Possible Speed Sensor Problem

[georgehenry]

Hi, this is a bike I bought second hand from the classified pedelec ads.

Its a Oxygen Emate bike from around 2011 vintage.

It had 500 miles on it when I bought it and had reached 3536 when the speedometer stopped working as well as the odometer.

The electrical components are generic Chinese I assume but branded Oxydrive.

So this failure happened when I took the bike on holiday to ride from the beach to get provisions. Rather than in a garage as usual it was locked to a railing at the rear of the Hotel. So more exposed to wind and rain than at home.

The symptoms seem to indicate a speed sensor failure. The speedometer and Odometer have stopped working. It rides like normal but switches itself off after about 5 minutes. As a lot of the journeys I do on it are to the shops and back, I have been lazy and put up with it, as you can switch it back on while riding by pressing the handlebar buttons, but now that I am out in the dark more, it is more inconvenient as the lights also go out.

This speed sensor is attached to the front fork leg. I did buy a new spoke magnet in case this was a factor but after attaching it the fault still persists.

I have taken some photographs and would be very grateful for any help and particularly grateful if some one could post a link for a suitable replacement with the correct connectors that I could buy and fit.




Speed sensor attached to front fork.



New magnet attached, but fault remains.



Assumed Chinese display but branded by selling company OXYDrive



Control buttons on handlebar.



Rear hub motor, apologies for poor photograph



Pulled apart connector for current speed sensor



Other half of pulled apart connector for speed sensor

Here is a link to a thread I wrote about the bike which has more pictures and information.

https://www.pedelecs.co.uk/forum/threads/the-tale-of-a-£100-second-hand-electric-bike.33079/

 

[saneagle]

You need to find the pinouts with a meter. One pin is ground, one is 5v and the third is the signal. Connect the black probe to the black wire's bullet connector as ground, set the meter to 20v and see which pin is 5v, then set it to continuity or resistance to find the ground wire. It could be that the signal wire is pulled up to 5v or down to ground by a resistor, in which case, you might get two grounds or two 5vs, so try both in the next test.

Whichever you decide is the signal wire, make a bridge that you can tap to the ground to mimic the speed sensor pulse. If that doesn't work, tap it to the 5v one and see if that works. In the case of two 5vs, try each one tapped to ground, and if there are two 0vs, tap each one to 5v. Hopefully, one of those combinations work. When you find the right pair, you can cut the sensor of an old cycle computer or buy the cheapest one from Ebay (about £3). Cut off the old sensor and join the wires to the matching positions. Cycle computer sensors only have two wires, which is all you need to connect.

That's assuming that your sensor is faulty. If you get no speed displayed by tapping any combination, then something is wrong with the cable or a connection at the controller end.

To try and make the above clearer, the sensor is powered by two wires (5v and ground) and sends a pulse back through the signal wire. The magnet makes the signal wire switch when it passes. The signal wire can be held up at 5v by a resistor, then shorted to ground when switched, or it can be pulled down to ground by a resistor and switched up to the 5v by the magnet. In other words, it either makes a 0v pulse or a 5v pulse when the magnet passes. Different controllers can do it either way.

 

[georgehenry]

Thanks saneagle for your comprehensive reply. I am very grateful.

There will be a delay to study what you have said and make the time to go through the tests you suggest.

At least I can still use the bike. It is predominantly an errand bike where my journeys are short enough for the motor not to cut out. I used to work in the Rail Industry and this sort of failure would have been called "A right side failure" ie one that allows you to carry on, as opposed to "A wrong side failure" that does not.

 

[georgehenry]

Fixing the speed sensor.

Today was the day to attempt to fix my speed sensor, which in a good way turned out slightly anti-climatically.

As they were so cheap I had just gone ahead and bought a wired cycle computer. I took the bike to my friend's house, who has a well lit work area and various electrical meters and other useful tools. First we unplugged the speed sensor and probed the mail connectors with an old BT swing meter, setting it to 20v to find that one of the posts gave a 5v reading.

Then we cut the two cable ties and removed the old speed sensor. At this point a hopeful simple solution presented itself. Not at all obvious until we removed the speed sensor but we found a small break to the outer covering of the connecting cable. We peeled the outer covering back to find underneath that a small section of one of the three wires had been ripped away, probably by contact with the wheel, with a small gap of missing wire. You could really only see this by peeling the outer covering back and before removing it the break in the outer cable was not at all easy to see.

My friend then found a suitable replacement section of wire and soldered it into the gap. Some shrink wrap over the top, and we put it back on the bike. We turned the bike on and span the wheel, and at first nothing happened. But I told my friend that the positioning of the magnet and sensor does need to be just right and after a little playing around it all started working. We cable tied the wire in place, cleaned the plug connectors for good measure, and all was well.

Thanks again for the very helpful reply provided by saneagle.

All's well that ends well.

As is perversely normal with anything that breaks, the loss of my speedometer and odometer coincided with me riding the £100 second hand bike almost every day as my main shopping/errand bike, as I had semi permanently lent my other Emate to my son who uses it to get to work and back. So there are four months of almost daily riding unrecorded.

 

[saneagle]

Another happy ending.I'll sleep well tonight!