How can we protect controllers from motor stalls?

[nasukaren]

So...... I received the ESC for my moped conversion and installed it. A short test run later and on a downhill run, my rear wheel locked up and the controller blew up. It shouldn't have happened because I have a centrifugal clutch, I'm still not sure what happened. Here are the gory details:

http://visforvoltage.org/blog/nasukaren/4235

I have a techie question.... I've now heard of multiple controllers that have blown because of motor stalls, brushed, brushless, etc. So in some sense, I'm in good company.

How can we better protect our controllers? The one that I blew was $30, but its replacement is $220. I was wondering if it was possible to put fuses on the motor leads (between the motor and the controller) that would blow before the FETs did on the controller.

Is this doable?

Karen

 

[knoxie]

Hi

It may help but in most cases the fet will let go before the fuse, I used to run them on the BMX, it was more hassle than it was worth to be honest, also sometimes you would pull out across the road and blow a fuse! stopping right in the middle of the road, not good.

Others may be able to comment on the anti stall thing? not sure whats going on there?

Knoxie

 

[Lessss]

the real question is why does the motor stall?

 

[Drunkskunk]

A good controller should be able to handle a stall. it should sense the amp draw is too high and cut it off. Depending on what you're running, the controller should shut off if the brake is pulled anyway.

I stall my C-Lyte all the time, when it's set to 20 amps. There are some hills it simply can't power up from a dead stop at 20 amps, and it shuts off.

 

[fechter]

Basically all motors are stalled when you start out from a stop. The current limiter circuit is supposed to protect the controller from stall conditons. Most controllers also have a locked rotor detection that kills the output if a stall condition lasts for more than a second or so. If things are properly designed, it should be bulletproof. "Proper" design might add too much to the cost or the designers really don't know what they are doing (or both).

 

[MyPC8MyBrain]

Would a freewheel have helped here ?
When the ESC told the motor to brake, you go into coast mode with freewheel overrun when the motor slows or stops.

No engine braking available, but do you really want to engine brake with a tiny motor ?

[Using the term ESC instead of controller led me to think RC type motor.. the above may not apply here in in the second look]

 

[nasukaren]

Thanks everyone for your tips. I think the problem was that it was a cheapo $30 ESC designed for model airplanes. But even model airplanes have propeller stalls when they land, so it must have been poorly designed. Either that, or I somehow reprogrammed it for an engine brake (I doubt it since the program mode is deliberately hard to get to).

I have a much more expensive ESC on the way and hopefully that will be stall proof. I'm really not sure why my motor stalled when I have a centrifugal clutch (and pretty heavy flywheel) on the thing. Oh well, one of those mysteries, I guess.

Karen

 

[nasukaren]

Basically all motors are stalled when you start out from a stop. The current limiter circuit is supposed to protect the controller from stall conditons. Most controllers also have a locked rotor detection that kills the output if a stall condition lasts for more than a second or so. If things are properly designed, it should be bulletproof. "Proper" design might add too much to the cost or the designers really don't know what they are doing (or both).

Fetchter-san

I wonder if the RC motor controllers (that don't have Hall sensors for spindle rotation and use back-EMF instead) are inherently more sensitive to motor stalls because they can't tell quickly enough that the rotor isn't rotating.

Have you heard of fuses on the motor leads? Would this have helped or is the armature locked current so high and quick that a fuse wouldn't protect a FET fast enough?

Karen

 

[dirty_d]

i think that most of the rc controllers dont have an active current limit, they are just designed to be used at below their max rating, and above it to some degree for a certain amount of time, like if an airplane is climbing at a steep angle. some of the more expensive ones probably do have a current limit, but i think most dont because a propeller goes from stall to high speed, in a very short amount of time, unlike a bike with a 100+ lb rider on it.

 

[fechter]

Some people use fuses in the motor wires. It probably can't hurt.

I think the real issue is RC controllers are expecting the inertia of a propeller or small RC car, which is like hundreds or thousands of times less than a bike. Without current limiting, they don't stand much of a chance on a large vehicle. I designed a current limiter circuit for an RC controller that uses a servo tester on the throttle. Properl set, this should limit the current to a safe level.

 

[nasukaren]

Fechter-san

You're the best!

Can you post the schematic for your current limiter?

Karen