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Two battery setup in camper (lemmy.world)

submitted 1 year ago by figurys@lemmy.world to c/askelectronics@discuss.tchncs.de

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I want to change te battery setup in the camper van a bit.

Currently there is a single battery which is charged by either solar, engine or 230v. Then a transformer to 230v to power the outlets.

The idea is to add an extra battery. A lot of people are saying that it isn't a good idea to put those batteries in series or parallel if the batteries are not exactly he same. Now our idea is to switch between the two batteries with the help of some relais and an Arduino or something. So then + of both batteries would be connected to a relay and after the relay we can connect them together. Is this a good/safe way of doing that? Or will we be running into issues that I'm not seeing.

Thanks in advance!

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[–] IsoKiero@sopuli.xyz 3 points 1 year ago (1 children)

Get a switching relay or one normally closed and another normally open one. That way there's no paraller connection at all. Connecting two batteries together with different voltage levels causes a huge current spike, think jump starting a car and how thick those cables are. Arcing will happen on the relay contacts no matter how you switch it if there's load connected.

And since you're not talking about a trailer, is one of the batteries for the car itself? Since if you're planning to use the secondary battery as a car battery too you need very heavy wiring to give starter enough amps to run plus running that over a relay is a whole another beast to manage since starter motor can pull hundreds of amps momentarily.

[–] figurys@lemmy.world 1 points 1 year ago (1 children)

Is an extra utility battery. So that shouldn't give any issues for starting. That's a separate battery. I'll try to find one of those relays. I know I can search myself but if you have any suggestions they are always welcome:)

[–] IsoKiero@sopuli.xyz 2 points 1 year ago (1 children)

So you'll have total of 3 batteries at the car? One for engine, existing utility battery and now you're planning to install another utility battery, right? That should work. I don't know how much current you're pulling from the battery, so it's difficult to recommend anything. Common bosh switching relay is something you can find from pretty much every car part store for ~5€, but I think they're rated only up to 40A and I wouldn't push them to the limit. Check your inverter datasheet how much current it can draw and preferably get a relay which can do double the maximum rating for longevity and stability.

[–] figurys@lemmy.world 2 points 1 year ago (1 children)

That is correct. 1 battery for the engine and 2 for utility. I guess it has to be quite a beefy one. The interter is rated for max 166 amps. So that's quite a bit. Which also makes it a bit hard to find a suitable relay.

[–] IsoKiero@sopuli.xyz 2 points 1 year ago

12V 200A relays are pretty easy to find (I wouldn't get one from alibaba tho), but that much current requires quite beefy wiring as well. Personally I'd review options to place auxiliary batteries in parallel since that would simplify wiring and the whole system a bit, but as I don't know how your camper is built it can be tricky or you need to sacrifice storage space somewhere.

And as you're placing a battery at the same space where people stay be careful with hydrogen. Charging lead acid battery produces hydrogen and in the worst case scenario, specially if you have a gas stove be dangerous if not lethal.