Series connected packs with paralleled balance leads

[Kepler]

Not sure if I am missing something here, but is there really a problem with say connecting 2 x 6S packs in series for 12S 1P then connecting the balance leads in parallel?

I have always been of the belief that you can only connect the balance leads in parallel if the packs are connected in parallel but now thinking more about it, I cant really see a problem regardless if the packs connected in series or parallel.

Going to the extreme, the pack in my bike is 30S 3P. I am now thinking I could just parallel the balance leads on all 15 of the 6S packs back to a single big 6S pack. Theoretically I could then charge through the balance lead connection as a 6S pack even though it is still configured as a 30S 3P pack.

So am I missing something here?

 

[itchynackers]

I believe your balance wires will melt/spark/flame if those are all connected together in parallel while you are wired in series. Don't ask me how I know.

 

[mistercrash]

I read in here that the only problem would be during charging the packs, you would have to make sure all of your series connections be disconnected before attempting to charge from your paralleled balance leads.

 

[Kepler]

I believe your balance wires will melt/spark/flame if those are all connected together in parallel while you are wired in series. Don't ask me how I know.

Sounds like some field testing has been carried out :lol:

 

[Kepler]

Yep, figured it out. Balance leads will go up in flames. Needed to draw it out to understand the short circuit created.

 

[itchynackers]

Unintentionally. I was getting the battery out of winter storage. It was all paralleled up (mains and balances). I went to series the pack up, but forgot to disconnect the balances. Snap, crackle, pops ensued. Time to build a new balance harness. No harm done to batteries, just the harness.

You can/should always keep your smallest group of paralleled packs connected at the balance level. For you it looks like you'd have 5 groups of 6s 3p. So, parallel the 3 packs in each group. If you charge like I do, you'll have a main wire harness that parallels the 5 positives, and 5 negatives. Also, if you want to balance charge, you will need to temporarily parallel the 5 (already paralleled) balance taps via a balance tap harness. I only balance charge once in a blue moon. The batteries just don't seem to get out of balance.

The way I've explained it is probably clear as mud. If you want pics, I can take shots of my 2 harnesses.

 

[GMUseless]

I drew you some pictures so you can sort it out. What you're talking about is setting up internal shorts in your pack as a whole. In the 6s 2P example, notice how, if you trace from - to +, you can never create a loop in the flow...now matter how you cross between packs:



Now, if you series the packs and parallel the balance leads, look what happens. You CAN in fact, tracing from - to +, create all kinds of internal loops:



That essentially is the issue. When you connect the + and - lead together at the end of pack...you're doing the same thing.

 

[Kepler]

Nice. Thanks for that. That certainly makes it completely clear.

 

[mistercrash]

Ok that drawing made me understand how wrong I was. Thanks for taking the time.

 

[chilledoutuk]

charging similar packs in parallel is ok but you do have to be very careful to make sure they are no longer connected in series before paralleling them up.

You could arrange your wiring so that it would be physically impossible to plug the packs into parallel without disconnecting the series connection first.

 

[amberwolf]

wikied:
http://www.endless-sphere.com/w/index.php/Why_You_Can%27t_Connect_Your_Batteries_in_Parallel_and_Series_at_the_Same_Time

 

[liveforphysics]

I love your diagram labels. Nice work!

 

[TheBeastie]

I have a 36v controller and aside from just being more safe I believe I need some kind of voltage meter/cell log as my controller won't cut the power out for my 12s 1p lipo build (which I received today.)

My solution was going to be 2 cell-logs in parallel to each of my two lipo groups with the meters mounted on the top of my bike frame. But now I am afraid that if I use my battery serial/paralleled harness into my controller with my paralleled cell-logs connected to watch over my batteries I will cause a short?
Is it that if I want to use cellogs while riding I need to have 4 while riding? So that its all seperate? Please say no.

Here is a pic of my setup. I used MS Skydrive as I can post larger higher res pic.
http://sdrv.ms/T6Pdzh

 

[cohberg]

As long as you parallel the same packs at pack level that are paralleled at cell level you'll be fine.

Numbering the packs and connectors from top to bottom 1-4, packs 1-2 are paralleled at cell level and should be connected to position 1-2 on the harness. Same for 3 and 4

 

[EdwardNY]

What confused me about this is if I connect packs in a series and then check the voltage at the balance connectors they stay exactly the same. The main battery leads will change.

If the voltages stay the same at the balance connectors no matter how many packs you connect in a series, you would think that you can connect them together.

I must have done something wrong or I am overlooking something.

 

[cohberg]

What confused me about this is if I connect packs in a series and then check the voltage at the balance connectors they stay exactly the same. The main battery leads will change.

If the voltages stay the same at the balance connectors no matter how many packs you connect in a series, you would think that you can connect them together.

I must have done something wrong or I am overlooking something.

gnd your voltmeter on the first pack's black wire. test each balance pin. each pin (excluding the first balance pin in each pack) should read 3.7-4.2 higher. when you get to the red balance tap at the end of the series pack you should be at full pack voltage.

pic?