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podolefsky
13 May 2011, 1321
For a while I've been trying to put together a way to compare across some common motors. I think I've figure out a way to plot all this data that might actually be useful.

I'm doing this because there don't seem to be any standards, which makes it almost impossible to compare data from different manufacturers. I've tried to compile the best data I could find. As much as possible, these graphs are based on real dyno data (or what appears to be real dyno data). In some cases I've made assumptions to fill in gaps in the available data, e.g. assuming torque is directly proportional to current. It might not be perfect, since this data is all kind of sketchy.

Therefore: I am not responsible if you get one of these motors and find out it doesn't perform as expected. There are a million reasons this could happen, including bad data (don't blame the messenger!), bottlenecks in your system (such as weak batteries), etc. Just sayin'.

The graphs below show kW, motor torque, and adjusted wheel torque at 72V and 5:1 gearing on the left. On the right I adjusted the gearing so that all motors made 300 ft-lb at the wheel, and listed the gearing required.

Notes:
-Motors are running at different currents. I'm using the current limits that I could find from manufacturers. I think this is fair. If an AC-20 can handle 550A and the ME0709 can only handle 300, that's how they should be compared.

-The ME1003 is treated like an ME0709 with a 500A current limit (67% increase in torque, all else the same).

-I used the max efficiency listed. I did not adjust for changes to efficiency with RPM or current.

-The Dual Agni is assuming a parallel configuration. It looks impressive, but keep in mind it needs 800A to achieve this performance. Plot made by doubling torque.

-AC-20 96V plot was made by extending torque knee to 33% higher RPM.

Please let me know if you see anything glaringly wrong with this data. I'll keep trying to fix it up and get it as accurate as possible.

PDF (http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/all_motors.pdf) of the graphs below.

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/all_motors.png


Plots below are for rated continuous current (under construction) and geared for 70 mph top speed.

- Note that the AC-20 is RPM limited to 70 mph at 8000 RPM. All others are power limited.

PDF (http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/all_motors_2.pdf) of the graphs below.

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/all_motors_2.png

frodus
13 May 2011, 1409
Pretty slick dude!

can you do a dual agni 95R?

podolefsky
13 May 2011, 1606
Pretty slick dude!

can you do a dual agni 95R?

Yup - but before I do, I should get straight how this set up works.

You could do parallel at 72V, then do you assume both motors can have 400A (so an 800A controller)? Or in series, do you have 144V and 400A?

Or you could also do series / parallel with 72-144V, or anywhere in between. Then you'd have full current and 1/2 voltage in series, then full voltage and 1/2 current in parallel.

Just want to know what I should be plotting, since I'm not 100% on how people set this up.

magicsmoke
13 May 2011, 1632
I think regardless of the actual setup, to remain consistent with the existing plots a parallel 72V is preferrable.
i.e. series or parallel, both motors will have their max current and 72 volts available to them so the plots should be the same anyway.

Just to dot the Is, cross the Ts etc. perhaps you could indicate the tyre radius for the mph calcs.

Edit : And while you're doing nothing :) what about 'continuous rating' plots. The Agni for example is only rated to handle 400A for about 30 seconds according to their datasheet.

frodus
13 May 2011, 1710
do them in parallel the entire time, so torque doubles.

EVcycle
13 May 2011, 1727
How about our current motor...the ME 1003?

podolefsky
13 May 2011, 1729
Okey doke - I'll do them in parallel, no special series / parallel switching. I'll just assume an 800A controller and batteries that can handle it.

Continuous rating plots is a good idea. Easy to do...in my copious spare time :)

podolefsky
13 May 2011, 1737
How about our current motor...the ME 1003?

Oh yeah, I should do that too. I'll have to make some assumptions to do 72V cause I can only find 48V data.

Have a link to 72V data for the 1003?

podolefsky
13 May 2011, 1759
Dual Agni 95Rs is up (you might need to refresh your browswer).

It's very impressive, but I added a note that you need 800A to get this kind of performance.

I should also plot the AC-20 at high voltage (say 96V), since I think this would be a fairer comparison with the dual Agnis. These graphs are going to get full quick.

podolefsky
13 May 2011, 1821
One more update - added AC-20 at 96V. I did this by moving the torque knee to 33% higher RPM.

http://www.elmoto.net/showthread.php?1271-Comparison-of-motor-curves&p=14478&viewfull=1#post14478

magicsmoke
13 May 2011, 1843
Thanks for doing this Noah, much easier to assess options when layed out this way.
Earlier I stated that the plots, by which I meant torque, for a dual Agni (or any motor) would be the same regardless of series or parallel connected. Assuming the same current through the motors, say 100A through each in parallel or a series of 100A, that is true isn't it? Starting to doubt myself, but my thinking was two one pound weights both total the same whether stacked (series) or side by side (parallel) on the scales.

Edit : ok, just had a can of thinking lager and I'm quite happy it is true :)

jpanichella
13 May 2011, 1855
You wouldn't have a graph for the es-10e-33 Sepex would you? I've looked but can't find anything.

DaveAK
13 May 2011, 1925
Here's a chart for the D&D SepEx

1172

podolefsky
13 May 2011, 2045
Thanks for doing this Noah, much easier to assess options when layed out this way.
Earlier I stated that the plots, by which I meant torque, for a dual Agni (or any motor) would be the same regardless of series or parallel connected. Assuming the same current through the motors, say 100A through each in parallel or a series of 100A, that is true isn't it? Starting to doubt myself, but my thinking was two one pound weights both total the same whether stacked (series) or side by side (parallel) on the scales.

Edit : ok, just had a can of thinking lager and I'm quite happy it is true :)

I haven't actually done this, but in theory I think this is how it works.

Yes, if both motors see 100A, then you will have the same torque whether series or parallel. The difference is that if they are in parallel, then the controller has to supply 200A (split between the two motors), whereas if they are in series the controller only has to supply 100A. The problem with series is that the motors split the voltage, so if you have a 72V system, each motor only gets 36V. So basically 1/2 the RPM. That's fine until you hit that RPM limit, then you want 72V per motor. That's why people do series / parallel switching.

