Small 24V 7s Charger for hardcase

Hi guys,

i would like to build a small hardcase (mobile battery pack) with a 24V system (7 packs with 40 18650 cells each) and i am currently looking for a small charger for this system. I would like to install the charger permanent in the case. So it should be as small as possible.

Could you recommend something?

Thank you!

I use the same charger linked above (or very close to it) to charge my portable battery (7s8p). Charges my pack up overnight. However, for a 40P, 2A might be a little slow for you. ~ 2 days. But it is small, and cheap.

Note that this charger doesn't balance charge, although my BMS should watch out for over/under voltage of individual strings. I check the individual voltage occasionally, hasn't been an issue. I use this little meter for looking at voltages quickly. https://www.amazon.com/dp/B07QKZ3PPB

I'm also looking into building a tool case mobile power pack, for occasional use with powertools in remote locations, but mostly for use during emergencies. So it will likely sit for weeks fully charged.

One major issue I have with those sealed 2pin CC/CV chargers is that they charge cells to 4.2V. Leaving Lithium Ion cells fully charged will shorten its lifespan, so I'm going to instead use some combination of:
* Balance charger (ie. with 2+5 leads) with adjustable voltage
* Adjustable CC/CV charger set to 4.05V*cells
* Programmable BMS to start balancing at 3.9V and cut off charging at 4.05V/cell

I did a 'portable' solar power source in a cooler with wheels and a handle I was able to fit in 7s60p ~ 3000wh. I used MPT-7210A as my 'charger' since it accepts a variety of inputs such as 1) couple of 100w solar panels in series, 2) a 120v power supply that produces 24v, and 3) maybe even a couple of wire from car alternator since its a v booster. You can also set the max charge level to anything you want.

I'm able to balance it with a ISDT BattGo BG-8S Battery Meter and is good enough (for me) that it beeps rather than spend on BMS. Power delivered using 24v@1500w inverter and of course one can bypass (turn off) inverter and use the 12v cigarette plugs and USBs directly.

I guess what I learned, is that a bit of cheap/non-optimal/manual (charging, balance, BMS) was OK for me since I rarely use it and when I do I'm the only one. I leave it sitting at around 3.7v most of the time.

ajw22 said:

I'm also looking into building a tool case mobile power pack, for occasional use with powertools in remote locations, but mostly for use during emergencies. So it will likely sit for weeks fully charged.

One major issue I have with those sealed 2pin CC/CV chargers is that they charge cells to 4.2V. Leaving Lithium Ion cells fully charged will shorten its lifespan, so I'm going to instead use some combination of:
* Balance charger (ie. with 2+5 leads) with adjustable voltage
* Adjustable CC/CV charger set to 4.05V*cells
* Programmable BMS to start balancing at 3.9V and cut off charging at 4.05V/cell

Click to expand...

FYI, if you open the charger up, you'll find a trim pot on board to adjust the max voltage. I don't know the minimum voltage that it can be tuned to, but it is somewhat adjustable.