Balance charge/BMS circuit problem starting handtools
 

Once upon a time on usenet Charlie+ wrote:
On Mon, 21 May 2018 18:22:34 +0100, Charlie+ wrote
as underneath :

On Mon, 21 May 2018 10:30:39 -0400, Bob Engelhardt
wrote as underneath :

On 5/20/2018 2:56 PM, Charlie+ wrote:
... so a bypass switch would be a bit of a nuisance, any simple
better ideas in your drawer!?
...

A brute force approach would be to use a time delay relay to
connect the battery directly to the fan (through the switch, of
course). NC at start & then opens a couple of seconds later.
You'd have to test whether the relay in parallel with the BMS would
be enough off-load.

Or, it could probably be done with a honking big BJT that has its
base biased with a capacitor that's charged in the off time and then
discharged through the base in a few seconds when on. But I'm much
too transistor illiterate to be more specific. Try S.E.Basics or
S.E.Design if you don't get help here.

OK Bob thanks for thaughts, think I might just have a start button
and release once running. Thats cheap and cheerful, Ill report if it
works ok. C+
Ok Done and dusted - instant-on press button works fine (just bypasses
the BMS negative on startup) - time will tell if it keeps on happily
trucking! Thanks for help everyone... C+

That's what I did when I converted a battery powered rotary tool from 3 x
NiMH to an 18650 and the charge controller / battery protection module did
the same as you're reporting. My system also worked fine. ;)
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)