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A Charging Disaster

Posted: Sat, 30 May 2009, 00:00
by Johny
This is a timely reminder to all of us who might, in our haste to get the "EV grin", might do not quite what we should. Scared me...
EV Burns
Apologies if it's been posted here already.

A Charging Disaster

Posted: Sat, 30 May 2009, 00:41
by acmotor
Sad.
So intense a burn and not a drop of petrol in site ! I guess he will never know the real cause.
The -5deg ambient and balancing charge in progress plus "work in progress" status may well have been contributing factors. e.g. was the BMS and charger still working withing voltage calibration at the low ambient temperature etc.

It may have been as simple as the charger on the back seat catching fire.

There is a concern for battery packs in general.
Are they safe if they are kept within true voltage and current ranges so that a catastrophic failure only happens if the management system gets it wrong ?
Assuming this is true, then the BMS and charger need to have redundancy in their operation.

If you consider the types of BMS and charger we run now, there are many potential single point failures that could result in damage.
Some of these would (should) just blow a fuse, however the finer voltage critical tasks can cause problems. This is without planning to cope with a cell failure itself that the BMS cannot stop.

   Image

A Charging Disaster

Posted: Sat, 30 May 2009, 06:28
by coulomb
Imagine if it was a hybrid. They wouldn't have slept through it then   Image

A Charging Disaster

Posted: Sat, 30 May 2009, 17:31
by Johny
There is a clue somewhere in the post mortem that his charger didn't have a current back-up system. It kicked out at 3.7V and back in at 3.6V then had to adjust for current again.

A Charging Disaster

Posted: Sat, 30 May 2009, 18:07
by acmotor
There is a lot to be said for logical charging times and rates.

Why charge in 2 hours from 5:30pm ? That's peak electricity $ rate in winter in Oz. (have a timer on the charger)
Also, if you are not using the vehicle for 12 hours, then take 12 hours to do a gentle charge. Your batteries will thank you for that !
The lower the charge rate the less risk of system failure (and BMS error). i.e. variable charge rate in the charger.

Include logic in the charger that limits the kWh of a recharge to the kWh removed from battery. i.e. SOC cued charging. (some systems do this already).   

In general, add safety checks to remove single point failure potential.
Battery temperature is one such check.

All speculation of course. The vehicle may have been struck by lightning ! Image

A Charging Disaster

Posted: Sun, 31 May 2009, 00:12
by Johny
Ha ha - I hadn't considered that! Image