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Old 24-05-2015, 08:22   #1
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Combining two "house" banks

I got rid of the 2007 era starting battery when I bought my boat three months ago. Rather than a new starting battery, I just made the 2013-era deep cycle house battery the starting battery (it was a very small Diesel engine) and put in a new deep cycle marine battery for the house load. The batteries are right next to each other physically, and electrically are combined/separated through the typical perko switch (off 1 2 both) and also have isolator diodes so the engine alternator would charge both no matter where the switch was.
However, with the dead diesel being replaced by a pull start outboard, I no longer need a start battery in reserve.
While all my research (Calder, Internet) says that connecting batteries of different vintages is a no-no as far as battery replacement goes, would it be okay to do for a month or two until I get home and pull the 2013-era deep cycle and replace with new? I was thinking that it would just be nice to have the extra amp hours in the bank for now, and the solar setup is only charging the new battery right now so the 2013-era battery is just being wasted. Thanks!
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Old 24-05-2015, 08:29   #2
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Re: Combining two "house" banks

Whatever charging source you are using for the second battery is being negated by the isolator. You should get rid of it, it drops almost an entire volt, so your charging is getting killed right off the bat. Calder shoulda told you...

You can use the 1-2-B switch in B ONLY when charging to do this manually.

If the new battery handles your house loads, then wait. If you charge without the isolator, then your second battery can at least get a good charge and be used as a reserve.

Good luck.
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Old 24-05-2015, 09:16   #3
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Re: Combining two "house" banks

To further what Stu said:
I would charge together, use each bank separately, until you can get back and make the batteries equal. You can still use both banks, just not at the same time.
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Old 24-05-2015, 10:27   #4
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Re: Combining two "house" banks

Sorry, I left out an important detail! I have hooked up my solar system directly to the house battery's terminals (the engine battery was just there for the engine, after all). I was thinking that I would just wire the old (engine) battery to the new (house) battery so that I would have a larger house bank, and that the old battery would get the benefit of the solar charge. The old battery now is basically useless because without the Diesel engine, it has nothing to do, and no way to get charged.
The isolator diodes are inefficient, but they worked so well when the engine was working!
Thanks for the advice.


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Old 24-05-2015, 10:33   #5
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Re: Combining two "house" banks

I personally would put the switch on both and not worry about it.

There are other threads discussing this situation here if you choose to search for them.
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Old 24-05-2015, 10:41   #6
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Re: Combining two "house" banks

Yes you can combine them. I sailed for over a year with different combined batteries with no issues. Gel and wet cell!
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Old 24-05-2015, 10:56   #7
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Re: Combining two "house" banks

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I personally would put the switch on both and not worry about it.

It's that simple?! The threads I was reading were talking about ACRs and voltage regulators, etc. Over my head. Of course, it does make perfect sense that putting the perko on both would allow the house battery to pass the solar current it's receiving into the perko switch and on to the engine battery. I just wasn't thinking out of the box of strapping them together with copper wire which is how the installation directions showed it. Thanks everybody!


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Old 24-05-2015, 10:57   #8
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Re: Combining two "house" banks

*reaches over and flips switch* (it's just for a little while!)


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Old 24-05-2015, 12:02   #9
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Re: Combining two "house" banks

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Yes you can combine them. I sailed for over a year with different combined batteries with no issues. Gel and wet cell!
Interesting Cheech,
I have a house bank of 450 amp-hrs, and then a starter battery. I fry my starter battery every few years when I leave the switch on both, even though they are all wet cell. I think the big alternator goes directly to the starter bat, maybe that is what is doing it.
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Old 24-05-2015, 12:15   #10
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Re: Combining two "house" banks

s/v Beth, make sure your "big" alternator is going directly to your house bank. But, maybe you are "frying" your start battery by deep discharging it when you leave them combined (most likely I think). Start batteries do not like to be deep discharged and it only takes a few cycles to ruin them. And I don't thing the discharge has to be that deep to do the nasty deed.

The OP on the other hand has stated that both of his batteries are "deep cycle marine" batteries.
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Old 24-05-2015, 13:13   #11
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Re: Combining two "house" banks

put the switch to both for now.


when you get new batteries wire them direct together with a single lead to the swtich. (replace swtich with on / off one if you want)
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Old 24-05-2015, 21:49   #12
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Re: Combining two "house" banks

Interesting idea Deep. I try not to discharge below 80% at all, but maybe that is what is frying it. Going to replace with an identical house bank soon. First want to get solar up and running.
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Old 25-05-2015, 08:34   #13
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Re: Combining two "house" banks

For now I would lose the isolators, connect you solars to the common terminal of you perko. That way you can select either 1 or 2 and charge either battery.
I would say run on them alternately. If you run on both you are going to weaken the new battery to the state of the old one.
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Old 25-05-2015, 10:56   #14
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Re: Combining two "house" banks

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For now I would lose the isolators, connect you solars to the common terminal of you perko. That way you can select either 1 or 2 and charge either battery.
I would say run on them alternately. If you run on both you are going to weaken the new battery to the state of the old one.

Ditto that!!
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