Peak Horsepower - Maximum Output Watts ... How to determine!

[DrkAngel]

Warning! - reasonably accurate ... only if controller is capable of full powering motor at 40% of no load speed.
See how to determine if controller will output peak watts - Peak HP - Controller Have Enough Amps?

I am talking about DC, Brushless, Permanent Magnet, hub motors. ...

After delving through the ebikes.ca Hub Motor and Ebike Simulator for way too long, I noticed a distinct relationship between peak output watts (HP), speed and efficiency!

OK ...
How to determine output watts - horsepower.
You will need a watt meter and speedometer.
1. Find motors no-load top speed. (speedometer on raised motor wheel)
2. While running on road at almost 40% of no load speed, observe watt meter, give full throttle and observe max watt usage. You want the maximum watt input at the 40% of top no load speed. (12mph if 30mph no load)
No watt meter? Use an amp meter and a volt meter(or just use battery voltage) Amps x Volts = Watts.
3. Take max watts multiply by .55. This is your watt output, horsepower.

Brushless motors, at 40% of no load speed, are near the point of maximum output, which coincides with a near 55% efficiency.

At 40% of no load speed, Input (electrical) watts x .55 efficiency = output watts / 750w = horsepower
These percentages seem fairly consistent!
At worst, this is a good yardstick method of determining max watt output!

Accuracy declines sharply if controller is not max capable at 40% speed.

Test my observations at Hub Motor and Ebike Simulator before running test, if test seems to be too easy to be true.

 

[Arlo1]

Warning! - reasonably accurate ... only if controller is capable of full powering motor at 40% of no load speed.

After delving through the ebikes.ca Hub Motor and Ebike Simulator for way too long, I noticed a distinct relationship between peak output watts (HP), speed and efficiency!

OK ...
How to determine output watts - horsepower.
You will need a watt meter and speedometer.
1. Find motors no-load top speed. (speedometer on raised motor wheel)
2. While running on road at almost 40% of no load speed, observe watt meter, give full throttle and observe max watt usage. You want the maximum watt input at the 40% of top no load speed.
3. Take max watts multiply by .55. This is your watt output, horsepower.

Brushless motors, at 40% of no load speed, are near the point of maximum output, which coincides with a near 55% efficiency.

At 40% of no load speed, Input (electrical) watts x .55 efficiency = output watts / 750w = horsepower
These percentages seem fairly consistent!
At worst, this is a good yardstick method of determining max watt output!

Accuracy declines sharply if controller is not max capable at 40% speed.

Test my observations at Hub Motor and Ebike Simulator before running test, if test seems to be too easy to be true.

It is to easy to be true! Here is the thing. If I understand you correct you are saying this is how you can know rear wheel watts (hp)?
I can set my controller to 2x what it is now and at 40% of max speed it will use 2x the power it is no and not make anymore at the wheel in fact its less because it uses more power to heat which raises the resistance in the motor lowering the efficiency to a amazingly low number!

 

[DrkAngel]

It is to easy to be true! Here is the thing. If I understand you correct you are saying this is how you can know rear wheel watts (hp)?
I can set my controller to 2x what it is now and at 40% of max speed it will use 2x the power it is no and not make anymore at the wheel in fact its less because it uses more power to heat which raises the resistance in the motor lowering the efficiency to a amazingly low number!

At 40% of no load speed, If you double the available amps and at the same speed it outputs no more watts at the wheel, then it is already accepting all the watts it can handle.
More available amps does nothing! No heat! No waste!

Just added link explaining how to determine if your controller outputs enough amps to hit peak watt output.
In original post.

 

[Arlo1]

Ok So what you are saying is you are tying to show people if they need a bigger controller?

 

[DrkAngel]

Ok So what you are saying is you are tying to show people if they need a bigger controller?

Link is to an explanation of how to determine if your controller is sufficient to attain your motors peak watt output.
Important to be sufficient or the "Horsepower - Output Watts ... How to determine!" test will not be accurate.

 

[liveforphysics]

Imbecilic.

 

[DrkAngel]

Imbecilic.

And yet ... if you run the numbers on the Hub Motor and eBike Simulator the numbers work.

Of course you had to respond ... without testing ... or even looking ... right? P&I

 

[sn0wchyld]

Imbecilic.

And yet ... if you run the numbers on the Hub Motor and eBike Simulator the numbers work.

Of course you had to respond ... without testing ... or even looking ... right? P&I

Well what do you expect when you write stuff like 'more amps just do nohting - no heat no waste!

Maybe something is lost in translation, but if those amps arn't doing usefull work, ie more motor output power, then that energy has to go somewhere - ie be wasted. and it ain't turning into sound, or light... so it is turning into heat. lots of it.

 

[DrkAngel]

Imbecilic.

And yet ... if you run the numbers on the Hub Motor and eBike Simulator the numbers work.

Of course you had to respond ... without testing ... or even looking ... right? P&I

Well what do you expect when you write stuff like 'more amps just do nohting - no heat no waste!

