Overpowering 250W electric motor to 500W for 3 minutes

baikiewheelie · Mar 26, 2015

Can those typical Chinese (Bafang or cute etc.) motors specified as 250W sustain 500W power for roughly 3 minutes without damage? If yes, would the damage be caused simply by overheating or anything else?

I plan t use 7s4p top-notch Li-Ion battery pack which could easily output 20A in total (5A per single cell), so 24V*5A*4cells = 480W of power.

Doctorbass · Mar 26, 2015

baikiewheelie said:
Can those typical Chinese (Bafang or cute etc.) motors specified as 250W sustain 500W power for roughly 3 minutes without damage? If yes, would the damage be caused simply by overheating or anything else?

I plan t use 7s4p top-notch Li-Ion battery pack which could easily output 20A in total (5A per single cell), so 24V*5A*4cells = 480W of power.

I would say NO PROB! :wink:

Sometime these motor are used in both 250, 350 and 500W rated ebikes.. it's only the controlelr that limit the current depending on regulatin to witch country these are sold to...

we have long expeirence with 750W rated motor being used to 12kW and 3000-4000W for couple minutes without problem !

It's all a matter of heat.. that's it

Doc

motomech · Mar 27, 2015

baikiewheelie said:
Can those typical Chinese (Bafang or cute etc.) motors specified as 250W sustain 500W power for roughly 3 minutes without damage? If yes, would the damage be caused simply by overheating or anything else?

I plan t use 7s4p top-notch Li-Ion battery pack which could easily output 20A in total (5A per single cell), so 24V*5A*4cells = 480W of power.

Wow, you are privledged to be answered by Dr. Bass, the most famous of Ebike builders(ck. out you tube).
But in the future, no need to double post.

d8veh · Mar 27, 2015

They can handle a lot more than that. I've run most of those small motors at 48v and 18A, which is 864w. If you're not to heavy 0r if you have a low speed one, you can go as high as 1000w. When you go that high on power, you have to be careful about efficiency. You shouldn't let the motor run at less than half of its maximum no-load speed for too long at full power.

baikiewheelie · Mar 27, 2015

All clear, thanks for the good news guys,
Cheers,
A.

tahustvedt · Mar 27, 2015

I have a BAfang 250 W crank motor. It's a 250 W nominal motor, but the max power is much higher even in stock form. I have a power meter and measured over 400 W with a rear wheel power meter and a nearly empty battery.

d8veh · Mar 29, 2015

The 250w Bafang BBS01 is 36v 15A, so it will take about 600w from the battery if you let the crank go slow enough; however, you won't get any more power at thevback wheel because it'll have lower efficiency.

tahustvedt · Mar 29, 2015

d8veh said:
The 250w Bafang BBS01 is 36v 15A, so it will take about 600w from the battery if you let the crank go slow enough; however, you won't get any more power at thevback wheel because it'll have lower efficiency.

I measured wheel power for a short time when the battery was full. 520 W. Just for a few seconds though, as I accelerated beyond the max torque speed.

DrkAngel · Mar 29, 2015

baikiewheelie said:
Can those typical Chinese (Bafang or cute etc.) motors specified as 250W sustain 500W power for roughly 3 minutes without damage? If yes, would the damage be caused simply by overheating or anything else?

I plan t use 7s4p top-notch Li-Ion battery pack which could easily output 20A in total (5A per single cell), so 24V*5A*4cells = 480W of power.

250w is motor output!
480w input might be the normal for this motor ... probably more during acceleration.

Bafang crank drive motor:
Notice! 48V 20A = 960w (input) = Rated 48V 500w (output)

With full amp motor systems:
controller is capable of enough amps to provide the maximum possible watt output
maximum watt output is typically at 40% of motors no load speed and 50% efficiency

Although a full Amp motor system will supply full possible watt output from e.g. 20A, At 0 rpm the motor is capable of much higher input (60-80A ,,, possibly more)
Increasing amps will neither increase top speed or maximum motor output!
It can, improve acceleration to mid speed, at the sacrifice of energy efficiency and increased heat production ...

See - Efficiency?

tahustvedt · Mar 30, 2015

Like I said, I measured power OUT. 400 W sustained output, and 520 W when I loaded it heavilly. Throttle only.

