Bafang Rear Hub Grinding and wrong speed

2nd2none

1 mW
Joined
Mar 18, 2022
Messages
10
Hi all,

I have an ebike running a 250w Bafang rear hub motor. It occasionally makes a grinding whirling noise. Also the display is showing the wrong speed. If I'm pushing the bike it's showing 6-20kmh. Riding the bike I'm doing 70kmh (I wish).

I have another ebike running the same motor. Swapped the motor over and its fine, correct speed.

Could it be the hall sensor? If yes, where can I buy one and how can I replace it? Looking for the easiest repair option.

Cheers
 
2nd2none said:
Hi all,

I have an ebike running a 250w Bafang rear hub motor. It occasionally makes a grinding whirling noise. Also the display is showing the wrong speed. If I'm pushing the bike it's showing 6-20kmh. Riding the bike I'm doing 70kmh (I wish).

I have another ebike running the same motor. Swapped the motor over and its fine, correct speed.

Could it be the hall sensor? If yes, where can I buy one and how can I replace it? Looking for the easiest repair option.

Cheers

When it makes the grinding noise, does the bike's actual speed change? Maybe the clutch is going out?
 
The grinding mostly happens at high speeds and the speed changes.

In hill assist mode it shows 6kmh and when you stop the assist in shoots to 20kmh then 0kmh.
 
First, closely inspect the cable and plugs connecting your motor to the controller. Most of the time, that's the source of the problem.
 
What's the normal behavior of the working hub? Does it only show speed under assist and zero when coasting?

If it's a geared hub and always shows speed, then it would have a separate speed sensor (and wire). If not, then it uses the motor halls for speed. You can test the sensors if you have a 5V supply, via the cable that goes to the motor, but good to know if you're testing the motor hallm wires, or the separate speed sensor wires.
 
It is a geared hub and it does show speed under assist and coasting. I'm unable to see a separate speed sensor.

I did check the wires but I'll double check.
 
2nd2none said:
It is a geared hub and it does show speed under assist and coasting. I'm unable to see a separate speed sensor.

I did check the wires but I'll double check.
I think most hubs use a white wire for a speed sensor or temp sensor, if they have that additional wire, so check for that in the wiring harness to the motor.
Here's a video on testing the hall sensors:
https://www.youtube.com/watch?v=efYFOHnXh0E
 
Geared hubs that shows speed when coasting have a separate speedo wire coming from a separate hall sensor inside, that uses magnets (often six) mounted to the inside of the side cover.

It's probably a wiring or connector issue, but there is a small chance that one of those magnets has come off and is either bouncing around in there or stuck to another magnet in a way that someitmes hits the sensor itself, or other wiring/etc near it, and the "stuttering" of the field beimg moved around as the sensor passes creates extra signals in the sensor, fooling the ocntroler into thinking it ssi faster than really is.
 
What display are you using?

I'm using an SW900, (a version with P14 current control locked out/unusable from the factory).

When settings are 26" wheel and 20 motor magnets the display reads 4x high at 30-32 mph yet I'm only doing 7-8 mph.
Ebikeling lists 20 magnets, and I opened the motor and counted 20 magnets. P07 =20 does not work with this display, controller, & motor. 80% of other values 1-100 for P07 result in the 30-32 mph error.

I ran the entire range of P-setting options. Finally found that when I set P06 to 16" wheel and P07 to 93 magnets, the motor runs normally and display reads just a little high, maybe 10 mph.
I'm thinking of dropping to 15" wheel for P06.

Sellers often include SW900 displays with Bafang motor kits.

Granted, it could be the controller, could be the wheel, but the only control we have over them is the display parameters.

My ebikeling motor made grinding/groaning noises until I freed up the clutch last week.
 
Is your motor still grinding at high speed?
Have you checked all you wires and connectors like other experienced people suggested?

First, my motor's problem was very different than yours. Mine started with a clutch completely slipping, and the solution there is to literally hit the tire tangentially forward with a hammer. Doesn't sound anything like your problem. But, once I got the motor to engage, it groaned at 3-4 mph and then slipped again.

So, in my situation, I opened the case. And, whereas in all the disassembly videos I watched the clutch and gears came off really easily-literally falling off in some videos, I couldn't pull mine off by hand.

I ended up using a crow bar and hammer to pry the clutch off. Once reassembled it ran fine...have 12 miles on it under fairly rigorous conditions and it's run great. I can't understand the reason, but all I know, freeing up the clutch shaft from the motor shaft seemed to resolve the problem...some sort of binding I'd guess. I reopened again and, like all the other videos, the clutch slid of the motor shaft easily.
 
Thanks.

I'm going to check out the cabling again today.

I suspect it's internal to the hub as the other motor I tested on the bike ran fine and showed an accurate speed.
 
2nd2none said:
I suspect it's internal to the hub as the other motor I tested on the bike ran fine and showed an accurate speed.

Don't make the mistake of assuming that the wire color code of one controller or motor corresponds to that of another controller or motor. It might, but it surely doesn't have to. There are a lot more ways to get it wrong than there are to get it right.

I installed a generic controller with a 9 pin breakout cable to a a Jump bike motor just the other day, and I had to fiddle with the teach wires quite a lot to get it running quietly at the right speed. I matched the wire colors, but it didn't work right at first.
 
Opened the hub and wires are all intact and looks quite clean. Motor has hardly done any miles.
White wire is going to the SP point which looks good.

I'm out of ideas.
 
2nd2none said:
Opened the hub and wires are all intact and looks quite clean. Motor has hardly done any miles.
White wire is going to the SP point which looks good.

I'm out of ideas.

Did you try any other phase and Hall wire assignments? Your problem seems like they're incorrect, but you can't fix the problem if you don't find the correct combination.
 
2nd2none said:
Sorry what do you mean by finding phase and hall assignments? How will I know which is the right combination?

You'll know you have the right combination when the motor runs quietly at the correct RPM, in the correct direction, with good torque and low unloaded current. With some experience, you can hear and see it running right and you won't have to measure RPM or amps.

fetch
 
Thanks, I'll give another once over.

I was riding the bike last night for an extended period of time. It's no so much a grinding noise but a louder whirling noise at low speeds. Goes away at high speeds.

Cheers
 
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