Motor Power Output Question

thehoags

New Member
Hi I was wondering if speed affects motor watt output? From my understanding, a motor can actually peak higher than what its rated because motor wattage is determined by how much power is fed to it from the controller.

With this in mind, let's say an individual has a motor rated 750 watts but due to local regulations, they limit the speed down to 20 mph (32 km/h.) By doing so, does that also restrict the motor output to 500 watts?

My assumption would be no, because while the motor may not output any more than 500 watts of power when riding along level ground at speeds of 20 mph (32 km/h,) when a rider accelerates or starts climbing a hill, it would make sense that the controller would send the motor as much power as needed, which may in fact exceed 500 watts.

But I am no expert in this area at all.

I recently came across a particular e-bike online that had a motor rated 1000 watts. However, on the website it stated that when the speed limit is set under 30 mph, the motor is restricted to 750 watts. So I'm curious.

Does anyone have any technical insights? Thanks so much.
 

richard.rivers

New Member
Motor power won't be limited for legal reasons. But If a motor nominal power is 750 watt it can work under 1000 watt easily. In this case I worry that the motor actual power is 500watt. Because 500watt motors can reach 1000watt peak power but it is dangerous for the e-bike. so they always limit peak output to 90% of x2 of nominal power output.
 

thehoags

New Member
Motor power won't be limited for legal reasons. But If a motor nominal power is 750 watt it can work under 1000 watt easily. In this case I worry that the motor actual power is 500watt. Because 500watt motors can reach 1000watt peak power but it is dangerous for the e-bike. so they always limit peak output to 90% of x2 of nominal power output.

Wait, motor power won't be limited for legal reasons? Technically, 1000 watts is not street legal for most states so it would have to be limited for legal reasons though I'm not sure that electronically limiting the motor power would satisfy the law, if the motor itself is rated over 750 watts.
 

AHicks

Well-Known Member
That 750 watt motor will carry that same 750 watt rating no matter it's speed. If there is a speed restriction placed on it, they're just choking the power available to the motor at a certain speed electronically - whatever that speed is.

To take that a step further, into something more practical maybe, that 750 watt motor will have more guts than a motor rated for 500 watts for instance (all else being equal). If there is a 20mph speed restriction placed on both, and they were to race each other, the 750 watt motor would get to 20mph first.

On the aftermarket stuff, they're assuming that if you purchase a 1000 watt motor for instance, that it will be used for off road purposes only. In reality, that 1000 watt motor will be pretty tough (impossible?) to spot in use once installed, and if unmarked with manf wattage data (like most are), nearly impossible to prove it's illegal for on road use. Hopefully, if you go this route, you will do it responsibly.....
 

thehoags

New Member
That 750 watt motor will carry that same 750 watt rating no matter it's speed. If there is a speed restriction placed on it, they're just choking the power available to the motor at a certain speed electronically - whatever that speed is.

To take that a step further, into something more practical maybe, that 750 watt motor will have more guts than a motor rated for 500 watts for instance (all else being equal). If there is a 20mph speed restriction placed on both, and they were to race each other, the 750 watt motor would get to 20mph first.

On the aftermarket stuff, they're assuming that if you purchase a 1000 watt motor for instance, that it will be used for off road purposes only. In reality, that 1000 watt motor will be pretty tough (impossible?) to spot in use once installed, and if unmarked with manf wattage data (like most are), nearly impossible to prove it's illegal for on road use. Hopefully, if you go this route, you will do it responsibly.....

No, I am not buying a bike with a 1000 watt motor. In Canada, where I am, the limit is actually 500 watts unlike the US, which allows 750-1000 watts depending on the state (the max in most states is 750 watts.)

The motor on the e-bike I am getting is only rated 500 watts to comply with restrictions.

However, I have heard that its possible to restrict a motors power output by limiting the controllers max current output. But if one were to restrict a 1000 watt motor to 750 or 500 watts max, I would be curious to know as to whether that would satisfy the law if in fact the motor is technically rated for a 1000 watts?

Either way, its irrelevant to me because I am getting a bike with a motor rated 500 watts. But I'm still curious.
 

Timpo

Well-Known Member
No, I am not buying a bike with a 1000 watt motor. In Canada, where I am, the limit is actually 500 watts unlike the US, which allows 750-1000 watts depending on the state (the max in most states is 750 watts.)

The motor on the e-bike I am getting is only rated 500 watts to comply with restrictions.

However, I have heard that its possible to restrict a motors power output by limiting the controllers max current output. But if one were to restrict a 1000 watt motor to 750 or 500 watts max, I would be curious to know as to whether that would satisfy the law if in fact the motor is technically rated for a 1000 watts?

Either way, its irrelevant to me because I am getting a bike with a motor rated 500 watts. But I'm still curious.
When you talk about motor ratings, it is typically nominal output, not maximum output.

