Expand RV capacity with physically split banks?

Swamplizard

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I currently have a 24 V volt 280 amp hour battery pack in my RV. I would like to double the capacity however space is at a premium. Is it possible to have the second battery bank be comprised of two 12 volt packs located about 6 feet apart and combined into a 24v pack?

There is a small amount of room in front of each wheel well inside the RV which could accommodate a 12 V pack. I am not sure what gauge wire would be needed to connect them and make a 24 V secondary battery pack. Has anyone done that successfully?

As always …. Thanks
Swampy
 

Don B. Cilly

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Well, what are the actual distances (including bank-to-bank), what chemistry are the batteries, and how many amps do you plan to draw?
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Swamplizard

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So the batteries are EVE280AH in the 24V primary bank. 100Amp BMS, routinely pull 50Amps for A/C (RV in Florida)

Current battery bank is in corner of driver side near back doors (this is a Promaster 3500 van) and it is adjacent to the LV2424 combo inverter/charger/MPPT with a 2-foot cable from inverter to BMS.

Was hoping I could put half the cells in front of the wheel wells (4 feet as crow flies) which would require running about 8 feet of cable to one side and 12 feet to the other. I understand I should use same length cable to both. Wheel well to wheel well is 6 feet plus some routing distance so let's call it 10 feet.

Sorry not good at doing diagrams on line.

Swampy
 

Don B. Cilly

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50A is quite a bit. Search for "ampacity chart" for the wire sizes.
Same chemistry 12Vs in series, make sure their BMSs allow that... which is unlikely... if you could get small enough 24V ones, and parallel them, it would probably be better.
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DThames

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What size/type of cells for the 12v pack(s). Do you want to make a second 24v pack and just split the cells into different spaces? (one new battery with 8S BMS?)
 

Don B. Cilly

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Yeah, I thought about that, but then 6' of wires (12 actually) between one lot of 4 cells and the other... not sure if that would be a good thing either.
 

Swamplizard

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50A is quite a bit. Search for "ampacity chart" for the wire sizes.
Same chemistry 12Vs in series, make sure their BMSs allow that... which is unlikely... if you could get small enough 24V ones, and parallel them, it would probably be better.
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It is - we have a coleman 3,000btu roof A/C - spikes to 50 on compressor kicking in and then runs 1200 watts. Has not been an issue for existing battery bacnk/BMS or inverter to date. The idea of two 24s might be a solid approach and of course BIG fat wires from battery to battery and to the house power bus.
 

Swamplizard

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What size/type of cells for the 12v pack(s). Do you want to make a second 24v pack and just split the cells into different spaces? (one new battery with 8S BMS?)
I was thinking of buislding the same pack I have now - 8x280AH 3.2s but phyysically splitting them. PErhaps finding two 24v smaller (physically) and parrallelling them is better idea? Not sure
 

DThames

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I was thinking of buislding the same pack I have now - 8x280AH 3.2s but phyysically splitting them. PErhaps finding two 24v smaller (physically) and parrallelling them is better idea? Not sure
Not saying it is bad but if 4 here and 4 there with one BMS, the cell voltage sense lines would be several feet long and not sure if noise on those lines might be an issue for normal BMS function. If that indeed was a concern, then two smaller 8s packs might be a better choice.

Edit, Cat5 cable is made of 4 pairs of twisted wire designed to reject noise. Maybe use twisted pair for signal wires on the BMS.
 

Don B. Cilly

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spikes to 50 on compressor kicking in and then runs 1200 watts

But... 1200W at 24V is 50A. OK, it's not really 24, they'll be around 26.4 most of the time, but...

Still, I'm very much a "don't worry, be happy" sort of chap, I don't really worry about balance, optimal performance, and all that - I can pretty much afford it because I draw very little power - but, having a "split" battery (which will never be balanced voltage-wise) paralleled - via long cables - to a non-split one, the lot drawing some 50A for extended periods of time... I don't know.
Meaning I really don't, I have no idea (or experience) of such setups, I always packed my batteries really close together and as close as possible to any real loads.

Maybe a couple of 24V 100Ah Chins or such, if dimensions allow it... at least you would limit the imbalance to a parallel only setup... which might at least be simpler... hopefully someone who knows better will chime in.
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Swamplizard

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One of the nice things about this site is the ability to "bounce some ideas around". I don't know either if this can work but it would be nice to use every inch of free space wizely in a small RV/conversion Van. I do not use every Amp available nor do I charge to 100% capacity choosing a more conservative longer-lasting and forgiving approach. I'd rather add another 200-280AH and baby them than push my luck - especially when I need off grid A/C for 4-5 hours.....it's a bit of a power pig.
 

Swamplizard

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Maybe I need to re-orgainze my RV's "garage" to simply accomodate another 280AH DIY box. Those Chins are too big. Thanks Tho
 

Don B. Cilly

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Well, if you're getting the cells anyway, try the "split" thing. Use really thick cable.
If you see the "imbalances" actually cause (or seem to cause) problems, you can rearrange them in a close configuration and find a better space.
I mean, unless someone comes up and says, no, voltage imbalance will destroy them, and amp imbalance make them seasick... or something... maybe it's not such a big deal.
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Don B. Cilly

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Maybe use a BMS with active balancer, and that tells you cell voltages.
It would be interesting as an experiment, if it turns out fine, we all learn something, right?

Personally, I don't care much about imbalances. I may be wrong, but I think if they're small enough, and you lose a wee bit of capacity, performance, or whatever, who cares, really.
My (parallel) batteries are always a bit out of balance. I don't really care. Nothing complains, they have some five times the capacity I need... now, maybe voltage (series) imbalance is worse. Maybe not.
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Swamplizard

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I use smart BMS that shows me details per cell and it actively balances ... like you they are rarely perfect especially when fully charged .... but I can live with a little less total capacity and the BMS is mart enough to shut things down when one cell goes a bit high or low.
 
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