burnt MiniMotor

[rolf_w]

We have built a number of e-velos, some using 36V MiniMotors with 48V batteries. 2 Motors we have already 'fried' ! It seems that a continuous current of 15-20A overheats the motor windings and damages it beyond repair. Anybody else with similar experiences? any recommendations to protect the motor? we consider to use either a 16A MCB (mini circuit breaker) or the throttle overrun of the cycle analyst. r

[GoldenMotor]

did you use our controllers? our controllers should have been equipped with circuit breaker protections.

[Russell]

We have built a number of e-velos, some using 36V MiniMotors with 48V batteries. 2 Motors we have already 'fried' ! It seems that a continuous current of 15-20A overheats the motor windings and damages it beyond repair. Anybody else with similar experiences? any recommendations to protect the motor? we consider to use either a 16A MCB (mini circuit breaker) or the throttle overrun of the cycle analyst. r

You're complaining because a motor burns up when you run it continuously at 3 to 4 times its rated power? Sure for short sprints the motor can take 1,000 watts but running it continuously that way as you have found is simply driving it waaaaaay too hard.

I recently purchased a Golden Motor 24V Mini-Motor which I laced to a 700C rim with 35mm tires. I run the little motor at 36V (41Vp) with a 15A controller with peak power under 600W. Low end torque is a little weak as I figured it would be but it suits my riding style. Running stock at 24V the motor would have topped out at maybe 17 mph (27 kph) but on 36V it'll do about 23 mph (36.8 kph) maximum and provide good assistance up to 26 mph (41.6 kph). I did some experimentation with a 22A controller and even a 48V battery with the 22A controller drawing a maximum of 1057W. At that power level the little 250W motor was pretty impressive however it was just a test for the fun of it and I went back to the original 36V/15A combination to ensure a longer life for the motor.

I also have a Bafang 36V 250W motor on my other bike on which I have accumulated over 2,500 miles (4,000+ Km) with two-thirds of that at 48V (54Vp). The combined weight of me and this bike is 251 lbs (114 Kg). The secret to longevity I think is that I use a 15A controller, I pedal all of the time and I take it easy on the throttle.

It's all about chosing the right motor for the job so if you want a nice little motor for assistance then get a Mini but if you want something to haul you around and not raise a sweat or run higher than rated voltages at full throttle all of the time then go for something larger.

-R

[rolf_w]

did you use our controllers? our controllers should have been equipped with circuit breaker protections.

hi Yao Yuan, yes we use your controller (BAC 36V). For test purposes we added an eagle tree (http://www.eagletreesystems.com/) data logger/display. Using the 36V battery the MiniMotor draws at absolute peak up to 700W. To increase max speed we decided to experiment with the 48V battery and damaged the 2 MiniMotors before we even had useful readings from the data logger. It seems however that the current went beyond 20A which obviously is too much for the windings. And no - the controller didn't cut out at a max. current! If it would do that at the rated current of the controller (50A?) it would possibly be too much anyway. Is there a possibility to adjust the max. current on the controller??

Btw: the 1000W GM motor uses 10 strands of 0.6mm Cu wire for the windings (total cross section 0.28mm2). The MiniMotor uses 4 strands thus 2.5 times less cross section. Considering the different construction (air gap between housing and magnets and much smaller diameter) we derated the current another 10A and assumed the MiniMotor should carry 30A - obviously too optimistic. What is the sustained max. current of the MiniMotor? r

[Jose]

I am new on ebikes but as my first minimotor failed after two rides, I am very carefull testing a second unit. I temporarely installed an ammeter to monitor the current and a fuseholder for 7.5 A, which is the nominal for 36V battery and 250 W motor. However, reading previous replies, Yao said that the controller has a breaker protection, but my controller is BAC-281 36V/50A, and if the protection is 50A, it is way too much for the minimotor. Others have been testing with higher voltages and power, but the advice is not tu exceed 15A continuous.
As I am scare to exceed the low nominal value of 36V and 7A, I would like a confirmation about the real safe limit for continuous operation.
Thanks to you all

[TRK]

Seems to me that the "real safe" limit for a 250W motor (continuous) would be:

250W / 24V = 10.42A
250W / 36V = 6.94A
250W / 48V = 5.21A

In contrast, like Russell pointed out, 48V * 15A = 720W and 48V * 20A = 960W is way to much for a 250W motor to handle continuously.  Using the throttle override from a properly configured cycle-analyst (as suggested by rolf_w) seems to be the ideal solution in my opinion. 

[Bikemad]

I temporarely installed an ammeter to monitor the current and a fuseholder for 7.5 A, which is the nominal for 36V battery and 250 W motor.  Others have been testing with higher voltages and power, but the advice is not tu exceed 15A continuous.
As I am scare to exceed the low nominal value of 36V and 7A, I would like a confirmation about the real safe limit for continuous operation.
Thanks to you all

Jose,

You might want to consider fitting a 10Amp auto-resetting circuit breaker like this one:


Click for further details

That should limit the maximum input power to approx 360Watts giving a maximum output of approx 285Watts, and it's auto-resetting, meaning you wouldn't have to replace any blown fuses if the 10Amp limit was unintentionally exceeded.