For example, Grin Technologies (well known ebike tuner) in Vancouver, Canada tested Bosch 250W motor, so they used this tool that's similar multimeter and found out that max rating was well over 800W.

Pedego Interceptor in Canada for example, has 500W of "rated" wattage.
Which is nominal, however, the max is well over 1000W.

Pedego Canada website:

Pedego Interceptor Specs:

It's not just Pedego, it is the same with any ebikes.
 

thehoags

New Member
When you talk about motor ratings, it is typically nominal output, not maximum output.

For example, Grin Technologies (well known ebike tuner) in Vancouver, Canada tested Bosch 250W motor, so they used this tool that's similar multimeter and found out that max rating was well over 800W.

Pedego Interceptor in Canada for example, has 500W of "rated" wattage.
Which is nominal, however, the max is well over 1000W.

Pedego Canada website:

Pedego Interceptor Specs:

It's not just Pedego, it is the same with any ebikes.

Yeah and the regulations are for norminal (continuous) power not peak output. But there are some e-bikes rated 1000 watts norminal, but the rider should be using these off road only since 1000 watts is not street legal in most areas. Ultimately, its the riders responsibility to be informed on the local e-bike laws and comply with them.
 

AHicks

Well-Known Member
<<<< be informed on the local e-bike laws and comply with them. >>>>

Or not, as you see fit!

Personally, I look at motor wattage as a common sense issue. I'm really not to concerned with the regulations regarding max wattage. It's not like it's a safety issue. Max wattage regulations were written during the dark ages and have very little practical value. If I were a manf. faced with loosing my business because of a silly lawsuit, I might think differently.

I ride a bike conservatively rated at 1000w nominal, and have yet to draw a second look from ANYONE. I'd really enjoy seeing somebody prove I'm riding a bike powered by an "illegal" motor. No guilty conscience here. You do as you wish! -Al
 

Bruce Arnold

Well-Known Member
With this in mind, let's say an individual has a motor rated 750 watts but due to local regulations, they limit the speed down to 20 mph (32 km/h.) By doing so, does that also restrict the motor output to 500 watts?

My assumption would be no, because while the motor may not output any more than 500 watts of power when riding along level ground at speeds of 20 mph (32 km/h,) when a rider accelerates or starts climbing a hill, it would make sense that the controller would send the motor as much power as needed, which may in fact exceed 500 watts.
Power to the motor from the controller can be restricted by firmware. Effectively, you now have less horsepower. I'm with A Hicks. The whole thing is silly.

My last BMW R1200RT would easily do 125 mph, which is not legal anywhere, but as long as I stuck to the speed limits, no one ever blinked an eye. Why should ebikes be any different?

(I never took the Beemer over 125; it might have had more to give but that was enough for my taste. I tested it on a straightaway on a deserted rural two-lane blacktop. Completely illegal, and I'm not making excuses. Just wanted to know what I had.)
 

thehoags

New Member
Regardless as to whether one thinks the restrictions are silly or not, its still the riders responsibility to be informed of the e-bike laws in their local area and comply with them. If one chooses not to comply, then that individual risks getting a fine. My choice is to comply with the rules. :)
 

AHicks

Well-Known Member
Regardless as to whether one thinks the restrictions are silly or not, its still the riders responsibility to be informed of the e-bike laws in their local area and comply with them. If one chooses not to comply, then that individual risks getting a fine. My choice is to comply with the rules. :)
Not going to fault your choice for a second. I'll just say you may change your mind once you've been into it for a while....
 

Sierratim

Well-Known Member
Hi I was wondering if speed affects motor watt output? From my understanding, a motor can actually peak higher than what its rated because motor wattage is determined by how much power is fed to it from the controller.

With this in mind, let's say an individual has a motor rated 750 watts but due to local regulations, they limit the speed down to 20 mph (32 km/h.) By doing so, does that also restrict the motor output to 500 watts?

My assumption would be no, because while the motor may not output any more than 500 watts of power when riding along level ground at speeds of 20 mph (32 km/h,) when a rider accelerates or starts climbing a hill, it would make sense that the controller would send the motor as much power as needed, which may in fact exceed 500 watts.

But I am no expert in this area at all.

I recently came across a particular e-bike online that had a motor rated 1000 watts. However, on the website it stated that when the speed limit is set under 30 mph, the motor is restricted to 750 watts. So I'm curious.

Does anyone have any technical insights? Thanks so much.
In the most straight forward sense, yes motor speed will affect motor wattage output. Take a look at this test data for several popular mid-drives;

mceclip10.png


As to your other points, the Federal street legal ebike limit in the States is 1Hp, ~750W with assist limited to 28mph. I strongly suspect that a reputable manufacturer would comply with the FED power limit when also setting the bike up to comply with the FED speed assist limit, so a 1KW motor is limited to 750W when it is also limited to 28mph.

The same reputable manufacturer would do the same for power and speed limits imposed by other jurisdictions.