Can Lipo balancing wires be paralleled? (diagram incl.)

[zooz]

Hi people,

I am a bit confused over Lipo balancing leads wiring. I tried to find a clear explanation whether balance wires can be paralleled or not, but couldn't find any good explanation. Some people say, that balance wires can stay in parallel, but must be disconnected if connecting packs in series.

Please see the below diagram (excuse me for my drawing skills) of what I think should be doable, but I have not tried it. So I would like to get your advise whether it's safely possible. What I am trying to achieve is to connect balancing wires of three 6s packs in parallel permanently (that makes charging a lot easier). What I am going to have is two 6s large capacity (15Ah) separate packs and then I connect them in series to achieve required voltage - this part seems simple.

But my question is if I can really have balance wires in parallel even when two packs (3x6s in parallel) are connected in series? Please note, that I end up having two separate balance plugs.

So for charging I just:

1. break series connection
2. plug main charge/discharge leads and balance plugs to my parallel charging board
3. start charging

Another concern is (if having balance leads in parallel permanently as shown below is possible) if I ever need to break balance leads and main charge/discharge leads to do a balance charge for each of those 6s packs, so that every single cell of those 6s packs will get balanced properly? Or is this totally unnecessary?

Thanks in advance for your answers. If this thread gets some good ideas and suggestions, I might write a wiki page about this, because I believe there are lots of noobs who have the same questions as I do.

 

[ZOMGVTEK]

It's a very good idea to parallel the balance wires on all paralleled cells. You can't parallel the balance taps on series cells, since that would be a short, making the tiny balance wires go up in smoke.

Your diagram looks right. Lots of people break series connections and parallel all the balance taps for charging. I used to charge my pack at 6S8P and discharge at 24S2P.

As long as you have all the balance taps connected in parallel, you should just about never need to split them to 'balance' the pack. The idea is they will more or less 'self balance'. And paralleling a few cells does help keep them in check. The only real issue is when you have an issue, and need to diagnose what cell is at fault. It's nice to be able to just break the parallel connections so you can individually cycle the cells to know which one to replace. But for balancing, charging, and discharging, parallel is good. Obviously having a few cells connected together makes it awfully hard to tell which one is giving you issues.

 

[dogman dan]

Like you drew it, it's perfectly ok. What you cannot do, is take a jst balance wires Y cable and then connect the two packs of paralelled cells into one big paralell pack, while the two sets are still connected in series. THAT will cause sparks to fly.

Like you drew, you CAN paralell the cells at the balance wires, that are already paralelled with each other at the main wires. Do not paralell sets of packs that are still series connected at the main wires


In general, I don't bother with it myself. Why not? Because if one cell in the pack of three is going south, I want to see it clearly when I look at my packs with a Cellog. If I paralelled them, then I would know what cell number is going bad, but not which pack.

Here's my logic, if they are good, they have no particular need to be paralelled. If they are going bad, I don't want to support the bad cell with good ones, I want it identified and gotten rid of. Occasionally, I may paralell the jst leads to do a balance charge. But mostly I just unplug the weak pack, balance it by itself, and then see if that fixes it. If it doesn't, then into the recylce later bunker.