# Improving DC series motor torque.



## Yabert (Feb 7, 2010)

Hi all.

I drove my little Smart Fortwo since a year now and all seem to work well. My battery pack coupled with the Soliton 1 provided up to 125 Kw (125v 1000A) at the terminals of the short Warp Impulse 9 and that is especially fun in a Smart. 

But since few months now, I would like to have more torque (not necessary more power, only more torque from start). The problem is I don't have clutch, so start in first gear is pretty much useless since in a second or two I hit rpm limit (5000 rpm Soliton limited) and to shift the second gear would require 2-3 sec. 

So I tried to find a solution at this problem.

-Change the motor is a real pain since any motor is too long to fit in the rear end of the Smart (my Impulse 9 is mount inside transmission bell housing).
-Add a clutch would require to highly modifying the rear end of the Smart (same as add a bigger motor). 
-Change the Soliton 1000A for a 1400A controller seem realistic, but the S1 work so well and the Warpdrive isn't really attractive to me (Ignoring extra $$, new wires, tach and throttle).

So the only easy solution I can see is to reduce the brush adjustment of the Impulse 9 to recover a bit of torque. From what I know, the brush advance is 12° from Netgain and that permit to some guys to pass up to 200v in those 9'' motors.

My questions are: 

1- Do you think it's possible to securely pass up to 125v with a brush adjustment at only 6°?

2- How much torque can I recover by the 6° change. 12%? 
12% of what? The torque doesn’t seem linear with amp, so what is the real effect at 1000A.
Based on some reading, I actually have 170-180 lbs-ft of torque at motor shaft. Is it right to estimate than I can obtain up to 190-200 lbs-ft of torque after the change?

More info:
My Impulse 9 use dual wafer H60 brush. Limit the motor to 125v is definatly enough because this short motor spin fast with relatively low voltage.

Thanks for your help


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## Ziggythewiz (May 16, 2010)

The obvious solution: Mount a Shiva on the roof.


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## major (Apr 4, 2008)

Yabert said:


> Hi all.
> 
> I drove my little Smart Fortwo since a year now and all seem to work well. My battery pack coupled with the Soliton 1 provided up to 125 Kw (125v 1000A) at the terminals of the short Warp Impulse 9 and that is especially fun in a Smart.
> 
> ...


Hi Yab,

I have never even seen an Impulse 9 motor but have heard a few things about it. So here are a few things you might consider.

The 6 degree advance. Roughly each degree is worth about 2 percent in torque per amp. This should be valid at all current levels.

Pole shims to reduce air gap. This would be most effective at light load and may not be noticeable in saturation (like 1000A) much at all.

Investigate changing the field coils from series-parallel (S-P) to series (S). I heard someplace that the Impulse 9 has a pretty weak field. This might help as it would double the ampere-turns at all loads. However it will be less effective in saturation and it increase the field loss by a factor of 4, so beware of heating problems.

I think the shift to 6 degree advance is probably your best bet.

major


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## Yabert (Feb 7, 2010)

Ziggythewiz said:


> The obvious solution: Mount a Shiva on the roof.


Hahahahaha! 1000 hp Smart fortwo! I accept sponsorship....



major said:


> Roughly each degree is worth about 2 percent in torque per amp.


Why roughly? Do you have an explanation about the non linear (curve torque line, not straight) on the torque graph of the Warp motor compare to the linear line (straight torque line) than we can see on the graph of the Warp 11 HV and Kostov motor. Is it related to the brush advance compare to the neutral advance of the interpoles motor?

Just for you Major (and all others curious) I post few pics of my Impulse 9 when it was new. It has H49 racing brush on pic.


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## Yabert (Feb 7, 2010)

major said:


> I think the shift to 6 degree advance is probably your best bet.


How I can be confident to don't destroy my motor if I pass 125v 1000A on a Impulse 9 with 6° of advance?
What is the general rule of thumb about brush advance for typical EV motor (Warp, ADC). Those motors are based on forklift motor who run at 48v with neutral advance. So, what is the link between 48v = neutral, 170v = 12°, 125v = 6° ??


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## major (Apr 4, 2008)

Yabert said:


> Why roughly? Do you have an explanation about the non linear (curve torque line, not straight) on the torque graph of the Warp motor compare to the linear line (straight torque line) than we can see on the graph of the Warp 11 HV and Kostov motor. Is it related to the brush advance compare to the neutral advance of the interpoles motor?
> 
> Just for you Major (and all others curious) I post few pics of my Impulse 9 when it was new. It has H49 racing brush on pic.


