# WarP-9 RPM vs. Voltage at various currents



## major (Apr 4, 2008)

Tesseract said:


> The basic rule of thumb is that you need 50V per 1000 RPM at 1000A. That decreases to around 36V/1000 RPM at 400A. The incremental voltage between those incremental currents gives you the total resistance of the system, or 14V/600A = 23.3 milliohms.


Hi Tesser,

I don't believe this calculated resistance is accurate. Although the motor is likely into saturation at 400A, there will be some increase in flux from 400 to 1000A, therefore an increase in generated voltage. The method you have used for resistance calculation is only valid at stall where the Eg = zero.

Should you specify "motor" current for those who may assume otherwise?

I do enjoy your graph, and data 

Regards,

major


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## Tesseract (Sep 27, 2008)

major said:


> ...The method you have used for resistance calculation is only valid at stall where the Eg = zero.


Yep. In retrospect that was totally obvious. I thought the calculated resistance seemed reasonable for the motor + cables and didn't give it much additional thought. I added some comments to my original post to correct it without removing the incorrect parts.




major said:


> Should you specify "motor" current for those who may assume otherwise?
> 
> I do enjoy your graph, and data


You know exactly why I did this, don't you? 

Next I'll try to figure out when the WarP-9 goes into saturation. My plan is to hold the RPM constant (at, say, 2500 RPM) while increasing dyno load such that motor current increases in, say, 100A increments.

Sound reasonable? IIRC you once stated that many motors are approaching saturation at their S2-60 current rating... Correct or no?


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## jtgreeson (Aug 14, 2009)

Jeffrey,

That's enlightening. Your graph gives me a little more understanding of what's happening to my WarP9.

Thanks for sharing your data.


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## major (Apr 4, 2008)

Tesseract said:


> You know exactly why I did this, don't you?


To show off your 1000A controller 


> Next I'll try to figure out when the WarP-9 goes into saturation. My plan is to hold the RPM constant (at, say, 2500 RPM) while increasing dyno load such that motor current increases in, say, 100A increments.
> 
> Sound reasonable?


Not the usual motor test curve, but would yield interesting data, so reasonable? Sure.



> IIRC you once stated that many motors are approaching saturation at their S2-60 current rating... Correct or no?


For a series wound, class H, vented fan cooled motor, yeah, kind of, probably, maybe, wouldn't bet my house on it, but for the lack of better data, sure why not?

But you are correct, I did say that


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## Guest (Mar 31, 2011)

> You know exactly why I did this, don't you?


Cause maybe your pissed at someone.


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## Guest (Mar 31, 2011)

What does it all mean when it's in a car and your going pedal to the metal? Won't the Soliton1 do better than 1K. Question, when you do your bench testing and you hit your motor limit of 1K what is your battery current output? It should be at or near the same if the duty cycle is at or near 100%. Can you show that? Will you?


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## Tesseract (Sep 27, 2008)

gottdi said:


> What does it all mean when it's in a car and your going pedal to the metal?


Depends what the RPM of the motor is, simple as that. The throttle controls motor torque, not motor power, in a Soliton1 (same as pretty much every other controller for EVs). Our vehicles would be damn near undriveable if anything besides torque control was used.



gottdi said:


> Won't the Soliton1 do better than 1K.


No. Why would you expect a 1000A controller to deliver more than 1000A?



gottdi said:


> Question, when you do your bench testing and you hit your motor limit of 1K what is your battery current output?


As above, it depends on the motor RPM and the battery pack voltage. The controller adjusts the duty cycle as needed to maintain a desired motor current (ie - pulling power, or torque) regardless of motor RPM, up until the point at which motor voltage = battery voltage. If RPM continues climbing from that point on then current must drop a corresponding amount. There is no escaping this reality any more than putting a windmill on my car won't recharge my battery pack while driving.



gottdi said:


> It should be at or near the same if the duty cycle is at or near 100%. Can you show that? Will you?


Correct, battery current = motor current at 100% duty cycle, and we HAVE shown that, Pete. We are pretty much the ONLY people that have ever shown that. Do you see dyno charts from any other controller manufacturer here on this forum, or any other for that matter?


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## Guest (Mar 31, 2011)

> Do you see dyno charts from any other controller manufacturer here on this forum, or any other for that matter?


No, yours is the only so far.