Check the power graph in the picture. Measured with a Powertap rear wheel hub.

DrkAngel · Mar 30, 2015

tahustvedt said:
Like I said, I measured power OUT. 400 W sustained output, and 520 W when I loaded it heavilly. Throttle only.

Check the power graph in the picture. Measured with a Powertap rear wheel hub.

If measured with a PowerTap hub, you need to subtract your pedal assist.
But, if your motor was outputting 519w at 15.5km/h (9.6mph), input would have to have been 24V 40A++.

tahustvedt · Mar 30, 2015

I also said this was throttle only.

It's a 36 V motor. No such thing as a 24V BBS01. The highest recorded electrical power in was 560 W. Current maxed out at 15 A. Would have been lower at 519 W out if it had been more than peak. The average efficiency was 78%. Batteries were 10S lipos.

DrkAngel · Mar 30, 2015

519w(highest output)/560w(highest input) = 92.67% efficient ... full throttle? ... at slow speed?
Something doesn't sound right!

tahustvedt · Mar 30, 2015

Peak. It's there in the graph I posted.

EDIT:
I used a Watt's Up to measure electrical input, so it might not be sensitive enough to record quick peaks.

the point is that a 250 W motor (or 500 W motor) isn't limited to 250 W. It's the nominal rating.

DrkAngel · Mar 31, 2015

In many countries, the 250w motor is legally and stringently regulated to 250w output!

Of course, the same 250w output motor, might input 500-1000w+ under acceleration at low speed or on steep grade.

Most of the reputable, name brand, motor manufactures match and regulate controllers that limit the watt input as a safety measure.

As long as you limit prolonged low speed-high throttle use ... reputable oem motor-controller configurations are very resilient-durable.

chas58 · Mar 31, 2015

baikiewheelie said:
Can those typical Chinese (Bafang or cute etc.) motors specified as 250W sustain 500W power for roughly 3 minutes without damage? If yes, would the damage be caused simply by overheating or anything else?

I plan t use 7s4p top-notch Li-Ion battery pack which could easily output 20A in total (5A per single cell), so 24V*5A*4cells = 480W of power.

If you really want to know, the ebike.ca calculator will show you when the motor will over heat. Still, doesn't look like you are in the danger zone with a 24v battery. That is going to be kinda slow though - what speed are you shooting for?

d8veh · Apr 1, 2015

DrkAngel said:
In many countries, the 250w motor is legally and stringently regulated to 250w output!

I've not heard that before. Australia, Europe and some other countries have adopted EN15194 as the standard for ebikes, where the power requirement is for a motor with a maximum continuous rated power output of 250w. There is no maximum power limit or measurement.

DrkAngel · Apr 1, 2015

tahustvedt said:
I also said this was throttle only.

It's a 36 V motor. No such thing as a 24V BBS01.

Bafang crank drives seem to have a motor only cadence limit of <80 ... ?

But your chart indicates cadence as high as 166!
How was this achieved with "throttle only"?

and ... OOPS!

tahustvedt · Apr 1, 2015

Because the Powertap tries to measure cadence through pedal pulses, and since there are no pulses, it doesn't measure cadence correctly. I don't have a cadence sensor. It has nothing to do with the power measurement. If you look closely you can see that the power goes up in uphills as the speed drops and down in downhills where the speed increases. The elevation graph doesn't zoom in to see the changes in detail. Also see that the average was 250.

Ok, I was wrong about the 24V motor. It's a rare unit. Bosh, and other manufacturers also have much higher than nominal at max. They are current limited, not power limited.

DrkAngel · Apr 19, 2015

My point ... is that, inputting 480w (24Volts x 20Amps), the systems rated output 250w (watts) is usually normal and designed as sustainable. (50% efficiency at maximum motor output is a reasonable expectation)

At speed, efficiency can be increased-prolonged via severe current limitation.

Plausible motor profile of the 350w Bosch equipped HaiBike

Compare to the same motor without severe current restriction.

Of course this motor would not survive very long if run at possible usable amperage!
The increase of input watts, multiplied by the increase of inefficiency produces a great increase in waste-damaging heat.

Overpowering 250W electric motor to 500W for 3 minutes

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