Hi all,

I was asked to look at an electric scooter for a friend today. His
friend bought it directly from China, ran it ok for a couple of months
and then it just stopped working (so no point trying to send it back
from the UK).

Whilst I'm reasonably comfortable with basic electrics and electronics
I'm not familiar with the sort of things you find now days around Lixx
type cells and packs and hence why I am looking for some advice here
please.

FWIW, we connected the 36V, 40 cell pack (possibly 4 x 10 or 10 x 4 in
parallel?) up to the scooter charger and saw the terminal voltage go
from around 36 to 40V (charger max 42V) and the current initially sit
at 2A and then start dropping to about 1.8A after maybe an hour. I
believe the cells are these:

http://www.ax-ps.com/pdf/datenblatt/LR1865_SI.pdf

(making the pack ~36V x 8.8 Ah)

Putting a load (3 x 12V x 21W lamps in series) across the battery
output showed nothing. Putting the load across the cell monitoring
wires (eg, directly on the battery) had the lamps shining brightly
(indicating there was nothing wrong with the battery itself, at least
with a load of around 2A)?

We then turned to the BCM, un wrapped it and found and tested a (65
degree) thermal switch and that seemed ok (short cct).

I've since split the BCM and this is the working side (the other half
is the monitoring board [1] and connects the main board via a 4 pin
link shown at the top):

https://dl.dropboxusercontent.com/u/5772409/BCM%201.jpg

The two wires you just see top right go to the 5A thermal switch, the
blue wire top left is the negative out ... and the pad J2, top right
is as marked, connected directly to the battery -ve. So this board and
all the cell monitoring connections work WRT the battery Ov?

The charging connector is basically across the output.

Now, from Googling about I think I understand some of the components
on that board may control the charging and that seems to work (or at
least not be dead), so I think we are looking at something that may
enable the output, presumably as long as the battery voltage is
sufficiently high and the pack temperature is less than 65 DegC etc?

The T0-220 devices seem to be 3 x RU75ND8R mosfets + 1 x HY1807.

https://dl.dropboxusercontent.com/u/...0datasheet.pdf

https://dl.dropboxusercontent.com/u/...0datasheet.pdf

From what I can see the gates of the two devices to the left are
driven from the two EL817 photocouplers seen bottom left.

https://dl.dropboxusercontent.com/u/...0datasheet.pdf

I found something that might give some hint of a similar issue he
https://endless-sphere.com/forums/vi...p?f=14&t=67012

And a more detailed description of how it might work on the last post:
https://endless-sphere.com/forums/vi...67012#p1008437

So, I'm not sure where to go next. I do have one of those little
component testers so, assuming I couldn't test the power devices in
circuit I could de-solder them (FETs) and may be able to test them but
what are the chances of that being the fault and it not be some of the
other (SM) circuitry please?


Cheers, T i m

[1] https://dl.dropboxusercontent.com/u/5772409/BCM%202.jpg
https://dl.dropboxusercontent.com/u/5772409/BCM%203.jpg