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## Tesseract (Sep 27, 2008)

It appears that the WarP-9 goes into saturation (changes over from torque being proportional to the square of current to being linear) at 400A. The direct pressure readings from our hydraulic dyno:

200A 1014 rpm 24.7V <200 psi <- too low to read on gauge
250A 1010 rpm 28.7V 325 psi
300A 1010 rpm 31.6V 500 psi
350A 1015 rpm 34.4V 625 psi
400A 1008 rpm 37.6V 850 psi
450A 1015 rpm 39.0V 900 psi

(HP = RPM x PSI x 0.0000182)

I couldn't hold ~1000 rpm at 500A with the dyno set to maximum load but the change in psi per 50A increment has already dropped radically so I feel pretty good about the results.


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## MN Driver (Sep 29, 2009)

Tesseract said:


> You know exactly why I did this, don't you?


I do. It shows that the Warp 9, and likely pretty much any series DC requires a very high battery voltage to get the RPM needed for 1000 amps of battery current to be matched. It seems it could possibly be enough to add another to your count of motors versus Soliton's. I only recently realized that a large portion of the EV community doesn't understand the dynamics of back EMF and the relationship of motor voltage and motor current being different than battery current. Oh well, its something that will be understood soon enough.

I am very interested at what you find the amperage saturation point of the Warp 9 to be at. Would this be the most efficient point of operation, or would RPM/voltage be a larger factor? I'm looking to operate at the most efficient point possible when I complete my conversion and am thinking that the Warp 9 might be too big for a highway cruising ~2500 pound car to get maximum efficiency but I could be wrong, I'm not sure on the specifics of efficiency and its what I'm trying to figure out right now. I wouldn't mind flying down the road with a bigger motor than I need though and it seems the differences may be negligible.


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## Tesseract (Sep 27, 2008)

MN Driver said:


> ...I only recently realized that a large portion of the EV community doesn't understand the dynamics of back EMF and the relationship of motor voltage and motor current being different than battery current....


Yep - and it's depressing how vocal some are in their ignorance. Not that I'm the least bit bitter, angry or frustrated... 



MN Driver said:


> I am very interested at what you find the amperage saturation point of the Warp 9 to be at. Would this be the most efficient point of operation, or would RPM/voltage be a larger factor?


I just posted this data around the same time as you posted, but saturation seems to occur around 400A, and it appears to be rather abrupt as major said, rather than a "gentle bend" as I predicted.

I'll defer to major on your second question, but I would *expect* for the RPM per volt ratio to go up quite a bit once in saturation because the ratio of flux per amp went down quite a bit.


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## major (Apr 4, 2008)

Tesseract said:


> It appears that the WarP-9 goes into saturation (changes over from torque being proportional to the square of current to being linear) at 400A. The direct pressure readings from our hydraulic dyno:
> 
> 200A 1014 rpm 24.7V <200 psi <- too low to read on gauge
> 250A 1010 rpm 28.7V 325 psi
> ...


I'll try this.









I guess I pasted it in here  Ain't the smoothest sat curve I ever saw, but not bad. Looks like it just starts to saturate about 200A and continues to "knee" over thru 400A. Which one would expect with straight sided slots. Also, this isn't a true representation of the saturation characteristics because we have resistive voltage drops mixed into the voltage measurements. So we're not looking at the generated voltage alone. This is why saturation curves are most often taken at no load.

But interesting data Tess  Not sure what good it does anybody 

major


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## major (Apr 4, 2008)

MN Driver said:


> I am very interested at what you find the amperage saturation point of the Warp 9 to be at. Would this be the most efficient point of operation, or would RPM/voltage be a larger factor? I'm looking to operate at the most efficient point possible when I complete my conversion and am thinking that the Warp 9 might be too big for a highway cruising ~2500 pound car to get maximum efficiency but I could be wrong,


Hi MN,

I don't think you need to worry about saturation when considering motor efficiency in your context. Maybe if you were over exciting a SepEx or something like that. But "cruise" efficiency will best be maximized by choosing the proper ratio so the loading and RPM are "right" for the motor. And if the "cruise" power level is under the rated motor power, it means the motor 1) should not overheat and 2) should run efficiently. 

Until you're very close to no load, if your RPM is reasonable, the larger motor should be more efficient than a smaller motor because the iron is stressed less and winding resistance is less. There may be a little more friction and windage with the larger motor, but the previously mentioned factors should offset that. Also the larger motor should run cooler, and cooler copper has less resistivity.

Regards,

major


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## major (Apr 4, 2008)

MN Driver said:


> It shows that the Warp 9, and likely pretty much any series DC requires a very high battery voltage to get the RPM needed for 1000 amps of battery current to be matched.


