How can I drop voltage to store cells easily?

[18650destroyer]

Hello, I just picked up 11,000+ cells and a couple chargers with no idea what to do so in the meantime I would like to discharge the cells slightly for storage, what is the best way?
I have been building packs for a few years and paid $700 for batteries and chargers and didn’t think what I would do with it all, just got excited over the goodies.
I am going to redo the charging area for better air flow.

 

[OffGridInTheCity]

Me? I'd start the test process on these cells

 

[Korishan]

I would like to discharge the cells slightly for storage, what is the best way?

If you get a few Blue Leds in parallel, and connect it in series with the cell and a load resistor (about 5W would be fine, max of 1.1A discharge), it'll turn off around 3-3.3V. This will keep the cell from being overly discharged. Having a few in parallel will share the current
(there's probably a better way, but this was a quick response if you happen to have leds available)

But I agree with OffGrid, start processing and sorting according to the capacity and voltage drops after resting. With that many cells, it'll take awhile to process unless you have a lot of chargers/testers read to go.

 

[floydR]

How long will you be storing them? ≤12 months reducing the voltage isn't really needed, agree with OGITC. What is the voltage of the cells now?
later floyd

 

[harrisonpatm]

If you get a few Blue Leds in parallel, and connect it in series with the cell and a load resistor (about 5W would be fine, max of 1.1A discharge), it'll turn off around 3-3.3V. This will keep the cell from being overly discharged. Having a few in parallel will share the current
(there's probably a better way, but this was a quick response if you happen to have leds available)

Ooo, this is a good idea, thanks for that. I will add that function to my discharging bank. I also agree with starting the testing of all those (great find on everything for 700, btw). However, if and when you get around to needing to discharge them:

You can get a bunch of those cheap 4-cell holders and connect as many as you want in parallel and connect those to a resistor bank of appropriate size. I made this to bulk charge low voltage cells slowly, but I also upgraded with several resistitors to discharge 40 at a time as well. Other members have showed me similar setups, nicer ones, where each slot is individually fused and he can daisy chain a bunch with connecters. Principal is the same.

 

[Korishan]

Do keep in mind (found this out myself recently in another thread) that "practical" application and "realworld" application is a bit different. You may need to play with resistor values, perhaps a voltage divider to make sure the voltages are where they need to be.

 

[OffGridInTheCity]

Probably not what you're after, but I use an iCharger X8 + some 20" long flat nickel strips and small round magnets. I line up the cells with magnets on each end and the nickel strips 'stick', paralleling about 20cells. Then use the iCharger storage mode (e.g. auto cut-off) to discharge to 3.6v. Rinse and repeat.

 

[harrisonpatm]

Do keep in mind (found this out myself recently in another thread) that "practical" application and "realworld" application is a bit different. You may need to play with resistor values, perhaps a voltage divider to make sure the voltages are where they need to be.

Same. In my above setup, I added a certain number and value of resistors that I thought would give me an appropriate discharge rate for 40 cells. When I connected it and measured with a multimeter, amp draw was by like 50% from what I had on paper. There's wire length, tray length, varying voltages, ect...

 

[Korishan]

amp draw was by like 50% from what I had on paper. There's wire length, tray length, varying voltages, ect...

amp draw will be dependent on voltage with a set resistance. So if you have 4V @ 20 Ohms, that'll be 0.2A/0.8W. But when the voltage drops to 3.8V, then it'll become 0.18A/0.648W. Not sure what resistances you are using, but just keep in mind that as voltage changes, amp/watts used/consumed will drop as well.
When all cells are in parallel (if you're doing this) all cells will have the same voltage. But I'm guessing you are using the same drain resistance for different single cells connected.

Also have to remember that the wire used, how ever long it is, will add resistance, as well as any connection. Obviously you aren't soldering the cells/wires together, so that pressure contact adds a layer of resistance. Perhaps a good idea would be to measure the overall resistance w/o the cell in place. This will give you a better idea of what load resistors to use.