# Jet-starter engine, DC compound.



## Salty9 (Jul 13, 2009)

Hi Go,

I'm only replying since none of the motor mavens have. From the little I know about motors you might want to check sepex controllers. Good luck.

Chuck


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## Go-carter (Dec 18, 2011)

Salty9 said:


> Hi Go,
> 
> I'm only replying since none of the motor mavens have. From the little I know about motors you might want to check sepex controllers. Good luck.
> 
> Chuck


Hi, thanks for reply!

Yeah, I've read on another page here on the forum that Kelly has a updated controller that can control the motor.

But I've also read that Blue Meanie had a engine like this in its early years, and that plasmaboy made his own controller for it. Sent him an email today, so hopefully he will answer it...


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## Salty9 (Jul 13, 2009)

Nils,

I'm interested in the Locost. Do you have a build thread for your vehicle?

Chuck


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## Go-carter (Dec 18, 2011)

Salty9 said:


> Nils,
> 
> I'm interested in the Locost. Do you have a build thread for your vehicle?
> 
> Chuck


Hi!

I bought my locost used, but you can check out my homepage(in Norwegian):
www.henningstad.com

And I have a small album from two years ago, when I rebuilt my car:
http://www.facebook.com/media/set/?set=a.6052721611.13897.547141611&type=1&l=c9b4c383e5


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## Tesseract (Sep 27, 2008)

Go-carter said:


> The only think I haven't understood yet, how does one run/control the speed of a DC compound engine? ...


I'll defer to any motor mavens that choose to respond, but, in general, the shunt field in a compound DC motor is mainly to prevent overspeed with no load. The behavior of the motor is dominated by the series field, in other words. So, you use a regular old DC motor controller to drive it.

One of the regulars here, gottdi, has used this type of aircraft starter motor in road-going conversions, though I think the general consensus is they are a little bit too light duty for all but the smallest cars. Would make a helluva go-kart motor, though.


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## Salty9 (Jul 13, 2009)

The description in post #4 seems to describe your motor.
http://www.diyelectriccar.com/forums/showthread.php/kaylor-adaptor-fixed-65260.html


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## Go-carter (Dec 18, 2011)

I haven't gotten hold of the motors yet, but I guess that the motor he is running is exactly the same as thow I plan to use 

He describes two ways of controlling it:

- The modified(?) Kelly controller
- Steps of volts, like 24, 48, 72, 96, 120V

The last one seems both cheap, durable, and easy to make but... it also looks like something fred flintstone wold use. In other words, a bit too rough. wouldn't it be very "steppy" to use? Well, racing normally is 100% throttle but still... 

Ofc, if I had to choose between a $3000 1000a kelly controller, and a simple kontroller just to test it.... I would go with the last one


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## Tesseract (Sep 27, 2008)

Go-carter said:


> ...Ofc, if I had to choose between a $3000 1000a kelly controller, and a simple kontroller just to test it.... I would go with the last one


You can certainly use contactors to tap the battery pack at different voltages as a "controller", but there are three downsides to this:

1. It is, indeed, "steppy" - changes in torque will be somewhat abrupt. Then again, streetcars (trolleys?) used this method for many years successfully.

2. The battery pack will be severely imbalanced by this control method; namely, the first battery (e.g. - 12V) will be the most depleted while the last battery (e.g. - 72V) will be least-depleted.

3. At some point, the cost of good, high-current DC contactors will exceed that of a PWM controller. You could save a lot money by taking your chances with cheap Chinese knock-offs of the Albright SW-200 contactor, but expect this to end in tears...

Depending on the application, however, contactor control might make perfect sense. Can't hurt (too much) to try, anyway.


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## Go-carter (Dec 18, 2011)

I think I found the controller he's using, a Kelly SepEx controller. But they won't do more than 600A, and thats a bit too little juice for me 

But they were cheap... only $999!

So it seems that for the power and reliability I want(the kelly could only handle 600A for one minute) it seems that I have to make up something my self.

http://www.youtube.com/watch?v=_RTIb_dUeO0

This dude controls the speed by putting different voltage on the shunt field(right?)... Could that be another lane to walk?


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## Go-carter (Dec 18, 2011)

OK, I've read a bit more... And now I THINK I understand how it works 

If you apply for example 100V directly to the motor it would spin up(probably until it overrevs and dies). If you then put a 100V power supply on the shunt field, and a variable small resistor in series, you can control it. Resistor on zero(full 100V on the shunt field) would result in "idle", what ever RPM that would be. And resistor on max(i.e. 0-10V or something) would result in top RPM.

This because, 100V on the shunt field would make the field as strong as possible, and give the motor max torque, and low RPM. Low power to the shunt, would make the shunt field weak, and the RPM high.

That's what reading, and the youtube-vid has made me conclude. Can someone, a bit more lectured on compound/shunt/series motors, correct me? 

If that is true, it would be fairly easy and cheap to control the motor. I would only need a small variable resistor/potmeter. And the only downside would be that I had to make a clutch assembly, as the RPM would never hit zero.


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