The Electrac has a weird SepEx motor tho and the Alltrax controller for those tractors does the reversing without a reversing contactor.

I regular SepEx motor controller doesn't work, not sure why.

Is the motor DC, BLDC (brushless DC), AC, etc.?

OK, with out getting too technical in order to reverse a motor with a reversing controller like the Alltrax you need a circuit called an 'H' bridge. The problem with 'H' bridges is that you have to drive the upper 'N' type MOSFETs with a boost circuit because they won't turn on otherwise. So you need a boost circuit and then there is dead time because you can't have both sides on at the same time or you get a condition called "shoot through" which is basically a short in the circuit. All this has to work with the inductive kick back of your specific motor so you wind up paying for an expensive controller.

What I'm planning on doing with my Elec-Trac side steps all of that, we'll see when the circuit is finished this spring. I'll post it here so if others want to build it they can.
In your case with a reversing tranny and a motor that only has to spin in one direction, the circuit should be a piece of cake.

Rob

Most GE Elec-Trak drive motors are Separately excited, some are PM type.
This is the Alltrax controller that is recommended for the Elec-Trak with SepEx motors.

Electronic Controller - $418.00 : The Electric Tractor Store :: Elec-Trak Parts

With the manual and Wiring diagram.
I am currently doing a Alltrax conversion on an E15 tractor.

Doug,
Doesn't matter.

Why throw out the 'baby with the bath water?' Let's say we use a microcontroller to 'dry' switch the motor direction using the relay from the ET, which should last indefinitely dry switching it. All we need to do then is PWM the field or armature with the same uC using a quadrature encoder as the throttle. The uC does all the work and programming it is what I do. The simplicity of the design goes way down.
I'm planning on building a couple of these for 50 to 75 bucks tops, if there's enough interest I may see about selling boards and programmed chips.

Rob

The Alltarx reverses the Field polarity.

Right, and that requires an 'H' bridge circuit. See my explanation of 'H' bridges above and the complexity they add to the circuit.

The main thing we want to do is control the speed of the motor. The direction it turns is controlled by the transmission or the reversing relay, so why go through the complexity of the 'H' bridge, at several hundred dollars, to do what can easily be done with the original machine?

What we're doing is specializing and contouring the electronics to fit our application. Alltrax is making a unit to fit many applications, the problem is this multiplies the cost considerably.

Rob

Well if you can come up with a controller package for the Elec-Traks, I think they would sell.
When I say "package" I mean controller and pot box.

The biggest problem with the Alltrax conversion is it doesn't come with a pot box that fits the GE tractors as I found out. Your left to figure that out for yourself and it adds to the cost.
Some people want hand control and others want foot control.

I'm setting it up with something called an optical quadrature encoder which I can setup as a foot or hand operated control.

Hopefully I'll have a small prototype in a week or two depending on what goes on around here. I have a motor sitting outside my electronics lab from an E15 (I think?) that I'll experiment on.

I'll post my findings.

Rob

Doug,
This is an amazing thread. I am impressed and very interested in seeing more. I am not much in the way of an electrician and have been following posts here, but yours has been one of the most impressive builds. Nice reconstruction on the tractor and nice paint job too. I love your efforts. I am Doug 2
:thumbup:

Thanks
You know the first one I did, I did it to see if I could.
The 2nd one I learned and tried to make it so it could do some work.

If anybody is thinking about doing there own conversion I say just do it.
If you don't try, you'll never know.