Electric Vehicle Conversion Help

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Wiring Diagrams

Isolated Systems

The figure above is a simplified diagram that illustrates how the electrical systems in an electric vehicle are isolated from each other. There are two main isolated systems:

1. 12-V automobile electrical system

2. High-voltage system based on the battery bank

Each system has its own battery charger.

The figure below shows an alternative method of charging the 12-V battery using a power converter/charger that operates from the high-voltage battery bank. In this case, the battery charges as needed from the high-voltage bank during use.

System Control

The system control circuit, in the green box, is an interface control and safety circuit between the two systems. The control circuit contains relays that energize according to operational rules.

Rules:

1. The high-voltage motor and control system must not energize if the parking brake is on.

2. The high-voltage motor and control system must not energize if the operator has his/her foot on the gas pedal.

3. The high-voltage motor and control system must not energize until the gas-pedal foot (right foot) is on the brake pedal.

If the control circuit is designed to follow these rules, safe operation can be ensured. The following wiring diagram shows the control circuit that I designed for my Chevy S10 conversion:

The small black box is the control box that contains the circuit just above.

The gray box contains the heavy-duty contactor and fuses (F).

Note: If you would rather purchase the above circuit already built and ready to install, please contact Mark: mail@evhelp.com

The control unit will include a mounted seven-screw terminal strip for easy wire connection, a 10 W pre-charge resistor and the external inline diode for the brake. $59.95

Note: The heavy-duty contactor, PB6 throttle unit and wiring are not included.

Relays and Diodes Make Up the Control Circuit

Soldering and wiring skills are required to build the control circuit shown above. Relays RL-2 and RL-3 used in this control circuit are 12-V single-pole single-throw with contact ratings of 5 to 20 A at 125 V (not critical). RL-1 is a single-pole double-throw. RL-2 and RL-3 can be replaced with one double-pole single-throw relay. Relays such as these are readily available at Radio Shack. All diodes shown (black arrow symbols) are 50-V and at least 1 A. The components marked with an F are 125 V or 250 V rated 2-A to 4-A fuses, which are placed close to the contactor terminal posts using either inline fuse holders or mounted snap-in holders.

The 50-Ohm, 10-Watt pre-charge resistor limits surge current to 2 to 3 A and allows the capacitor bank in the controller to charge quickly. After the capacitors quickly charge, the current through this resistor is less than 0.2 A and drops to 0 A when the accelerator peddle is pressed and the contactor is activated. The pre-charge resistor keeps the capacitor bank in the controller charged while coasting or stopped. When the vehicle is off (key turned off), the pre-charge resistor circuit is opened via RL-3, which is good because no current will continue to flow to the controller and no dangerous voltages will be present at the controller and motor.

Note that the above control circuit is actually safer than what is shown in the Curtis Instruments controller manual (1209B/1221B/1221C/1231C Manual). Curtis recommends that a 750-Ohm pre-charge resistor, for the 1231C, be placed across the heavy-duty contactor terminals. If this is done, high-voltage from the battery bank will be present at all terminals of the motor and controller even when the key is off. The user would be required to remember to turn off the main circuit breaker before working on the motor and controller system, which of course is a good practice anyway. The modified circuit above helps you avoid unnecessary shock if you forget.

Disclaimer: Mark E. Hazen, the author of this Electric-vehicle Conversion Web site, is not responsible for injury or losses of any kind resulting from use or misuse of information contained herein.