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How would I go about balance charging either 100 or 75 lipo cells?

This is a very serious question by the way, it's for an electric vehicle and we use either 75 or 100 cells at a go and currently balance them 6 at a time... very time consuming.

Why couldn't we charge them with 100 single cell chargers? Surely they would then all be at the same voltage and therefore "balanced"?

EDIT:

There are 25 cells in series that make a box and 4 boxes in parallel to make the total.

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  • \$\begingroup\$ What is the configuration of the cells? How many in parallel/series? \$\endgroup\$ – Gorloth Nov 18 '14 at 22:30
  • \$\begingroup\$ Sorry if I've misunderstood something but, 25x4 batteries.. and varying from 75 to 100, that means 1 package/box is varying, either missing or inserted, I guess if you would put 4 separate chargers, for each box, you'd be balancing the charging, however, if each cell charge level will vary, maybe you will need to put a specific voltage for the whole box so each cell charges what it needs and at the current it should \$\endgroup\$ – OverCoder Jul 27 '15 at 23:59
  • \$\begingroup\$ I have tried to charge many Lithium cells, what I've noticed that if you supply a 3.7-4.2 battery with 5 volts, the cell would charge at it's reliable current, and after it charges/the more it charges, the current goes lower and lower until it's full, a small current keeps passing to the cells, maybe that will damage them later, you might want to put some charging time limiter or some protection for that \$\endgroup\$ – OverCoder Jul 28 '15 at 0:02
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The cell balancing is performed by a specific circuit a BMS (battery management circuit). Balancing allow to protect a lowest cells from venting and thermal runway. Your configuration is 25S4P, so using a BMS to control current and voltage is the best solution. If you use 100 single cell charger, it will be difficult to control them, since they have different Stat of charge, so the weakest will be rapidly damaged.

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The problem is that if the cells cannot be separated then each charger must have its own isolated power supply. It is usually much cheaper (and simpler) to make one high voltage charger, than having 100 single cell chargers all independently powered.

The usual solution is to have a single high voltage charger, with a balancer circuit on every cell. Once a Lipo battery has been balanced it usually stays that way unless a cell becomes damaged or wears out, so the balancer circuits don't normally have a lot of work to do.

Of more importance is monitoring the cell voltages to make sure that they don't go out of wack. If all the balancers are linked to the charger then it can provide a readout of cell voltages, detect and warn you of any possibly bad cells, reduce current if needed to help the balancers do their job, or even have complete control over the balancing process.

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