WOW! High amperage on my 500w CHINA HUB MOTOR.

420b

100 W
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Aug 13, 2018
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126
I just got a wattmeter for my China hub motor kit, rated 500w at 36v. Let me tell you, I did NOT expect the results. Going on flat ground that thing pulled 1200w straight from the jump! 30v (that’s a 10 volt drop) and 39 amps! Meanwhile, my battery is a hover board pack rated for 20 amp maximum and I was like what the hell: it can handle 13 amps at 36v. I’m just so lucky my battery didn’t explode! I paid for the cheapest 500w kit and China sends me more than double that, these are the miracles of Chinese economics.
 
Miracles?

You mean it's cheaper for them to make one item, then sell it as whatever people want to believe it is? You have a 250W limit in your jurisdiction? Of course this is a 250W kit, We'll send you the stickers to prove it.

Your jurisdiction is 750W? Ummm, give me a second, I'll swap this kit. What Oh yes, they look the same, except the sticker... And of course this does 750w.

You want a kit for off road? Hey, look over there for a second! What was that? Oh this? Yes, this is our 1200w kit for off road use. Yes, it does look like I removed the 750w sticker, but that just ummm, lets more heat escape, giving it a higher power limit.

Test everything you get from China. 90% will be under-rated, but some things are just labelled for "compliance" reasons, not over-rated.
 
Sunder said:
Miracles?

You mean it's cheaper for them to make one item, then sell it as whatever people want to believe it is? You have a 250W limit in your jurisdiction? Of course this is a 250W kit, We'll send you the stickers to prove it.

Your jurisdiction is 750W? Ummm, give me a second, I'll swap this kit. What Oh yes, they look the same, except the sticker... And of course this does 750w.

You want a kit for off road? Hey, look over there for a second! What was that? Oh this? Yes, this is our 1200w kit for off road use. Yes, it does look like I removed the 750w sticker, but that just ummm, lets more heat escape, giving it a higher power limit.

Test everything you get from China. 90% will be under-rated, but some things are just labelled for "compliance" reasons, not over-rated.

That was hilarious and so true. They know the police will not start bringing a wattmeter to the job and neither will most customers, so they I guess they just pull numbers from a hat.

The miracle is that I got the kit for 40$ less than a “1000w” kit that has the same exact cheapo motor, so I felt I can’t complain. I do wonder how many fires this practice has started/will start, it seems quite unsafe that they would rate a motor at 500w and then just go and allow it to take 3x the power.


I just remembered, they threw in a 40a fuse. Seems convenient that over my whole ride I never broke 40a... maybe it’s not a coincidence and the controller has a 40a cap. Also, what the hell is my BMS doing? Today I’ve shorted my battery and driven it at 3x it’s max rating, no response from the BMS AFAIK.
 
My bet is that the controller is rated nominally for something like 13 amps and has a peak output rating about double that. So they call it a 500 watt system based on 36 volts x 13 amps = 468 watts.

My "1000 watt" system has a 48v controller just like that (13 amp nominal, 26 amp peak) which should rate it at 624 watts or fudge up a bit to 750 watts. But since the peak wattage is 1250, they are being "conservative" by calling it a 1000 watt system? :^)
Of course, these are all input watts, not output watts ... which are probably about 80% lower.

If your motor is a geared hub, you may want to dial back the max amp draw. Some systems let you do that with the right LCD display. If it is a DD hub, I wouldn't worry about the motor's safety, though you might kill that poor battery soon if you keep doing this.
 
wturber said:
My bet is that the controller is rated nominally for something like 13 amps and has a peak output rating about double that. So they call it a 500 watt system based on 36 volts x 13 amps = 468 watts.

My "1000 watt" system has a 48v controller just like that (13 amp nominal, 26 amp peak) which should rate it at 624 watts or fudge up a bit to 750 watts. But since the peak wattage is 1250, they are being "conservative" by calling it a 1000 watt system? :^)
Of course, these are all input watts, not output watts ... which are probably about 80% lower.

If your motor is a geared hub, you may want to dial back the max amp draw. Some systems let you do that with the right LCD display. If it is a DD hub, I wouldn't worry about the motor's safety, though you might kill that poor battery soon if you keep doing this.

It’s a DD Hub motor, though I don’t have an LCD or anything programmable on my controller unfortunately. Took her for another ride today, and we hit 41a at 30v! I did buy a second battery to parallel so it hopefully keeps the load on them down. I’m still quite surprised that my BMS didn’t trip over 40a.
 
The big enemy to a battery under load is heat, there's nothing inherently limiting the amount of current a cell can supply, just that if you're pulling past their rating they will get hot over time. They're not going to explode/catch fire immediately at a given current, but long periods pulling higher than rated amps will eventually get them to a dangerous temperature.

Chances are you're not maintaining 40+ amps for very long at all, most likely that's a spike from a standstill that tapers off as the motor speeds up. That could be why the BMS doesn't trip, it's designed to allow brief overcurrent spikes that are fairly common with motor loads.
 
Lithium batteries will deliver far more current than their rating and they're more than willing to kill themselves doing it. The big hint is the large voltage drop under load which is cause directly by the internal resistance of the battery, which results in energy loss in the form of heat. Some of that voltage drop is occurring in the wiring.

Welcome to the club. Imagine the fun I'm having drawing 245A from my pack at 115V nominal. :mrgreen:
 
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