How to read motor performance charts

[Functional Artist]

These are supposed to represent the type of motor that I have on ElMoto, my electric motorcycle.

Can someone please explain what these graphs are saying?

Also, maybe discuss the differences between what the data on the 36V chart
...& the 48V charts are telling us.

 

[NewbCarter]

To my knowledge , EFF is short for efficiency , the rest is self explanatory .

You can see from the blue graph that your maximum efficiency is achieved when your motor is drawing around 100A in order to produce close to 6HP (between 5 and 6). At that load the motor is supposed to be spinning at around 3300RPM , while providing close to 120 lbin of torque.

Or pick any point in the graph and draw your needed info from there ... for example .. lets say you want to know how much torque the engine can provide at a certain RPM , and how much amps will it draw doing that .

Lets say 2500 RPM : you follow the horizontal line from that RPM till you hit the HP curve , from that point you go down and read the torque . Now take the same horizontal but go a bit further to the AMP line , and you can see that to output 5HP you will need to draw roughly 100A .


Maybe im doing it wrong , i am not 100% certain , but bottom line is the graphs are supposed to show you how the motor "should" behave under those conditions , and what kind of performance to expect from one .

 

[Functional Artist]

Thanks for the reply

Still having a hard time wrappin' my head around this.

I don't understand why there are "fixed" headings & numbers along the sides (EFF, RPM, Amps & HP)
…& also "projected" lines for/with the same designations (EFF, RPM's, Amps & HP)

To me, it looks like the blue graph shows the EFF (the top "projected line) topping off
...@ ~90% EFF
...@ ~4,700 RPM's
...@ ~180A
...@ ~120 lbs. of torque
...& @ a little over 9HP

Even the HP & EFF seem to cris-cross right in this area too.
So, is this telling us that this motor runs most efficient (~90%) when running
...@ ~4,500RPM's
...drawing ~180A
...producing ~120 lbs. of torque
...which would/should be ~9HP?

But, then it looks like, using the 2,500 RPM's example, this motor would be only running @~50% EFF
...while drawing ~100A
...producing ~100 lbs. of torque
...which would be ~5HP?

Still confused

 

[Functional Artist]

Well, lets go at this a different way

Here are some specs for a Kawasaki 440LTD motorcycle (like my El Moto)

Bikez.com states: 27 HP / 19 kw @ 7,000 RPM's (as max power)
https://bikez.com/motorcycles/kawasaki_z_440_ltd_1980.php

but,

Motorcycle specs states:

Max Power 41 HP / 30.5 kw @ 7,000 RPM's
Max Torque 3.6 kgf-m / 26 lb-ft @ 7,000 RPM's
Top Speed 154.0 km/h (95.7 mph)
Dry Weight 166 kg / 366 lbs.
https://www.motorcyclespecs.co.za/model/kawasaki/kawasaki_z440ltd 80.htm

If I am looking to max out @ ~50MPH (~1/2 of the listed top speed) it seems like I would/should aim for ~1/2 of the power & torque specs?

Which would be ~20 HP & ~13 lb-ft.
...or ~13.5 HP & ~9.5kw depending on where you get your info
(we'll work with the larger numbers for now)

Looking at the blue graph (which is labeled in lb-in NOT lb-ft)
(Torque is listed at the bottom of the graph on the X axis)

So, if we are looking to produce ~13 lb-ft of torque (13 lb-ft x 12 = ~ 156 in-lb) we look for/find 160 in-lb on the graph
...then, follow that line up vertically to the first intersection with the RPM line
...then, follow it horizontally to the left where it shows ~3,300 RPM's.

Now, follow the line vertically to the second intersection with the AMP's line
...then, follow it horizontally to the right where it shows ~140A

Now, follow the line vertically to the third intersection where it shows the Horse Power line
...then, follow it horizontally to the right where it shows ~9HP

The fourth intersection, with the efficiency line, also intersects at about the same area as the HP line
…& if you follow it horizontally to the left where it shows ~0.90 (operating @ ~90%)

So, it looks like to produce 160 in-lbs, this motor would be spinning at ~3,300 RPM's
...while drawing ~140 Amps
...producing ~9HP
...all while running at ~90% efficiency.

Does this make sense?

 

[itsid]

first, theres a european limit for motorcycles (young[beginner] drivers / experience drivers)
that was 27hp a few years ago then changed to 34hp
but that limiter is likely why you got a 27hp version for the bike

unrestricted it'd be 41 horses!

Anyways back to electic motors.

Charts like that are not a pain to read..
although the "line" does not represent the meaning of it too well in most cases.

It works as follows:
Say you require a specific amount of torque
(weight // acceleration or climbing hills most likely)
you look up that requirement on the X-axis (say 120 lb/ft.. )
[what a BS idea with metrics on the y-axis.. aaaanyways]

take the Manta for example
for that torque requirement you now know your motor cannot
rev more than ~3200 rpms (to calculate your speed under max load)
you know your motor puts out ~6hp of power and draws about 110 Amps
running at 93% efficiency.
( everything left is still relevant for you however.. since you can still speed downhill @3500 rpms drawing as little as 5 amps or such)

You can also read the graph another way..

say you know your batpack cannot deliver more than 120 Amps for some reason
you get the x-axis intersection for the amp-curve at 120Amps ,
so you now know you MUST NOT exceed a torque demand of ~138 lb/ft
and now what to gear you vehicle for in order to stay below that number.