Or you could go always parallel with a honkin 800A controller. But then you need batteries that can supply 800A...sort of. You can trade volts for amps motor side, so you could have 400A from the batteries and 800A to the motor by cutting the motor voltage in half. But no matter what you do, if the batteries won't give you more than 400A at 72V, you can't make more than 28.8 kW. To get performance like the graphs I posted, you need 800A at 72V from the batteries.

Clear as mud?

podolefsky
13 May 2011, 2125
Here's a chart for the D&D SepEx

1172

Thanks. I'll add the sepex. But I need to know the actual peak torque. Those graphs show 45 ft-lb at 2500 RPM. I'm guessing it goes a bit higher...want to say 65 ft-lb, but that's just a guess.

BaldBruce
13 May 2011, 2223
Noah, thanks for consolidating differrent motor graphs in one place.
What I did for my motor choice matrix was change the gear ratio for each motor to attain a certain theoretical max speed based on rpm and/or kw limits. (I used 70mph) You can then compare the wheel torgue and resulting performace that particular motor and gear ratio will produce in your real world example. You might be intrigued by some of the results....

Of course you can also slice this kind of data a bunch of ways including cost, weight and many others on the x axis. But that's a different kettle of fish.

podolefsky
13 May 2011, 2225
How about our current motor...the ME 1003?

I added the ME1003. It treated it like an ME0709 at 72V, but with a 500A limit instead of 300A, so it boosts the torque by 67%. All else the same. That seem correct?

Please check me, I don't want to post incorrect data.

podolefsky
13 May 2011, 2240
Noah, thanks for consolidating differrent motor graphs in one place.
What I did for my motor choice matrix was change the gear ratio for each motor to attain a certain theoretical max speed based on rpm and/or kw limits. (I used 70mph) You can then compare the wheel torgue and resulting performace that particular motor and gear ratio will produce in your real world example. You might be intrigued by some of the results....

Of course you can also slice this kind of data a bunch of ways including cost, weight and many others on the x axis. But that's a different kettle of fish.

Good idea. I started doing this - it is pretty eye opening. Different motors really shine in different circumstances.

Will update with all geared to 70mph top speed. Stay tuned.

teddillard
14 May 2011, 0321
These shall heretofore be known as "The Podolefsky Curves" (http://evmc2.wordpress.com/2011/05/14/the-podolefsky-curves/).

We lay ourselves at your feet. We are not worthy.

<iframe width="640" height="390" src="http://www.youtube.com/embed/9TbFcFohbs4" frameborder="0" allowfullscreen></iframe>

larryrose11
14 May 2011, 0426
Cool plots Noah.
Cool to see all the plots consolidated like this in a relevant way.

I wrote a motor simulation (in simulink) while in GradSchool, but I think I set it up for a series wound motor, but a lot of the basic calculations are similar.
Controller voltage out, and motor speed were the sim input, motor torque and motor current were the result. I believe I included a saturation to limit the current, and hence limit the torque. It would need to be updated for PM effect, as the magnets have their own saturation limits.
It did rely on the availability of either motor KV, or test data to calculate KV. You could use it to see the effect of different voltages on motor setups.
I could dredge it up if it would be useful, just let me know of anyone on here is up to it.
However....I would like it if it could be validated against published data before letting it into the wild.

EVcycle
14 May 2011, 0457
Oh yeah, I should do that too. I'll have to make some assumptions to do 72V cause I can only find 48V data.

Have a link to 72V data for the 1003?

Nope, just the 48V version.

ME1003
(http://www.evdrives.com/images/Motors/Mars_Electric/ME1003_CW_48_VDC.pdf)

EVcycle
14 May 2011, 0459
I added the ME1003. It treated it like an ME0709 at 72V, but with a 500A limit instead of 300A, so it boosts the torque by 67%. All else the same. That seem correct?

Please check me, I don't want to post incorrect data.

I would think so. I know it hauls our bike around much easier that the 709.

podolefsky
14 May 2011, 1113
I would think so. I know it hauls our bike around much easier that the 709.

Thanks. Did you increase the current output on your controller to get better performance?

Speaking of the 1003, this is interesting: EMC-RT200 (http://www.electricmotorsport.com/store/ems_ev_parts_motors_me1003.php) EMS claims 5000RPM and 400A peak, but when you look at the data it's for the 1003. ???

jpanichella
14 May 2011, 1123
Thanks. Did you increase the current output on your controller to get better performance?

Speaking of the 1003, this is interesting: EMC-RT200 (http://www.electricmotorsport.com/store/ems_ev_parts_motors_me1003.php) EMS claims 5000RPM and 400A peak, but when you look at the data it's for the 1003. ???

I was under the impression that the RT200 was the 1003.

podolefsky
14 May 2011, 1138
I was under the impression that the RT200 was the 1003.

I think so - but as far as I know the 1003 doesn't do 5000 RPM, even unloaded. If it did, it wouldn't just be a really nice motor, it would be an Agni killer at less than 1/2 the price.

jpanichella
14 May 2011, 1148
I think so - but as far as I know the 1003 doesn't do 5000 RPM, even unloaded. If it did, it wouldn't just be a really nice motor, it would be an Agni killer at less than 1/2 the price.

1/2 the price but twice the weight. Regardless, if that's true...I'll take 2 please! I'll just need a 1000 amp controller.

DRZ400
14 May 2011, 1253
i think the agni 95r is 6000rpm / 84volts....

podolefsky
14 May 2011, 1306
i think the agni 95r is 6000rpm / 84volts....

