how to deal with li-ion protection circuitry

Who is your insurance company?

martin

schreef in bericht news: snipped-for-privacy@c19g2000prf.googlegroups.com...

Charge up a big capacitor slowly from your Li-ion battery, and use the capacitor to source the start-up current.

A small NiCd or NiMH button cell might also serve in the same role - they have relatively low internal resistance, and correspondingly high maximum outptu currents.

Not all Li+ batteries have this kind of protection, but it sounds like you've already commited to one type (packs?). The permitted current profiles are likely outlined in the part's spec.

The use of intermediate capacitive storage is going to take quite a bit of real estate, so it might be just as good an idea to change the battery type.

Have you tried limiting your pwm current limit? It's possible that the motor may actually start, though slowly, at a reduced but fairly high current that the battery will tolerate.

RL

This sounds reasonable. The problem is the protection circuitry reacts in 200us, so even a VERY short current pulse above 6A will trip the breaker. But maybe i can run a very short duty cycle somehow..

I cant use a pack that doesnt have protection circuitry...I really need that because these cells are dangerous and something has to make sure things dont get out of hand...EVER..ya know?

This sounds reasonable. The problem is the protection circuitry reacts in 200us, so even a VERY short current pulse above 6A will trip the breaker. But maybe i can run a very short duty cycle somehow..

I cant use a pack that doesnt have protection circuitry...I really need that because these cells are dangerous and something has to make sure things dont get out of hand...EVER..ya know?

Sounds like you're trying to squeeze a quart out of a pint pot.....

Sometimes the designers of these add-on widgets don't realise what the safety requirements actually are, only that it 'works' in the initial application. No skin off their nose.

Even so, if you can current limit at 5A8, the fast internal latch may ignore it. I'd say 200uSec was probably meant to deal only with failing external controllers that were normally expected to respond in a shorter time interval - not an unreasonable requirement, but not one looking for real internal battery pack problems, as such.

Another brand can easily have produced a more robust protection circuitry without ignoring real Li+ failure modes, which seldom stem from transient loading (in my experience and from the available literature).

RL