Roughly????? Because I do not the exact relationship  But the most torque is produced when the field and armature fields are at 90º (vector cross product). If you rotate the brushes 90º mechanical you reverse rotation. If you rotate brushes 45º you get zero torque (that would be 90º electrical or aligned for the cross product). Therefore 45º mechanical degrees equals 100% loss of torque. 2.2%/º. Although it may not be exactly linear % w/r/t º.

The non linear torque per ampere you see on the characteristic plots has little to do if anything with brush advance or interpoles but rather the saturation of the magnetic circuit.

Thanks for the photos. It appears the Impulse9 has quite a few turns on the fields so my idea of converting to series connection is probably a bad thing and would cause overheating.


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## major (Apr 4, 2008)

Yabert said:


> How I can be confident to don't destroy my motor if I pass 125v 1000A on a Impulse 9 with 6° of advance?
> What is the general rule of thumb about brush advance for typical EV motor (Warp, ADC). Those motors are based on forklift motor who run at 48v with neutral advance. So, what is the link between 48v = neutral, 170v = 12°, 125v = 6° ??


I've never seen a quantitative analysis on the subject. The only way I know for sure is to test. We used to do it on a dynamometer. You're likely stuck with tests on the vehicle. Nowadays you could shift it to 6º and mount a camera towards the comm and test it. If you spark too much, go back to 12º or increment to find the sweet spot.


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## Yabert (Feb 7, 2010)

Hummm, test it. Well, I think is the best way.

I know I only push 48-96v at motor terminals most of the time at cruising speed, so no problem there. 
The problems will occur at 125v and 1000A. So, is it more adequate to test at lower voltage and grow up voltage (96v 1000A, 110v 1000A, 125v 1000A) or limit the voltage at 125v and grow up amp (125v 800A, 125v 900A, 125 1000A)??

Thanks for your help Major


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## major (Apr 4, 2008)

Yabert said:


> The problems will occur at 125v and 1000A. So, is it more adequate to test at lower voltage and grow up voltage (96v 1000A, 110v 1000A, 125v 1000A) or limit the voltage at 125v and grow up amp (125v 800A, 125v 900A, 125 1000A)??


Either way......or both  For some reason, I'd set voltage and increment up current limit. Make sure your brushes are well seated as improper face seating can throw off apparent advance a few degrees as well as increase the contact current density.


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## Yabert (Feb 7, 2010)

I understand proper brush seat is very important.
And this add some confident about the idea to change the advance to 6° when I remember I pushed 125v 1000A in my motor with the brush seat at around 70% without any trace of arcing. (I only discover the inappropriate brush seat after few weeks.. )


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## Frank (Dec 6, 2008)

Yabert,

That appears to be one of the newer motors with 1/2" studs and a thermistor installed. Do you record internal motor temperature at any time?


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## ruckus (Apr 15, 2009)

Let's not overlook the obvious here.

#1. The easiest path to more torque is lower profile tires!

I know the Smart uses an odd size, but this could easily get you 10% and be an item you would change out anyway.

#2. How much sag are you getting at 1000A? I bet it is considerable. Major has talked about capacitor banks, maybe they could help here and be an 'add on' that wouldn't require re-engineering your drive setup.

Good luck!


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## Yabert (Feb 7, 2010)

Frank said:


> That appears to be one of the newer motors with 1/2" studs


Yes.



Frank said:


> Do you record internal motor temperature at any time?


No specifically. Why?




ruckus said:


> How much sag are you getting at 1000A? I bet it is considerable.


Sag isn't the problem here. But for your information, 154v nominal, 125v under load (1000A) (with good condition).


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## Frank (Dec 6, 2008)

Yabert said:


> No specifically. Why?


Typically motor temperature is a limiting factor in performance applications using Series DC. Just curious what typical temperatures are...

I would expect it to be fairly low (I have an ADC 9" in an old pickup truck that barely gets warm) but you never know.


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## Tesseract (Sep 27, 2008)

Frank said:


> Typically motor temperature is a limiting factor in performance applications using Series DC. Just curious what typical temperatures are.......


*Commutator* temperature is the primary limiting factor, not field winding temperature, which is what the integrated thermistor on the latest model WarP and Kostov motors reads. You can measure the commutator temperature with an optical thermometer (often using an infrared sensor).


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## Frank (Dec 6, 2008)

Good point!


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## PaulS (Sep 11, 2012)

Have you considered independently excited fields? Rather than running your motor with the voltage divided between the armature and fields (series wound) if you separate the fields and armature then when you need more torque you can apply more current to just the fields and when you want more speed you can reduce current through the fields while running a constant power through the armature or controlling it in any way you wish.


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