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Old 31-05-2012, 08:54   #1
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Mixing Battery Groups: 8D and Group 24

Hello all,

I just replaced most of my battery bank. It used to be made of all Goup 24 batteries (that were free). I had two battery banks. Bank one was just one group 24 that I kept isolated to start the engine. Bank two was the rest of the group 24 batteries. When plugged into the shore, I placed the battery selector switch to both so that all batteries are charged together.

I now have two 8D batteries in Bank 2 and 1 Group 25 battery in Bank 1. Does this create a problem if the battery selector switch moved to both? Is there a problem mixing different battery groups?

Your input is appreciated.

Rene "The Witchdoctor" Steinhauer

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Old 01-06-2012, 18:55   #2
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Re: Mixing Battery Groups: 8D and Group 24

No. Just my 2 cents, Mike.

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Old 01-06-2012, 19:28   #3
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Re: Mixing Battery Groups: 8D and Group 24


You might get away with it for awhile, depending on how you use the boat and how diligent you are in setting the switch in the right position.

However, this is far from the most desirable setup.

Much better is to route all onboard charging sources -- alternator, battery charger, generator, wind generator, solar panels, etc. -- directly to the house batteries (the two 8-D's). Then, use a voltage follower device like the Xantrex EchoCharge or the Balmar DuoCharge to maintain the start battery.

These devices do this need to switch anything, and no need to worry about making a mistake (and possibly blowing out the diodes in your alternator if you pass thru the OFF position while the engine is running).

So-called "battery combiners" or ACR's also would work...they combine the batteries whenever a charging current is present. I much prefer the voltage followers, though, because they don't "combine"; rather, they sense the presence of a charging current on the house batteries and bleed off a little to maintain the start battery...automatically. This avoids any possibility of creating huge in-rush currents when you combine, e.g., a deeply discharged large battery bank with a near fully charged start battery.

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Old 04-06-2012, 08:48   #4
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Re: Mixing Battery Groups: 8D and Group 24

You can do the same with a Combiner but you don't even need to change all the wiring to the house bank. A Combiner has no voltage drop so the house bank will get a full charge and leaving the charging source on the starting battery gives it priority so you can start an engine even if the house bank is LOW.

A Combiner100 (or a Combiner160 if your alternator/charger is rated over 100 amps) regulates the amout of charge delivered to the second battery to a safe level to avoid overheating the alternator. It limits inrush current to a safe level and will never steal charge from the starting battery.

If connected directly to a large discharged houxe bank an alternator originally designed to maintain a starting battery could be overloaded but by passing the charge through the Combiner it may take a few minutes longer to charge and protect your alternator. Only when the house bank has reached a safe level of charge will the Combiner hold them connected together.
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Old 04-06-2012, 08:56   #5
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Re: Mixing Battery Groups: 8D and Group 24

no problem
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard

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