# An Electric Pulling Tractor



## dtbaker (Jan 5, 2008)

Jimdear2 said:


> Hi all,
> 
> ... I see all types of conversion and competition being done but no tractor pulling, I think it's about time to see what an electric can do in pulling. ...
> Jim



a good friend of mine has had great results pulling in local fairs and competitions in Maine with a little electric Cub. check out his stuff at http://www.solarcarandtractor.com


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## madderscience (Jun 28, 2008)

Interesting Idea.

I don't know much about Tractor pulling but I know that you need a lot of power for a little time, so (like drag racing) energy capacity isn't the problem, its all about power. Battery weight might be an advantage in your case (like with an electric forklift) for balancing and traction.

As for your specs, a 72v, 450A setup, if installed in a roadgoing car, would give top speed around 50mph and pretty leisurely acceleration. It would probably be about equivalent to a 20 or 30HP gas engine. 

"High Performance" EVs typically have at least 156V of battery and can go up to nearly 400v. They also have at least 1000A controller, and the really mean ones have 2000A zilla controllers. Of course, that all costs a lot more than your proposed setup too.

Of course, it isn't about speed. its about torque and traction. Look for a motor with the biggest torque constant you can get (basically, larger diameter the better) Know that the 450A is the maximum motor current the controller will allow, so it will be easy for you to figure your maximum torque. Your maximum power will be found at the speed where it is possible to put the full 72V across the motor at the full 450A. Doing some further research on your motor choice should tell you what this RPM is. Then its just a matter of gearing things for that RPM at the speed you want your wheels to be going.

72V at 450A is equivalent to 43 horsepower. (1 horsepower == 746 watts)

As for batteries, you will probably want AGMs. You need those to dump the kind of amps you will need for this. Lifespan may be cut short in this sort of usage but maybe you don't care. 

as for over-revving the motor, thats definitely a concern. Fancy aforementioned Zilla controllers have automatic over-rev protection but I don't think the alltrax does. but it should not be too hard to come up with some kind of RPM kill switch.

Good Luck!


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## Jimdear2 (Oct 12, 2008)

madderscience,

Thanks for your response. 

I've been doing research on AGM batteries and am getting closer to using those for the cost base for my project list (my but the costs do grow) budget. I won't purchase untill just before the season starts next May so I do have some time to put cash aside (economy willing).

I need to absorb more of the relevant math and formulas. I have a thick head, I need to pound that stuff in.

I already have the motor and controller. I chose them because they are just a bit more (almost the same HP and twice the torque) then the ICE I was using and already breaking parts with. The AllTrax was recommended as a good match to the motor. I want to stay with proven stuff until I have a better feeling about how to use electric power. I hadn't heard or read about the Zilla until later on in my research. I'm already thinking about stage two.

I wish I had known about the runaway problem before I bought though. The person I bought from didn't think of it before hand because it's not a concern in his world. Is there anyone who has seen something "off the shelf".

You all be well now,
Jim


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## judebert (Apr 16, 2008)

Nothing off the shelf that's been tested. I'm looking for the same thing for my commuter car. They're often called "rev limiters" or "rpm switches" in the motorcycle world.


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## Jimdear2 (Oct 12, 2008)

I've been reading all the threads about tachometers, runaway shut down devices, rev limiters and downhill over speed prevention devices with much interest.

This sounds like something a young fellow with a bit of education could make a bit of money with.

My own problem with this runaway thing is getting closer to resolution.

By the way, should we define these as: 
*Runaway* when a DC series motor destructively speeds up out of control when electrically powered with no load.
*Over speed* when any type motor destructively speeds up out of control when driven by an external mechanical source

Should these terms go into the WIKI?

D&D Motors has a hall type speed sensor kit for the motor I bought from them. It has 4 N/S pole pairs and fits into a pocket on the end of the motor; it's on its way now UPS. Prior to that I was going to build a hall sensor into the adapter and coupler. I had seen sensor kits in amateur electronic catalogs so that wasn't a problem. 

I now have a 5 inch 11,000 RPM tach with a settable shift light. ($17.00 on ebay, new, with dents and no documentation) It’s a generic stepper motor type tach I've seen before; it will hook up to anything that will produce pulses. The tach has a switch to set it for 4, 6 and 8 cylinders. 2 pulses per counted revolution for a 4 cylinder, 3 pulses for a 6 cylinder and 4 for an 8 cylinder. So if your sender produces 2, 3 or 4 pulses per counted revolution set the tach accordingly. I believe it will work on pulses from around 5 to 15 volts. 

By removing and unplugging the shift light I have a signal (I have yet to measure voltage and amperage) produced at an rpm I set into the tach. 

I am now looking for some form of interruptible switch or relay to place in the contactors control circuit. In looking through catalogs I know I've seen something, I just can't remember where. 

I don't know if a mechanical switch would be fast enough. Anybody have any Ideas.

Baring something available off the shelf, well my brother is an EE, I just hate to ask him for help (it's a sibling thing).

I'll post my final solution. Until I finish up, next spring now I can no longer work outside, I want to hear anyone else's.


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## ElectriCar (Jun 15, 2008)

I'm anxious to see how this thing turns out on the track, more specifically if your drive train can make it for 30 seconds! 

Re motor runaway: Instrumentation and control is something sorely lacking in the EV community. There is little in the way of gauges. I've got to come up with a way to monitor the motor RPM myself and probably a rev limiter tach tied into the run circuit is the easiest solution.

I'd love to buy a custom EV dash for my S10 with status LED's, meters etc or even an LCD display with all sorts of data inputs etc. Oh well I guess we'll live with the Fred Flintstone instruments for now.


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