Correct method of wiring three Lithium-ion batteries.

[Russ Hobbs]

New to forum, I tried to find a previous post to no avail. I wold like to wire three new Lion batteries in my RV. I looked at the proper way to wire 4 units in parallel, but I cannot find any information to correctly wire three. Lastly, would it be appropriate to bring all three up to full charge separately the first time? I will be charging to 80% once there installed correctly.

Thank you in advance, Russ

 

[Russ Hobbs]

Oops, Would like.

 

[Russ Hobbs]

Is this appropriate

 

[Itsasprinter]

Well, assuming you are putting together a 12V system and these are 12V batteries you just connect the three batteries in parallel. Meaning the 3 positive terminals are interconnected to each other with two wires and the 3 negative terminals are interconnected with two wires.

P1--P2--P3--to house system positive
N1--N2--N3--to house system negative

 

[Russ Hobbs]

Thank you for the reply. I need to know the correct post to take off to the ground and positive. On a 4 battery system they recommend taking a lead off of the middle two batteries. Yes, it is a 12V system. Russ

 

[Itsasprinter]

Take the connections off the middle battery if you are OCD because that reduces current in the battery interconnects. However, if you use the same gauge for the interconnects as for the connection to the house system then you are already running all the current through that gauge wire. Personally, I'd do it the way it is most convenient while using quality over-sized wire.

 

[BiduleOhm]

That's not correct. The best (there's actually a more complicated way that is even better but it only works for an even number of batteries so it'll no work here) is to take power from a diagonal. So either from N1 and P3, or from N3 and P1. It ensures the current is shared equally between each battery.

This document is a very good read: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf I can't recommend it enough

 

[Russ Hobbs]

Thank you, I really appreciate the help.

 

[Itsasprinter]

That's not correct. The best (there's actually a more complicated way that is even better but it only works for an even number of batteries so it'll no work here) is to take power from a diagonal. So either from N1 and P3, or from N3 and P1. It ensures the current is shared equally between each battery.

This document is a very good read: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf I can't recommend it enough

I beg to differ. In the case of three batteries a center connection is a fine option. That's in theory. In reality, tapping one side is no problem if gauge is adequate. Expect a a worst case voltage differential of maybe 0.05V between batteries at 100 amp. Nothing to get excited about. In an RV you are likely to see much lower average discharge and charge currents.
In theory a diagonal connection might be optimal but in most cases it requires a longer wire run to the house system with higher voltage drop and higher cost.
I would agree that when you are interconnecting dozens or hundreds of batteries paying attention to these wiring issues becomes relevant.

 

[BiduleOhm]

I prefer not to debate about the number of batteries, or current, or wire gauge, ... where it gets useful as it's dependent on a lot of factors, including what difference are you ready to accept between each battery so I have the feeling it'll end nowhere. Personally I deem it always useful for example, as the less difference you have the better.

The OP asked for the correct method, I gave the correct method.

 

[Freds northwoods]

That's not correct. The best (there's actually a more complicated way that is even better but it only works for an even number of batteries so it'll no work here) is to take power from a diagonal. So either from N1 and P3, or from N3 and P1. It ensures the current is shared equally between each battery.

This document is a very good read: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf I can't recommend it enough

Would you need bus bars?

 

[BiduleOhm]

between what and what?

 

[Russ Hobbs]

I did take a lead off each end. I ended up using the Redarc 40 amp system with built in 40 amp MPPT solar charger. It was a fun build and I had Redarc check out my install and reading. Everything checked out okay. I did use busbars for both the positive and negative leads. Someone suggested running a negative lead from the battery back and a negative to the chassis ground, I did both. Etrailer has an overmolded battery connect for 2 or 3 battery systems. It was a bit pricey, but it is 1/0 wire and has a cover over each post, (I think it was worth every cent.)and two external bolts to mount your wiring. It worked excellent on the life4PO batteries from Lion. I insulated the compartment and placed a 80w battery heating pad under the batteries.