Electric Bikes - Why is there a short-circuit in the electrics?

Hi there! I am new to the Forum and hope I can get some advice. I live in Dublin, Ireland and have a bike called a 'Synergie Commuter', bought in Scotland. The power failed completely while going uphill using the throttle. The main-fuse has blown. Having removed the battery and replaced the fuse, the battery seems okay but my test-meter shows a short-circuit across the terminals on which the battery rests. No evidence of wire-breaks as far as I can see. Any ideas about where to start looking and what tests to perform? Can the motor fail, displaying these symptoms? Any help appreciated

can you go to the speed controller and unplug as many connections that you can? it'll help you isolate the problem.

can you go to the speed controller and unplug as many connections that you can? it'll help you isolate the problem.

Thanks very much for the reply, SeizeTech. So far I've only been able to isolate a couple of circuits where there is an inline plug/socket in the wiring, one being the throttle, the other the voltage indicator. This has no effect on the short. There are wires going into the bottom bracket shell so I assume that's where a controller would be but I don't have the tools with which to get in there. The crank has what looks like a keyhole in it and the circular plate covering the shell has 3 holes drilled in it which requires a 3-pronged tool of some description.

A few general questions if I may. Is it likely that a controller failure could result in a short? Same question regarding the motor (brushed). I assume that a failure in the brake switches isn't likely to be a problem?


many thanks, thanks for the help,


Fep127

yes, electronics can fail with a short or an open.

just a few more ideas...

with your nose, can you smell a cooked odor at the motor or controller?

Have you traced all external cables and inspected them for wear or damage?

If you can hotwire the motor and prove that it still works, then a controller failure is very likely.

Thanks for the good ideas SeizeTech. Nothing obvious so far but hot-wiring the motor isn't possible without cutting wires, which I'm reluctant to do. I've managed to pull the cranks however and am trying to figure out how to get into the BB shell. The chainring is separate to the crank and is still attached and I'm no nearer to determining how to open the plate on the left side, the one with the 3 indentations in it (I suspect a special tool is needed). I've just heard from the dealer however and it may be possible to speak to their mechanic next week.

Thanks again,


Fep127

re: hotwiring the motor without cutting wires

If you can get at the controller, you'll likely find a connector on the wires that go off to the motor

re: hotwiring the motor without cutting wires

If you can get at the controller, you'll likely find a connector on the wires that go off to the motor

I've managed to isolate the motor leads to find that there is a dead short across them. Can I take that to mean that the motor (24V brushed) is damaged and needs to be replaced?

I've discovered that the frame on my bike is commonly-used under different bike-makers'/sellers brands. For anyone who might be interested, having removed the cranks - which on the right-hand side is separate from the chainring - the bottom-bracket is removed by unscrewing a circular plate on the left-hand side of the bike and withdrawing the complete unit from the right. The controller is an integral part of the unit so that the complete thing has to be replaced if the controller is faulty.

If I measured a short across the power leads of a brushed motor I would assume it's toast. Not to say a brush couldn't have disintegrated and spread itself around causing a short. Could also be something much simpler like the positive wire insulator being defective. These days it's mostly not worth it to start pulling one apart.

"I've managed to isolate the motor leads to find that there is a dead short across them. Can I take that to mean that the motor (24V brushed) is damaged and needs to be replaced?"

In general, I would say yes.

However, I am always a bit reluctant to use this method for diagnosing a motor.

Why? Because a motor is essentially 1 really long wire that is wrapped around a rotor....even long wires, with NO FAULT, can measure very low on an Ohm meter.

I suggest the following:

1 - use an ohm meter to determine if the motor is 'open' circuit, but only take a 'short circuit' reading with a grain of salt.

IMO, its good that you don't have an open circuit. but you should try to apply power to the motor to see if it is truly short circuit.

If I measured a short across the power leads of a brushed motor I would assume it's toast. Not to say a brush couldn't have disintegrated and spread itself around causing a short. Could also be something much simpler like the positive wire insulator being defective. These days it's mostly not worth it to start pulling one apart.

good advice. I agree.

Please post pictures of how you measure the short circuit issue from. This way, we can get better ideas and to give you a more accurate answer & solution. :)

Please post pictures of how you measure the short circuit issue from. This way, we can get better ideas and to give you a more accurate answer & solution. :)

Thanks everybody for the very useful contributions. I appreciate you all taking the time. This is turning out to be a real voyage of discovery! Turns out to be excellent advice not to attempt to use an ohm meter to measure a short. I borrowed another digi-meter and dug out an ancient analog meter of my own. Both confirmed there is a very low resistance and not a short, so I hot-wired the motor and it works!

There is now a question as to whether I measured a short or simply a low resistance across the input terminals in the first place, but as the battery's 25A fuse blew, it seems reasonable to assume that the battery was seeing at least a very low resistance.

