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View Full Version : Anyone tried the wire-em-together method of top balancing?



nedfunnell
01 August 2015, 2206
I need to top balance my pack and was researching how to do it without 10000 multimeter measurements. This source seems pretty legit. Anyone tried it?

http://liionbms.com/php/cell_prebalancing.php

furyphoto
01 August 2015, 2244
Wiring batteries in parallel is an easy way to pre-balance cells. You can think of electricity a bit like water, it wants to find level. Current will flow to the lowest voltage cells until they are all even. If you have widely varying Internal Resistance in your cells, they might not balance perfectly. But if all of your cells are decent it should get you very close.

Make sure you get you connections correct! All positives together, all negatives together, and never the two shall meet. If you get one backwards, it will be spectacular! :O

You have to connect them all at the same time for them to all balance perfectly. If you do them in batches, the batches could balance at different voltages from each other if some batches had higher or lower cells.

Athlon
02 August 2015, 0542
parallel charging is a very good way to do balancing but is time consuming. I generally when get new cell first charge in series up to 90% , then switch to parallel and finish the latest 10%. Doing a complete parallel charge on big battery ( 10 kwh or more) it takes very long time because you are charging at low voltage.

One important thing to do in parallel charging is to connect one wire of the chareger on one end of the parallel network and the other on the other side , this will take care of voltage drop across wire. If you don't use this trick you will end with a 20-25mV unbalanced cells

nedfunnell
02 August 2015, 1448
Thanks for your responses. I am now trying to figure out how to do this with Leaf modules, which are internally connected in series- I have eleven 2s modules that can't be broken down to 22 cells. I could do 11 and 11, I guess, with parallel charging, and get pretty close.

furyphoto
02 August 2015, 1650
You are right. You will have no choice but to do 2 groups. You can balance them at the same time though. Turn the cells so all of the red terminals line up (as opposed to having them alternating for your 90v pack) Connect all of the reds together. All of the blacks together. All of the whites (middles) together.

If you are going to be parallel charging as Athlon mentioned then I would only do one side at a time. Positives and middles. Then negative and middles.

DRZ400
02 August 2015, 1950
When I did mine, I charged them in series to 90v. Then used (2) single cell 2amp chargers to bring 1 module at a time up to 4.2v Took 4-5 days to do all 11.

nedfunnell
04 August 2015, 1953
When I did mine, I charged them in series to 90v. Then used (2) single cell 2amp chargers to bring 1 module at a time up to 4.2v Took 4-5 days to do all 11.

Maybe I will try something like this. I can bulk charge to the same voltage (I also have 11 modules), and have 6s and 7s balance chargers available. I am not sure what the balance current of the Accucel-6 or Hyperion 0730i Net3 are. I wonder if I'd be better off setting them to balance 6/7 cells at a time and letting them roll, or manually charging one at a time like you did.

nedfunnell
05 August 2015, 1823
I checked my cell voltages tonight and found I'm within 30mV all around, so I am going for manual balancing. With a 12v automotive light bulb, I am drawing down cells and pairs that are higher than the rest of the pack. The pack is pretty well balanced because I charged each module individually before assembling, so I am just evening out the deviation that has crept in since last year. I didn't pay strict attention then, either.

A thought: once I am top balanced, could I them just discharge nearly all the way, and identify the cell which is weakest, and then only need to monitor that one for LVC when riding? Which cell is the lowest is not really going to vary, so it seems that that could be a poor man's way of doing a safer LVC than just pack voltage.

Also: what kind of voltage deviation is a good target for balancing?

Athlon
06 August 2015, 0106
monitoring just one cell for LVC is not enough. The weakest cell is not always the same , for sure you can find 4-5 cel that are below the average of the pack , but probably one wil be the weakest when you ask high current ( high internal resistance) , another will be the weakest on low current ( smaller capacity) also temperture will change the spec , maybe one of the weakest cell wil perform well in cold and other cells wil be the limiting factor of the pack