Yup, that's what the spec sheet says. The 1003 has twice the torque, so if it tops out at 3000 RPM, the motors are actually pretty equivalent. If the 1003 does 5000 RPM, then it blows the Agni away. But I don't think it does - seems like a mistake by EMS, or they know something Motenergy doesn't (??). Still, similar overall performance to the Agni for $650. (yes, it's heavier)

DRZ400
14 May 2011, 1331
good to remember its specs being compared....just like with batteries specs and actual can differ, the agni motor has a pretty solid track record as being a premium pm motor. I had a Mars 709 and it was a decent motor...don't doubt their newer ones will be even better.

frodus
14 May 2011, 1338
those Agni's won't do 400A continuous, that should be noted. They need massive cooling for that.

but pretty sweet. Thanks for this.

podolefsky
14 May 2011, 1402
good to remember its specs being compared....just like with batteries specs and actual can differ, the agni motor has a pretty solid track record as being a premium pm motor. I had a Mars 709 and it was a decent motor...don't doubt their newer ones will be even better.

I tried to base all of my plots on real dyno data (or graphs from manufacturers that look like dyno data). But yeah, all things are subject to conditions of the real world.

Should be noted that I am not responsible if you spend a bunch of money and don't get what you see in these graphs. :)



those Agni's won't do 400A continuous, that should be noted. They need massive cooling for that.

but pretty sweet. Thanks for this.

True...actually none of these curves are continuous. I'm working on plots with continuous current limits imposed.

DRZ400
14 May 2011, 1518
ALL of them will need cooling at their stated maximum currents. Couple K of loss watts to disipate easy.

podolefsky
14 May 2011, 1548
Plots are now up for gearing to 70 mph top speed.

http://www.elmoto.net/showthread.php?1271-Comparison-of-motor-curves&p=14478&viewfull=1#post14478

Continuous current limited plots are in the works, but I'm 'having some trouble pinning all these numbers down. Anyone have continuous current and / or power rating for the AC-20?

DaveAK
14 May 2011, 1551
Nice work Noah.

Can you get some yellow in there for something? :D

podolefsky
14 May 2011, 1618
Sorry, can't see yellow against white background :(

I think it's only fair to point out that if you re-gear the AC-20 @ 96V to have the same torque as the Dual Agni (450 ft-lb), you end up with a top speed of ~95 mph for the AC-20.

What's interesting to me about the PM motors, assuming I'm interpreting the data correctly, is that they make full torque nearly to max RPM, then they're done. In other words, the torque knee is very close to the mechanically limited RPM. I'm not sure if this is a property of brushed PM motors, or just the way the Motenergy and Agnis are wound.

The AC and series motors have the knee lower relative to mechanically limited RPM. The AC makes more torque after the knee because the controller can field weaken and change the timing electronically (I believe). Sepex (which I have yet to graph) does field weakening, but it's only marginally effective.

BaldBruce
14 May 2011, 1637
Very nice work Noah. Thanks for plotting all the curves when normailzed to 70mph. I found this approach to be the most useful in comparing and contrasting motor selection. I still like my Agni, but thanks for adding the 1003 to the list of very interesting choices indeed.....

podolefsky
14 May 2011, 1654
If anyone wants a nice guide to different motor types, this is pretty comprehensive:

http://www.reliance.com/mtr/mtrthrmn.htm

Scroll about 2/3 down to "field windings" to see speed vs torque curves (or just click below). What I'm not 100% clear on is why the PM motors like Agni & Motenergy act more like a shunt wound motor. I suppose it just depends on the motor design?


http://www.reliance.com/mtr/images/mtdfig19a.gif

http://www.reliance.com/mtr/images/mtdfig19c.gif

http://www.reliance.com/mtr/images/mtdfig19d.gif

frodus
14 May 2011, 2142
What's interesting to me about the PM motors, assuming I'm interpreting the data correctly, is that they make full torque nearly to max RPM, then they're done. In other words, the torque knee is very close to the mechanically limited RPM. I'm not sure if this is a property of brushed PM motors, or just the way the Motenergy and Agnis are wound.


How can you tell from a graph that only shows a narrow band of RPM? I don't think that's right....

Do you have an agni graph over the full range of RPM?

podolefsky
14 May 2011, 2218
How can you tell from a graph that only shows a narrow band of RPM? I don't think that's right....

Do you have an agni graph over the full range of RPM?

I don't have a graph of the full range. Here's what I did, you can tell me if this makes sense. I'd really like to know, because when I first did this, I though it was damn odd that the torque curve was so flat. But I remembered asking about this in another thread (that I can't find now) and got confirmation that it was right.

For the Agni at 72V (http://agnimotors.com/95_Series_Performance_Graphs.pdf), follow the line from 400A straight up. It hits about 4800 RPM and 53 Nm (about 39 ft-lb). Since 400A is the max current, that's also the max torque. I assumed that you get that torque at 4600 RPM, and at all RPM below that.

The upper limit is 0A and 0 ft-lb at about 5100 RPM. In between it's basically a straight line in the torque vs RPM curve.

I double checked this by doing kW = 4800 RPM * 39 ft-lb / 5252 * 745.7 and got 26.5 kW. Just about spot on.

As a second sanity check, I believe people say they can hit 65-70 mph with an Agni geared 6:1. That seems consistent with the graphs.

I did the same for the Motenergy.

Again, definitely want to be checked on this stuff, so let me know.

magicsmoke
14 May 2011, 2301
How can you tell from a graph that only shows a narrow band of RPM? I don't think that's right....

Do you have an agni graph over the full range of RPM?

What do you mean?
There are six performance graphs which show the rpm spread for the motor at supply voltages of 6,12,24,48,60 and 72

As for being able to tell that they make full torque to nearly max rpm again is very clear.
At 72V for example, the rpm can only be between 5100 unloaded and 4800 maximally loaded (400A)

frodus
15 May 2011, 1135
Magicsmoke,
They only cover about 300RPM of the entire motor curve. I mean, yeah they have the curves, but they're not over the entire RPM, just a very small portion of it.

magicsmoke
15 May 2011, 1200
They only cover about 300RPM of the entire motor curve. I mean, yeah they have the curves, but they're not over the entire RPM, just a very small portion of it.