There is no sign of wiring damage. Based on what the supplier's mechanic told me, I won't be able to get at the controller itself when I withdraw the integrated unit from the BB shell but the wiring is all accessible and I am now trying to make sense of it, to see if there is anything obviously wrong.

Any ideas about how to test the controller would be very useful. Thanks for your suggestion about photos lyen. I'll see what I can do.

Thanks everybody for the very useful contributions. I appreciate you all taking the time. This is turning out to be a real voyage of discovery! Turns out to be excellent advice not to attempt to use an ohm meter to measure a short. I borrowed another digi-meter and dug out an ancient analog meter of my own. Both confirmed there is a very low resistance and not a short, so I hot-wired the motor and it works!

There is now a question as to whether I measured a short or simply a low resistance across the input terminals in the first place, but as the battery's 25A fuse blew, it seems reasonable to assume that the battery was seeing at least a very low resistance.

There is no sign of wiring damage. Based on what the supplier's mechanic told me, I won't be able to get at the controller itself when I withdraw the integrated unit from the BB shell but the wiring is all accessible and I am now trying to make sense of it, to see if there is anything obviously wrong.

Any ideas about how to test the controller would be very useful. Thanks for your suggestion about photos lyen. I'll see what I can do.

Further to the above....

With the wiring re-connected, the resistance as measured at the input terminals (on which the battery rests) appears to be the same as read across the motor wires, in other words the battery is 'looking' directly at the motor. I confirmed this by installing the battery and when it's switched on the motor runs immediately. I would have thought that this should not happen as the controller should not supply power to the motor until the crank is turned.

That seems to indicate that the problem is either the controller or possibly the switch (or whatever) which is activated when the crank is turned. I'm now looking for a replacement bottom-bracket unit.

Thanks again for your patience and help.

I have a few more ideas...

If I am reading you correctly, if you connect the battery to input of the controller, your motor works.

Lets entertain the possibility that your controller is good, and something external to your controller is causing it to run full out...

....here's a test you can try: while the motor is running what happens when you pull the brakes? a functioning controller should still turn itself off even if it is detecting a full throttle condition. so therefore, if your controller turns itself off, I would say that the chance of an external fault is likely, ie something like a stuck throttle.

However, if the controller does not turn itself off, then I would say that the chance of a controller fault is more likely than an external fault because the stuck throttle would be fault #1, and the malfunctioning brake lever would be fault #2. Although, 2 faults are not impossible, 1 fault is more likely.

I have a few more ideas...

If I am reading you correctly, if you connect the battery to input of the controller, your motor works..

That's correct.


Lets entertain the possibility that your controller is good, and something external to your controller is causing it to run full out...

....here's a test you can try: while the motor is running what happens when you pull the brakes? a functioning controller should still turn itself off even if it is detecting a full throttle condition. so therefore, if your controller turns itself off, I would say that the chance of an external fault is likely, ie something like a stuck throttle.

However, if the controller does not turn itself off, then I would say that the chance of a controller fault is more likely than an external fault because the stuck throttle would be fault #1, and the malfunctioning brake lever would be fault #2. Although, 2 faults are not impossible, 1 fault is more likely.

Pulling the brakes (the front one! The back-brake locks up the wheel causing the fuse to blow) has no effect.

The throttle has no effect, whether connected or not. I don't use the throttle much but I'd have reckoned that it doesn't function until after the bike has built up some speed, in other words I'm not sure if it'll work from a standing start. I don't know if this is typical of e-bikes in general.

universal controllers are $20-$40 dollars, so even if the synergie bike gouges you for a controller, it shouldn't break your bank account.

I think it's time to try another controller. Personally, for the cost, trying another controller right away might have been a good idea.

universal controllers are $20-$40 dollars, so even if the synergie bike gouges you for a controller, it shouldn't break your bank account.

I think it's time to try another controller. Personally, for the cost, trying another controller right away might have been a good idea.

Update on progress, for anyone who has or is thinking of getting a similar type of cheap bike which uses what seems to be a widely-used, mass-produced frame. I finally opened the cover on the BB shell using an adjustable angle-grinder wrench and withdrew the entire unit complete with chainring. It is the case that the controller is hidden somewhere within this unit and there is no obvious way to get into it. I have a photo if anyone is interested. I am now awaiting the delivery of the replacement.

Incidentally, SeizeTech, compared to a replaceable controller as you mention, my unit costs around £63 ($90) plus $26 delivery charges in my situation. There is in addition the labour costs if someone needs to have the unit replaced professionally. On the other hand I have some indications that it may be possible to source the unit directly from China but I didn't get as far as getting a price.

Thanks again for all the help.