Electric scooter works only wheel off ground?

Hi

I have an electric scooter/patinete that's 900w. Lately, it's acting strange. Basically, when the scooter is off the ground ( wheel in the air ) then it works fine when it's on the ground, it hardly spins if at all.

My batteries voltage seem good. 13.2volt.

So I cut the two power wires to test voltage and it shows it gives 38Volts to the motor when is on the air but as soon as the wheel touches the ground it stops and the volt is now just 1.5volt and I can hear the motor but it doesn't spin.

Shouldn't the controller give full 36volt when the wheel is on the ground ?

Bad controller ?

Many thanks,
Mer

Bad battery... that's what the voltage being good but then droppping under load usually means.

Is it a brushless motor?

Yes, repeat your test while measuring the battery voltage.

The battery voltage doesn't drop at all or very little when wheel on ground and when off ground it drops around (EDIT: around 38v) from 39v. Measuring volt at motor shows 38v off the ground, 1.5volt on ground and 0v with no throttle.

The motor is brushed and I tried to give 36volt directly but spark was so big I didn't want to test again like that, Im pretty sure I need switch and circuit break

How old is the battery? Is the battery lithium, or lead-acid?

Relatively new (one-year?) good deepcycle 3x12V LAcid . Less than 50 cycles.. and never extreme deep drain of the battery, always stored them charged etc...

The battery voltage (39volt) doesn't drop at all when full throttle and wheel on the ground, yet it drops to around 37-38volt when full speed when the wheel is off the ground.

When I measure the voltage to the motor when the wheel is on the ground, only 1.5volt go to the motor, when I lift the scooter around 38volt go to the motor and it achieves full or near to full speed....

That's a bad connection somewhere between battery and motor.

When more current is demanded (on-ground load) then resistance of bad connection prevents current flow and drops voltage.

Set meter to DC volts. Put meter black on battery positive, and use meter red to measure each connector's voltage on the positive wires from battery to controller to wheel, with everything connected, and wheel on-ground, while applying some throttle.

When you begin to measure a voltage, the problem is between the last point you measured and this one.

If none have a voltage, then repeat the procedure on the negative battery terminal and negative battery/controller/motor wires.



Controller and motor must both be working fine or else they would not vary in speed as throttle is varied, even off-ground.

A brushed system is pretty simple. If the connections from the controller to the motor and battery to controller are good, then it pretty much has to be the controller.

If I had to guess, I'd say the current shunt unsoldered itself inside the controller. You might want to disconnect the battery and open up the controller and just do a visual inspection for anything obvious.

Since the motor runs from the throttle while it's off ground, it couldn't be a failed controller.

But it could be a bad connection that presents a high resistance, so if the shunt is still partly connected to the PCB, it might have a high enough resistance to cause overcurrent shutdown at anything other than offground loads.

For those interested ( and those who said it couldn't be the controller , I fixed my scooter.

I opened the controller and I found two bulged capacitors ( 40v 220uf ) which I replaced ( with 50v 220uf ) and it works fine now !

Thanks for the suggestions to isolate the problem and fix it

Vzzzzzzmmmmmmmmm!

Enjoy summer!!!

If you have a picture of the capacitors on the board, please post.

Bulging typically happens when they get overheated from too much ripple current. Using a higher voltage rating is good. Using a higher quality, low ESR cap is even better.

mer said:

I opened the controller and I found two bulged capacitors ( 40v 220uf ) which I replaced ( with 50v 220uf ) and it works fine now !

Click to expand...

That's one I haven't seen before. (I've seen blown caps like that, just not them allowing controller to work off-ground but not under load).

At a guess, under load the voltage ripples so much without the caps there to fix that, that the controller shuts down, while off-ground it's not bad enough to cause shutdown.