is this post correct?

Electric Motors and Controllers
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jimmyhackers   100 W

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is this post correct?

Post by jimmyhackers » Oct 09 2019 10:05pm

recently on youtube i noticed this comment on an eletric motorbike video.....didnt know what to make of it. (the quote is between the zeros)

0000000000000000000000000
It would be interesting to see how much horsepower that this 3 kilowatt electric bike puts out on a dyno rig.

For those who know nothing of how electric motors and vehicles are rated, the Wattage IS NOT the power output but the peak load power consumption. (I did my second apprenticeship as an electric traction motor technician when I was younger. I used to build, tune and dyno test the electric traction motors).

Performance wise, I would put this bike on a par with an average unrestricted 1970's 50cc sports motorcycle regarding performance. 70 to 80 KPH was flat out on the old Yamaha FS1E (OEM quoted top speed = 44 MPH).

The Wattage of the motor can be measured by putting the motor under heavy load (such as riding it up a steep hill laden with weights) and measuring the voltage and current it draws. (Volts x Amps = Watts).

The motors I used to test (for Lansing & Bagnal electric fork lift trucks) were rated at 22 HP @ 2,000 RPM with 48 Volts @ 54 Amps (2,592 Watts) consumption at peak load. If a 2.6 KW motor can produce 22 HP then I'd expect more from a 3 KW motor.

Something is very wrong here!!
00000000000000000000000000

soooooo.....can someone explain to me how a motor that takes in 2600wats of electrical power can output nearly 16kw of mechanical power?

is there some kind of sneaky maths wizardy going on with the dyno graphs....or something else?
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dustNbone   10 kW

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Re: is this post correct?

Post by dustNbone » Oct 09 2019 10:46pm

Just incorrect data. If you want that motor to actually make it's rated 22HP, you'd need to give it enough work to require that 22HP.


If it's not loaded enough, and can just spin up to operating speed, the current will taper off to only what is required to maintain that speed.

A forklift motor will draw considerably more than 54A. you can tell by the massive ass wires that connect their batteries. I'd say 500A peaks are not out of the question.

Just because a motor is rated for a given power level, doesn't mean it will draw that much power all the time under all conditions, it just means it's mechanically, thermally, electrically capable of doing so without breaking/exploding/catching fire.

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amberwolf   100 GW

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Re: is this post correct?

Post by amberwolf » Oct 09 2019 11:05pm

"Rated" for a certain power in the case he states is it's *peak* power, which means the instantaneous max peak it would have at stall, zero RPM. It's not actually doing much besides generating heat at that point, though, and the rest of teh system (batteyr, controller) if rated for less power, can only handle that for a very short burst, before overheating, failing, or engaging it's protections. Then it'll begin to spin faster and do more work and make less heat, as long as the load on it isn't more than it can move.

By the time it's past that point, it would only be able to output less power than the rest of the system is rated for (because some of it is making heat instead of work).

SO if the rest of the system is only able to output, say, 2600w, then the motor would be outputing less than that. If it's say, 80% efficient, then 2080w is all the mechanical output you get, with the ohter 520w as heat.

Go to http://ebikes.ca/simulator , read the entire page to see how it all works, then play with different systems to see this. There is also a trip simulator.


If the motor is actually rated at the higher power level, then it won't overheat doing that, but it can't actually do that if the rest of the system can't supply that power. So a 22hp motor can't ever supply 22hp if the battery and controller and wiring aren't capable of supplying more than 22hp worth of power (because of efficiency losses, it has to supply more).


But in my experience, motors with nameplates are rated for their *continuous* power, not peak (they may *also* list a peak power).

Many non-plated motors are also rated this way, but in the ebike world (and sometimes things like powertools and lawnmowers), peak power is not an uncommon rating for systems, rather than what it can actually handle all day long.


(There are other rating methods, usually marked on teh plate, for other duty cycles, for motors meant to operate only intermittently, like starters, pumps, etc).

flat tire   1 MW

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Re: is this post correct?

Post by flat tire » Oct 10 2019 1:56am

From actual input power drop the kw and replace with horsepower for a good minimum approximation of peak mechanical output power.

Motor ratings mean little or nothing.

Punx0r   100 GW

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Re: is this post correct?

Post by Punx0r » Oct 10 2019 2:52am

jimmyhackers wrote:
Oct 09 2019 10:05pm
For those who know nothing of how electric motors and vehicles are rated, the Wattage IS NOT the power output but the peak load power consumption.
Industrial electric motors are rated by power output not input. Hobbyist/RC motors might be rated by input power because it's a bigger number and also obscures the motor's (in)efficiency. So I'd say the youtube guy quoting the above is confused, especially when you factor in the 22HP output from 2.6kW input statement he also made.

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jimmyhackers   100 W

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Re: is this post correct?

Post by jimmyhackers » Oct 10 2019 9:22pm

thanks for the info.....it kinda reaffirmed what i already expected.

peak input/output power isnt continuous input/output power...but shifty manufacurers will try and blur the line between the them.

this guys number did seem rather out....

to get about 22hp (16kw) output....id expect about 20kw input @ 80% efficiency. at 48v that would be 416 amps!!
if you do learn from your mistakes, i should be a genius by now.

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