IMO, it is the opposite. When you have a high voltage battery, your controller will likely always be reducing voltage to the motor and therefore motor current will always be higher than battery current (except when = 0). Take Tesser's last test there. If you extrapolate you would see a 1000A at maybe 45 to 50 volts. So if one had a 48V or lower V battery, the controller would go 100% dc at the 1000A CL whereas if you had a much higher voltage battery, it would not. Of course that was at 1000 RPM. So you could double the voltage at 2000 RPM and see 100% dc at CL or triple V (to 144) and see 100% dc at CL for 3000RPM. But if you have a 300V battery, 100% dc at CL would occur at or above 6000RPM, so your battery current would never equal motor current (except at 0 dc) because you're well beyond the zorch limit 

Well, that's pretty confusing I hope you can follow it.

major


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## Guest (Apr 1, 2011)

Just a bit for all those who have decided to NEVER go back to see what's up with Jack.

Jack Rickard said...
My my my my my. Such a tremendous number of very strongly held opinions. Well, well, well, well.... 

I'm having a very happy end to a marvelous day thank you. And truly delighted to meet the EV Whisperer, Mr. Sebastien Bourgouis. We had a lovely day, and thanks to his very rapid analysis, we were drinking whiskey and partying lock Rock Stars by two in the afternoon.

Hate to give away this week's show, but I can't read any more of this battery amp/motor amp theory nonsense that of course never was and never could have been the issue. The motor loading issue was interesting, but as I noted, rather paints us into a corner of never getting well even with a nuclear power plant driving a 12000 lb motor.

Apparently, if the calibration of the hall effect sensor INSDIE the Soliton is off, it is quite possible for the Soliton to be entirely convinced it IS putting out 1000 amps, while the rest of the real world, including the fat kid, is kind of convinced it's more like 722. In that event, the device has a cunning strategy for self preservation, it simply limits itself to 1000 amps, even if they are not real.

If you replace that unit with a DIFFERENT Soliton1 from the magic bag, that does NOT have this calibration issue, guess what you get on the very first test drive?

A TOTALLY SMOKED Stage 2 clutch and pressure plate assembly. I mean NASTY SMELLING and pretty much destroyed.

Throught the mircacle of time lapse photography, we should have a new CB Performance kevlar double sided ceramic trick double throw me down stage 4 unit with 4000 lb pressure plate by AM tomorrow.

0-60 times to follow.

Quite a relief. And quite an impressive show on the first run.

Jack Rickard
March 31, 2011 11:10 PM


More is posted on the blog for you all to read.


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## jddcircuit (Mar 18, 2010)

Tesseract said:


> 200A 1014 rpm 24.7V <200 psi <- too low to read on gauge
> 250A 1010 rpm 28.7V 325 psi
> 300A 1010 rpm 31.6V 500 psi
> 350A 1015 rpm 34.4V 625 psi
> ...


Does this mean that you are spending about 1kW per HP? Would that equate to a little over 60% conversion efficiency? I am interested in trying to gather similar data for another motor-controller combination to compare efficiencies.


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## major (Apr 4, 2008)

jddcircuit said:


> Does this mean that you are spending about 1kW per HP? Would that equate to a little over 60% conversion efficiency?


Hi jdd,

One HP = 746 watts. So Power out / Power in = 746 / 1000 = 74.6 %. Not too shabby for efficiency of controller, motor and pump at these loads, RPM and voltage. 

I did not calculate the power out, just commenting on your 1kw/HP statement.

Regards,

major


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## jddcircuit (Mar 18, 2010)

major said:


> Hi jdd,
> 
> One HP = 746 watts. So Power out / Power in = 746 / 1000 = 74.6 %. Not too shabby for efficiency of controller, motor and pump at these loads, RPM and voltage.
> 
> ...


thanks. I was calculating wrong.


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## Tesseract (Sep 27, 2008)

major said:


> IMO, it is the opposite. When you have a high voltage battery, your controller will likely always be reducing voltage to the motor and therefore motor current will always be higher than battery current...


Loathe as I am to disagree with you, I think that it's worth pointing out that few battery packs appreciate having 1000A sucked out of them (much less the 2000A the Z2K could do), but most cars would benefit from having full torque beyond 3000 rpm, so I'd say it is definitely worthwhile to have more than 200V on tap even with an advanced motor like a WarP-9. 

