Bafang g020 500w rear hub - strange behaviour

[LocoCity1991]

Hi everyone,
Last week I got a brand new Bafang g020 500w 48v rear hub motor.

While riding along a friend with an ordinary bike, I noticed that sometimes when the PAS kicks in there is a noticeable shock going thtough the bike combined with a dull noise. After that the bike works fine as normal.
Also when I lift the rear wheel and push the throttle this sometimes happens.
When riding normal this issue cant be seen

I made a video of this that I posted on this forum here: https://www.pedelecforum.de/forum/index.php?threads/bafang-g020-mit-seltsamen-verhalten.99902/post-1947178

I have no idea what this could be
The bike did this more or less right from the beginning.
I already swapped the motor cables and the controller and the issue persists.
Im using a KT 22A Controller and a KT LCD 8

Any help is welcome

 

[LocoCity1991]

I narrowed the story down a bit:

Controller and motor cable were changed - error remains.
The problem only occurs in the lower support levels or when you give full throttle with thumb throttle after lifting the bike - Ergo; Never under full load.
It can't be a fallen off permamagnet, because changing from p2=6 to p2=5 brought no improvement.
It can't be the battery either, as the problem occurs with a different battery as well.
I shorted the phases to each other and the motor responded as you would expect - but a motor tester should arrive today; that gives clarity.
It can't be a defective planetary gear either, since the motor runs whisper-quiet; no rattling, rattling or grinding.

However, I saw a video from a repair guide where one of the planetary gears was seized onto the underlying plate. Something like that may have happened here. But also rather unlikely, since it cannot be reproduced cleanly.

 

[LocoCity1991]

Update #2
Engine tester found no errors
Phases and hall sensors work perfectly

 

[LocoCity1991]

Update #3
I think I found the mistake.

The controller I use is labeled: (KT48ZWSRMT)

I don't think I need to explain what KT and 48 stand for

As is well known, ZWS stands for block commutation

R stands for the light connector

M stands for 9 Mosfets

T stands for Dual Mode

Somehow I had the feeling that the incorrect control could have something to do with the dual mode of the controller and I connected another controller without dual mode, which is dependent on Hall sensors (I know from the tester that the Hall sensors work).

Lo and behold
The problem is gone

I still can't explain it
Maybe that helps someone

 

[LocoCity1991]

Update #4 -- Problem Solved

Yesterday I tested some more regarding my problem.
I changed the L3 parameter from 1 (Factory standard; Controller decides if he wants to use sensoreless or sensored mode to operate) to 0 (Controller is forced to use the hall signal if available and free of errors).

This solved the issue.
The motor is now running much smoother and also more silent.
Befoure this change when accelerating from a stop, your whole body would vibrate and the process was way louder.

As it seems, if L3=1 the controller uses sensorless to start and then changes to sensored mode.
For whatever reason....

Anyways.
I hope this trubleshooting might help others in the future =)

 

[TommyCat]

:thumb:

Thanks for the updates and fix.

I've been curious if you could force a dual mode KT controller into one or the other.



Regards,
T.C.

 

[amberwolf]

Yes, thanks for the functionality info--it will certainly be useful.

As it seems, if L3=1 the controller uses sensorless to start and then changes to sensored mode.

That's a bizarre choice of operational order for them to use.

Sensorless usually sucks to start with under load, so controllers that do switch modes use sensored start, then run sensorless....

 

[LocoCity1991]

Im glad you can at least force it one way

Best would of course be

Force sensored
Force sensoreless
Force dual

But KT...I guess ^^

Ordered a sinus controller nonetheless
Lets see what happens then
But glad I could figure out the source of my issue
Already thought there might be sth. wrong with them planetary gears or a permamagnet got loose

 

[LocoCity1991]

Yes, thanks for the functionality info--it will certainly be useful.

As it seems, if L3=1 the controller uses sensorless to start and then changes to sensored mode.

That's a bizarre choice of operational order for them to use.

Sensorless usually sucks to start with under load, so controllers that do switch modes use sensored start, then run sensorless....

