Gas To Electric Conversion Experience At CIT-Day 3

Gas To Electric Conversion Experience At CIT-Day 3 (Theory Component)

Electric Vehicle Wiring Diagram For Gas To Electric Conversion Which Uses A Curtis Controller And Series Wound DC Motor

Day 3 started with the theory component, this time working out the wiring diagram. Some of the formulas learned on Day 2 were used.  The steps involved:

  • checking out the Curtis Controller manual on page 14;
  • modifying the diagram to suit our needs since we do not require a reverse switch (as the transmission has a forward / reverse feature);
  • circuit calculations – working out the current going through the various components and the ratings required; and
  • bench testing the Curtis Controller.


Checking Out Curtis Controller Manual On Page 14

The first part of the day was spent working out how everything will be wired up. The quickest way was to look at the Curtis Controller manual for the Curtis 1209B controller. There is a wiring diagram on Page 14 of the manual. The thick lines represents the higher voltage cables. The thin lines represents the lower voltage and lower current wires.

This wiring diagram facilitates forward and reversing of the series wound DC motor. This is made possible using a reversing contactor. I believe the reversing contactor works as follows:

  • when the switch is selected to F for forward, Armature A2 is connected to Field Winding Terminal S1. Field Wining Terminal S2 is connected to M-.
  • when the switch is selected to R for reverse, Armature A2 is connected to Field Winding Terminal S2. Field Winding S1 is connected to M-.

I believe that is how the reversing contactor works.

Modifying The Wiring Diagram To Suit Our Needs

Since, we do not require the Series Wound DC Motor to go reverse due to the buggy having a transmission with a forward and reverse gears, we could remove the

  • forward and reverse switches and
  • reversing contactor.

A 48 to 12 volt DC converter has been added.

Since, we are going to use 48 volts for the traction batteries, we can start making some calculations. We also know that the Series Wound DC Motor we are using has a power rating of 9600 watts.

Circuit Calculations

With the motor having a power rating of 9600 watts and the traction batteries delivering 48 volts, we can work out the current rating of the circuit using the formulas from Day 2.

P = VI can be re-written as I = P/V = 9600 watts /48 volts = 200 amps

This means the

  • power wiring; and
  • main contactor

needs to be able to handle (be rated for) 200 amps or higher. The power wiring fuse should be 200 amps.

According to page 10 of the Curtis Controller manual for the Curtis 1209B-6402 controller, a precharge resistor of 620 ohms and rating of 10 watts is recommended.

The 12 volt circuitry is going to be determined by the main contactor used. In this case, the main contactor must be able to handle 200 amps, but that is only for the traction side of things. To control the contactor, usually a lower voltage and current is required. The contactor that we had in mind is the Nanfeng ZJW200A Contactor which is triggered by 12 volts and 1 amp.  This means the

  • polarity protection diode;
  • key switch;
  • interlock; and
  • throttle micro switch

must be rated at 1 amp or higher. The control wire fuse will be 1 amp.

Bench Testing The Curtis Controller

Page 35 of the Curtis Controller manual for the Curtis 1209B controller has a suggested way of bench testing the controller prior to installation in your Electric Vehicle.

We had a power supply capable of delivering 48 volts and a globe that could handle up to 50 volts. We did not have a main contactor and bypassed it. We did not have a pot box, but instead a rheostat. Unfortunately, this was not rated at the required 5 kilo ohms, hence, we were not able to bench test the Curtis Controller. The rheostat had a resistance of 20 ohms which is not suitable for this controller.

Lessons Learned From The Theory Component Of The Third Day Of The Petrol (Gasoline) To Electric Conversion Experience At CITace?

The main lessons learned were:

  • have access to the correct manual for the controller you are using;
  • know the rating of the motor you are using;
  • know what voltages you are using;
  • apply the formulas to work out current ratings; and
  • get the correct components when bench testing.


When doing your Electric Car Conversion, it is imperative to have the wiring diagram sorted so that you can do the various current rating calculations. We used some of the formulas learned from Day 2 of the gas to electric conversion experience. The practical part of Day 3 discusses the practical component of the day where we struggled with the drive train.

This is Crazy Al signing out.

P.S. Please check out the practical part of Day 3 of the Gas To Electric Conversion Experience.


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