Topic: Battery cut off with LiFePo4 packs

[joerg]

Hi folks,

finally, I've got my new LiFePo4 packs from pingbattery.com to use in my two C5s!
Compared to my old 12V 35Ah lead acid battery, the 12V 40Ah LiFePo4 is amazing. I rode the C5 all afternoon and evening (not pedaling very much) on hilly terrain without any problems. After that I even found out that the rear brake was blocking a little bit all the time which caused even more motor load...

Anyway, at the end, I got a battery cut off by the C5's electronics: 20 seconds beep and then no chance to turn on the motor again!
My battery has a BMS with a low voltage cut off, but that wasn't triggered.

My question to you folks is now: Do you know how the battery cut off of the C5 works? And how I can get rid of it, because my BMS does the job?

The battery is still at 12.25V and probably there's still a lot of capacity left...

Any help and suggestions would be very appreciated!

Thanks in advance,

Jörg

[radiomarty]

The ULA chip in the pod monitors the voltage in the battery - have a look at the unofficial service manual starting on page 9 - this explains in block diagram form - I assume if you disable the battery cut off signal or some way make it think there is no voltage variation then you will be fine (maybe playing with the battery offset pot?):

Unofficial service manual
http://c5alive.co.uk/index.php?com=pages&page=5

Pod circuit diagram
http://c5alive.co.uk/oldstuff/pub/downloads/C5-FIG-3.pdf

The other way of doing it is just run it on a plain relay set up and by-pass the pod and control box

[coverman]

Are you sure this wasn't a thermal cut-off rather than a battery cut-off?

[joerg]

No, that was definitely a battery cut off: one looong beep and then the cut off.
As far as I know, on a thermal cut off, it would first start to beep periodically to warn you and then cut off if you ignore the warnings and don't turn the motor off.

I have had a look at the Unofficial Service Manual already, but I didn't really get it.
I asked Ping from pingbattery.com about this and he said, that the voltage of the cells rises after the discharging is stopped. So it maybe that the ULA cut it off at around 11V or so and then it rised to 12.25V - I measured the voltage half an hour after the cut off when I had pedaled home.

Jörg