speedometer reads 0 when not pedaling

rocketman58

10 mW
Joined
Aug 6, 2022
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I have a Bafang 500w geared rear hub drive. I swapped out the stock controller and display supplied with the kit to a KT 22A controller and a KT LCD8H display. Everything works great except the speedometer. When I stop pedaling, the speedometer drops to 0.0 when coasting at low speed, or registers 49.6mph when coasting at higher speeds. When I start pedaling the correct speed is displayed once again. This also impacts the odometer since the correct speed is not being recorded all the time.

From what I have read, I would need to connect an external speed sensor to allow the bikes speed to be recorded and displayed correctly when not pedaling. MY controller has the waterproof typed connectors, but there is no wire to connect a speed sensor. Is there a simple way to connect a sensor without having to disassemble the controller and start splicing in wires? Would a speed sensor even work with my KT controller?
 
Only the newest Bafang motors have built in speed sensors that won't do what you are describing. The older ones will need the external sensor like you've read about.

No major disaster, there is some splicing that will need to be done.

This might be most easily done inside the controller. That way you aren't chopping up the harness, but that's your call.

The external speed sensor is going to need a 5v hot and ground, which can be borrowed from the 5v hot and ground leading to the PAS sensor. For the 3rd speed sensor wire, locate the white wire coming from the motor, and cut it where it will be convenient to splice the 3rd speed sensor wire to the white wire leading to the control board.

That's it. Reassemble and test.
 
Thanks for the reply.

I know just enough about electronics to get myself in trouble. Opening up the controller and splicing in wires makes me a little nervous. By splicing in, would I be soldering wires to locations inside the controller? I was told you can make a sensor out of an old bike computer (which I have). My old bike computer sensor has 2 wires. In the quote below, you mention a 5v hot, a ground, and a third speed sensor wire.

The external speed sensor is going to need a 5v hot and ground, which can be borrowed from the 5v hot and ground leading to the PAS sensor. For the 3rd speed sensor wire, locate the white wire coming from the motor, and cut it where it will be convenient to splice the 3rd speed sensor wire to the white wire leading to the control board.
 
rocketman58 said:
Thanks for the reply.

I know just enough about electronics to get myself in trouble. Opening up the controller and splicing in wires makes me a little nervous. By splicing in, would I be soldering wires to locations inside the controller? I was told you can make a sensor out of an old bike computer (which I have). My old bike computer sensor has 2 wires. In the quote below, you mention a 5v hot, a ground, and a third speed sensor wire.

The other option is to splice into the cable, by carefully removing some of the casing in order to access the smaller hall wires. If your controller is the version of KT that has a white speed sensor wire, then you could cut the wire, and connect the external speed sensor's signal wire going to the controller instead. You will also see a red and black wires, 5V and Gnd, that are used by the motor hall sensors. you can tap into those at the same time, but don't cut them since the motor still needs them. I would tap into the wires and add a 3 pin JST connector so you can just plug in your external speed sensor.

One thing to note is that just because the cable has the white wire, there's no guaranty that it's connected inside of the controller. It may just be a standard 9 pin cable, but unterminated.

Again, this assumes that you have the version of KT that supports a speed sensor through the motor cable. One version has it, and the other has an empty slot. Since you have the HiGo connector cable, you can't easily see the wires unless you open the controller or slice open the cable housing.

kt hall.jpg

EDIT: some other experts might chime in, but if the white wire is connected inside the controller, and you turn the controller on, you may see 5V on it, if the controller uses an internal pullup resistor.
 
The last post is starting to get over my head. Does anyone know of a video that shows this? It might make more sense if I see it.
 
Nixunen said:
Make sure that setting P2 is set to 1. I think now it is zero.

Mine is set to 5. Speedometer works fine as long as you keep pedaling. The problem is when you stop pedaling.
 
rocketman58 said:
Nixunen said:
Make sure that setting P2 is set to 1. I think now it is zero.

Mine is set to 5. Speedometer works fine as long as you keep pedaling. The problem is when you stop pedaling.

To clarify, absent an external or internal speed sensor, the controller/display uses one of the motor hall sensor signals to determine speed, so as long as the motor is running, you'll get a speed readout, whether it's running from pedaling or using throttle.
 
rocketman58 said:
Nixunen said:
Make sure that setting P2 is set to 1. I think now it is zero.

