for my House bank.

I also agee with not being a fan of 1 2 Both switches. I simply have a seperate On Off switch on each battery bank to the Load bus.
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Old 14-08-2019, 05:36   #9
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Re: Too many batteries

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Originally Posted by Q Xopa View Post
Agree with what you suggest.
With 1 possible differences.

I have a B2B charging my Start batt, not House bank.

Alts, Solar and AC charger all charge my House bank. Then my B2B charges the Start batt via an ACR.

The B2Bs are only 60A which is plenty for the Start bank, but less than I want for my House bank.

I also agee with not being a fan of 1 2 Both switches. I simply have a seperate On Off switch on each battery bank to the Load bus.

You can do it either way, but the advantage of using the B2B charger to charge the house rather than start batt is that you are getting the full multistage charge program on your deep cycle batteries, which your alternator will not give you unless it is externally regulated.


If you do it the other way around, then the B2B charger is kind of a waste of money -- you might as well use a simple echo charger.
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Old 14-08-2019, 10:55   #10
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Re: Too many batteries

cross-reference

Keeping the starting battery charged
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Old 14-08-2019, 13:38   #11
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Re: Too many batteries

At ZENA we recommend using two externally regulated electrically isolated alternators. Small one for starting battery -- larger for house.
This sort of system can easily support any mix of batteries that might exist on a given vessel -- simple to wire -- works seamlessly with both wind and solar charge sources -- provides redundancy -- with a minimal amount of components to fail.
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Old 14-08-2019, 14:09   #12
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Re: Too many batteries

Quote:
Originally Posted by Dockhead View Post
To the OP: If you do stay with two banks, then the above is good advice about the right architecture.

I hate 1-2-Both switches. Use an echo charger to charge the start batt, as SMac suggests, or better a B2B charger to charge the house bank. In either case, don't worry about emergency switching, and toss out that infernal 1-2-Both switch -- jumper cables are all you need for that -- KISS.
Two banks, as OP described on his boat, is a pretty good system allowing for some redundancy.

Yes, you can start the engine on the house bank, (we always do), but the start battery is there for when our house bank is too low (it happens). Usually after a long night sailing when the loads are highest and the batteries were not charged up before we left our last anchorage. No start? switch to #2 (or both), start the engine and let the #2 charge up for a while.

So we do use a 1-both-2-off switch. We don't find it to be infernal. We like it fine. We charge and manage all this manually, as described in another current thread on this subject. As far as KISS? This is the simplest.
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Old 14-08-2019, 20:25   #13
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Re: Too many batteries

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Originally Posted by blazina View Post
At ZENA we recommend
The alternators that can both charge banks and be used as stick welders?

https://www.zena.net/
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Old 18-08-2019, 08:52   #14
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Re: Too many batteries

Personally, I'm of the opinion that engine starting power should be considered a critical system and supplied separately from house power.

On my twin engine power boat, I've got 3 battery banks. House (2x L16 6V), start 1 and start 2 (each a single group 27). House has just an on/off switch. Each engine and the generator has a 1/2/both/off switch, normally configured as follows: port engine set to 1, stbd and generator set to 2. That gives each engine independent starting power (but with the ability to start either engine or the generator from either or both start batteries). The generator does share a start battery with an engine, but that's not of much concern and giving it a separate battery was deemed to be not worth the extra weight and systems complexity. An engine start from the house bank would require use of jumper cables, but needing to do that is very unlikely.

For charging on shore power or generator, each bank is charged independently by a 3 bank battery charger.

Each engine has an ACR next to it (interlocked to that engine's ignition switch) so after starting each engine, once voltage comes up enough, it'll connect that engine's battery to the house bank. With the ignition interlock, the ACRs disconnect immediately on engine shutdown regardless of system voltage to preserve the independence of starting power.

My alternators feed to the engine batteries, as keeping those charged and engine systems powered is more critical if an ACR fails, I can always start the generator to get house power through the battery charger or just let the other engine supply house power on its own.
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Old 18-08-2019, 13:29   #15
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Re: Too many batteries

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Personally, I'm of the opinion that engine starting power should be considered a critical system
Absolutely.

But the same level of reliability through redundancy can be designed in many ways.

Greater simplicity is worth striving for, not just cost / weight etc issues but in itself contributes to greater reliability.
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