9S or 10S Discharger

Has anyone got any suggestions on how to build a simple discharger for a 9s or 10s battery. Like the Foil drive one but to support bigger packs. I have 4 batteries now and occasionally when I charge them all up I don’t get to use 1 or 2, then it’s a couple of weeks before I can next use them.

Just want to discharge to storage voltage. Thought about making a simple DC powered fan or something with an xt connector on it but requires me to monitor and disconnect at the right time.


If you use an RC style bancing charger, you can charge an empty battery with a full one.

Cool thanks I’ll look into that. Do the packs have to be the same number of cells? Assuming that’s the idea of the balance part of it?

If your running vesc you can use the open_loop command. It will use the motor as a heat sink with out spinning the motor.

Other wise connect three 12V 50W halogen bulbs in series (36V, 150W) and set a timer. And then set another timer so you don’t over discharge the battery.

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It depends, banancing RC chargers have an input voltage range, you need to stay within that range. Make sure not to deep discharge the battery (lipo beeper on the balancing connector of the source battery might help).
If the battery to charge has a built in BMS, you can‘t use this method as the supply voltage has to be ecactly #S x 4.2V of the batttery. You would need a DC-DC converter but this would be overkill…

Thanks. I’m not running Vesc unfortunately.
Will look into the 150W lightbulb jig. Any idea roughly how fast that would discharge a fully charged 10s pack? Ideally I would be able to use it to bring my 10s packs down to 37V and my 9s packs down to 33V. No idea what sort of time that might take.

my simplest solution

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The math is is super easy,

Look for the Wh capacity of your cells, a 2170 molicel is about 15Wh.

Then 10S x 5P (if you had a 10S5P pack) x 15 = 750Wh for your whole pack.

At 150W draw it would be completely flat in 5 hours (750Wh/150W). So an hour on the discharger would be enough to get it down to 80%. 2 hours to 60%.


Discharging my 6S packs to charge my 7S packs.
I set the LiPo beeper to 3.7V. You need to be around to swap the source when the beeper starts. I was charging 2 7S LiIon@10A each from one 6S pack, thischarge current was 22 A, much better than the 2A with the charger.

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