Replacing a Soleq EVcort Motor Controller

By Tim Wong


Soleq was a company that built electric vehicles from the early 1980's to the mid 1990's. Their conversions were very technically advanced, and the owner of the company, a Mr. Shunjiro Ohba, oversaw the design of all components from scratch. From what I know, Mr. Ohba had a PhD in electrical engineering and completely designed the motor controller, DC-DC converter, charger, heating, and all sub systems, as well as specifying the custom GE motor.

The Soleq Evcort boasted an impressive specification sheet, all in a very utilitarian Ford Escort, the shell used for the conversion:

60 mile range.

40Kw max power output (400A @ nominal 108V).

Powerful regenerative braking (220A @ nominal 108V).

600Watt 108V to 12V dc-dc converter.

Current selectable charger up to 30A.

3Kw heating system that can be set to preheat/cool the cabin while plugged in.

Air condition system.

Separately excited motor controller.

These specifications are still at the top of the class for converted DC electric vehicles. New Li-ion and Ni-mhi batteries are significantly eclipsing these specs, but only 20 years later.

The Motor Controller

While this car performed well and had top specifications, there was a problem; at some point the motor controller seems to fail. I know of 6 failures to date. While the separately excited Soleq motor controller designed by Mr. Ohba was an amazing feat of engineering, with Soleq now out of business, repairs have been very difficult. I know of several attempts to repair broken controllers, and have yet to hear of a success. I believe that there is probably a solution that would make these great controllers reliable, and I hope someone will find it. Also, many of the components are no longer available.

There are several solutions to get the car back on the road. One is to rewire the custom separately excited GE motor as a Series wound motor. This would no longer allow for regenerative braking, but would allow the new controller to be selected from a wide range of options from Curtis to Kelly to Zilla. Another is to get a conventional Series controller to power the armature and use a rheostat to adjust the field current. This solution works and has been implemented by a resourceful EV driver.

My Solution

The solution I have implemented is to use a Kelly KDH12801B controller to power the armature and a special Kelly KDH14030 to power the field. The KDH12801B allows for regenerative braking and operates in a permanent magnet motor control mode.

A word about Kelly - they were very helpful and I have to say their customer service was way above and beyond anything I have experienced or ever would have expected. Steven Li, the US sales representative was very helpful not only in management but also technically - he is very well versed in the Kelly products. He and the Kelly staff answered my nearly 100 emails over the whole project! I would recommend them as a good place to go for a motor controller.

The Kelly KDH14030 controls the field current, and also enables the armature controller. It is a special controller which Kelly made for this project. It has an output that allows it to send a signal to the armature controller when the field is on and stable.

There are 3 potentiometers which act as inputs to the motor controllers. The original Soleq pots are replaced with two Bourns 5Kohm single turn high cycle potentiometers (part numbers at Technical Specification page). The brake and accel pedals both have enable switches on them - mounted on the Soleq pot box. When the accel pedal is pressed, the switch closes, enabling the field controller. When the field reaches 5 Amps, the field controller then brings one of its I/O points to ground. The point is connected to the enable pin of the armature, and enables the armature. The armature then ramps up the current proportional to the accel pot (providing a 0-5V signal). The field current, during acceleration, is controlled by a knob on the steering column. It allows for 5A to 15A range.

Unfortunately, the car needs more like 2 Amps to allow the motor to run at higher RPM; 12A allows for about 2000RPM and 5A allows for about 2700RPM. I would like to get up to 3600 RPM with a 2A field.

IF YOU ORDER ONE OF THESE FIELD CONROLLERS FROM KELLY, it a 2-15 Amp Field current range may perform better. I think it would make the car a very good performer at high speeds, but have not tried it so cannot say for sure. The old Soleq controller went down to 2 and below, allowing for 65MPH in 3rd gear.

During regen, a similar process is followed. The brake pedal closes a switch that enables the field controller. The field ramps up to ~4-5 Amps, then enables the armature controller with an I/O pin separate from the accel pin. The armature controller ramps the regen current proportional to the regen potentiometer. The field regen current is also connected to the same potentiometer instead of the user adjustable pot on the steering column.


The car performs fairly well with the new configuration. It accelerates well with the field current on high, although it is weaker than the original system, since the 4-5 Amps minimum field controller will only allow it to drive up to 2600 motor RPM. The original controller would automatically adjust the field to allow for acceleration up to 3600 to 4000 RPM. This makes freeway driving somewhat difficult, as 2600RPM only gets about 55MPH in 4th gear, and the car is sluggish to accelerate in 4th. I was hoping to use 3rd gear to get to 55, like the old controller, but it works fairly well for what I use if for, and my batteries are still breaking in.

Regenerative braking is very good. From any speed it will stop the car to 1-2MPH without the use of the friction brakes! It takes some modulation to keep it in regen mode, but after a few drives it is pretty easy to stop the car with only a small touch of the friction brake to stop the car from rolling at 3MPH or even less. It will regen over 200A.

Hopefully the car will continue to run well without too much trouble.