Bafang 180mm (7 inch) CST grinding noise+total loss of power

Hi all,

My Bafang CST (180mm variety) with 15a no-brand controller setup, unfortunately after 600 miles of intermittent losses of power and (M) (motor error) messages on the LCD-861 display, recently made a lot of sad grinding/vibrating/ noises, followed by a total loss of power after a few seconds, and is basically not working.

Previously I'd get 5 or 10 miles between error messages/losses of power (which seemed to get 'reset' & fixed by sometimes, or switching power off & on, waggling the bag with the controller & wires, and then turning the throttle, etc), now it will do 20 yards, make the noises, get the error, lose all power, and not revive except for maybe that 20 yards, and often with the nasty vibrations.

Would anyone have any pointers as to what might be the problem, please? This is the controller, https://drive.google.com/file/d/0B7ym9WvyF_P7VzFyUEJicmpGOFk/view?usp=sharing shunted to 18a (though the error used to appear before I shunted it).

Thanks - J

Which thing seemed to fix it most often? Wiggling things? Or power cycling? Etc?

Wiring and connectors are the most common cause of intermittent problems. It can be anywhere from the point a wire is soldered onto something (like a hall sensor) to the point a wire is crimped into a contact for a connector, to the connection between the contacts on either side of a connector pair.

That's where I'd start, especially with the problem as described, which sounds like a hall sensor issue.

But batteries are another cause of stops like you get, either from internal connection problems like balance wires between cells/bms, or between cell groups, or even from cell groups that are unbalanced far enough that any load beyond a certain amount causes pack shutdown. Sometimes removing the load momentarily will reset it, sometimes not.

The latter type of failure would also tend to get worse over time in the way that you describe.

amberwolf said:

Which thing seemed to fix it most often? Wiggling things? Or power cycling? Etc?
...
But batteries are another cause of stops like you get,
...
The latter type of failure would also tend to get worse over time in the way that you describe.

Click to expand...

All of your message was really helpful - thanks. Power cycling,i.e. switching off and on again, tended to fix things more often. The battery is ageing, not used in a long time, and hadn't been balance-charged (left to charge after reaching full capacity) for ages either (if ever), so there's definitely a suspect available matching your description. The wiring is suspect too. Starting now with ruling out these causes in order of easiest to work on.

If you used it in the rain, it's probably full of rust. Take the side off and look inside.

You often get grinding noises because of electrical problems around the hall sensors. If you continue to run like that, you can blow the mosfets in the controller, so anything could be wrong now. Start with looking in the motor because that's easy.

Might be worth it at this point to get a motor and controller tester, starting with seeing if the motor is sound.

Definitely sounds like it might have all begun with loose connections to the motor though. Grinding is often the description people use for motor stutter.

Overheating the motor can kill halls though, which might have happened if you ran on two of three phases enough.

Thanks Dan. After a year or two’s law exams I’ve found time to start work on this again (!)

I used a purpose-built motor/controller tester and it was identifying *multiple* problems with the motor (I can't remember what they were but it wasn't good).

With professional help on the battery front I ruled out

-loose connectors (as immediate cause)
-battery (as immediate cause).
-obvious rust

Is the next step to remove the screws here and have a look at the wires/circuit board?

https://drive.google.com/file/d/1NuQrnsyLIqVO7OO2cRXeAeLrpZxQhs6T/view?usp=sharing
https://drive.google.com/file/d/1esWWNZSxQQRdJDPMHEa8BOo42FfeTGqY/view?usp=sharing

dogman dan said:

Might be worth it at this point to get a motor and controller tester, starting with seeing if the motor is sound.

Definitely sounds like it might have all begun with loose connections to the motor though. Grinding is often the description people use for motor stutter.

Overheating the motor can kill halls though, which might have happened if you ran on two of three phases enough.

Click to expand...

Can't seem to get some of the screws out - even a sharp new philips-head bit seems to just damage the grooves on the screws. Would anyone have any tips on this please? Image: https://photos.app.goo.gl/UFccE8zeHDXQb3P49