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Old 07-12-2012, 03:57 PM   #1
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2 6v in series and 1 12v

Anyone have any input on using 2 6v golf cart batteries in series along with 1 12v battery? Then paralleled to charge converter?
Reason being, stock battery box on my 75 31ft will only fit one battery, can fit 2 golf cart batteries under curbside bed acessable by the storage compartment .
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Old 07-12-2012, 04:23 PM   #2
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What do you really hope to gain?

You will have a bit or cable re-routing, and I would build a box for the storage space. Don't forget, it is highly recommended to isolate any battery from your airspace. The space you refer to is right under your bed, isn't it?

Also, I don't believe that you can wire in series for operating and parallel to charge. Both those activities happen at the same time.

In your place, I would just get the best battery you can in a single 12V.
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Old 07-12-2012, 04:33 PM   #3
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I'm putting 2 X 6 V golf cart batteries under the bed of my overlander. I wouldn't recommend using the 12V in parallel, just use the 6V's in series.

Make sure they are in a sealed box properly vented!
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Old 07-12-2012, 05:00 PM   #4
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Quote:
Originally Posted by Okotoks View Post
Anyone have any input on using 2 6v golf cart batteries in series along with 1 12v battery? Then paralleled to charge converter?
Reason being, stock battery box on my 75 31ft will only fit one battery, can fit 2 golf cart batteries under curbside bed acessable by the storage compartment .
It will work OK electrically. In telco and marine applications they parallel mismatched strings all the time.

Be sure the 6v pair is vented and is installed in such a way that the acid does not pose a corrosion problem.
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Old 07-12-2012, 05:16 PM   #5
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Quote:
Originally Posted by Aage
What do you really hope to gain?

You will have a bit or cable re-routing, and I would build a box for the storage space. Don't forget, it is highly recommended to isolate any battery from your airspace. The space you refer to is right under your bed, isn't it?

Also, I don't believe that you can wire in series for operating and parallel to charge. Both those activities happen at the same time.

In your place, I would just get the best battery you can in a single 12V.
Well the 6v batteries would be in series to create 12v then connected in parallel to the 12v battery then the 12v battery is connected to the charge converter, my thinking is the 6v in series is over 400amp hours and the 12v is 100 so with 3 batteries I should have about 500 amp hours capacity 12v .
The best single 12v deep cycle is 120 ah? The one I have is 100ah but I got 2 for cheap and they are new. One I am using in my argosy and the other in the AS, I can get golf cart batteries from Costco for $220 for both.
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Old 07-12-2012, 05:24 PM   #6
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I planned to build an enclosure of diamond plate aluminum under bed and then put battery boxes in there and as stated earlier would be acessable from outside .
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Old 07-12-2012, 05:33 PM   #7
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You may have problems charging them properly. Just thinking out loud here, but I suspect the converter will not see them as one 12V battery and therefore undercharge the 12V battery. Someone with more knowledge may be able to help.
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Old 07-12-2012, 05:34 PM   #8
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Well the 6v batteries would be in series to create 12v then connected in parallel to the 12v battery then the 12v battery is connected to the charge converter, my thinking is the 6v in series is over 400amp hours and the 12v is 100 so with 3 batteries I should have about 500 amp hours capacity 12v .
The best single 12v deep cycle is 120 ah? The one I have is 100ah but I got 2 for cheap and they are new. One I am using in my argosy and the other in the AS, I can get golf cart batteries from Costco for $220 for both.
Are you saying that your 6 volt battery is 400 ah?

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Old 07-12-2012, 07:04 PM   #9
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I'm wrong Andy, as soon is I read your post I realized what I did, the 6v batteries are 110Ah each not 200 each! Oops.
I do see what you mean about possible charging problems as 2 6v in series are 12.2-3v where as the 12v should be 12.5-6? If thats the case then the charge converter might overcharge the 6v batteries,am I wrong about the charge state of the 2 6v batteries? I have never used 6v batteries before so this is new to me,
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Old 07-12-2012, 07:07 PM   #10
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When you use 2 6 volt batteries you do not add the amp hours together. If they are both 120 amp hours your total is 120 amp hours.
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Old 07-12-2012, 08:09 PM   #11
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Lol! while ohms law and series-parallel circuits are great to know, if it isint used frequently then it's almost forgotten, as I have just shown!
yes series connection doubles voltage?, parallel doubles amperage?.
So while I didn't actually look at the golf cart battery specs I just assumed.In actuality the 6v golf cart batteries are probably 200-220Ah? If I used the 2 6v in series and paralleled them to the 12v I should have around 300Ah, this week of 30+ temperature must have fried my brain. My math and logic on the last 2 posts makes me feel like a noob.

If I am now correct then back to the possibility of making this work.

