Very intermittent power

[Stu Summer]

I have an old ebike with an old Bafang 350w rear hub motor. When I plug in the battery, the throttle shows power. When I twist the throttle the motor gives an instant of a jolt and then.....nothing. Only if I unplug and wait a few hours does it then give this smallest of signs of life. Where should I look for the problem?

 

[fechter]

I would suspect the battery. Measure the battery voltage while trying to run the motor. If the BMS is tripping, the battery voltage will drop to zero and stay there until reset by disconnecting. If this happens, I would try to measure the individual cell voltages in the pack, but this may require some disassembly. If the pack is bad, little risk in taking it apart to check.

 

[Stu Summer]

I would suspect the battery. Measure the battery voltage while trying to run the motor. If the BMS is tripping, the battery voltage will drop to zero and stay there until reset by disconnecting. If this happens, I would try to measure the individual cell voltages in the pack, but this may require some disassembly. If the pack is bad, little risk in taking it apart to check.

Thank you, Fechter, for the suggestion. Doesn't seem to be the battery. Alternate batteries, all fully charged and functioning on other bikes, do the same thing. Unfortunately for me, the controller is a black box I don't have the knowledge to access. I did open it up and did not see any burn marks.

The unit is so old I guess I will just buy another kit!

 

[E-HP]

When I plug in the battery, the throttle shows power. When I twist the throttle the motor gives an instant of a jolt and then.....nothing.

Can you manually rotate the wheel a bit while applying throttle replicate the jolt (careful of your fingers)?



Sent from my iPhone using Tapatalk

 

[fechter]

Thank you, Fechter, for the suggestion. Doesn't seem to be the battery. Alternate batteries, all fully charged and functioning on other bikes, do the same thing. Unfortunately for me, the controller is a black box I don't have the knowledge to access. I did open it up and did not see any burn marks.

Good test. One other thing I would check is the motor hall signals. A flaky connection on one signal could cause that kind of problem. It can be challenging to get a meter probe on the hall sensor wires while plugged in. Using a short stiff piece of wire jammed into the back of the connector usually works. From battery negative, each hall signal should alternate from near zero to near 5v when the motor is slowly turned by hand. If it's a geared motor with a freewheel, turn the rear wheel backward slowly.

 

[amberwolf]

Except the part about having to wait for hours to get any further response from the system.

Speculation: That only makes sense for either a battery that shutdown it's BMS from a low cell that took that long to recover, or a severe overheating problem somewhere (controller?) which shouldn't happen for only an instant's worth of sort-of-operation. Blown (or leaky/swollen) caps in a controller might cause wierd operation, but shouldn't take hours to recover.

 

[dogman dan]

Its bad connections 99,9% of the time. The hours waiting is not doing anything. Its just randomly getting a poor connection back later on.

Don't get me wrong though, controller could be toast, or throttle, so after you go through the wiring very closely, if it does not fix it, start doing some diagnostic tests.

First one may be bypassing the throttle. With the wheel off the ground, try connecting the two positive throttle wires. Three wires, + and - in, and + back out. Somehow short the two +, and the bike will run if your problem is just the throttle. ( or its plug)


Second one, does the motor resist hard when you turn the wheel by hand either way? It might resist some but I mean hard. If it does, unplug the motor wires. If the resistance goes away, your controller is blown. Controllers can fail for other reasons though. But a blown fet on the power wires is easy to diagnose. If the hard resistance does not go away, the motor is melted down, or mabye rusted to the point it cant turn.

 

[Stu Summer]

Wow! I got all the heavy hitters working on my post! Thank you!

But I figured it out. I opened up the controller, thinking one of the connectors had come loose, and saw that the yellow Anderson connector was lightly melted/distorted. I had to use pliers to separate the two halves and was thinking about replacing the more melted one when I noticed that the lead wire from the motor up to connector had broken insulation, as if the insulation had been cheap and just gave out and cracked (quite a bit.) This must have been shorting against the metal housing of the motor.

Anyway, I put liquid electrical tape on the lead and it worked!!!!

I should have put the liquid electrical on all the wires before I closed it up.

I'm particularly happy because this would have been the second controller to go bad (on two BBSHD's) and I was starting to research DD hub motors(since I don't do any off roading anyway.)

Thanks again for all of your efforts to help me.

 

[fechter]

Nice! Thanks for reporting the result. If the connection was weak, the connector may have heated up enough to actually melt the insulation on the wire. I've had Andersons fail when the metal contact part was slightly bent so there was not enough tension.

 

[wturber]

Had a friend's bike that had a similar intermittent/under load power issue. Replace the controller (cheap fix since it was a 250 watt bike) and no joy. Finally determined that even though the wiring tested out as having good continuity with a standard continuity test, one of the power leads was corroded from moisture and simply wouldn't carry much amperage. New wires yielded much joy. Amazing how many different ways that wiring issues can create problems.