Yes, because at any applied voltage that is the only range it can have.
Unloaded the rpm will equal 71rpm/volt. If you then load it sufficiently, the resultant drop in the back emf causes the torque to rise to a max equivalent to 400A.
This equates to a drop of 300-400rpm. Always!

podolefsky
15 May 2011, 1209
I think it would help to think about how these plots are done. From what I understand (talking to Travis), they put full voltage on the motor and apply a load. They start with 0 load (torque = 0 ft-lb) and increase it. At 0 load, the motor spins up to the unloaded RPM. As they increase the load, the motor slows down and the current increases. When they hit the current limit for the motor, they stop. For the Agni, they stop at about 4800 RPM and 400A.

They could decrease the voltage at that point, maintaining 400A and plot the rest of the RPM curve down to zero. The torque should stay flat, but efficiency might change. In fact, it does. Like magicsmoke said, we have the curves at different voltages. At 400A, efficiency stays around 90% down to 48V (~3000 RPM), then it drops like a rock. At 12V (~570 RPM) it's 65%.

That's nothing unique to the Agni. All motors drop efficiency at low RPM.

frodus
15 May 2011, 1224
Yes, because at any applied voltage that is the only range it can have.
Unloaded the rpm will equal 71rpm/volt. If you then load it sufficiently, the resultant drop in the back emf causes the torque to rise to a max equivalent to 400A.
This equates to a drop of 300-400rpm. Always!

I realize that. But its not a full torque curve. I'm used to seeing real torque curves that show a fully unloaded motor, being loaded with more and more force and you watch the HP, RPM, Efficiency, Current do their thing.

I know what loaded and unloaded look like, it'll be a 3-400RPM drop sure, but that only shows a small part of the larger picture. Its not a real dyno curve.

I'd like to see all of these motors, tested at the same voltage, and loaded equally and we can really see how they perform. Unfortunately, I don't have another motor to set up as a load. Maybe once I'm done with my bike I can start messing around with one.

magicsmoke
15 May 2011, 1237
I'm used to seeing real torque curves that show a fully unloaded motor, being loaded with more and more force and you watch the HP, RPM, Efficiency, Current do their thing.
Each of the graphs do show exactly that!
Anyway, we're just going to have to agree to disagree on this one then :)

Noah, check this out re the efficiency, waddaya think?
Because we know the Kv (rpm/volt) of the motor and we observe from the graphs that a loading equivalent to 400A causes a 300rpm drop, then we can work out that the armature resistance must be (300/71)/400 = 0.0106 ohms
From this we can deduce then that at 400A, the motor is wasting 400*400*0.0106 = 1696 watts.
At 12V supply, 400A = 4800 watts
(4800-1696)/4800 = 65% efficient

podolefsky
15 May 2011, 1309
Noah, check this out re the efficiency, waddaya think?
Because we know the Kv (rpm/volt) of the motor and we observe from the graphs that a loading equivalent to 400A causes a 300rpm drop, then we can work out that the armature resistance must be (300/71)/400 = 0.0106 ohms
From this we can deduce then that at 400A, the motor is wasting 400*400*0.0106 = 1696 watts.
At 12V supply, 400A = 4800 watts
(4800-1696)/4800 = 65% efficient

Huh...yeah, that seems correct to me. It also explains something that's always been a mystery to me. You should have HP = torque*RPM/5252. If you go to full throttle at 0 RPM, you expect to get like 72V*400A = 28.8 kW (maybe a bit less due to voltage sag). But it should be 0 HP, since RPM = 0. I think I finally understand that it's because motor efficiency drops to zero at 0 RPM, so kW_out = kW_in * efficiency = 0, and increases as the motor speeds up.

I checked this same calculation at high RPM and it gives you about 94% efficiency, a few % more than rated. Probably due to neutral timing being non-ideal at high RPM (maybe?).

frodus
15 May 2011, 1313
I agree it shows that data, but It shows it for a very narrow RPM range.

The long and short, there is no standard for motor testing, and everyone does it different and shows different data, so its up to whoever to interpret it how they see fit.

I just have a hunch that if we DID compare all these motors on an actual dyno, the results would probably be a bit different. Motor manufacturers (from what I've seen) seem to exaggerate the performance levels so that continuous and peak and all the in between aren't that clear.

podolefsky
15 May 2011, 1316
I realize that. But its not a full torque curve. I'm used to seeing real torque curves that show a fully unloaded motor, being loaded with more and more force and you watch the HP, RPM, Efficiency, Current do their thing.

I know what loaded and unloaded look like, it'll be a 3-400RPM drop sure, but that only shows a small part of the larger picture. Its not a real dyno curve.

I'd like to see all of these motors, tested at the same voltage, and loaded equally and we can really see how they perform. Unfortunately, I don't have another motor to set up as a load. Maybe once I'm done with my bike I can start messing around with one.

I see what you're saying. It would be nice to have all that, but the only motor data I've seen like that is from HPEVS.

The data I have from D&D stops at 1600 RPM and 450A. The ADC K91 data stops at 2000 RPM and 325A (for the 75V curve). They all stop taking data once the motor is fully loaded. It's just that with the PM motors, it appears the motor fully loaded only drops you 300 RPM or so.

Which reminds me, I should do the ME0913 so we have a PMAC for comparison...back to work...

magicsmoke
15 May 2011, 1316
I checked this same calculation at high RPM and it gives you about 94% efficiency, a few % more than rated. Probably due to neutral timing being non-ideal at high RPM (maybe?).

Maybe, but also at higher rpm, the windage loss is greater. For a long time I thought this referred to windings, but of course it is wind. i.e. the rotor spinning in the air.

frodus
15 May 2011, 1318
but what is the definition of fully loaded? Do we go by winding size? Temperature?

podolefsky
15 May 2011, 1320
I agree it shows that data, but It shows it for a very narrow RPM range.

