Brand new conversion, motor's stopped. Hall sensor?

handmadematt

Pedelecer
Hi guys. So I've fitted my new conversion kit. Consisting of the following:

BMC V4 rear hub motor
BMC 50A Controller
14S 10Ah 58.8v lithium polymer battery pack
Cycle Analyst V3

It was working fine on the workbench, I even took it for a spin briefly before I neatened up all the cabling etc.
I took it out for the first proper ride this morning and hit a problem. It wouldn't go at all!
The throttle position indicator on the C.A indicates movement so it is alive, I get a little blip from the motor sporadically, when off the ground this blip causes the motor to rotate a little bit.

I called my supplier and he suggested checking all the connections and cabling, he mentioned that if it's not that simple then it sounds like it could be the "hall sensor." I then researched this term and have a basic understanding of what it is. I have visibly checked all the connections and everything is fine, I disconnected and then reconnected everything. No joy, same fault.

Are there any tests I can do to confirm or deny this hall sensor theory, or any other suggestions/ theories?
Thanks.
 

Geebee

Esteemed Pedelecer
Mar 26, 2010
1,256
227
Australia
I know you have checked the cabling but one important step of fault finding is "what happened between working and not", you tidied up the cabling and it stopped working, maybe one last very thorough check?
 
D

Deleted member 4366

Guest
Hall sensors don't go for nothing, so no reason to think that one might have blown. The first thing to eliminate is your Cycle Analyst. There's thousands of possibilities in there. Connect the throttle directly to the controller and try again. Check that you have 5v between red and black throttle wires.
 

handmadematt

Pedelecer
Thanks guys, I'll check these things.

More important info perhaps:
When the cables are disconnected the motor turns freely in both directions. When the cables are connected it judders strongly when turning backwards as if you can feel all the magnets.
 
D

Deleted member 4366

Guest
There's a clutch in the motor, so if you spin it forwards, it will free-wheel. When you turn it backwards, the clutch engages and you turn the motor five times the speed of the wheel because of the internal gears. You should. therefore, feel some resistance. If it's hard and notchy to turn backwards, you have a blown MOSFET in the controller. It will feel obviously wrong and different to just a bit of resistance and the normal cogging of the magnets.
 

handmadematt

Pedelecer
OK. Having just spent half an hour relaying back and forth with my supplier I think we have got somewhere. My supplier agrees with you about the controller.
He is amazing by the way and I would highly recommend dealing with him. Mobile email iPhone responses right into the evenings and excellent after sales service.

(Unmentioned in this thread I was having another issue which I assumed was unconnected, it was that there was jerky acceleration in speed settings one and two (out of three) The third speed setting was full power and seemed fine. (Selectable by a handlebar mounted three position switch.)

My supplier has said the following:
"My guess is that the jerky acceleration has caused the controller to blow a fet. In my experience, in the rare case that a controller blows it always seems to happen in the first week, unfortunately in your case maybe in the first day! I think it needs to be run in, a bit like a new engine. I will get a brand new one in post today as along with the motor hall tester (just in case) and then you can send both back to me tomorrow."

Why would a MOSFET blow?
 
D

Deleted member 4366

Guest
They blow when the controller is trying to power the motor, but it can't go because:
  • It was stopped by the brakes or stalled out on a steep hill
  • Incorrect phase/hall connection sequence. You can't always go colour to colour unless the system is matched by the supplier.
  • Faulty connection on a phase or hall wire.
I don't agree with your seller. They don't go for nothing, but I suspect that many of his customers don't understand the importance of not giving full throttle when the motor isn't running properly, and the need to get the correct phase/hall sequence before giving full throttle.

To anybody else that reads this. If your motor stutters, do not give it full throttle.

Having said all that, you haven't proved that you have a blown MOSFET. Did you eliminate the Cycle Analyst? When you turn it backwards, is it obviously bad?
 

handmadematt

Pedelecer
To anybody else that reads this. If your motor stutters, do not give it full throttle.
On the flat it was stuttering (as described) and I did give it full throttle. Why it was stuttering I don't know. This is probably when it happened.
Having said all that, you haven't proved that you have a blown MOSFET. Did you eliminate the Cycle Analyst?
I didn't do that, I chose to simplify the procedure and not confuse him by just going through what he said and he didn't mention the C.A.
Agreed, a blown mosfet is not proved but does seem highly likely from what's been said.

Thanks again mate.
 
D

Deleted member 4366

Guest
Never make an assumption - always test.

You can test if a MOSFET has blown by measuring resistance between each phase wire and the controller's red battery wire, and again each it's black battery wire (not the actual battery). Each group of three should be approximately the same. Something like 11K to 14K and 4K to 11K.
If a FET is blown, you'll get one completely different. Depending on your meter, you might see changing results (continuously going down) because the capacitors might still be charged, so be quick and precise with each measurement and write down the result. If you faff about, you might get different results. It's a one-time measurement; however, if a FET is blown, there will be a massive difference in the result.
 

handmadematt

Pedelecer
The new controller arrived this morning. Top service!
Having fitted it everything's back to normal. Phew.
he talked me through the settings on the Cycle Analyst to adjust the acceleration parameters, essentially instead of it limiting volts it's now limiting amps. (Or was it the other way around? Oops.) Anyway, it's working fine and no longer feeling jerky in speed one and two, no more "bucking bronko."

He did say that I need a clamp on ammeter to calibrate the settings because every controller is different. I got a bit lost with what needs doing and why but he said it'll be fine for now.
 

Advertisers