Coasting Downhill => Damaging Battery/Controller ! ?

The7

10 kW
Joined
Jul 11, 2007
Messages
761
Location
Vancouver
For non-freewheeling motors only:

If you coasting downhill with an speed greater than the no-load top-speed, the motor becomes an generator which will generate an voltage greater than the battery voltage.

Good point :
1) Charging your battery for free.

Bad points:
1) Overcharging and damaging your battery.
2) If you isolate (mechanically switch OFF) the battery, the motor will generate a higher voltage which will damage your controller because it is still connected to the controller.
3) If you try to isolate (mechanically switch OFF) the motor windings from the controller during running or coasting, an very high voltage spike will occur (due to motor inductance) and will surely damage the controller.
 
Ypedal said:
Pros to running high-voltage setups i guess ! lol.. but i've never had problems with this hapening or heard of it being a problem .. yet...

What is your no-load top-speed?
What is your coasting speed downhill and for how long?
What voltage of controller do you use?
What type of battery?

It all depends on the above whats?
 
I agree.

I've used everything from 36v to 90+v ,.. SLA, Nimh , Nicad, Li.. 20 to 700C wheels.. etc....

Example of my lst years setup, 72v 8ah NIMH on a 406/409 20" wheel, no load in 409 = aprox 45 km/h, going down a big hill at 55 once a day for weeks.. no problems to report.

If you had a 36v setup on a 4011 or something going down a very big hill... i see how problems could occur.. but from all user reports on various forums/groups/etc.. over the past 3 years or so .. i dont recall a single failure reported for this type of problem ?

If anyone know of a situation that happened.. please link !
 
Ypedal said:
I agree.
Example of my lst years setup, 72v 8ah NIMH on a 406/409 20" wheel, no load in 409 = aprox 45 km/h, going down a big hill at 55 once a day for weeks.. no problems to report.

The no-load speed = speed when drive-wheel off ground.
For exmaple my AL1020 with 48V batt has an no-load speed of 61 km/h and only about 45 km/h on flat.

If yours 45 km/h is top speed on flat, then your no-load speed would be higher (about 55-60 km/h). So no problem at all for 55km/h downhill. But if you coast at above 60km/h, the story will be different.
 
Ypedal said:
Have you had this happen ?

An old version X-controller was damaged during the first road test. It could be related to bad point (2). There is no big cap (100V 100uF) in this old version.
The X-controller was bench tested OK on my AL1020 ebike with 24V, 36V and 48V under no-load and braking load condition.

On the first road test with 36V battery, an ammeter (DMM) was used to measure the battery current. So there was an high chance of loose connection.
Riding on an gentle slope with FULL throttle, the ammeter showed an limiting current of about 18A.
Suddenly the controller died due to a small plump.
Apparently during the plump (at 18A ), part of the connection was loosen. An very high voltage spike (due to motor inductance) occurred and damaged the controller. If it had the 3 big cap, the energy of the short-time high voltage would be absorbed by these cap and the damage would not occur.

Later it was found that all FTEs are OK. The yellow FET driver was faulty.
So I am not going to repair this old version.
Instead I bought an new version which has 3 big cap which has been working OK on AL1020.
 
The7 said:
Suddenly the controller died due to a small plump.

Plump = bump(?)...

speed_bump_488.png

:)
 
TylerDurden said:
The7 said:
Suddenly the controller died due to a small plump.

Plump = bump(?)...

:)

'died due to a small plump' = His fat folds smothered the controller so it overheated...:D
 
The7 said:
For non-freewheeling motors only:

If you coasting downhill with an speed greater than the no-load top-speed, the motor becomes an generator which will generate an voltage greater than the battery voltage.

It depends on your batteries. When you approach that no-load speed the motor acts like a brake only if your batteries are unable to absorb the charge quick enough.

For example, when I was running my SLA setup, the motor was a big brake at it's no load speed. Worked very well as a coaster brake on speed hills.

When I switched to NiMH on the same controller (same voltage as SLA before), the no load speed could be exceeded by 5-10 MPH before I would feel the braking effect. I attributed it to the NiMH being able to absorb (recharge) the extra energy better than the SLA could.

The only thing that happens with friction in our setups is heat. So unless the controller or battery begins to overheat, you should be just fine.
 
knightmb said:
When I switched to NiMH on the same controller (same voltage as SLA before), the no load speed could be exceeded by 5-10 MPH before I would feel the braking effect.

What is the nominal voltage of the NiMH and that of the SLA?

At the same nominal voltage, the NiMH requires a higher charging voltage than SLA.
That is why the braking effect for the NiMH is at an higher speed.


My AL1020 has an freewheel motor so the motor stops during coasting downhill. There will be no braking effect and no battery charging.
 
I think what happens is the motor acts as a brake.