'Course, I am somewhat biased here... 




gottdi said:


> Just a bit for all those who have decided to NEVER go back to see what's up with Jack.....


While I obtained the data reported in this thread to support the argument that Jack Rickard had run out of voltage, I didn't start this thread as a rebuttal to Jack - it was strictly to share the data because I figured others would find it valuable. 

It turns out Jack was right all along, but he never did tell me what the motor amps were. Seb had to fly up there to make that measurement in person, but then he was able to diagnose the likely culprit immediately. 

We don't claim to be perfect, and we don't claim our products are perfect, but we are honorable people so when something goes wrong we try our damnedest to make things right.


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## major (Apr 4, 2008)

Tesseract said:


> Loathe as I am to disagree with you, I think that it's worth pointing out that few battery packs appreciate having 1000A sucked out of them (much less the 2000A the Z2K could do), but most cars would benefit from having full torque beyond 3000 rpm, so I'd say it is definitely worthwhile to have more than 200V on tap even with an advanced motor like a WarP-9.


You missed my point. What I was trying to say is that if you have a battery voltage higher than the maximum voltage your motor can tolerate, your battery current will never equal your motor current because your motor controller will always be less than 100% dc. Not that that is a bad thing , just contrary to what I thought MN said. 

But on the other hand, if you have a 1000 pound battery pack capable of 150 kW, what difference to that battery is it if you configure the cells for 300V, 500A or 150V, 1000A assuming your motor is good for a maximum of 150V? Let's just neglect sag for the example


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## MN Driver (Sep 29, 2009)

major said:


> You missed my point. What I was trying to say is that if you have a battery voltage higher than the maximum voltage your motor can tolerate, your battery current will never equal your motor current because your motor controller will always be less than 100% dc. Not that that is a bad thing , just contrary to what I thought MN said.
> 
> But on the other hand, if you have a 1000 pound battery pack capable of 150 kW, what difference to that battery is it if you configure the cells for 300V, 500A or 150V, 1000A assuming your motor is good for a maximum of 150V? Let's just neglect sag for the example


I worded things badly and it was probably hard to interpret. I agree with what both of you said. I'm all for raising voltage to extract more performance, I'm glad to see have controllers that let us go to 200 volts and beyond.


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## MN Driver (Sep 29, 2009)

I also noticed there were enough people asking Jack to show motor current, yet since he didn't show it, it was clear that the easy answer wasn't being provided that would have made it immediately clear to all of us. It was funny to watch the blog comments go every direction though.


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## jddcircuit (Mar 18, 2010)

I watched the Jack Rickard video. I am surprised that he felt the controller was limiting his current without providing any evidence about the controller duty cycle at that max rpm. If the controller was at 100% duty then obviously something else is limiting the current.

I am still unclear on one item.
Does the battery see the full 1000Amp peak during the high cycle of the of the switching when the controller is limiting current. I understand that the average battery current is lower than the motor current when lower than 100% duty. If the battery does see these high current peaks for brief instances then does that play into battery pack design? For example, does going higher voltage and lower duty cycle really stay below my battery current limits or do I need to consider those peak current values?

Thanks
JDD


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## Guest (Apr 3, 2011)

Go read through the long blog. You will understand if you listen. Might need to rewatch the video too.


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## jddcircuit (Mar 18, 2010)

gottdi said:


> Go read through the long blog. You will understand if you listen. Might need to rewatch the video too.


I was hoping to not have to read a long blog or watch the video again. I did fast forward through a lot of it. Ok, I will search for the blog.


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## jddcircuit (Mar 18, 2010)

gottdi said:


> Go read through the long blog. You will understand if you listen. Might need to rewatch the video too.


I read through the blog. It sounds like they concluded a miscalibrated current sensor and the controller was still limiting the current but that was not my point.

My point was, the next time an attempt to monitor battery current to see what type of power can be delivered might also monitor the PWM duty cycle of the controller. If the controller never gets to 100% duty then it is obvious that the controller is still limiting the current for whatever reason. If the duty cycle is 100% and you are not getting the battery current that you expect then we can talk about loading. That is all. Just a piece of data that may have helped track down where the limiting factor was.


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## Qer (May 7, 2008)

jddcircuit said:


> If the controller never gets to 100% duty then it is obvious that the controller is still limiting the current for whatever reason. If the duty cycle is 100% and you are not getting the battery current that you expect then we can talk about loading.


Yes, correct.


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## Guest (Apr 3, 2011)

> If the duty cycle is 100% and you are not getting the battery current that you expect then..........