The long and short, there is no standard for motor testing, and everyone does it different and shows different data, so its up to whoever to interpret it how they see fit.

I just have a hunch that if we DID compare all these motors on an actual dyno, the results would probably be a bit different. Motor manufacturers (from what I've seen) seem to exaggerate the performance levels so that continuous and peak and all the in between aren't that clear.

I totally agree. My biggest issue with the Agni data is that it just looks drawn. If it were real dyno data, it would be noisy.

That said, it's consistent with other specs and the performance people have reported, as far as I can tell.

magicsmoke
15 May 2011, 1323
but what is the definition of fully loaded? Do we go by winding size? Temperature?

When the motor is taking the max current that the manufacturer says it can take.

podolefsky
15 May 2011, 1328
but what is the definition of fully loaded? Do we go by winding size? Temperature?

I would guess pulling max rated amps for the motor.

In other words, what he said ^^^^^^^^^^ :)

frodus
15 May 2011, 1331
guess you didn't get what I'm asking

how does the "manufacturer" define max rated current?.... what is their definition of fully loaded amps.

podolefsky
15 May 2011, 1348
I'm just guessing, but maybe when I^2*R = maximum power, where max power is the point at which the motor overheats in a specified time. Agni says 30 kW limit for 5 sec.

frodus
15 May 2011, 1409
but where are they getting their "max".... you two keep saying "max rated", well, how are they rating? Like what is the benchmark for "max" or "full amps"

podolefsky
15 May 2011, 1414
What I just said - current at which motor will overheat in a specified time.

DaveAK
15 May 2011, 1436
Max rating is entirely up to the manufacturer, within physical limits of course. They can test until destruction and then apply any safety factor they like. One might rate at 80% while another takes a moreconservative 70%. It's entirely up to them. The only way I can see getting auniform rating system across a range of manufacturers and motors is to independantly test to destruction and apply a uniform safety factor. Since that ain't going to happen I'm with Rob. You have to take the manufacturers rating and go with it.

frodus
15 May 2011, 1515
What I just said - current at which motor will overheat in a specified time.

That's my point, its arbitrary. Its set by the manufacturer. What "overheating" means, is up to the manufacturer most times.

I'm just wondering if there's something we could use as a "control" if we did a dyno run.

podolefsky
15 May 2011, 1556
That's my point, its arbitrary. Its set by the manufacturer. What "overheating" means, is up to the manufacturer most times.

I'm just wondering if there's something we could use as a "control" if we did a dyno run.

I thought you were all about following the manufacturer's specs ;)

Seems like the only way to know involves destroying a motor. Actually several, since the 5 sec limit will be different from the 1 min limit and the 5 min limit...etc.

Or else know the thermal limit and stopping just before you hit it. It depends what fails first...whether it's the insulation, or the commutator, or if the wires actually melt.

Maybe there's knowledge out there from people who have actually destroyed these motors? Seems like the race teams who push these should know what the real failure limits are.

lugnut
15 May 2011, 1601
If you go to full throttle at 0 RPM, you expect to get like 72V*400A = 28.8 kW

No, I would not expect that at all. I expect the controller to current limit at 400A therefore reducing the voltage to the motor so that the motor sees 400A and maybe 4 or so volts. But you are correct; the motor is always zero percent efficient at zero RPM :-)

frodus
15 May 2011, 1613
I thought you were all about following the manufacturer's specs ;)

Seems like the only way to know involves destroying a motor. Actually several, since the 5 sec limit will be different from the 1 min limit and the 5 min limit...etc.

Or else know the thermal limit and stopping just before you hit it. It depends what fails first...whether it's the insulation, or the commutator, or if the wires actually melt.

Maybe there's knowledge out there from people who have actually destroyed these motors? Seems like the race teams who push these should know what the real failure limits are.

I am, I'm just asking where the limits come from, thats all, it was rhetorical and you two kept guessing. lol.

A really good test would be to do all motors with a battery side current limit of 400A, compare them all and go from there.

lugnut
15 May 2011, 1616
but what is the definition of fully loaded? Do we go by winding size? Temperature?

Typically, full load, for drive motors, is the one hour rating. Often this is on the nameplate, not always, and sometimes in a specification. Which means, if you run the motor at the specified voltage and load it to that "one hour" specified current (or HP) it will reach its rated temperature. Depending on the motor design, running longer at that load may overheat it. Running the motor at greater loads is o.k. for lesser time periods.

Maximum power is easily defined when you know the controller current limit. Recommended maximums from a motor seller or even a motor manufacturer are mostly guesswork where they attempt to keep you from damaging the product. Any such maximum number for load, current or power is likely to apply for just a matter of seconds unless otherwise specified.

podolefsky
15 May 2011, 1625
No, I would not expect that at all. I expect the controller to current limit at 400A therefore reducing the voltage to the motor so that the motor sees 400A and maybe 4 or so volts. But you are correct; the motor is always zero percent efficient at zero RPM :-)

That might happen, but not necessarily. If you go to 100% throttle, then at least with my controller it puts 100% battery voltage to the motor. It will try to current limit if you exceed the set threshold. But it doesn't do anything like limiting to 4V.

Take a look at the plot below. This is going full throttle from a stop. There's about 0.3 sec where the throttle is ramping up to 100%, then the controller has essentially connected the battery directly to the motor. If the controller were limiting to 4V, it would have to reduce throttle (technically duty cycle) to about 6%.

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/hard_pull_log.png

podolefsky
15 May 2011, 1631
I am, I'm just asking where the limits come from, thats all, it was rhetorical and you two kept guessing. lol.

A really good test would be to do all motors with a battery side current limit of 400A, compare them all and go from there.

That would give a nice controlled comparison. Only issue is that it doesn't tell you what the motors are actually capable of, only what they do when you limit them.

podolefsky
15 May 2011, 1638
This is interesting:

http://www.go-ev.com/motors.html

lugnut
15 May 2011, 1639
That might happen, but not necessarily. If you go to 100% throttle, then at least with my controller it puts 100% battery voltage to the motor. It will try to current limit if you exceed the set threshold. But it doesn't do anything like limiting to 4V.