I actually also thought that would be the mode of operations here
I honestly dont know why they chose it that way around
Anyways maybe its just better to buy a hall dependant controller if you got hall sensors in the motor

 

[amberwolf]

If a motor does have sensors, it's more likely to startup ok under load with a sensored controller...but a sensorless controller will run "any" motor of the type it's made for, whether it has sensors or not (it just doesn't use them)...but it doesn't matter if the motor has sensors or not, it still won't start it up under load as well as it could if there were sensors being used, for most generic sensorless controllers.

There *are* some sensorless controllers with better startup software than others, but they generally are FOC controllers that require programming and tuning to the specific motor and system in order to do that.


Personally, because of that, I prefer a controller that can do either one, but that defaults to sensored operation and uses sensorless either after it's moving well enough or only if the sensors fail or are unplugged, since my usages are nearly always difficult-to-get-moving heavy-cargo bikes, trikes, trailers, etc.

 

[LocoCity1991]

If a motor does have sensors, it's more likely to startup ok under load with a sensored controller...but a sensorless controller will run "any" motor of the type it's made for, whether it has sensors or not (it just doesn't use them)...but it doesn't matter if the motor has sensors or not, it still won't start it up under load as well as it could if there were sensors being used, for most generic sensorless controllers.

There *are* some sensorless controllers with better startup software than others, but they generally are FOC controllers that require programming and tuning to the specific motor and system in order to do that.


Personally, because of that, I prefer a controller that can do either one, but that defaults to sensored operation and uses sensorless either after it's moving well enough or only if the sensors fail or are unplugged, since my usages are nearly always difficult-to-get-moving heavy-cargo bikes, trikes, trailers, etc.

Well, personally I´d be interested if this specific controller has the same behaviour also mit other motors or if this is just a simple compatibility issue between controller and motor.

As far as I know, KT Controllers are pretty universally usable.
There are some exceptions that some friends told me about.
Mainly with high powered Puma Hub Motors.

Also I dont really understand why the motor toggles between sensored and sensorless when L3=1
The KT LCD 8 manual states that "3.2 When L3=1, the controller will choose the proper model to use according to
the controller system optimization."

I dont know why it would be any kind of optimization to dump the sensor signal at any point since the motor runs better with sensored control in general. Like really way better, smoother and also way more silent.

However I like the idea of a universal controller that can do both
My idea in this regard would be more of a "Have Halls - Use them ; Have no Halls - Also fine" approach not a "Lets see what we choose by random today" since eventhough I know the source of the initial problem I am still unable to really reproduce the issue on a way that I could determine any sort of steps needed for this issue to occure. Sometimes it happens and sometimes it does not.

 

[amberwolf]

Also I dont really understand why the motor toggles between sensored and sensorless when L3=1
The KT LCD 8 manual states that "3.2 When L3=1, the controller will choose the proper model to use according to
the controller system optimization."

I dont know why it would be any kind of optimization to dump the sensor signal at any point since the motor runs better with sensored control in general. Like really way better, smoother and also way more silent.

FWIW, the Grinfineon I have (slightly different, older than what they have now) runs in sinewave mode with sensors, but switches to trap mode if they fail or are not connected. That's much noisier and doesn't run as well. It doesn't have a way to manually change anything about it, so I can't test what it would be like in trap mode with sensors, or vice-versa.

Regarding their "optimization" terminology, that's more likely to be marketing speak, because big words sound cooler. :lol: Probably also bad translation in addition to that; it's very common especially with anything even remotely technical.

However I like the idea of a universal controller that can do both
My idea in this regard would be more of a "Have Halls - Use them ; Have no Halls - Also fine" approach not a "Lets see what we choose by random today" since eventhough I know the source of the initial problem I am still unable to really reproduce the issue on a way that I could determine any sort of steps needed for this issue to occure. Sometimes it happens and sometimes it does not.

I agree, it would be great if it were like that--it is, in general, for the dual-mode controllers I've seen (though there are those like yours that have a setting to choose).

For the problem you have, I would guess there is an intermittent issue, most likely a hall signal (or hall power or ground) connection (since wires and connections are almost always the cause of such things). When the problem happens, the controller reverts to sensorless operation, and you get the symptoms....

Won't know until (unless) you locate a correctable physical problem (if there is one), and the issue then goes away, though.

 

[LocoCity1991]

Another short update.

Got a KT sine wave controller.

The engine runs almost silently.

Even with maximum assistance, the running noise of the tires is louder than the engine.

Acceleration itself is buttery smooth.