 Still continuing the drama I see. The problem was found and corrected. End of story. It's not about you. Its about finding out the truth. Truth is there was a problem and it was noted and fixed. It's everyone else that dramatized the situation. Time to move along kiddies. 

Next?


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## jddcircuit (Mar 18, 2010)

gottdi said:


> Still continuing the drama I see. The problem was found and corrected. End of story. It's not about you. Its about finding out the truth. Truth is there was a problem and it was noted and fixed. It's everyone else that dramatized the situation. Time to move along kiddies.
> 
> Next?


Please do not quote something I said and then imply something about drama or a situation. I am not involved in any situation. I am only exchanging on this forum to participate in the learning process. I have a lot to learn and I apologize if I opened a wound.


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## Guest (Apr 4, 2011)

It's old news now and you can still learn but the issue has been resolved and there is no need to keep the drama going. That's all. No wounds opened. Time to move along now.


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> It appears that the WarP-9 goes into saturation (changes over from torque being proportional to the square of current to being linear) at 400A. The direct pressure readings from our hydraulic dyno:
> 
> 200A 1014 rpm 24.7V <200 psi <- too low to read on gauge
> 250A 1010 rpm 28.7V 325 psi
> ...


Hi Jeffery,
I compared these numbers to a field map that I generated from Zilla dumps from the Electrabishi. Excellent agreement!
Gerhard


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> Hi Jeffery,
> I compared these numbers to a field map that I generated from Zilla dumps from the Electrabishi. Excellent agreement!
> Gerhard


Thanks for doing that data check, Gerhard. I'm hoping I'll be able to test the new Kostov motors at both a fixed 600A and 1000A sometime in the near future. Since I'm in the mood to acquire semi-practical data these days, any requests?


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## Batterypoweredtoad (Feb 5, 2008)

I would be interested in knowing how much higher the saturation point is on larger motors and if the saturation point of a motor can be estimated by something as simple as weight, etc...


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## Bowser330 (Jun 15, 2008)

_Major:"But if you have a 300V battery, 100% dc at CL would occur at or above 6000RPM, so your battery current would never equal motor current (except at 0 dc) because you're well beyond the zorch limit"_

Very interesting...what _IS_ the zorch limit of an interpoled 11" HV Kostov?


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> Thanks for doing that data check, Gerhard. I'm hoping I'll be able to test the new Kostov motors at both a fixed 600A and 1000A sometime in the near future. Since I'm in the mood to acquire semi-practical data these days, any requests?


Hi Jeffrey. First I should spell your name correctly .
Glad you are in that mood! Here is my request:

1. Set your dynomometer at maximum load.
2. Set the motor current to 50 amps.
3. Run at full throttle.
4. Reduce load slowly until say, 3000 RPM.
5. Turn off and save log file.
6. Repeat 1-5 for 100, 150, 200... amps.

For each set observe a straight line when plotting motor voltage vs. RPM
Note the projected value of voltage at zero RPM [= stall voltage]
Plot stall voltage vs. current.
The projected stall voltage at zero current is the brush loss.
The slope gives the resistance

Set the dyno at a resistance which will allow max RPM at max current.
Advance the throttle slowly from zero to max and then slowly back to zero.
From this log, we can extract the saturation curve and hysteresis.

Monitor coil temperature occasionally.

Repeat for various motors.

Yours, 
Gerhard


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## Bowser330 (Jun 15, 2008)

GerhardRP said:


> Hi Jeffrey. First I should spell your name correctly .
> Glad you are in that mood! Here is my request:
> 
> 1. Set your dynomometer at maximum load.
> ...


why only to 3000rpm?


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## GerhardRP (Nov 17, 2009)

Bowser330 said:


> why only to 3000rpm?


Higher wouldn't hurt, but those measurements are meant to get resistance and brush voltage which come from the zero RPM extrapolation of voltage.
Gerhard


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> *2. Set the motor current to 50 amps.
> 3. Run at full throttle.*


Aren't those two mutually exclusive or am I misunderstanding what you are asking here?



GerhardRP said:


> ...
> The projected stall voltage at zero current is the brush loss.
> The slope gives the resistance


How about I just measure the actual voltage drop across the field and armature resistances with my 0-200A constant current load? That's bound to be a lot more accurate than the current and voltage measurement circuits inside the Soliton1 (5% for I and 1% for V).