Maybe something is lost in translation, but if those amps arn't doing usefull work, ie more motor output power, then that energy has to go somewhere - ie be wasted. and it ain't turning into sound, or light... so it is turning into heat. lots of it.

You can't force more amps into a motor than it will accept! Go to the motor simulator and set up a bike with a 40a controller, open B go to controller and custom a 150a controller.
"Simulate" you should clearly see that the extra amps only have an effect at minimal speed.
A 1000a controller won't pump in an extra single amp at the motors top, no load, speed,
The only way to force in more amps, at higher speeds, is by upping the volts=pressure.

 

[Arlo1]

I was speaking at the 40% of the top speed and yes you can force all the amps you want until you are at a limit of the resistance/voltage. Which Luke proved with video can make a hub motor dieing in flames!

 

[DrkAngel]

I was speaking at the 40% of the top speed and yes you can force all the amps you want until you are at a limit of the resistance/voltage. Which Luke proved with video can make a hub motor dieing in flames!

Sure ... if you apply enough volts=pressure you can jamb in enough amps to get a nice puddle of molten goo.
But there is no way to increase the amps a motor will accept except by increasing the voltage-pressure!
Try the Hub Motor and eBike Simulator, as recommended ... repeatedly!
I haven't heard anyone complain that it was wrong! ?

 

[Arlo1]

OK so here Do I need to go ride my bike to show you???? Or dyno it with the amps reading on the CA?? My amps don't drop off until ~70% of the no loaded top speed! With my current settings I run about 140 amps Showing on the CA from 0-~60 km/h then It starts to fall until 85km/h 93 is the unloaded speed.
I can crank up the controller and see over 250 amps on the CA from 0-~60km/h and it is slower because it turns more into HEAT.
Remember Justin used stock motors with out up graded phase wires and controllers without all the things we do to lower the resistance he made the simulator for the average ebike and its a guideline to help you put a package together but its not the bible on what limits a motor.

 

[DrkAngel]

OK so here Do I need to go ride my bike to show you???? Or dyno it with the amps reading on the CA?? My amps don't drop off until ~70% of the no loaded top speed! With my current settings I run about 140 amps Showing on the CA from 0-~60 km/h then It starts to fall until 85km/h 93 is the unloaded speed.
I can crank up the controller and see over 250 amps on the CA from 0-~60km/h and it is slower because it turns more into HEAT.
Remember Justin used stock motors with out up graded phase wires and controllers without all the things we do to lower the resistance he made the simulator for the average ebike and its a guideline to help you put a package together but its not the bible on what limits a motor.

Open "System B"
Set up identical except for 300a controller instead of 150a controller
Compare!

 

[Arlo1]

Ok here you go. But as I said this proves nothing. And Im still not sure im understanding what you are trying to say....
What limits a motor/controller combo from using more amps is based on system resistance combined with voltage combined with speed and force against the bike ie hill rolling resistance etc. Its not just as simple as 40% of the max unloaded speed. I have proven this simulator to be off for things like this. But that's because Justin did not use 100 amp plus controllers on modified X5 motors to get data in fact I don't think he can put the load on it required to make the data at those power levels accurate.

 

[Arlo1]

Ok here is the same test with lower controller and battery resistance. I can't change the resistance of the motor but the phase wires are uber thick in my case!

 

[DrkAngel]

OK so here Do I need to go ride my bike to show you???? Or dyno it with the amps reading on the CA?? My amps don't drop off until ~70% of the no loaded top speed! With my current settings I run about 140 amps Showing on the CA from 0-~60 km/h then It starts to fall until 85km/h 93 is the unloaded speed.
I can crank up the controller and see over 250 amps on the CA from 0-~60km/h and it is slower because it turns more into HEAT.
Remember Justin used stock motors with out up graded phase wires and controllers without all the things we do to lower the resistance he made the simulator for the average ebike and its a guideline to help you put a package together but its not the bible on what limits a motor.

Open "System B"
Set up identical except for 300a controller instead of 150a controller
Compare!

Results!
Using my "Imbecilic" (LFP) formula
85kph no load speed x .4 = 34kph

@ 34kph electrical watt usage is 8287w
8287w x .55 = 4557.85w - output watts

Simulator says peak output is 4700w = 6.1hp

Damn!
My "Imbecilic" (LFP) formula is off by 3%
Guess I might have to tweek it a bit. ... Sorry ... :<{

 

[pchen92]

GrkAngel you can't mix theory and practice like you do. Arlo1 speaks of practice, which is what we want to know.

 

[Arlo1]

Ok here is the same test with lower controller and battery resistance. I can't change the resistance of the motor but the phase wires are uber thick in my case!

Did you miss this post.
There is some variables. I run a 21 inch tire and a 120% speed setting. But I think I am starting to see what you are saying.

IN short you see a way to determine what the max output wattage (RWHP) is on some motors as a very rough rule of thumb. This will change as you say is the controller is not up to the task or it is turned down. But there is other timing issues that will change it. As well I think the more advanced controller algorithms will make for different results.

