battery pack with easy change 18650 cells

robowarman

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Feb 11, 2023
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hi guys. i am wanting to build a battery pack where the cells can be changed easily to make use of the low grade 18650 cells. is seams a shame to recycle them. the pack would only be used to power led 12v lights and charged from either solar panel or small wind turbine. i have a rough design in my head. i just wondered what everyone else thinks of this idea as i don't have much experience yet.
 
If you design something with cell holders, make sure they are the ones with beryllium springs (they kinda look goldish/copperish in color). They will hold their tension a lot better/longer than nickel plated steel, and they have a much lower resistance thereby decreasing waste heat.

There are several modular pack designs out there on the market. Aliexpress has several different designs. You could make your own as well.

I've actually thought of doing something like this. But my design would also monitor each cell. It would record the energy feeding/leaving the cells and chart their progress over time. Also monitor the temperature of each cell. And the controller would have the ability to severe the cells connection if there is a fault detected.
I haven't designed such a system yet as I'm still learning the pcb design, general electronics and microcontroller coding and such. Another is that it wouldn't be cheap. So minimizing the pcb footprint is a definite necessity to keep costs down.
 
If you design something with cell holders, make sure they are the ones with beryllium springs (they kinda look goldish/copperish in color). They will hold their tension a lot better/longer than nickel plated steel, and they have a much lower resistance thereby decreasing waste heat.

There are several modular pack designs out there on the market. Aliexpress has several different designs. You could make your own as well.

I've actually thought of doing something like this. But my design would also monitor each cell. It would record the energy feeding/leaving the cells and chart their progress over time. Also monitor the temperature of each cell. And the controller would have the ability to severe the cells connection if there is a fault detected.
I haven't designed such a system yet as I'm still learning the pcb design, general electronics and microcontroller coding and such. Another is that it wouldn't be cheap. So minimizing the pcb footprint is a definite necessity to keep costs down.
thanks for the reply. i cannot do anything as complicated as you describe with the monitoring. so i think a standard bms will have to do for me. im going to order the parts and have a go. its in my head now so i need to do it. cheers
 
Yeah, I was just giving an example. You of course don't need to do that level of monitoring per cell :p

But in either case, I would recommend definitely to go with the beryllium contacts. They are a little more, but will outlast the nickel plated steel easily and maintain good contacts.
And depending on your location, if humidity is an issue, corrosion at the contacts are a lot less, too.
 
Uhm, you know what @robowarman : "low grade" cells I have seem to degrade so much faster than "healthy cells", at least mine. Are you talking about cells with high IR measurements, lets say over 120mOhm? IR is higher every time I measure them. I wouldn't use them for anything a part from the lights on my (pedal, no electric) bike. I'm too afraid of a cell failure, and I have 100 or more of these cells. I would use them only with some extra automatic security, yes, voltage measurement and DC relays to disconnect them immediately in case of out-of-range measurement.
It might be a false problem or maybe it's just me a big exaggerated when it comes to risk management!
 
hi meant cells with a low capacity. a lot seam to get thrown away/recycled it would be nice to use their full potential before sending them for recycling. i appreciate your safety concerns and im right their with you on that. to be honest what these little batteries can do when they go rouge scares me a little. you cannot be to careful. it may just be a bad idea to use the low capacity cells and stick to the better ones. i appreciate your input.
 
cells with a low capacity
Ah ok, low capacity cells. I don't really know how much they will lose, lets say, in the next year; so, it would be impossible for me to make a balanced battery. I have quite a few pink Samsung 26 series cells which have lost capacity... I don't like them! LOL
 
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