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Series parallel

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camerart

Well-Known Member
Hi,

I am making a battery charger, that charges a number of cells independently. They are connected in series to make a battery.

I've just found what could be an obvious problem, but I hadn't noticed till now. That each of the separate charge circuit GNDs need to be somehow connected together, so they can be connected to the negative of the power source. (Not sure about the positive side)

Does anyone know how to do this please?

Cheers, Camerart.
 
You would have to disconnect and isolate every cell if you want to charge them individually.

Normal practice is to simply charge them in series as they are.
 
You would have to disconnect and isolate every cell if you want to charge them individually.

Normal practice is to simply charge them in series as they are.

I am trying to make a safe Li-ion cell charger (See my other thread on this subject) After the Boeing problem, I came up with the idea, that with each cell being charged carefully, with it's own circuit and temperature monitor, then this would make a safe charger. I did think of switching between cells but it didn't pan out properly.
 
Buy an inexpensive Li-Po battery charger from a hobby store. The battery has a wire from each cell and the charger senses each wire and balance charges the cells.
 
Buy an inexpensive Li-Po battery charger from a hobby store. The battery has a wire from each cell and the charger senses each wire and balance charges the cells.

For my purpose I eliminated balanced charging.

I was hoping to keep weight down by having 6 cells all charging as I am using them. As this seems impossible, I think I will have two banks of 4 cells. I can use bank one, while I charge the other 4X cells independently.

Cheers, Camerart.
 
You could just limit the voltage on each cell with a bypass device that conducts above the maximum voltage for each cell.

It is also a good idea to reduce the charge rate to C/10 or so if any cell has a very low voltage, but really the discharge should have been stopped before that point.

When I needed to have three LiIon cells in series, I used a relay to disconnect them for charging. Each cell has a separate charger, and they all share a common negative when charging.
 
You could just limit the voltage on each cell with a bypass device that conducts above the maximum voltage for each cell.

It is also a good idea to reduce the charge rate to C/10 or so if any cell has a very low voltage, but really the discharge should have been stopped before that point.

When I needed to have three LiIon cells in series, I used a relay to disconnect them for charging. Each cell has a separate charger, and they all share a common negative when charging.

I have the charging/discharging covered ok, I'm only stuck on the parallel/series problem.

I think your relay idea, or FETs might be the answer.

Thanks Diver300.
 
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