GerhardRP said:


> Set the dyno at a resistance which will allow max RPM at max current.
> Advance the throttle slowly from zero to max and then slowly back to zero.
> From this log, we can extract the saturation curve and hysteresis.
> 
> Monitor coil temperature occasionally.


Just ramp throttle up to max then back down again?

BTW - the pump on our dyno starts cavitating at 3500 rpm so that does set an upper limit on how much power we can pump into a single motor (we run two WarP-9's in series for testing controllers).



GerhardRP said:


> Repeat for various motors.


It is a LOT of work to change motors on the dyno these days, so, it might be awhile before I can do these tests on anything besides a WarP-9, ok?


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> Aren't those two mutually exclusive or am I misunderstanding what you are asking here??


I mean set the potbox to max, let the controller go to current limit. 



> How about I just measure the actual voltage drop across the field and armature resistances with my 0-200A constant current load? That's bound to be a lot more accurate than the current and voltage measurement circuits inside the Soliton1 (5% for I and 1% for V).?


That could work, but I am trying to set up a protocol where any owner with a logging controller could analyse their EV. There it would be set current limit then floor it in maybe 3rd. [ actually, I would like to know the field and armature resistances separately]



> Just ramp throttle up to max then back down again??


Yes



> BTW - the pump on our dyno starts cavitating at 3500 rpm so that does set an upper limit on how much power we can pump into a single motor (we run two WarP-9's in series for testing controllers).
> 
> It is a LOT of work to change motors on the dyno these days, so, it might be awhile before I can do these tests on anything besides a WarP-9, ok?


 No rush. do others when they are mounted on the dyno for other tests.

Gerhard


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> I mean set the potbox to max, let the controller go to current limit.


I misunderstood you, then... You basically want to regulate motor current at 50A (etc.) with the shaft stalled. No problem. BTW, I think our dyno can stall the motor up until around 150A.



GerhardRP said:


> That could work, but I am trying to set up a protocol where any owner with a logging controller could analyse their EV. There it would be set current limit then floor it in maybe 3rd. [ actually, I would like to know the field and armature resistances separately]


Ok, that's what I thought. Heed my warning about the relative inaccuracy of the voltage and current measurements inside the typical motor controller (mine included). After all, it's a motor controller, not a piece of test equipment. You'll either need a rather large data set from a given controller model or need to verify the measurements against more accurate test equipment to have confidence in your extrapolations from controller-reported data (once again, mine included).

Another caveat: the motor controller will only be able to measure the *total resistance* of the motor loop. If the cables to the motor are more than a foot or two in length they will be a significant portion of the total resistance measured. So obviously what I need to do is measure the resistance of the field and armature separately with my constant current source then compare that to what is inferred from a Soliton1 or Junior.

I have no idea what you meant when you said "set current limit then floor it in maybe 3rd", though...


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> I misunderstood you, then... You basically want to regulate motor current at 50A (etc.) with the shaft stalled. No problem. BTW, I think our dyno can stall the motor up until around 150A.


Yes,but actually, I think the motor has to be turning to get at the brush voltage.


> Another caveat: the motor controller will only be able to measure the *total resistance* of the motor loop. If the cables to the motor are more than a foot or two in length they will be a significant portion of the total resistance measured. So obviously what I need to do is measure the resistance of the field and armature separately with my constant current source then compare that to what is inferred from a Soliton1 or Junior.


Again, the effort is aimed at a total system analysis rather than motor specs [but that would be good too].


> I have no idea what you meant when you said "set current limit then floor it in maybe 3rd", though.


The attached file shows data derived from Zilla dumps from Mike Willmon's Electrabishi. He set various limits on the controller and then ran various max acceleration trials. I extracted brush voltage and combined resistance from these measurements.
Gerhard


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> Yes,but actually, I think the motor has to be turning to get at the brush voltage.


This data seems like it would only be useful for a motor design engineer... how would the average DIY'er use this?


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> This data seems like it would only be useful for a motor design engineer... how would the average DIY'er use this?


Well when I am done, I will be able to provide a simple means of calculating expected motor voltage, torque and power output given motor current and RPM. This could be included in various EV model programs to figure out gear ratios and the like. The second use would be a live display using the controller data stream to monitor system integrity; it could recognize brush deterioration, loose connections and impending zorch.
Gerhard


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## Tesseract (Sep 27, 2008)

WarP-9 Field resistance: 3.8 mΩ
WarP-9 Armature resistance: 8.6 mΩ

Measured via 4-terminal (Kelvin) method with the shaft stalled at 40A and 100A to verify correlation. Resistance was the same at both currents. So, total resistance of the motor (minus the field to armature jumper) is 12.4 mΩ. 

