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Hub motor (true) amperage rating... where???

Posted: Jul 23 2020 1:18pm
by BDamari
Hi guys, it's obvious the wider the stator (and the heavier the windings) the more power it can draw/handle but I've seen people reporting there are 500w hub motors that can handle 33a peaks at ease, so nothing is really concrete, unfortunately.

Because of this, I'm having trouble choosing the specifications for my next build.
I'm planning to run 16s with a 50a controller, which should make just shy of 3kw of peak power.
Now, should I get the 35mm stator 1500w rated hub motor? or the 30mm 1000w rated motor is enough?
1000w:
https://www.aliexpress.com/item/8164558 ... web201603_

1500w:
https://www.aliexpress.com/item/3232297 ... 55c5VlG9pW

Thanks

Re: Hub motor (true) amperage rating... where???

Posted: Jul 23 2020 2:30pm
by j bjork
It is impossible to answer with so little info.
Either could take a lot more, it is a question about how long?
I haven't looked at the links, but I assumed you are talking about direct drive hubs.
Look at the calculator at ebikes.ca

Re: Hub motor (true) amperage rating... where???

Posted: Jul 23 2020 5:02pm
by Voltron
You'll rarely regret going with the 35mm, unless minimal weight is one of the design goals.

Re: Hub motor (true) amperage rating... where???

Posted: Jul 23 2020 5:17pm
by Voltron
There's a possibility that they will run at different rpms. The 35mmv says 60v, which is nowhere close to the actual voltage limit. But when they list a voltage, sometimes it means the voltage that the motor will turn the right rpms for street legal speed at the rated voltage.
Othertimes, it's a completely made up number, and the seller has no real idea how many turns the motor is wound with.
Apologies is you know this already, but that's what the kv rating is about. It's the rpms per volt ratio on an electric motor, and if they don't list it, then it's a mystery usually on when you will actually get.
One way it works out is if you say sell two versions of the same bike, one 36v, and another that is 48v, you can change how many turns of wire are wound around each tooth of the stator in the motor, so the each run at the same rpm despite the different voltages .

Re: Hub motor (true) amperage rating... where???

Posted: Jul 23 2020 5:52pm
by BDamari
Voltron wrote:
Jul 23 2020 5:02pm
You'll rarely regret going with the 35mm, unless minimal weight is one of the design goals.
Close! the goal is minimal cost :)
The kv is actually the same between the two motors, I'm just concerned about the heat...

Re: Hub motor (true) amperage rating... where???

Posted: Jul 24 2020 1:39pm
by Voltron
That will probably depend on your driving style then. Doing isolated bursts of high acceleration followed by long steady medium high speed flat road sessions where the back emf and air cooling are both high the 30mm would probably be fine. Repeated high acceleration combined with hills, like drag racing cars thru hilly city streets with stops every few blocks, or long windy mountain road punching it out of every turn, but steep enough to slow you to where the back emf and air cooling are low, then more motor more better. 👍

Re: Hub motor (true) amperage rating... where???

Posted: Jul 24 2020 10:34pm
by markz
https://www.ebikes.ca/learn/power-ratings.html
While an actual watt is an actual watt, There is NO SUCH THING as a "rated watt" or any standarized method for rating ebike motor power. That's the truth, regardless of what other companies imply. With most electrical devices the term rated power has a very clear meaning. Like a 60 watt lightbulb can be counted on to draw 60 watts of power when it is turned on. A 1500 watt heater will produce 1500 watts of heat, regardless of which brand or model you use.

With electric motors, they do not produce a fixed amount of power when you turn them on. If you run the motor with your wheel off the ground, then it will spin at full speed and produce no power output. As you then load the motor with drag, it will slow down a bit and produce torque, and the more you load it down the more it slows down and the higher the torque and power it puts out. At some point as you continue to load and slow the motor down, then the output power will start to decrease. Even though the torque is still increasing, the lower RPM means that the mechanical power produced goes down. If you stall the motor completely, it might be making a ton of torque but it's producing zero output power.
The actual power output of a motor depends entirely on how heavily it is loaded in a given situation and the maximum electrical power that the controller lets flow into the motor, it has little to nothing to do with a rating anywhere.

Re: Hub motor (true) amperage rating... where???

Posted: Jul 24 2020 10:38pm
by Voltron
That might not true anymore, at least in the EU. I think they have a standardized test that involves how long it takes the motor to heat up under a load on a dyno.

Re: Hub motor (true) amperage rating... where???

Posted: Jul 25 2020 4:00am
by BDamari
Voltron wrote:
Jul 24 2020 1:39pm
That will probably depend on your driving style then. Doing isolated bursts of high acceleration followed by long steady medium high speed flat road sessions where the back emf and air cooling are both high the 30mm would probably be fine. Repeated high acceleration combined with hills, like drag racing cars thru hilly city streets with stops every few blocks, or long windy mountain road punching it out of every turn, but steep enough to slow you to where the back emf and air cooling are low, then more motor more better. 👍
I do live in a hilly area, so I'll just try my best to squeeze the 35mm into the budget.

Thank you :)

Re: Hub motor (true) amperage rating... where???

Posted: Aug 01 2020 1:29pm
by markz
BDamari wrote:
Jul 25 2020 4:00am
I do live in a hilly area, so I'll just try my best to squeeze the 35mm into the budget.

Thank you :)
Its all about the gearing, the voltage, amps. So gearing would be the Turn Count of the hub motor, the diameter of the wheel and how much watts your dumping into the ebike. Then worrying about heat, steel stator or aluminum stator and how beefy is it to shed the heat. Using statorade helps and is easy to get. I would be sure to use the temp sensor inside the motor hooked up to the Cycle Analyst so you dont have to worry about smoking the motor.