Help! Pedal assist doesn’t work anymore on TODO Mountain Rider E-Bike, please help

[AdHoc]

Hi,

A few months ago, I bought a cheap electric bike off eBay, the "TODO Mountain Rider E-Bike", for the price of 990 AUD, shipping included to Tasmania, Australia (from New South Wales, Australia).

It comes with a geared 250W rear-hub motor (Bafang I think), a Shimano Tourney drivetrain and a KT-LCD3 display with control buttons. The display is fully preconfigured out-of-the-box for that specific bike, so I never had to adjust any of the settings.

I’ve been reasonably happy with the bike, given the price, for the first 500 km or so. Until now.

Normally, the hub motor/assist function would activate either when I pedal, or when I push the assist switch. Now, the assist function only works when I push the switch, NOT when I pedal, like it used to. It happened overnight and I don’t remember doing anything to the bike other than maybe dropping it on its side by accident once.

The fact that the hub motor and the assist function still work normally when I push the switch makes me think that it’s not a software issue, and not an issue with the hub motor, but maybe a sensor issue? As in: the control box and LCD don’t seem to detect the pedalling and thus don’t activate the assist. That’s my best assumption anyway.

Unfortunately, because it’s a cheapo, Chinese made, no-name kind of product, there’s no official support for it. The manual is useless. I tried fiddling around with the cabling and cleaning the little part next to the derailleur (see red arrow on photo below), to no avail, and I don’t really know what else to try.



I have the black version, but you can see details here: https://www.ebay.com.au/itm/EBIKE-ELECTRIC-BIKE-36V-9Ah-250W-MOTOR-PEDAL-ASSIST-SHIMANO-GEAR-MTB-PAS-BICY/362326076778?hash=item545c512d6a:g:UmwAAOSw7HhcEgOb&frcectupt=true

Yes, I know, shouldn’t have gone for the cheap stuff, but if this is fixable, then I believe it is still a decent purchase.

Anyway, any help would be hugely appreciated

Cheers!

 

[Nealh]

KT stuff is pretty good as is Bafang hub or copy hubs, so you are doing the kit on the bike a bit of injustice. I have use these for years on most of my bikes without much issue.

If to works on the push switch then PAS is the issue and usually not the controller.
The sensor you correctly identified in your pic (Red arrow).
Firstly check the PAS magnet disc (opposite the sensor) make sure it only rotates when you turn the cranks, the disc shouldn't rotate around the BB axle on it's own. Check the gap between magnets and the sensor the gap needs to be 1 or 2mm.

Does the sensor at all have a small Red led ? If so this should blink on and off as the magnets pass the sensor.

 

[vfr400]

It all looks OK to me, so that leaves two possibilities that I can think of. Either the magnet disc isn't turning with the pedals or the sensor is faulty. To test the sensor, you need a voltmeter. There are three wires, normally black red and another (signal). When everything is connected and switched on, stick the voltmeter probes into the back of the connector to make contact with the crimps. if there's hot melt glue in there, pull it out. Measure the voltage between the black and red. It should be 5v. That's the power supply to it. Next, measure between the black and the signal wire while you turn the crank slowly. You should see the 5v going on and off as each magnet passes the sensor. You might need a helper to do that test.

If you need to buy another sensor, don't get anything fancy. the cheapest 5 magnet ones are normally the most compatible, but an 8 or 10 magnet one will also be OK. Sensors only cost a few dollars from Aliexpress or Ebay.

You made a good decision with that bike. Problems are always cheap and easy to sort out.

P.S. That was a really good explanation of your problem with appropriate photos. If only everybody could explain their problems like that. Some people think that we're FMRs.

 

[AdHoc]

Hi Nealh and vfr400, thanks for the quick replies, and sorry for my late reply, didn’t have access to the bike for a while.

I just did the following:
- check that all magnets are on the disk (they are)
- clean the disk+magnets
- clean the sensor
- check if the sensor has a LED (it doesn’t)
- open the controller box (everything looks healthy inside)
- put the rear of the bike on an improvised stand and test the wires with a voltmeter (steady 5V, even when pedalling)

The disk rotates with the crank, so no problem there.

If I understand correctly, it must be a PAS sensor issue. Any advice on where to get the correct one? There seems to be 10 magnets on the disc, wouldn’t want to get the wrong one!

Weirdly, the wires on the sensor cable are red/green/yellow on one side and red/yellow/blue on the other.


My creative mounting system (camping stove on one side, old Playstation 3 on the other!)




Sensor cable, wires are weird colours.


If you’re curious, inside the controller box.

Thanks again!

 

[vfr400]

You didn’t me tion whether you checked whether the signal wire switches when you move the pedal slowly.

 

[Nealh]

Test the hall operation between Gnd & signal.
If PAS is turned slowly then you see the V's fluctuate between 5 & about 1v for a working hall.

 

[AdHoc]

Yeah nah, no flipping on the 5V signal, nor on the 4.3V one. I also tried passing a bigger magnet in front of the sensor to no avail. I put the probes in all possible combinations in order to determine which signal does what. I get 5V on one, 4.3V on another (power?) and 0V on the last. Poked through the wires close to the sensor, same result.

I’m in Australia. I’ll order a new magnet and report on it (might be a while...). I just hope the new magnet fits, but I’m guessing it’s standardised.

Thanks again for your help.

 

[vfr400]

there are some issues with compatibility when you buy a replacement. the cheapest ones with 5 magnets are probably the most compatible. Avoid one with 12 magnets.

 

[AdHoc]

Will do, thanks!