Take a look at the plot below. This is going full throttle from a stop. There's about 0.3 sec there the throttle is ramping up to 100%, then the controller has essentially connected the battery directly to the motor. If the controller were limiting to 4V, it would have to reduce throttle to about 6%.

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/hard_pull_log.png

The graph shows throttle, not duty cycle. It does not show motor voltage. If this motor was stalled, at zero RPM, and you put 67 volts across the motor terminals, it would draw several thousand amps. So, in your plot, if the motor RPM = 0, then the motor voltage is a lot lower at 500A. At stall, there is no back EMF, so I = V/R. Motor R is likely about 0.01 ohms

edit: I just noticed that output (motor) current and battery current are the same at 500A. Therefore, it is impossible that this motor was at zero RPM for this test.

podolefsky
15 May 2011, 1706
The graph shows throttle, not duty cycle. It does not show motor voltage. If this motor was stalled, at zero RPM, and you put 67 volts across the motor terminals, it would draw several thousand amps. So, in your plot, if the motor RPM = 0, then the motor voltage is a lot lower at 500A. At stall, there is no back EMF, so I = V/R. Motor R is likely about 0.01 ohms.

Technically you're right. But 67V across the terminals for how long? The motor is an inductor, the current won't go to 1000A immediately. So yes, if you hold the motor stalled you will eventually see 1000s of amps, or the controller will limit, because you've put a HUGE load on the motor. But normally the motor sees much less load and starts to turn, so you don't get 1000s of amps.

This 0 RPM thing is missing the point. Let's see what happens at 500 RPM. At this point the motor is seeing at least 67V and 500A. That should be 33.5 kW. But this motor is rated 80 ft-lb at 450A, so the power should be something like 80 ft-lb * 500 RPM / 5252 * 745.7 = 5.7 kW. Why isn't it 33.5 kW? Because the motor efficiency is about 20% at this point.

You don't need to see the duty cycle, you know what the motor voltage is based on the motor and battery currents. (And once the controller isn't limiting, throttle% = duty cycle, and you know it's not limiting when battery current = motor current). If the motor voltage was 4V, then the battery current would be about 30A. It's not, just look at the graph.

lugnut
15 May 2011, 1717
Technically you're right. But 67V across the terminals for how long? The motor is an inductor, the current won't go to 1000A immediately.

You're beating me up on the millisecond time scale again :-) You don't indicate the time scale on your plot, but it is certainly much longer at 500A than the motor time constant.


Let's see what happens at 500 RPM. At this point the motor is seeing at least 67V and 500A.

Where is this data point? It is not a real operating point for this motor, for longer than a millisecond.

podolefsky
15 May 2011, 1731
You're beating me up on the millisecond time scale again :-) You don't indicate the time scale on your plot, but it is certainly much longer at 500A than the motor time constant.



Where is this data point? It is not a real operating point for this motor, for longer than a millisecond.

The timescale is along the bottom.

I'm beating you up on the ms timescale because you make the same point about 1000s of amps, but that just doesn't happen...unless you are literally holding the motor in place. Please stop editing my posts so that you only see the parts you want to argue about. If you read the whole thing you'll see exactly what I'm saying.

I really don't want to argue. I said you were right that if the motor is stalled, you will see a huge current. I'm just saying that controller limiting is *not* why the actual motor output (in kW = torque*RPM/5252*745.7) is less than V*I.

lugnut
15 May 2011, 1745
The timescale is along the bottom.

I'm beating you up on the ms timescale because you make the same point about 1000s of amps, but that just doesn't happen...unless you are literally holding the motor in place. Please stop editing my posts so that you only see the parts you want to argue about. If you read the whole thing you'll see exactly what I'm saying.

I really don't want to argue. I said you were right that if the motor is stalled, you will see a huge current. I'm just saying that controller limiting is *not* why the actual motor output (in kW = torque*RPM/5252*745.7) is less than V*I.

My edit was 1 minute before I saw your post. Sorry about that. But I was looking for a reply from you and noticed the current trace. And on the time scale, yes, I see that, but you do not indicate the units. Are those hours?

And can I not take issue with posts you make? Yes, motor efficiency does account for difference between input (battery) power and output shaft power, but not the whole thing as you say.

podolefsky
15 May 2011, 1759
My edit was 1 minute before I saw your post. Sorry about that. But I was looking for a reply from you and noticed the current trace. And on the time scale, yes, I see that, but you do not indicate the units. Are those hours?

And can I not take issue with posts you make? Yes, motor efficiency does account for difference between input (battery) power and output shaft power, but not the whole thing as you say.

It's min:sec.

Sure, you can take issue. Just want to make sure we're actually discussing the main point and not just arguing.

So if it's not efficiency, and in the case that the controller isn't limiting (because it's not always), then what does account form the difference? I really don't know, want to learn.

lugnut
15 May 2011, 2301
Let's see what happens at 500 RPM. At this point the motor is seeing at least 67V and 500A. That should be 33.5 kW. But this motor is rated 80 ft-lb at 450A, so the power should be something like 80 ft-lb * 500 RPM / 5252 * 745.7 = 5.7 kW. Why isn't it 33.5 kW? Because the motor efficiency is about 20% at this point.

I think we're talking about the D&D motor which you posted the curve here:
Here's a datasheet that I constructed from a very fuzzy scan for a D&D ES-15-6. I translated it as best I could into excel.

873


You can see by that curve that the RPM at 80 ft lb is 1600 with 58volts to the motor. Let's forget about inductance and the mS range. It is impossible to have a lower RPM and a higher voltage (disregarding heating the motor to increase resistance) at that load. So if you see 500RPM at that load, I estimate you are seeing about 30 volts on the motor and motor efficiency in the neighborhood of 35 to 40 percent.

