Bafang M400 (Max) Issue

I posted this on the Bafang group page and for some reason it wasn't allowed.

I'll have to swap out parts to narrow it down, my thoughts are electrical rather than mechanical:

Bafang Max (M400) Problem- Anyone have experience with these (or maybe the BBS does similar)? Mine seems to be getting a 'stutter' coming from the motor under load/ uphill and it seems to be when the battery is low (though iv'e only run through 3 battery cycles so far). It feels like it's a 'skipping teeth' type thing but no real noise, just feel it through the pedals and it looses drive. It's got me a bit baffled as i'm not sure if it's electrical (controller) or mechanical ((pawls) or the battery cells are tripping something when low? It's anything from a momentary loss of power to stuttering for half a turn of the crank then comes good. I'm sure I can work it out but considered also that the low power could also affect sensors etc (no error on the display). I'm not really sure where to start, some components are expensive for these.

I know this is a 'closed system' motor, not so popular here but any thoughts welcome?

Do you have a way to monitor voltage? Does it happen when fully charged?

Could be voltage sag under load is hitting the LVC, so either the battery or controller is protecting itself.

if cell lvc was hapening, the bms in the battery would probably cut opwer to the whole system, so the lcd would blank and it would just shutdown. wouldn't get a stutter.

but if the controller's lvc is being reached due to voltage sag in teh whole pack, it could indeed cut power, then votlage rises adn controller reenalbes, and this cycle continues as logn as there is that high a load on the system.


if thats the cause, then it will only happen either during hard enough acceleration or climbing a slope sufficient to cause that high a load.


if it doesnt' happen at full charge but does at partial discharge then the batteyr is too weak to sustain that laod at that state of charge. whether thats a defect in the battery or just that it's not big enough to handle the load you'd have to test, or check the specs on the battery to see what it's max continuous amps are rated for, vs teh amps the systme is actually drawing under that load..

Yeah, thanks E-HP & amberwolf, I think you are firming up my suspicions, and moreso that it's an overall battery sag. It's a stutter and occasion momentary cutout & has (so far) only happened dragging my fat chops up a steep hill when nearing the last of the battery charge, I'm a bit concerned at any mechanical damage it may do long term . The cells are 'Samsung 2600' but short of pulling the case apart I'm only guessing the pack isn't up to spec for the load. The seller is friendly but not very knowledgeable. I'll investigate a bit more.

Did you ever solve this issue? Was it the battery or something mechanical?

By bike has the very same problem.

Hey!

I have exactly the same issue as @palsi63 and @Ozzzz.
I have two batteries and one is more prone to the error than the other. But I can get it to happen on both. I also have two identical bikes - and on one bike this doesnt happen at all.

It really stutters sometimes and it feels like it is skipping cogs. Also the when applying the break (pedaling backwards) I can hear a "thump" probably coming from the motor. I have a Crescent Elora with no break or shifting sensors.

Any ideas?

It honestly sounds like controller cannot handle the load properly. Do keep in mind that bikes with "250W" motors usually have very small controllers with very limited and cheap fets so under load you get quite the drop in performance.