 

[DrkAngel]

GrkAngel you can't mix theory and practice like you do. Arlo1 speaks of practice, which is what we want to know.

Electric motors can accept massive amps at 0 rpm.
My eBike motor might accept 50a at 0 rpm.
My controller is a 35a.
At full throttle it (the motor) draws 35a until about 5mph.
Above 5mph the maximum amp draw steadily declines till at top speed it draws 10a.
It is being fed 35a constantly, but can only use 10a.
it is not turning the other 25a into heat.

If that was true, letting a motor run full throttle - full speed, no load would produce 0 power output and 35a heat! ... ???
It would overheat almost immediately! Does it ? No! There is almost 0 heat production from all those 35a being pushed at it, and 0w work coming out.


A 50a controller would increase the input amps, causing more heat but only until the 5mph mark, where motor input limit was below 35a.

Sorry ... I had to try to explain.
Gettin' tired, think I will write up a good explanation and use it as a stock response.
Have a good analogy in mind.

 

[Njay]

My controller is a 35a.
At full throttle it draws 35a until about 5mph.
Above 5mph the amp draw steadily declines till at top speed it draws 10a.
It is being fed 35a constantly, but can only use 10a.
it is not turning the other 25a into heat.

Not how it works. 35A controller should be read as "maximum 35A controller", the controller will let pass at most 35A. The motor sets a demand, the controller gives the motor what it asks but no more than 35A (I'm disregarding if the limit is imposed on motor or battery side).

 

[DrkAngel]

My controller is a 35a.
At full throttle it draws 35a until about 5mph.
Above 5mph the amp draw steadily declines till at top speed it draws 10a.
It is being fed 35a constantly, but can only use 10a.
it is not turning the other 25a into heat.

Not how it works. 35A controller should be read as "maximum 35A controller", the controller will let pass at most 35A. The motor sets a demand, the controller gives the motor what it asks but no more than 35A (I'm disregarding if the limit is imposed on motor or battery side).

Actually, you are agreeing with me, making my point.
I clarified my example as ...
"Electric motors can accept massive amps at 0 rpm.
My eBike motor might accept 50a at 0 rpm.
My controller is a 35a.
At full throttle it (the motor) draws 35a until about 5mph.
Above 5mph the maximum amp draw steadily declines till at top speed it draws 10a.
It is being fed 35a constantly, but can only use 10a.
it is not turning the other 25a into heat."

Sorry, I was up, way to late ... monitoring thread.
~DrkAngel

 

[DrkAngel]

OK so here Do I need to go ride my bike to show you???? Or dyno it with the amps reading on the CA??

Open "System B"
Set up identical except for 300a controller instead of 150a controller
Compare!

Results!
Using my "Imbecilic" (LFP) formula
85kph no load speed x .4 = 34kph

@ 34kph electrical watt usage is 8287w
8287w x .55 = 4557.85

Simulator says peak output is 4700w

Damn!
My "Imbecilic" (LFP) formula is off by 3%
Guess I might have to tweek it a bit. ... Sorry ... :<{

The 3% variance from projected peak watt output might well be be attributable to variations in motor or controller efficiency.
Anyhow, my method was not designed to be precise.
I rounded to 40% and 55% as being simple to work with and within a reasonable tolerance range of accuracy.
Please appreciate ~ DrkAngel

 

[John in CR]

The only rule of thumb there is about max power is that it occurs at full saturation (no more no less) and the point where efficiency is 50%. There's no fixed rpm relationship with no load rpm, because the % of no load rpm where peak power occurs varies as you change voltage. Max power changes too.

If you want to see interesting results and learn why I push everyone toward the highest Kv hubbie they can find, put the lowly 9C 2805 in the simulator. Switch the X axis to rpm so you don't confuse yourself with speed numbers. Put a nice 100V battery aboard with very low IR and keep bumping up the controller till you get to 185A in the little chart. Slide that dotted vertical line over to the peak power point with each sim. Not bad at all 9400W max output with the motor seeing 100V.

Now keep the current at the same full saturation and bump the battery up to 140V, since the simulator crashes at 150V. Look at that peak output, an eye popping 15.4kw Arlo1's big X5304 can't even hang with it, and the cheap little high speed wind much lighter hubbie sends the over-priced copper and steel anchor running home with it's tail between its legs. :lol: Of course the 9C has a lot less mass and less internal surface area of the stator to get sink and dump the heat, so you'd have to get extreme on the cooling.

Just imagine what a big high Kv hubbie can do.

For those who want hubmotors capable of true high power, low turn count motors are the only way to fly. 8)

 

[etriker]

I thought that thing was so the kids up north would have something to do in the winter when they can't ride ?

Real world tests rule ?

 

[999zip999]

Just 2 more months of rain sleet and slush.
Just as JohnCR has a magic battery temp.sensor in his hand I have a speed and torque sensor in my A-- plus a C.A.