I previously calculated a total motor loop resistance (ie - including the cables between controller and motor on our dyno setup) of 23 mΩ which despite major's protests strikes me as perfectly reasonable...


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## major (Apr 4, 2008)

Tesseract said:


> despite major's protests strikes me as perfectly reasonable...


Always on my case 

Actual armature resistance must be measured without brushes in circuit. It is likely very close to the field resistance. Not over two times. 

But WTH, a few milliohm here or there 

major


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> I previously calculated a total motor loop resistance (ie - including the cables between controller and motor on our dyno setup) of 23 mΩ which despite major's protests strikes me as perfectly reasonable...


Great..
Did you (or could you) measure the actual cable losses, or tell us the length and spec of the cables?
Gerhard


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## gor (Nov 25, 2009)

guys, can you post Warp9 test data? 
on Electrabishi's site and threads all links with data - broken
just simple torque/a/v/rpm data - the only one i could find - curves at 72v on netgain site
thank you


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## Tesseract (Sep 27, 2008)

major said:


> Actual armature resistance must be measured without brushes in circuit. It is likely very close to the field resistance. Not over two times.


Yeah, it makes sense that the resistances of the field and armature should be nominally the same, but seems to me the motor won't work that well without the brushes present so I guess I don't see the point in trying to measure the armature resistance alone - sans brushes, that is.

Also, wouldn't I have to take the motor apart and connect up several armature windings in parallel to measure the armature resistance because each brush contacts at least two comm bars at a time and there two brush pairs present?



GerhardRP said:


> Great..
> Did you (or could you) measure the actual cable losses, or tell us the length and spec of the cables?
> Gerhard


You mean, actually measure the cable resistance, rather than calculate it by subtracting the 12.4 mΩ of the motor from the previously calculated 23 mΩ of the motor loop?


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## major (Apr 4, 2008)

Tesseract said:


> Yeah, it makes sense that the resistances of the field and armature should be nominally the same, but seems to me the motor won't work that well without the brushes present so I guess I don't see the point in trying to measure the armature resistance alone - sans brushes, that is.
> 
> Also, wouldn't I have to take the motor apart and connect up several armature windings in parallel to measure the armature resistance because each brush contacts at least two comm bars at a time and there two brush pairs present?


Hi Tesser,

No, you can measure armature resistance (Ra) with the armature in place. Used to do it all the time when rating motors to determine armature temperature from the change in resistance. We would lift the brushes off the comm surface (tricky with a hot motor) and put the bridge probes on bars 90º apart. With the type of armature winding (simplex wave) on that motor, this gives a true reading of Ra.

Once you boil it down to the actual armature and field resistance, you're stuck with what to about the brushes. It is a voltage drop dependent on current and speed as well as temperature, film and seat condition, humidity and sunspot activity You don't even want to know how brush drop is measured 

Regards,

major


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## maxvtol (Nov 11, 2009)

Tesseract said:


> It appears that the WarP-9 goes into saturation (changes over from torque being proportional to the square of current to being linear) at 400A. The direct pressure readings from our hydraulic dyno:
> 
> 200A 1014 rpm 24.7V <200 psi <- too low to read on gauge
> 250A 1010 rpm 28.7V 325 psi
> ...


If you plug in Rickard's dyno results with original Soliton and the replacement with your data above, you get the chart below for maximum torque. Does this look right? And how much will voltage affect the maximum torque?


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## ev1234me (Apr 16, 2011)

Hi everyone,

I am new here and have been trying to understand the different concepts of EV motors by reading through some of the posts on this forum.

I too am interested in understanding how voltage and amperage through the Warp 9 motor are related to Torque output and RPM. The reason I am trying to figure this out is to be able to gear the car most effectively.

I am getting stuck with the following and was hoping someone could help me:

I get that as RPM increases, Torque decreases. So by using Torque=(amps*volts*7)/rpm I worked out a quick table for the Warp 9 with 1000A, 170V @70% eff. to the motors max RPM.

*RPM * *-> Torque*
500 - 1666 ft.lbs
1000 - 833 ft.lbs
1500 - 555 ft.lbs
2000 - 416 ft.lbs
2500 - 333 ft.lbs
3000 - 277 ft.lbs
3500 - 238 ft.lbs
4000 - 208 ft.lbs
4500 - 185 ft.lbs
5000 - 166 ft.lbs
5500 - 151 ft.lbs

Now at 1000A it was said that approx each 50v applied equals 1000rpm. So if the Warp 9 saw 170V then RPM = 3400.

