LIPO discharger

SSSF

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I got fed up with discharging my LIPOS at home after crashing my car. It takes hours to do on most LIPO chargers, especially if multiple batteries need to be discharged back to storage voltage.

So i decided to create a circuit that discharges a LIPO.

design principles:
  • safe
  • easy to use
  • set cutoff voltage

safe:
  • 2 ways to stop discharge, one to set normal stop voltage, one safety voltage
  • a fuse to protect against short-circuit
  • design that a failing component never leads to over discharge

easy to use:
  • be able to set stop voltage
  • start and forget: the device will be completely disconnected from LIPO when discharge is completed. So it will not discharge any further (means zero load). You can keep it connected forever without further discharging.
  • discharge cycle has acceptabele time

set cutoff voltage
  • the voltage when discharge is stopped can be set between 3 and 3.8 volt


I created a fully working prototype on a breadboard and now want to go the next step:
create a PCB

The prototype works for 2 and 3 cell Lipo, for 4 cell i need minor adjustments.
I am on holiday and forgot to take pictures to post here :( . But it also gives me 2 weeks to think about and that's the reason of this post.

Please give your feedback and suggestions to improve.

Please note that I try to keep the components under 20 euro, so not everything is possible.

The current prototype can support up to 3 amps (actually 2 times 1.5) of discharge. I use 100 watt resistors (over specified, but have a nice size) together with radiator and fan to get rid of the heat.
 

JvG

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It's always fun creating things that work, nice job.
You can also buy these 150w balanced dischargers and they are very cheap:

€ 18,92 | AOKoda CellMeter 8 150W Discharge Module Set with Lipo Battery Balancer Battery Protection For RC Models Helicopter Spare Parts https://s.click.aliexpress.com/e/b2lfQFgG
 

SSSF

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Can you leave them connect?
 

Primarrma

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I use this https://www.isdt.co/fd-100.html?lang=en it only cost $50 AUD, it doesn't balance discharge, but it's set by default to discharge to storage voltage, it has worked really well so far. It's a little noisy when it's really cranking, but gets a fully charged 6s 5000mha down to storage in about 1 hour. The one above would be quicker and it's cheaper, though this unit is all self contained no external load.
 
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