the 36 vs 48 Volt charts are providing you with quite an interesting observation...
Contrary to some idiots believe (*cough*) you CANNOT FEED Amps to a motor!
you can only supply and hope for the motor demand...
So no matter what the max draw on that motors coils are 105-110'ish amps

And as a direct result, the 36V setup only supplies 3.2'ish kiloWatts
wheras the 48V setup peaks at 4.5+ kW

And (dumbed down) since the Amps is what makes the torque,
there is very little difference in peak torque in the two setups.
The only noteworthy difference int he two setups is the motor speed
(changing from ~3300 rpms for the 48V to 2400 rpms for the 36V setup for 100 lb/ft)
so you are slower but have essentially the same oomph

'sid

 

[Functional Artist]

first, theres a european limit for motorcycles (young[beginner] drivers / experience drivers)
that was 27hp a few years ago then changed to 34hp
but that limiter is likely why you got a 27hp version for the bike

unrestricted it'd be 41 horses!

Anyways back to electic motors.

Charts like that are not a pain to read..
although the "line" does not represent the meaning of it too well in most cases.

It works as follows:
Say you require a specific amount of torque
(weight // acceleration or climbing hills most likely)
you look up that requirement on the X-axis (say 120 lb/ft.. )
[what a BS idea with metrics on the y-axis.. aaaanyways]

take the Manta for example
for that torque requirement you now know your motor cannot
rev more than ~3200 rpms (to calculate your speed under max load)
you know your motor puts out ~6hp of power and draws about 110 Amps
running at 93% efficiency.
( everything left is still relevant for you however.. since you can still speed downhill @3500 rpms drawing as little as 5 amps or such)

You can also read the graph another way..

say you know your batpack cannot deliver more than 120 Amps for some reason
you get the x-axis intersection for the amp-curve at 120Amps ,
so you now know you MUST NOT exceed a torque demand of ~138 lb/ft
and now what to gear you vehicle for in order to stay below that number.


the 36 vs 48 Volt charts are providing you with quite an interesting observation...
Contrary to some idiots believe (*cough*) you CANNOT FEED Amps to a motor!
you can only supply and hope for the motor demand...
So no matter what the max draw on that motors coils are 105-110'ish amps

And as a direct result, the 36V setup only supplies 3.2'ish kiloWatts
wheras the 48V setup peaks at 4.5+ kW

And (dumbed down) since the Amps is what makes the torque,
there is very little difference in peak torque in the two setups.
The only noteworthy difference int he two setups is the motor speed
(changing from ~3300 rpms for the 48V to 2400 rpms for the 36V setup for 100 lb/ft)
so you are slower but have essentially the same oomph

'sid

Wow! A member from Croatia (NewbCarter) & from Germany (Sid)
...but, no Americans WTF

Thanks fellas, very helpful.
...I think I'm starting to understand it now.


They also show a 60V chart.
So, it looks like when operated at 60V
…& producing 110Lb-in. of torque

This motor will still draw ~100A
…@ ~5.5 kW
…& the efficiency remains ~87%

But, the motor speed (RPM's) will increase to ~4,100 RPM's
...thus increasing overall speed
...with "essentially the same oomph"

 

[Functional Artist]

They also show a 60V chart.
So, it looks like when operated at 60V
…& producing 110Lb-in. of torque

This motor will still draw ~100A
…@ ~5.5 kW
…& the efficiency remains ~87%

But, the motor speed (RPM's) will increase to ~4,100 RPM's
...thus increasing overall speed
...with "essentially the same oomph"

Would running this type of a motor @ 60V be considered "over-volting"?

They (whoever they are) seem to have tested 'em @ 24V, 36V, 48V & 60V
…& I don't see any "red flags" on the charts.

 

[itsid]

Depends..
going by just the charts I doubt it can be considered overvolting running that particular motor @60V

The efficiency doesn't drop in a noteworthy manner (not visible in the chart let's say)
So there shouldn't be no ecessive heat built up at such voltage.

Fairly usual behaviour (having a wide band of volatages to run at) for a brushless motor really.
I think it should also run at 72V pretty nicely...

BUT that's just the most apparent thing to check,
some motor's internals are just not made to accept higher voltages
say it has internal hall effect sensors for position and rotation feedback.. and those are rated for no more than say 48V
Or it has a weak spot (for manufacturing reasons) in the insulation of the wires in a coil
(close to the breakout ports usually or the commutator bars in brushed motors)
And if two badly or even uninsulated wires are close enough for a spark gap @ XY Volts you must not exceed said voltage either.

The bearings might need a much better balanced rotor for higher rpms
So you want to be sure they don't cook off their grease under such additional loads.

Another thing to make sure -on internally fan cooled motors that is-
is the fan itself.. is it properly balanced for the additinal speed?
and if not will it self destruct or cause premature wear on the bearings?

So just stick with the manufacturers voltage recommendation to be on the safe side
unless you checked the internals yourself to be safe to run at higher voltages.

Sometimes you hit a resonating frequency in motor rpms
with a not perfectly balanced rotor..
you should avoid that motor rpm at all costs
(either run it slower or faster that is)
ideally you want such resonating frequency to be way above your motor speeds,
so that you can't hit it by accident.

But yeah.. 60V seems to be fine (and again I'd also say 72V should still be good)
since those charts to me read as brushless motor charts.
Or similar brushed motors wound for different voltages specifically...
since brushed motors usually have a much narrower voltage band
(I doubt that's the case tbh)

Short:
there's more to it than just efficiency at times...
and sometimes you need to look inside to know for sure
efficiency is only a very good indicator, no guarantee I'm afraid

'sid