Can serial connected cells also be paralleled?

[dendy]

Hello all,

I really hate to post a question so deep inside a thread but this is the most related thread I could find for my question about series and parallel connections of LiPo batteries. Please tell me if I should start a new thread now. I don't mind.

Can serial connected cells also be paralleled in order to keep them balanced during discharge and bulk charging? It seems that if the cell potential should be roughly the same, a parallel connection between cells should keep the cells balanced better.

What if we have a 10s battery comprised of two 5s packs. Can the cells of the two 5s packs be connected in parallel (using the balance leads) while being discharged and charged as a 10s battery (through the main leads)?

Thanks in advance for any guidance!

Dendy.

 

[Punx0r]

No...

Nothing (main leads nor balance leads) can be connected simultaneously in parallel and series.

Your plan would only work is the series connections were broken between the two packs, everything paralleled connected and then charged as a single, 10Ah 5S pack.

 

[dendy]

Thanks Punx0r for your quick reply!

Just curious about the reason for this. Is it that excessive amps will attempt to travel through the balance leads and fry these delicate wires. Or is there something else even more fundamentally flawed about this scheme. For some reason, I cannot get the reason but I have not done it because I too am convinced that something is wrong with it.

Thanks again,
Dendy.

 

[amberwolf]

Just curious about the reason for this.

draw it out on paper, you will see that the connections short each other out.

Smoke.

 

[999zip999]

Test and let us know. Please don't or take pic's and ?

 

[dogman dan]

If it's not clear yet, what we're trying to say is that you can't paralell 1s with 2s or any other combination that is connecting differing voltages. The 8v 2s would try to charge the 4v 1s very very quickly, and likely melt wires, or tabs in the packs.

YOU CANNOT connect two packs balance plugs paralell if the packs have the main wires series connected. Before you paralell the packs at the balance leads, you have to break the series connection at the mains.

 

[dogman dan]

Maybe I'm slightly confused, but I think once you make that series connection, cell one of pack one is 4v. Cell one of pack two is 25v since it's - lead is now connected to 25v from the othe pack.

 

[dendy]

Thanks all!

Dogman, I know you must be correct. I'm letting the incorrect use of my multimeter talk me into a very expensive mistake. I'm taking the potential difference across each cell and thinking, "It's the same." In fact, as soon as these serialized cells are connected in parallel they will see vastly different potentials and attempt to balance themselves in a hurry. What a mess!

Thanks for being patient in answering this question.

Dendy.

 

[Ypedal]

educational reading

http://ypedal.com/zippy/zippy.htm

http://ypedal.com/Cyclone/cyclone4.htm

 

[amberwolf]

In fact, as soon as these serialized cells are connected in parallel they will see vastly different potentials and attempt to balance themselves in a hurry.

No, they will short out. Not the same.

 

[dogman dan]

Yeah. They will try to balance in a REAL HURRY. Big enough hurry to call it a dead short.

Nit picking the use of english here, but the point is, the inbalance will be big enough to vaporize the wire, and scorch portions of your fingers holding the connector, in a nanosecond. We call it kentucky fried fingers, KFF.

Yeah, you know I learned it the hard way.

 

[GMUseless]

Just curious about the reason for this.

draw it out on paper, you will see that the connections short each other out.

Smoke.

I drew some pictures regarding this a while back...might help you visualize it better: http://endless-sphere.com/forums/viewtopic.php?f=14&t=38406#p560368

 

[dendy]

Thanks for all the great info!

I believe I completely understand now. Thanks Ypedal for sharing your projects as they are also very helpful and thanks GMUseless for the thread. I wish I had found that thread first as it was the same question.

Dendy.

 

[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

 

[cal3thousand]

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

He's on a roll folks!