# Motor Question



## Guest (Apr 14, 2012)

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## major (Apr 4, 2008)

gottdi said:


> Major,
> 
> I have a motor question and figured you'd be a good one to present it to. I have an old Military Starter/Generator motor. It is a strange beast in that it is an interpole motor that is a shunt style motor. It has one of the fields connected in common with the armature. When used in the past for conversions these usually had a contactor style switch and batteries dumping in everything. The field can be feed from a separate 24 volt battery while the armature was what ever you pumped into it but usually no more than 72 volts. I have a SepEx controller with software running the motor but I tried to just shunt the field to the armature which is done for low voltage running. I coupled it to two different Series motor controllers and ran the motor. I ran the motor under no load condition for no more than 10 minutes at different speeds and the controller as well as the motor were quite hot. The Controller is what was a concern. I have ran a series motor with no load and got no serious heat in 10 minutes. The SepEx controller does not heat up that way.
> 
> ...


Hi gott,

There are a number of these aircraft starter/generators on the surplus market. I suspect they differ in design. One that I studied to help Mike in Texas was J&H. It was primarily a compensated shunt generator with interpoles IIRC. We got him running by properly exciting the shunt field in the correct polarity from a tap off the battery pack. I always thought that we left his series field differential connected, but that was a weak component and he was running well.

I can't follow your write-up as to what is connected to what and when what is getting too hot. Sorry. I think I'd need some connection diagrams, current and voltage measurements, and maybe scope screen shots.

If it is that special Kelly controller, I suspect that is the reason  What does their field map look like for that motor?

And yes, the shunt motor has good speed regulation. But that is immaterial for EV propulsion IMO.

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

I, too, have been amazed how cool my Kelly Sepex controller runs.

Any chance you got the shunt and series field connections confused? That could lead to hot series but cool sepex.


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## EVfun (Mar 14, 2010)

Is it possible that either the shunt field or the series field is connected backwards? I could imagine a situation where each time the MOSFETs or IGBTs switch off the back voltage actually rises a little and it tried to regen through the intrinsic diode. You wouldn't see regen because you are still net using power and these would be a series of <1/15,000th second regen bursts.


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## jehan12413 (Feb 4, 2010)

gottdi said:


> Major,
> 
> The Jack Heintz Starter/Generator is internally just like what I have. It has one field connected directly and internally to the Armature.
> 
> ...


 This may or may not help you. Several years ago I tried running a a Jack Heinz starter generator from one of my modified curtis series controllers just to see what would happen. It worked fine during accel and steady state cruise but during decel and every time I lifted off the accelerator to shift gears I could feel the hard deceleration due to regen. This would generate large amounts of heat in the controller via the freewheel diodes. In fact the MOSFETS were still cool to the touch. Putting a large diode across the motor did solve the problem but the system is very inefficient. I finally decided to just not run a compound wound motor on a series controller.


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## major (Apr 4, 2008)

jehan12413 said:


> This may or may not help you. Several years ago I tried running a a Jack Heinz starter generator from one of my modified curtis series controllers just to see what would happen. It worked fine during accel and steady state cruise but during decel and every time I lifted off the accelerator to shift gears I could feel the hard deceleration due to regen. This would generate large amounts of heat in the controller via the freewheel diodes. In fact the MOSFETS were still cool to the touch. Putting a large diode across the motor did solve the problem but the system is very inefficient. I finally decided to just not run a compound wound motor on a series controller.


That's interesting. But I suspect it was really plug braking heating the FWD not actually regenerative braking. Regen current would not flow thru the FWD and would flow thru the antiparallel intrinsic diode in the mosfet package.

What you say may in fact account for the controller and motor heating when the machine was wired to a series motor controller with the shunt field connected to the motor terminals. When the FWD conducts it clamps the shunt field to 0.7V thereby eliminating that flux. What is left to produce flux is the series field and if as I suspected it is differential connected it would reverse resultant flux causing reverse EMF keeping the FWD forward biased and reversing torque (to slow the vehicle).



major said:


> I always thought that we left his series field differential connected, but that was a weak component and he was running well.


In Mike's setup we connected the shunt field to the battery separately exciting it and therefore didn't have your problem.

Regards,

major


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