I have a rather steep hill if I take university avenue downtown, I do about 15~20 mph going up it with a phoenix, and down it about 30 tops going down, I noticed my batteries had gotten warm from the downhill cruise. (downhill lasts about a mile either way)

Why I think its creating some sort of braking however is that my WE motor couldn't make it up the hill without assisting it, but going down I would have to hold the brakes because I would easily go over 35 mph (the speed limit, and not what I want to be doing on a normal bicycle)
 
Brucey said:
Why I think its creating some sort of braking however is that my WE motor couldn't make it up the hill without assisting it, but going down I would have to hold the brakes because I would easily go over 35 mph (the speed limit, and not what I want to be doing on a normal bicycle)

What voltage did you have the WE running at? I remember my WE motor (it was brushless) having about a 35 MPH wall at 60 volts. It's possible that you are at slightly below the speed that you would encounter resistance if you are running 60 volts through it. It also depends on wheel size as I was using 700C size wheels which might affect that rotation speed.
 
Mine was up to 35 mph regularly at 48 volts 25 amps and on a crystalyte brushed controller? 24 inch wheel. I was staying with traffic easily and the GPS backed up those numbers. Now if I go down the same hill with the brute, I hold up traffic. Theres definately something going on.

Maybe it was the cause of this?

connectorburned.jpg
 
Did you just stuff the bullet connector into the powerpole connector? From the scorch marks, it looks like there was a short....how'd that happen? Did it break, then pop out and then contact one of the other bullet connectors after the tape broke?

connectorburned.jpg
 
Yes, I just stuffed the connectors in, they held fine and I planned to make a proper connection soon with some connectors I found, (my motor came with those connections?) but it looks like I blew it too soon.

I can't imagine them shorting between each other, each was wrapped individually with vinyl tape then I wrapped them all together, what appears to happen is one pulled itself loose and then shorted between the two connections.

I've soldered proper connections now, but when connected all that happens is the light on the controller comes on, and then the motor pops (turns the wheel an inch) and then nothing, no throttle response, light stays on. Looks like I'm back to reading information instead of enjoying the bike for now. :roll:
 
Brucey said:
I've soldered proper connections now, but when connected all that happens is the light on the controller comes on, and then the motor pops (turns the wheel an inch) and then nothing, no throttle response, light stays on. Looks like I'm back to reading information instead of enjoying the bike for now. :roll:

I recognize that, something has gone bad in the controller. I had this happen to a WE controller a while back, had to make a video for them so they would accept my return. The motor was just fine.

The video I sent them is below, maybe it will help. (it's a low quality windows media, it's all I had)

[Note in the video, I blame the motor, it was actually the controller but controller seemed fine in some test but turns out it was really bad]
 
Brucey said:
what appears to happen is one pulled itself loose and then shorted between the two connections.

If it happened during a high motor current instant, an very high voltage spike (Bad point 3) would be produced and could damage the FETs in that (Blue) branch.
Motor windings are very robust and could withstand short-circuit current and overvoltage for quite a long period of time.
But FETs could die in splitted second under these faulty condition.

Brucey said:
I've soldered proper connections now, but when connected all that happens is the light on the controller comes on, and then the motor pops (turns the wheel an inch) and then nothing, no throttle response, light stays on
Too late.
Seems that FETs in that branch were already damaged.

You could check the resistance of the motor windings with DMM with the motor disconnected from the controller.
 
Brucey said:
I've soldered proper connections now, but when connected all that happens is the light on the controller comes on, and then the motor pops (turns the wheel an inch) and then nothing, no throttle response, light stays on
The7 said:
Too late.
Seems that FETs in that branch were already damaged.

You could check the resistance of the motor windings with DMM with the motor disconnected from the controller.

I bet the motor is fine, certainly sounds like a blown controller. In my previous response I blamed the motor, but that's what happens when you try to do too many things at once in the morning :) , I should have placed the blame on the controller as it was the source of my original problem.

But the video is good at showing what happens when something is blown in the controller and how the motor behaves.
 
arg

I don't have a digital multi-meter, just some analog one I stole.

I'll start some testing, I can't imagine anything not being under warranty at this point, the bike was only operational for about 4 days.
 
Brucey said:
arg

I don't have a digital multi-meter, just some analog one I stole.

I'll start some testing, I can't imagine anything not being under warranty at this point, the bike was only operational for about 4 days.

It is Ok to use an analog multi-meter to measure the res.

This is the first part of the "Bath-tub" failure rate.
 
Alrighty, friend let me borrow his DMM.

something like 0.03 ohm resistance on all 3 of the phase wires.

I hope thats good news.

I'm also pretty confident at this point it's the controller, I can't imagine the motor simply kicking when I turn the controller on if its a problem with the motor.
 
whats with the two different types of connectors...if those were plugged together that was probably the source of your burn up.
 
Brucey said:
Alrighty, friend let me borrow his DMM.

something like 0.03 ohm resistance on all 3 of the phase wires.

I hope thats good news.

I'm also pretty confident at this point it's the controller, I can't imagine the motor simply kicking when I turn the controller on if its a problem with the motor.

Yes. Only for motor but not for the controller.
 
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