Can i prallel first then series connect the two lipo's

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Can i prallel first then series connect the two lipo's

Postby recumbent » Tue May 04, 2010 3:44 pm

I purchased six, 8-s lipo's but would like to place three batteries on each side of panniers. 60 volts nominal to be plugged into the controler.

My panniers have a perfect tight sleave attached to the hard wall next to the rear wheel. Ideally I'd like to place three batteries in each pouch, in each pannier.

I hope this makes sense, it's mostly for weight balance.

Each 8-s pack is 30 volts nominal.

Can i parallel each bank of three cells, including the ballance leads?

Then series wire, (with a harness) the two banks together to make 60 volts.
Ebike in use:
LWB Recumbent bike, Sram i-9 internal gears.
Power: 58V, 16 amp/hr, lipo batteries.
max speed: 52 km/h (30 mph),
max range: 40 km's, incl stop&go few times, minimal pedaling.
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Re: Can i prallel first then series connect the two lipo's

Postby mwkeefer » Tue May 04, 2010 3:51 pm

Actually that's how your supposed to build a pack...

Parallel into clusters of smallest cell count (ie, 5 or 6S) but highest AH count (ie: 2P = 10AH), then connect those into series configuration...

You also want to parallel the balance leads between packs in parallel when possible using either solder method or balance extenders like those from Gary Goodrum.

-Mike
Regards,
Mike

{My Rides]
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Re: Can i prallel first then series connect the two lipo's

Postby SilverSurfer » Tue May 04, 2010 4:06 pm

This may seem like an idiotic question, but Im really curious, hell, I NEED TO KNOW! How do you balance 4 cells, in a 4p pack? Because, from what I can see of how a balance circuit is set up. And knowing how to make a battery pack. I cant see how a balancer can tell, or for that matter affect the state of charge in any single cell, in a paralell configuration. I am building a full 24s4p setup right now. two parts 12s4p one on each side of bike. And am planning to setup all my packs 12s with balancers, and hook into parallel after so I can do a full balance charge weekly.

One balance wire to pos side, one to neg side of each parallel set. How can the sensors tell which cell is in what state, and how can the balancer achive any single cell adjustment? God I must be a dork! I cant see it without some isolation diodes and crap. If you want to get the most of the pack, and maintian it properly, you NEED to balance it regularly dont ya? Is it properly balanced if once connected in parallel, the cells never get single cell attention?

Please, talk to me!

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Re: Can i prallel first then series connect the two lipo's

Postby mwkeefer » Tue May 04, 2010 4:23 pm

Silver,

Don't think of it as a 4S4P pack... think of it as a 4S1P 20AH pack - when properly paralleled, each of the balance taps would also be paralleled from the 4P configuration, these are connected to a balancer as if they were a single 4S pack of 20AH and then you balance.

If your going to ask next, but wait couldnt a failed block in the parallel cause failure of the surrounding cells? Yep it could, but monitoring the cells as a pack is good enough providing you don't over discharge or ove charge them as a pack.

Personally I would like balance taps at each P in the pack, atleast for cell level monitoring but really... cell level monitoring in our terms is more of "Parallel Strand monitoring".

Hope it helps!

-Mike
Regards,
Mike

{My Rides]
2010 Dahon Jack - GNG v1 - LYEN 6FET - 20/40A - 18S2P10AH - Nom:66.6v,1332w
2004 Hard Rock Pro Disc - Recumpence ms eDrive v4 - Astro 3220 4T - 12S2P16AH - HV110 - Left Side Drive - Gearing: 38mph
Nominal Peak Power @ 60 seconds: 5328 watts - Maximum Power: 49.8v, 120A, 5872w
2010 Downtube 8FH - Stock GNG v1 Stock Controller - EB809XC - 12-16S
2012 Downtube Nova 7spd - Stock GNG v2 - 12S2P10AH - EB809 - 12S-16S - 20A/30A,Nom VCC: 44.4, 888w
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Re: Can i prallel first then series connect the two lipo's

Postby tostino » Tue May 04, 2010 4:44 pm

Parallel strand monitoring is as good as it gets as far as a bms is concerned. After you parallel many cells, in effect, they become one large cell.

It would add WAY too much complexity to a BMS, and even pack construction, to individually monitor and balance each individual cell.
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Re: Can i prallel first then series connect the two lipo's

Postby SilverSurfer » Tue May 04, 2010 6:40 pm

mwkeefer wrote:Silver,

Don't think of it as a 4S4P pack... think of it as a 4S1P 20AH pack - when properly paralleled, each of the balance taps would also be paralleled from the 4P configuration, these are connected to a balancer as if they were a single 4S pack of 20AH and then you balance.

If your going to ask next, but wait couldnt a failed block in the parallel cause failure of the surrounding cells? Yep it could, but monitoring the cells as a pack is good enough providing you don't over discharge or ove charge them as a pack.

Personally I would like balance taps at each P in the pack, atleast for cell level monitoring but really... cell level monitoring in our terms is more of "Parallel Strand monitoring".

Hope it helps!

-Mike



tostino wrote:Parallel strand monitoring is as good as it gets as far as a bms is concerned. After you parallel many cells, in effect, they become one large cell.

It would add WAY too much complexity to a BMS, and even pack construction, to individually monitor and balance each individual cell.



LOL OMG!!! I bought 16 sets of balancing wires and was just about to bury myself in a nightmare of balancing wires! I thought the individual cell state was vital to the whole, This is gonna be alot easier than I thought! Thanks you guys!
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