So my questions are:

1) What does the Torque vs RPM curve look like up to 3400RPM? Is it similar to the chart above?

2) What happens after 3400RPM? Does Torque drop off much faster than the chart above? Will motor spin past 3400RPM with 170V?

Thanks so much.


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## major (Apr 4, 2008)

ev1234me said:


> I get that as RPM increases, Torque decreases. So by using Torque=(amps*volts*7)/rpm I worked out a quick table for the Warp 9 with 1000A, 170V @70% eff. to the motors max RPM.
> 
> *RPM **-> Torque*
> 500 - 1666 ft.lbs
> ...


Hi ev,

Nope, that doesn't work  And with a WarP9, you'd need like 6000 Amps  to get 1666 lb ft of torque. 

I don't know where you came up with the equation " Torque=(amps*volts*7)/rpm ", but it is incorrect. The basic equation relating power to torque and speed is HP = (RPM * lb ft) / 5252. One HP = 745.6 Watts. And of course Watts = Volts * Amps. But all that is basic physics and doesn't describe motor characteristics.

With series wound motors like the WarP9, torque is dependent on current and RPM doesn't play into the relationship. Trying to relate torque and RPM for the motor, you need to use the motor performance characteristic curve or have a very detailed model and the appropriate complex equation set.

Regards,

major


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## ev1234me (Apr 16, 2011)

Hi Major,

Thanks for replying.

I got the formula from the following thread:
http://www.diyelectriccar.com/forums/showthread.php/using-clutch-disc-measure-torque-34326.html

So I am guessing that the Torque for a Warp 9 motor @ 1000A (say 230 ft.lbs) would remain constant from 0-3400RPM @ 170V (assuming 50V per 1000RPM). Then Torque would start to drop off at a certain rate between 3400-5500RPM.

Trying to figure out how fast that rate would be on the Warp 9. Didn't have much luck trying to extend the motor performance characteristic curve.


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## GerhardRP (Nov 17, 2009)

You should go to http://jackrickard.blogspot.com/2011/04/graphs-is-always-greener.html look for the graphs down the page.
Gerhard


ev1234me said:


> Hi Major,
> 
> Thanks for replying.
> 
> ...


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## ev1234me (Apr 16, 2011)

Great Resource!

Thank You Gerhard


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## kennybobby (Aug 10, 2012)

*Re: WarP-9 torque vs motor current*



GerhardRP said:


> You should go to http://jackrickard.blogspot.com/2011/04/graphs-is-always-greener.html look for the graphs down the page.
> Gerhard


i was looking for warp9 motor dyno test data (other than the sales data) and found lots of useful info in this thread. Taking the data from jack's dyno testing and re-formatting gives some interesting data. i haven't added the data from maxvtol's graph to fill in the 200 to 450 amp range, but it should fit nicely also to help get a torque vs motor current curve from 0 up to 1000 amps based upon actual test data.

We have a diy project ongoing using a '86 celica with the warp9 and a 680 amp controller.


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## Dennis (Feb 25, 2008)

ev1234me said:


> Hi Major,
> 
> Thanks for replying.
> 
> ...



The *constant torque is ALWAYS a motor controller control characteristic* and never a motor characteristic. Motor characteristics are derived from a test fixture that has a high end DC power supply and a motor dyno that can apply more and more load on the motor under test. The result is a torque-speed curve with amps and what fixed supply voltage was used in the test.

So if you had no current limit and applied 170 volts DC then the motor would draw in however many amps that is limited by the overall electrical resistance of the system (if things did not blow up). As the motor speeds up, the current falls off, but it is not linear in a series wound DC motor like it would be for a PM or Shunt wound motors.

Now if we connected 170 volts into a motor controller with electronic current limit then the result will be different because current is limited to a fixed value that the controller maintains if the throttle input is at 100% from motor start up, till battery current equals motor current when accelerating a mass. Afterwards, motor current decreases because the motor's back EMF or generated voltage starts to get large to where the output of 170 volts minus the back emf voltage is applied across the electrical resistance of the motor; which in turn would be less current than the controller's current limit and since motor controllers do not boost output voltage then current will not be maintained.

Another way to look at is a motor controller "chops" the torque curve of a DC motor that would be in its natural state, if hooked up directly to a DC power supply accelerating a load.


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