Mine is set to 5. Speedometer works fine as long as you keep pedaling. The problem is when you stop pedaling.
Test to change it to 1. That P2 settings determine how many pulses per one wheel revolution. If that is zero, then controller uses only motor hall sensors. And that work fine when motor is running, but because you have geared motor, there is one way clutch so, when coasting motor it self not spin and cannot use motor hall sensors to measure speed.

You mention "or registers 49.6mph when coasting at higher speeds" that indicates you get some information. Because you cannot get any speed when coasting without that internal speed sensor. (Or can but in that case your one way clutch not work properly and get stuck and turn motor at some point) Now when it set to 5 it assume 5 pulses per revolution. Some motor have 5, or 6 magnets to internal speedometer. But mostly there is only one. Inside most geared motors is another hall sensor to read speed using magnet glued to motor casing, which spin always. And that hall sensor signal is connected to white wire.
 
Nixunen said:
Test to change it to 1. That P2 settings determine how many pulses per one wheel revolution. If that is zero, then controller uses only motor hall sensors. And that work fine when motor is running, but because you have geared motor, there is one way clutch so, when coasting motor it self not spin and cannot use motor hall sensors to measure speed.

You mention "or registers 49.6mph when coasting at higher speeds" that indicates you get some information. Because you cannot get any speed when coasting without that internal speed sensor. (Or can but in that case your one way clutch not work properly and get stuck and turn motor at some point) Now when it set to 5 it assume 5 pulses per revolution. Some motor have 5, or 6 magnets to internal speedometer. But mostly there is only one. Inside most geared motors is another hall sensor to read speed using magnet glued to motor casing, which spin always. And that hall sensor signal is connected to white wire.

I was told that with a geared hub drive you must have an external speed sensor. That said, it is certainly a good idea to play around with the P2 settings before taking more drastic measures.
 
rocketman58 said:
Nixunen said:
Test to change it to 1. That P2 settings determine how many pulses per one wheel revolution. If that is zero, then controller uses only motor hall sensors. And that work fine when motor is running, but because you have geared motor, there is one way clutch so, when coasting motor it self not spin and cannot use motor hall sensors to measure speed.

You mention "or registers 49.6mph when coasting at higher speeds" that indicates you get some information. Because you cannot get any speed when coasting without that internal speed sensor. (Or can but in that case your one way clutch not work properly and get stuck and turn motor at some point) Now when it set to 5 it assume 5 pulses per revolution. Some motor have 5, or 6 magnets to internal speedometer. But mostly there is only one. Inside most geared motors is another hall sensor to read speed using magnet glued to motor casing, which spin always. And that hall sensor signal is connected to white wire.

I was told that with a geared hub drive you must have an external speed sensor. That said, it is certainly a good idea to play around with the P2 settings before taking more drastic measures.
Nixunen's logic makes sense, especially if the speed worked correctly using the old controller. That would indicate that it's a newer Bafang motor with an internal speed sensor. Looking at some examples online, it looks like the 500W show 6 pulses for the speed sensor.
 
E-HP said:
Nixunen's logic makes sense, especially if the speed worked correctly using the old controller. That would indicate that it's a newer Bafang motor with an internal speed sensor. Looking at some examples online, it looks like the 500W show 6 pulses for the speed sensor.

I just tested setting P2 to 1, and the speed did not register correctly at all. I will repeat the test after setting P2 to 6. Curious as to where you found the tech info on the 500w Bafang motor. I had no luck searching the internet.

Thanks for your help, and thanks to all the others as well.
 
rocketman58 said:
E-HP said:
Nixunen's logic makes sense, especially if the speed worked correctly using the old controller. That would indicate that it's a newer Bafang motor with an internal speed sensor. Looking at some examples online, it looks like the 500W show 6 pulses for the speed sensor.

I just tested setting P2 to 1, and the speed did not register correctly at all. I will repeat the test after setting P2 to 6. Curious as to where you found the tech info on the 500w Bafang motor. I had no luck searching the internet.

Thanks for your help, and thanks to all the others as well.
Various sites will list specs, so just doing a search on Bafang 500W rear hub provided some results with the speed sensor info, such as this one:
https://m.media-amazon.com/images/I/61Lr8-iunNL._AC_SL1000_.jpg
 
Thanks everyone,

Setting P1 to 80, and Setting P2 to 6 resolved the speedometer problem. I can coast now and the speedometer continues to display the correct speed.

I do have a new problem now, but I was not paying attention to the display's battery usage bar before changing the settings to P1 and P2. I created a new post detailing this and two old problems I have not been able to resolve.
 
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