Single cell or multiple cell "charging board"

wagspe208

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Dec 8, 2012
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So, I am looking for a board I can put single cells (or multiple of the same cell.... ie 18650) in and use an existing charger. Many rc hobby chargers are super flexible, and can cycle, etc.
I have a nice charger.
I am looking for a "board" I can put the cells into.... IE 18650, 16??? etc.
Thanks
Wags
I hope that makes some sense.
 

poguy

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Oct 27, 2007
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Yes it does make sense. You can get single/multiple 18650 holders from dx.com and others. I mounted 3 PCB-mount holders on a home-etched PC board. There are also versions with wire leads.

A quick search turned up enough of them:
http://www.dx.com/s/18650+holder
 

wagspe208

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I have 18650's in one light. I have 17500's in another. I could just use a holder and charge as one big cell I guess.
I was trying:
a) not to have to make anything. To many projects in life.
b) to be able to balance charge the cells, so in parallel, with leads from each cell to equalize voltages, but a HUGE PITA to make up the connectors.
Maybe I'm just lazy.
If I charge as one cell, total voltage will be correct, however individual cell voltage could be different.
RC battery packs have the "balance lead" where there are multiple cells per "battery pack", but the balance lead allows the cells to be individually charged, maintaining balance.
More than likely I am just over complicating it.
Thanks
Wags
 

BringerOfLight

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I have 18650's in one light. I have 17500's in another. I could just use a holder and charge as one big cell I guess.
I was trying:
a) not to have to make anything. To many projects in life.
b) to be able to balance charge the cells, so in parallel, with leads from each cell to equalize voltages, but a HUGE PITA to make up the connectors.
You should only parallel cells that have about the same charge state.
If I charge as one cell, total voltage will be correct, however individual cell voltage could be different.
That's very literally playing with fire, using different sized cells, with a likely different charge state.
RC battery packs have the "balance lead" where there are multiple cells per "battery pack", but the balance lead allows the cells to be individually charged, maintaining balance.
For almost all RC chargers, the balancing is intended for packs comprised of the same cells with roughly similar charge state and won't work well for your use case (different capacity cells).

In terms of battery holders, most won't fit protected 18650 cells and I haven't found any high quality one.

I would either get a new charger (e.g. most Xtar chargers are decent and they have very cheap ones) or use something like the TP4056 (USB-powered board, extremely cheap on eBay) with magnet leads.

A ton of chargers are reviewed here:
http://www.lygte-info.dk/info/indexBatteriesAndChargers UK.html
 

wagspe208

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Dec 8, 2012
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I wasn't implying I would charge cells of different capacities at once. I get that is a no no. I was just saying I need different cell holders, as the 18650's and the 17500 cells are physically different sizes....Hence looking for a "board" or "holder".
Sorry for the lack of clarity.
Thanks
Wags
 

hiuintahs

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I wasn't implying I would charge cells of different capacities at once. I get that is a no no. I was just saying I need different cell holders, as the 18650's and the 17500 cells are physically different sizes....Hence looking for a "board" or "holder".
Sorry for the lack of clarity.
Thanks
Wags
I had a plastic box laying around and a sheet of copper clad board (copper on one side). I bought the different sockets and then just drilled holes where it would mount to a pcb. No need to etch the copper. I dremeled an isolation boundary between (+) and (-) down the full length of the board. You can kind of see the lighter color where that is. Now I can connect up to a hobby charger or any charger that has external banana jack outputs. Keep in mind with my equipment I can only charge one battery at a time. I got the sockets from either Digikey or Mouser. I do a lot of orders with those companies for work and so just piggybacked the parts so as to not pay shipping. The sockets aren't very much. Also I plan to add another set of sockets for 18650 batteries so that I don't have to put a spacer for my non-protected 18650's.

CSUpLm7.jpg
 

wagspe208

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Dec 8, 2012
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I had a plastic box laying around and a sheet of copper clad board (copper on one side). I bought the different sockets and then just drilled holes where it would mount to a pcb. No need to etch the copper. I dremeled an isolation boundary between (+) and (-) down the full length of the board. You can kind of see the lighter color where that is. Now I can connect up to a hobby charger or any charger that has external banana jack outputs. Keep in mind with my equipment I can only charge one battery at a time. I got the sockets from either Digikey or Mouser. I do a lot of orders with those companies for work and so just piggybacked the parts so as to not pay shipping. The sockets aren't very much. Also I plan to add another set of sockets for 18650 batteries so that I don't have to put a spacer for my non-protected 18650's.

CSUpLm7.jpg
I like this.. AND I could charge 2 cells (of same type, capacity, etc) at once with more sockets.... in parallel... this would not balance individual cells, but it would solve the more than one at a time PITA.
Thanks
Wags
 

HKJ

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I like this.. AND I could charge 2 cells (of same type, capacity, etc) at once with more sockets.... in parallel... this would not balance individual cells, but it would solve the more than one at a time PITA.

Parallel charging will balance cells.
Adding a small resistor (say 0.1ohm) in series with each socket would also reduce any problems with difference in initial voltage.
 

HKJ

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How does that work?

Instead of connected the plus pole directly to the socket, use a 0.1 ohm resistor from each battery socket. This way there will be 0.2ohm from one battery to the next, with a 1 volt different between the batteries the maximum current will be limited to 5A peak (In most cases it will be much less). This is safe for any 18650 cell.
The 0.1ohm will reduce the charging speed slightly.
 

Conte

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Instead of connected the plus pole directly to the socket, use a 0.1 ohm resistor from each battery socket. This way there will be 0.2ohm from one battery to the next, with a 1 volt different between the batteries the maximum current will be limited to 5A peak (In most cases it will be much less). This is safe for any 18650 cell.
The 0.1ohm will reduce the charging speed slightly.

Oh, so it just limits the flow between 2 grossly mismatched cells.
Makes sense, I'll keep that trick in mind. Thanks.
 
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