Will a setup like this work long term? I am crazy enough to try!
Comments, Suggestions and or ridicule ? I'm all ears(eyes?)
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Old 07-12-2012, 08:27 PM   #12
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I have been told many times that it is bad to parallel mismatched batteries since they will not charge evenly which will shorten the life of the batteries at best.
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Old 07-12-2012, 08:31 PM   #13
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Check out a thread on how to "add additional batteries " to your airstream I did a little write up up on what I did my 1975 with the single curbside battery compartment , I gutted the stock battery box to make more room and made a tray to hold 2 6 V sideways. It has worked out pretty well but I had to use AGM batteries (high dollar) because I could not seal them off from the cabin of the trailer adequately. I used two lifeline 220 amp hour batteries in series. That almost tripled the available amp hours. This makes dry camping much more luxurious with the available capacity(about two days with minimal power management). I also wired a battery meter so that I do not ruin the batteries from excessive discharge. Try to search for that thread if you have any trouble message me.
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Old 07-13-2012, 10:04 AM   #14
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I have been told many times that it is bad to parallel mismatched batteries since they will not charge evenly which will shorten the life of the batteries at best.
That is the received wisdom. While it is true that one battery may charge more quickly, there isn't any science to support the assertion that that will somehow affect the life of either battery string, using the converters typically installed in Airstreams.

Most problems with complicated battery strings have to do with corroded connections, not with the inherent limitations of the batteries themselves.
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Old 07-13-2012, 10:39 AM   #15
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Quote:
Originally Posted by Okotoks View Post
Lol! while ohms law and series-parallel circuits are great to know, if it isint used frequently then it's almost forgotten, as I have just shown!
yes series connection doubles voltage?, parallel doubles amperage?.
So while I didn't actually look at the golf cart battery specs I just assumed.In actuality the 6v golf cart batteries are probably 200-220Ah? If I used the 2 6v in series and paralleled them to the 12v I should have around 300Ah, this week of 30+ temperature must have fried my brain. My math and logic on the last 2 posts makes me feel like a noob.

If I am now correct then back to the possibility of making this work.

Will a setup like this work long term? I am crazy enough to try!
Comments, Suggestions and or ridicule ? I'm all ears(eyes?)
Your trying to cross the street by going around the block.

Series paralleling batteries is a very bad idea.

Using 2 six volt batteries in series as opposed to 2 twelve volt batteries in parallel, has a HUGE down side.

Example # 1. One of the 6 volt batteries gets weak. Your done. Nothing will work correctly.

Example # 2. When using 2 twelve volt batteries in parallel and one gets weak, simply disconnect the weak one, and your still in business.

Also, NEVER, EVER, parallel or series connect batteries that are not exactly the same. The charging of them will be very different, resulting in more trouble.

Ohms law has not changed. Following Ohms law rules, is the only safe way to go.

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Old 07-13-2012, 11:02 AM   #16
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Of course if one of your six volt batteries in series fails you still have the option of disconnecting them and running off the tow vehicle until you can get to the battery store.

While my experience is strictly subjective, I am now starting year 10 on 2 Exide golf cart batteries. Never made it past 4 years on any 12 volt deep cycle I had.

If I had both the 6 volts to put in series, and a 12 volt to parallel with it on hand I would do it. If I had to go buy the batteries I would not.
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Old 07-13-2012, 11:13 AM   #17
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That is the received wisdom. ... there isn't any science to support the assertion that that will somehow affect the life of either battery string,...
I started not to post this here, but it does seem in the general vein of the OP, so here goes...

Whats your thoughts on Science verses and Imperfect world when it comes to battery failures? I have gone through literally dozens of batteries in RV's and Trailers with many being parallel failures. I'm brutal on them...

My old RV had dual house batteries, most of the time I had two different types or ages and it seemed as soon as one got some age, I let it get low on water or ran it down on a trolling motor (the 'Brutal' part comes to play here...) I would end up with with one boiled and the other dead or injuried. (2 stage charger/inverter)

One outing, my 29' airstream killed the Group 24 that I had attached to the umbillical while the GRP 27 in the box survived. (Univolt)

My latest Galvani homicide involved a 3 battery set, the 1 year old boiled dry while the 2 newer matching ones survived. (3 stage charger/minder)

With my 'lack of attention' method of maintance, I just 'seem' to have better luck if all the cells in parallel are of the same type and manufacture. Thoughts?
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Old 07-13-2012, 11:29 AM   #18
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The problem with having batteries in parallel is that if you have a shorted cell you'll end up discharging the good batteries into the one with the shorted cell.

You can get a shorted cell from charging a battery that's low on electrolyte, or from lots of cycles, especially if you deep cycle a battery that isn't meant for deep cycling.

For that reason you don't want to leave junk batteries in parallel with good ones, but there's no actual problem mixing two serviceable batteries of different ages, or two batteries of different shapes or sizes. To some extent the newer/larger batteries will have lower internal resistance and will charge and discharge somewhat faster at the beginning of the charge or discharge cycle, but that doesn't matter much.
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Old 07-13-2012, 01:05 PM   #19
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Hate to keep repeating the same suggestion, but install a marine battery isolator switch; and use and/or charge them one at a time.

When one gets discharged, switch to the other one. Same with charging, which will take half the time compared to charging two batteries connected in parallel.

Also, if one battery goes bad, switch to the other one until you can buy a replacement. By isolating them, differences in battery size and age do not matter (though both should be 12 volts).

Additional advantage: Switching to OFF completely disconnects both batteries, so they hold a charge while Airstream is in storage.

=============

Link to battery isolator switch below is provided for reference only. Other brands and sources may be cheaper and/or better:

Amazon.com: Perko 8501DP Marine Battery Selector Switch: Automotive
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Old 07-13-2012, 01:51 PM   #20
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Pheonix a battery isolator switch is a really good idea with the setup the OP is talking about and also minimizes the problem of someone forgetting to turn off some light while boondocking since only 1 battery or the 2 6V in series would go dead and you could switch to the other battery.
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