The dynomometer results show the motor being tested to 13.53Amps, using 487.4 Watts to give an output of 362.5Watts.
(That's over a third more than a 10Amp limit would allow!)
current
Alan
 

[rolf_w]

did you use our controllers? our controllers should have been equipped with circuit breaker protections.

Yesterday I also burnt a 36VMiniMotor supplied by a 36V battery via a 36V controller (all GM equipment)! It was after climbing 100m up a rather steep road at low speed but without any additional load apart a light rider and bike (75kg total). My conclusion is, that the MiniMotor has a serious problem in dissipating heat even within, what I consider, normal operation range. It is interesting that all the MiniMotors we 'fried' and I checked afterwards had the insulation of the cables connecting the hall elements molten and the bare wires short circuiting. In one case I removed all hall elements and was able to run the motor again. Thus the windings did survive the overheating. The insulation of the hall wires are not appropriate for this application!
it would probably be a possibility to add an auto-resetting temperature switch into the motor housing to disconnect the power before the damage occurs?

r

[Jose]

Jose,

You might want to consider fitting a 10Amp auto-resetting circuit breaker like this one:


Click for further details

That should limit the maximum input power to approx 360Watts giving a maximum output of approx 285Watts, and it's auto-resetting, meaning you wouldn't have to replace any blown fuses if the 10Amp limit was unintentionally exceeded.

The dynomometer results show the motor being tested to 13.53Amps, using 487.4 Watts to give an output of 362.5Watts.
(That's over a third more than a 10Amp limit would allow!)
current
Alan

Thank you Alan for the information about the auto resseting circuit breaker. I will look for something similar in our local market in Spain.
About the 13.53A reached in the dynamometer test I don`t consider a value for continuous operation as the tests are probably run in a very short time.
Jose

[KES]

With the number of 36v/48v users and the reported "burnt" windings, I'm surprised no one has reported chewing-up the plastic planetary gears as Bafangs users seem to be doing.  

[GoldenMotor]

Seen lots of burnt mini motors, Time to check with the factory and to find the cause.

[Racer_X]

Seen lots of burnt mini motors, Time to check with the factory and to find the cause.

Hello Yao, while your at it can you check if there will ever be a 48v 500w version of this fantastic and good looking stealth mini-motor?

Louis aka (Racer_X)

[GoldenMotor]

Hello racer, you can put a 48V battery in and it will automatically give an output of 500W. However you might burn the motor easily.

I guess I need to clarify that the mini motor can only take a max load of approximately 120kg. Any heavier than that and you go uphill, the motor is gone. Which is why some users who are big boned (over 90kg) tend to send me an e-mail telling me about how the motor wasted itself after some uphill riding. However in my honest opinion, the motors should never burn if you don't stress it too much.

 Although weight is a sensitive topic for everyone, I still have to recommend that if you're heavy, buy the 901 motor, or the Magic Pie when it comes out. I think I have to write a disclaimer on the mini motor because i've been replacing quite a number of motors for users (I don't blame them) who do not really understand the max stress load of the mini motor.

[rolf_w]

... i've been replacing quite a number of motors for users (I don't blame them) who do not really understand the max stress load of the mini motor.

hi Yao, although I can understand your case I do not agree with your argument, that the users do not understand overload. A product which can destroy itself during normal use and without warning is not safe! There is no built in protection in the MiniMotor, neither the controller nor the driver has any feedback e.g. about any critical condition of the motor windings. There is also no fuse or similar device which could disconnect the power to the motor in case of a critical overload.
I think GM could help users of the MiniMotor by e.g. :
1) providing a chart displaying maximum motor current over maximum application time and a list of cut out devices which could disconnect the motor at overload to keep it safe (auto reset fuse).
2) install a temperature sensor in the motor winding to provide feedback or cut current (auto reset thermal fuse)
3) provide a possibility to limit the current of the BAC controller by adjusting the internal set value or by a throttle signal override (like the CycleAnalyst)

r

[rolf_w]

...It seems that a continuous current of 15-20A overheats the motor windings and damages it beyond repair...

By now we have 'killed' some 5 MiniMotors - and fortunately we were able to revive at least one of them. What happens is simple: the windings get hot at higher currents (each phase has approx. 200mOhm dc resistance thus at 20A a total power Cu dissipation  of ca. 240W). They seem to survive some higher temperatures although the varnish darkens / showing some signs of overheating. But what breaks down before that, is the insulation of the wiring to the Hall elements. This leads to a short circuit of the power supply to the elements and consequently to a short of the 5V internal power supply of the controller (i.e. everything fails). It is quite tricky to untangle the molten heap of wires and we first thought we simply remove the Hallelements and run the MiniMotor in senserless mode (see foto). However this doesn't work at all > the MiniMotor can not be operated in sensorless mode! We then tried to remove very carefully the molten insulation (the pins of the hall elements break off easily!!) and separated all the wires and voilà the MiniMotor worked again. Conclusion: if a MiniMotor seems burnt its probably neither the winding nor the Hallelement, it is the wiring which requires replacement!

So what should GM do :

• improve the insulation material of the Hallelement wiring and keep the wires as short as possible and don't place them directly on top of the coils
• improve the cooling of the stator winding by ventilation? partly fill the motor with some liquid?
• add an overcurrent cut out device (we test this with 10A http://www.e-t-a.de/uploads/prodb/D_1610_d.pdf)

r