Electric Vehicle Conversion/Auxiliary systems and control
Note the presence of hazardous materials and conditions that must be approached with proper precautions and procedures to avoid damaging, injurious, or even fatal consequences.
Vehicle service electrical system
The twelve volt system is maintained to operate the headlights and various running lights, instruments, radio, heater fan, and other components common to the ICE vehicle. This low voltage is also used to control both low and high voltage relays required by the EV conversion.
Using an auxiliary battery
A much smaller battery may be used as it is not necessary to crank an ICE to start it, so the large battery may be replaced with a motorcycle, garden tractor or similar battery with much less weight and capacity of that which came with the car. The additional space may be used for an EV component such as a power brake booster pump or the 12 volt converter that keeps this battery charged. The addition of a 12 volt battery of modest size greatly simplifies satisfying the basic electrical requirements of the vehicle and allows a relatively small capacity DC-DC converter to be used, since this need not supply peak current requirements. The battery should be large enough to provide several hours of emergency flasher or parking light use, a requirement that may be beyond the capabilities of a motorcycle battery. A typical installation will only charge the battery through the DC-DC converter when the vehicle is in operation. If the usage pattern for the vehicle includes long times at rest with automatic (timed) recharge you may find it desirable to activate the converter during the charge cycles. A system that is float charged for long periods could include a separate 12 volt float charge device, sold for use with vehicles that are infrequently driven.
Some means of operating the converter to recharge a dead auxiliary battery may be provided using a separate push-button for emergency bypass of the converter relays. The converter will then provide enough power to close the relays, even while the battery is being charged. As these are usually 12 volt relays, an EV with a dead service battery will be immobile since no voltage will be available to pull in the relays - even though the traction pack is fully charged. A conventional "jump start" from another vehicle will solve the problem. (It is possible to work around the situation using some wires, clamps, and a small portion of the traction pack, but that can be dangerous and/or damaging if not very carefully performed.)
Without an auxiliary battery
Some builders eliminate the auxiliary battery, using only a DC-DC converter to produce the required 12 volt output. For a vehicle intended for street and highway operation this will require a high capacity converter. This method has the advantage of eliminating the weight of the auxiliary battery.
- This requires the use of some relays operating at the pack voltage.
- The DC-DC converter must produce enough power to operate all electrical loads - the headlights, turn signals, horn, emergency flashers, heater fan, radio, and any other loads such as a spotlight - simultaneously and without failure.
- Power must also be provided for parking lights, turn signals, and emergency flashers without the presence of the ignition key in case the vehicle must be left alongside the road for some reason. An auxiliary switch may be provided for this emergency function but this must not be left on in normal use, so an associated warning light should be included in the installation.
If power steering is incorporated this is often done by driving a conventional pump with an additional small motor. The power steering pump may be driven directly from the traction motor, as can the air conditioning. Since the traction motor is stopped when the accelerator pedal is not depressed (unlike an ICE which "idles") special techniques will be necessary to drive the power steering when parking. Due to the complexity and inefficiencies power steering is not usually included in a conversion if the vehicle is suitably light. Note that if the original vehicle is equipped with power steering then it should be powered owing to fact that the ratios used in power steering units will lead to rather high wheel forces when the device is not powered. For this reason, vehicles with manual (unpowered) steering units are preferred. Some recent production ICE (e .g. late models of the Saturn) and particularly hybrid vehicles use electric powered steering, a solution well suited for an EV conversion, but not readily available as of 2005.
While production electric and hybrid vehicles have been provided with electric air conditioners this modern equipment is not generally available in a converted vehicle. Some versions of propulsion motors include a front end shaft that may be used as an accessory drive, and vehicles have been converted to use the existing air conditioning pump. An alternative is to drive the pump with an auxiliary motor as described for power steering above.
The typical ICE heater uses waste heat from the engine cooling system. The fluid circulated through the heater may be warmed by an electric resistance heater and circulated with an auxiliary pump. It is more usual in a conversion to provide heat by replacing the water radiator (heater core) with a ceramic resistance heater. The parts and materials for this conversion are available from EV conversion suppliers although for a reasonable range of pack voltages (96 to 120 volts) a common ceramic core space heater may be adapted. As this will likely require bringing pack voltage into the passenger cab the installation must be done with care to avoid creating a fire or shock hazard. A heavy duty relay is required for power control and is typically actuated by both fan operation and an intermediate or higher heat control setting. Thermostatic control is seldom included but would be appropriate for colder climates.
Radios are sensitive to electrical noise from the motor controller and the service voltage (12 volt) power converter. This noise can come through the receiver as radio frequency interference (RFI) or through the power supply as noise on the 12 volt system. A satisfactory radio installation is one of the most difficult conversion tasks to complete.