At low RPM (low motor voltage) and high load (high current and torque), motor efficiency does tank.

I hope this is back on track.

teddillard
16 May 2011, 0312
GREAT discussion, guys...

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/hard_pull_log.png

And Kyle this shows exactly what I was expecting on the other thread... about... gears and stuff. Note the battery current curve. :)

podolefsky
16 May 2011, 0921
I think we're talking about the D&D motor which you posted the curve here:
You can see by that curve that the RPM at 80 ft lb is 1600 with 58volts to the motor. Let's forget about inductance and the mS range. It is impossible to have a lower RPM and a higher voltage (disregarding heating the motor to increase resistance) at that load. So if you see 500RPM at that load, I estimate you are seeing about 30 volts on the motor and motor efficiency in the neighborhood of 35 to 40 percent.

At low RPM (low motor voltage) and high load (high current and torque), motor efficiency does tank.

I hope this is back on track.

I see what you're saying. On a motor dyno, you add load until you hit the load that gives you the max current, say 450A on the D&D. After that, you have to reduce voltage to get to lower RPM at the same current. 450A, 30V, and 40% efficiency works out just about right.

On the other hand, things seem to work a little differently when you're on a bike accelerating from a stop. The current and voltage curves above are for my bike going from a stop and accelerating with 100% throttle. Battery and motor current are nearly the same from the moment the throttle is on. That means the motor is seeing full pack voltage and about 500A. There is no point in there where the motor sees less than 95% of pack voltage, even with sag this is over 65V.

So at a minimum, the motor is getting 65V*500A=32.5 kW. But if it's putting out 80 ft-lb at 500 RPM, that's 5.7 kW. All I can come up with is that motor efficiency must be about 17% at that point.

That seem logical?

podolefsky
16 May 2011, 0921
GREAT discussion, guys...


And Kyle this shows exactly what I was expecting on the other thread... about... gears and stuff. Note the battery current curve. :)

What discussion? Link?

teddillard
16 May 2011, 0933
What discussion? Link?

...didn't want to take it off topic, but this one http://www.elmoto.net/showthread.php?1246-Brutus-s-5-speed-El-Moto-%28transmission-discussion%29/page3&highlight=transmission

Your plot of "Amps" does what I was trying to call "load".

"Sorry Ted, I didn't mean to avoid your question. I just don't understand your graph, mainly regarding load. I don't understand why you are plotting load on the left side of the graph. " (Thought it was Kyle... sorry)

(Oh wait, it was Kyle too: "but for me it is difficult to interpret. I am guessing you are displaying road load? why does that go down with speed, it should go up do to aero drag??")

podolefsky
16 May 2011, 0951
...didn't want to take it off topic, but this one http://www.elmoto.net/showthread.php?1246-Brutus-s-5-speed-El-Moto-%28transmission-discussion%29/page3&highlight=transmission

Your plot of "Amps" does what I was trying to call "load".

"Sorry Ted, I didn't mean to avoid your question. I just don't understand your graph, mainly regarding load. I don't understand why you are plotting load on the left side of the graph. " (Thought it was Kyle... sorry)

(Oh wait, it was Kyle too: "but for me it is difficult to interpret. I am guessing you are displaying road load? why does that go down with speed, it should go up do to aero drag??")

Ah, I see. That plot is actually buried in that (currently) 20 page long thread as well.

http://www.elmoto.net/showthread.php?1246-Brutus-s-5-speed-El-Moto-(transmission-discussion)&p=14167&viewfull=1#post14167

lugnut
18 May 2011, 1731
I see what you're saying. On a motor dyno, you add load until you hit the load that gives you the max current, say 450A on the D&D. After that, you have to reduce voltage to get to lower RPM at the same current. 450A, 30V, and 40% efficiency works out just about right.

On the other hand, things seem to work a little differently when you're on a bike accelerating from a stop. The current and voltage curves above are for my bike going from a stop and accelerating with 100% throttle. Battery and motor current are nearly the same from the moment the throttle is on. That means the motor is seeing full pack voltage and about 500A. There is no point in there where the motor sees less than 95% of pack voltage, even with sag this is over 65V.

So at a minimum, the motor is getting 65V*500A=32.5 kW. But if it's putting out 80 ft-lb at 500 RPM, that's 5.7 kW. All I can come up with is that motor efficiency must be about 17% at that point.

That seem logical?

Hi Noah,

I'm back and want to address this post of yours. The plot you show in post #64 starts at 41:02.7 and runs through 41:14.4, about 12 seconds. However, the first time stamps are 41:02.7 and 41:06.9, or 4.2 seconds apart. It is in this compressed time zone which the near vertical line exists and where the 500RPM point lies, although you do no show the RPM plot. This means that it is impossible to make a valid conclusion about the current or voltage at 500RPM.

What is needed is a plot with an expanded time scale of 1 or 2 seconds with RPM starting at zero time. After all, how long does it take you to accelerate to 500RPM from standstill at full throttle? And as far as transients, the mechanical time constant of the system is much greater than the electrical time constant, so for these studies, motor inductance is typically ignored.

podolefsky
18 May 2011, 1951
Hi Noah,

I'm back and want to address this post of yours. The plot you show in post #64 starts at 41:02.7 and runs through 41:14.4, about 12 seconds. However, the first time stamps are 41:02.7 and 41:06.9, or 4.2 seconds apart. It is in this compressed time zone which the near vertical line exists and where the 500RPM point lies, although you do no show the RPM plot. This means that it is impossible to make a valid conclusion about the current or voltage at 500RPM.

What is needed is a plot with an expanded time scale of 1 or 2 seconds with RPM starting at zero time. After all, how long does it take you to accelerate to 500RPM from standstill at full throttle? And as far as transients, the mechanical time constant of the system is much greater than the electrical time constant, so for these studies, motor inductance is typically ignored.

