Motor cutting out at high rpm

[Marskmil]

I have 1500w motor with. 72v 60a battery and a 72v 60a controller. When I get to high rpm I hear the motor cutting out and then it comes back in. Does the motor have an rpm limit? I've been getting to about 42 mph and the specs on ebay say the rpm of the motor is 540. I calculated that a 26in wheel at that rpm would go 41.8mph.

Also I don't notice any cutting out on hills or acceleration. Just when I get to that high rpm.
Do you guys think I'm reaching a rev limit on the motor?

 

[DogDipstick]

Generic controller? What is the make and model? 42mph on a 72v 60A sounds about right. My bike is right there, 72v. Motor does not " cut out " at all at top RPM, flat ground. Not mine. Maybe your controller is some kind that limits the top RPM? What controller?

@ ~8.5kV my motor runs the same speed about ( max loaded). Unloaded I reach 49mph. Loaded run 42ish. It will ride at 42mph and if you lift the rear wheel it runs to 49mph and wont go any faster.. but there is no distinct " cutting out".. it just does not go any faster.

 

[Marskmil]

Yeah

 

[Marskmil]

I guess my controller was 50a not 60

https://www.ebay.com/itm/72V-21ah-Triangle-Battery-Pack-for-3000W-motor-Electric-bicycle-Scooter-E-bike-/255291039350?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

https://www.ebay.com/itm/DC-48-72V-Brushless-Motor-Controller-2000W-For-E-bike-Electric-Bicycle-Scooter-/233104831122?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

https://www.ebay.com/itm/4-0-wide-Fat-Tire-Bike-Electric-Kit-20-24-26-Bicycle-Conversion-Ebike-kit-/164557000728?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

 

[Marskmil]

I notice if I lift the wheel up and free spin, that it makes the high pitched sound until the very end where the noise kinda changes like it's static and has some weird resistance. I feel like something's being limited somehow. It's a very crisp direct point where I feel the cutout while riding. But the wheel never cuts out when it's spinning freely in the air

 

[Marskmil]

Generic controller? What is the make and model? 42mph on a 72v 60A sounds about right. My bike is right there, 72v. Motor does not " cut out " at all at top RPM, flat ground. Not mine. Maybe your controller is some kind that limits the top RPM? What controller?

@ ~8.5kV my motor runs the same speed about ( max loaded). Unloaded I reach 49mph. Loaded run 42ish. It will ride at 42mph and if you lift the rear wheel it runs to 49mph and wont go any faster.. but there is no distinct " cutting out".. it just does not go any faster.

Yeah I have a generic controller, is that why? Not my bms or my motor? I can send you a link of each item if you want but they're all generic ebay parts

 

[DogDipstick]

On my bike ( very similar again, ) I pull 40A or more upon takeoff or up hills. Continuously. However, just rolling, on flat ground up to top speed, my current drops to 30A or less. Takes the power and amps to spin up but doesnt take power to keep it spinning ( well, less).. and this is typical.

So it probably is not the BMS or battery cutout, get a DC clamp meter on it and watch it to look for voltage getting cut if you really think this may be happening. I have once wired a controller that acted like that ( yours ) on the stand, where at top RPM unloaded the wheel would go "spinspinspin whoosh spinspinspin whoosh" where it would pulse at the very very top, about a third of the time. It would not when under load.

I chalked it up to the way the controller did its thing...

...hopefully someone with more experience will help more but it sounds kinda normal to me.

 

[Marskmil]

Yeah that's exactly what's happening! It pulses when I get to the top rpm. Hopefully someone knows why. I'm hoping now if I replace my controller with one that's rated for more wattage and amperage if that would change anything.

 

[SafeDiscDancing]

Yeah that's exactly what's happening! It pulses when I get to the top rpm. Hopefully someone knows why. I'm hoping now if I replace my controller with one that's rated for more wattage and amperage if that would change anything.

ERPM - Electrical Revolutions Per Minute

On my ebike I had a mismatch between the voltage to kV such that at high rpm it would not just cut out but get out of synch.

After rewinding the motor to a lower kV it works without problems at "half empty" voltage but when near full voltage I still get a little of it breaking up at full rpm when not loaded.

I'm going Sensorless on a (cheap chinese) sinusoidal brushless controller... the ERPM is somewhere low at 24,000 rpm.

And the more magnets and stator numbers you have will mean higher ERPM for wheel RPM.

Some guys are developing really fancy VESC controllers that can get ERPM up to 60,000 or more.

But you also said it spun up without difficulty when unloaded which might negate this ERPM issue... I get it unloaded.

This might be a design feature of the controller though... mine seems to dump current when I over rev.

 

[Marskmil]

So if I use an 84v 80a controller maybe this will stop the cutting out issue at high speed? My current controller is a 72v 50a controller. My bms is 50 amps though I'm not sure if it could take the 80ish amps without shutting down. I don't know know though. Does anyone know?