Bafang M420 jerky and low poer aftr controller replacement

gert

100 µW
Joined
Jul 4, 2011
Messages
8
I have a locally assembled retail bike that came equipped with the Bafang M420 motor, which I've been happy with. recently the controller gave up after lot of riding in hevy rain. Into the shop where i bought it it went. And back it came, but not as before. The display (which was previously a C18) was still a C18, but now it was missing the different sport and eco modes it previously had. I was assured that the highest setting (5) should be just as powerful as 5 on sport mode previously. This was not true.

Problems:
  • Power usage about 50% lower than previously, measured by how long the battery lasts
  • Very weak performance. Up hills where I would previously easily bike at 25kph, 17kph now takes a lot of work.
  • Jerky and slow to react. Seems to be in a very low power mode until it suddenly "wakes up", but the power boost doesn't last
  • There seems to be no coherence between torque I apply and how much power the motor provides. This used to be smooth, now it is anything but.

I have notified the store, of course, and they are contacting bafang to look into if the controller they are shipped have changed and if there is something they can fix with programming, but I thought I'd check here if someone had any tips as to what can be wrong.

I also believe they have changed the display to an old one they had lying around, as there are a lot of scratches on it that wasn't there before, and it has a completely different start up animation. It used to say Max or HD or seomthing on a dark background, now it says BPS (i think, i forgot to take a pic of course) on a bright orange background.

Pictures of controller info and display info from the display:

 
HI,
I ve the same problem, I had to replace my M420 du to a bad shortcut on the battery pin contacts that burned the controller inside.
New M420 came with new controller firmeware ( at this end 1.1 instead 1.0)
Now the motor is really " flat" as you describe.. , 17kph instead 25kph, etc...
In my case, I dont changed the display
I suppose that firmeware had been changed to save life of motor..?
I would to downgrad controller with previous firmware
 
mroupi said:
I suppose that firmeware had been changed to save life of motor..?
I would to downgrad controller with previous firmware
I also checked the error log on the display, and it shows error code 11 and 30. 11 seams to be a heat sensor error, and 30 a "communication error". Could be the controller is just wrong for the motor, but I'll see what changes they have done when it's fixed. The shop said Bafang said it was not the same software/programming the bike was supplied with, and they hoped toi fix it with a software solution, but it's strange that something listed as a spare for the motor is basically incompatible.
 
My HMI, Controler, and torque sensior
 

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You speak about controller, but you mean HMI display ?...
Controller is a motherboard into motor
 
I solved the problem with a simple sensor calibration
See the CiDi's post about CanBus interface and Hex code to do this
 
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