Thanks lugnut, I just learned something :)

It seems the Alltrax often pauses for a few sec when the current jumps - maybe the ADC needs to catch up?

I scanned through my data for a section that isn't missing a big chunk. Here it is. This is another run with the throttle full on. Just like you said, the controller is cutting back the throttle to limit output current. I guess the "throttle pos" data from the Alltrax is actually duty cycle, not necessarily the throttle input.

It's interesting that the limiter cuts in at 450A (which is the Alltrax's limit), but it keeps increasing to over 500A. Also makes me happy that even at 500A battery side, the cells don't drop below 2.8V/cell. (This was at about 80% SOC).

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/alltrax_3rd_run.png

lugnut
18 May 2011, 2142
Thanks lugnut, I just learned something :)

It seems the Alltrax often pauses for a few sec when the current jumps - maybe the ADC needs to catch up?

I scanned through my data for a section that isn't missing a big chunk. Here it is. This is another run with the throttle full on. Just like you said, the controller is cutting back the throttle to limit output current. I guess the "throttle pos" data from the Alltrax is actually duty cycle, not necessarily the throttle input.

It's interesting that the limiter cuts in at 450A (which is the Alltrax's limit), but it keeps increasing to over 500A. Also makes me happy that even at 500A battery side, the cells don't drop below 2.8V/cell. (This was at about 80% SOC).

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/alltrax_3rd_run.png

Hallelujah :-) Thanks for finding the data to confirm it. It also shows about 30A battery current at near zero RPM, doesn't it? This is what I've been trying to get across to you for some time now. Throttle position is a command which is overridden by the current limit (and sometimes a ramp). Sorry I wasn't able to express it well before. I never intended to argue, just to set things straight.

podolefsky
18 May 2011, 2228
I don't mind arguing - as long as it's towards learning. Learning accomplished. :cool:

I always understood that duty cycle could be overridden by current limit, I just didn't realize it was current limiting. In hindsight, now I see that it had to be.

podolefsky
21 May 2011, 1351
Was just looking into the Zero. I didn't know this, their pack is 58V, 70Ah, which explains why they have 98:28 gearing (3.5:1) and have a top speed of 67 mph. I believe the 2011's have an Agni-like motor, but not actually Agni, maybe Lemco?

jazclrint
12 June 2011, 1206
I have no idea how much work this is for you but thank you for doing it. Any chance you could put up the graph for a PERM 156 W motor?

From what it looks like the dual agni setup is the hot setup for the 75 class. Ay least until someone figures out how to keep the AC20s cool. :D

podolefsky
12 June 2011, 1218
It's not too much work, I just need the data for the motor. Got a link for me?

jazclrint
12 June 2011, 1241
http://www.perm-motor.de/fileadmin/users_upload/pdf/PMS_Motoren-Generatoren/Datenblaetter_PMS_Motoren-PGS_Generatoren_Englisch/PMS156_W-TD_E_technical_specs.pdf

podolefsky
12 June 2011, 1335
Thanks. That data is a little sparse - they only give torque at 3 rpm values. They also say 80 Nm up to 30% of RPM range, so I could use that to fill out the curve. But I'll still have to guess about values across a lot of the range.

These values are also with water cooling, and apparently power handling is lower with air cooling.

Interesting motor, though. I'd never seen these PERMs before. Let me see what I can do with the data they have.

podolefsky
12 June 2011, 1402
From what it looks like the dual agni setup is the hot setup for the 75 class. Ay least until someone figures out how to keep the AC20s cool. :D

yes and no. The dual Agni is more complicated, it needs a controller capable of putting out enough current (or voltage) for two motors. The AC-20 curve is at 96V, but it will take up to 130V so there is more power in there.

Comparing the two curves, the thing the AC-20 has going is that the torque and power curves keep going past 80 mph (in the plot on the left), while the Agni's fall off quickly at that point.

The heat issues do seem to put a cramp on the AC, but if it weren't for that it should beat the dual Agni setup by quite a bit. (At least, according to the data I've been able to find).

jazclrint
12 June 2011, 1634
Thanks. That data is a little sparse - they only give torque at 3 rpm values. They also say 80 Nm up to 30% of RPM range, so I could use that to fill out the curve. But I'll still have to guess about values across a lot of the range.

These values are also with water cooling, and apparently power handling is lower with air cooling.

Interesting motor, though. I'd never seen these PERMs before. Let me see what I can do with the data they have.

Yeah, that's all I've been able to find on those motors, and I have no intrest in air cooled anything. From all the problems it seemed the ACs had last year (from what little I've gleamed from Frodus) water cooled seems the way to go. Also BrammoBrian had suggested the PERM 150s which they used in the '09 IoM TT to their 3rd place. The 156 is just a bit bigger. I'd want to pair it with a water cooled controler. Anyone know how many of those are around?

podolefsky
12 June 2011, 1840
Yeah, that's all I've been able to find on those motors, and I have no intrest in air cooled anything. From all the problems it seemed the ACs had last year (from what little I've gleamed from Frodus) water cooled seems the way to go. Also BrammoBrian had suggested the PERM 150s which they used in the '09 IoM TT to their 3rd place. The 156 is just a bit bigger. I'd want to pair it with a water cooled controler. Anyone know how many of those are around?

Yeah, at race speed heat does seem like a problem for the air cooled AC.

I'll do my best with the curves for the Perm. Now you have me interested - is the 156 W available to consumers?

Seems like controllers are less prone to overheating, and at worst you could put on a large water cooled heat sink. Metric Mind has some water cooled AC controllers...not cheap. And would depend on if they are a good match for the Perm.

http://www.metricmind.com/

jazclrint
12 June 2011, 1907
Yeah, at race speed heat does seem like a problem for the air cooled AC.

I'll do my best with the curves for the Perm. Now you have me interested - is the 156 W available to consumers?http://www.metricmind.com/

Someone was selling one on V is for Voltage. It sounded like a vendor offering a clearence price. But other than I do not know.