INTEGRITY OF BODY, BRAKES & WHEEL BEARINGS
Most EV conversions wind up being from 400 to1200 pounds over stock weight. This represents additional strain on the body, wheel bearings, and brakes. Don't convert any vehicle that has cancer (road rust) because the additional strain could eventually cause structural failure of the body. It's mandatory that a conversion have the best brakes possible. When performing a conversion, always put on brand new brakes; use the best materials available. If the vehicle you're converting has power brakes, be sure to restore vacuum to the brake servo with a vacuum pump system. Also, check wheel bearings for signs of wear; if you have any doubts about them, replace them.
BATTERY PLACEMENT
Try to distribute battery weight throughout the vehicle for better handling as much as possible. Too much weight in the back of the car can cause over-steer with a sensation that the vehicle is too responsive to any change of steering wheel position. If there's too much weight over the front wheels, the under-steer created will make you feel like you're driving a snow plow. Also, try to place batteries as close as possible in the center of the car at a low position to lower the vehicle's center of gravity and to avoid the 'dumbbell' effect whereby the vehicle will yaw with each change of steering wheel position.
A vehicle is safer if batteries are kept out of the passenger compartment. If placement outside of the passenger compartment isn't possible, be sure to enclose and secure the batteries inside of a box structure.
SAFETY COMPONENTS AND SAFE TECHNIQUES
The power components in an electric vehicle propulsion system can be as simple as a motor, a motor controller, a set of batteries, and some cable to interconnect them. Using only these basic ingredients in the vehicle propulsion system will work. If you're lucky, you may never need additional components for safety.
This reminds me of the time a fellow was proof-testing components in a 2-seater dune buggy with no body. The propulsion system had no safe means of disconnecting battery power from the motor if a problem ever occurred. Sure enough, as Mr. Murphy might have it, the controller shorted out during a test run and the 'test mule' began to run away. Good thing that this fellow had a tool box sitting in the passenger's seat next to him. He was able to retrieve a hammer from the tool box, and after two well-placed swings he succeeded in knocking the post off of a nearby battery. This maneuver (at 50 MPH and climbing) interrupted power to the motor, and the vehicle was then brought to a stop. Brakes alone were not enough to stop the vehicle, and depressing the clutch would have caused the motor to blow. Fortunately, in this case, the only casualties were a battery with a broken-off post and some underwear that was badly in need of changing! The vehicle could have crashed or some part of the system could have caught fire.
This incident points to the fact that the more safety components you have in a propulsion system, the safer your vehicle will be in the event of some emergency condition, even if some seem redundant.
(1) FUSES. Fuses provide an instantaneous automatic interruption of power in event of a malfunction or short-circuit. No fuse is any good unless it is rated at the voltage/current/time characteristics appropriate to its application. Use at least one safety fuse in the main battery pack to protect system power components. An enclosed safety fuse such as the Ferraz-Shawmut is best because the fuse element is enclosed in a fire-retardant powder. A fuse link is usable, but with its open construction it can spew molten balls of metal when it blows. If a fuse link is mounted in the open over the top of a battery and it blows, molten balls of metal can burn through a battery case--causing a potential fire or explosion--or, at the minimum, a ruined battery. If using a fuse link, please enclose it in a piece of high temperature insulated tubing such as phenolic. Also, for maximum safety, any instrumentation line that ties into any part of the propulsion system should be protected with a small fuse of 1-amp or less that is mounted close to the propulsion system tie-in point. This will protect small gauge wiring from catching on fire if a short ever occurs within the instrumentation circuit.
(2) CIRCUIT BREAKERS. Whereas a safety fuse provides instantaneous automatic interruption of propulsion battery power in event of a malfunction, optional use of a circuit breaker can provide a fail-safe manual and/or automatic interruption of battery power in the event of a drive system malfunction. It also can be used to shut-off battery power during routine servicing of the system. A circuit breaker is no good unless it is rated at the voltage/current/time characteristics appropriate to its application. Use of a double-pole circuit breaker offers an advantage over a single pole unit by allowing both sides of a battery pack to be interrupted instead of just one. The circuit breaker should be mounted within easy reach of the EV driver for maximum safety.
(3) CONTACTORS. A contactor is used to switch high power remotely by means of a low-level control voltage--such as 12-volts DC supplied from a key-switch. In an EV propulsion system, high voltage, inductive loads, and extremely high current levels are encountered. A contactor should be correctly rated for the high voltage and current characteristics appropriate to its application. Even though a contactor's primary function in most EV systems is to carry current, the type used should be capable of breaking current to an inductive load (motor) In case of a shorted controller condition. This means that the contactor used should be fitted with magnetic blowouts which extinguish arcing--otherwise, a contactor could weld into a shorted condition if it can't break the arc. Magnetic blowouts work on the principle of Fleming's Left-Hand Rule. At least one main contactor should be used in a propulsion system to apply and remove main battery power to the motor and controller. Contactors used for electrical reversing should be fitted with magnetic blowouts as well.
(4) WIRE, CABLE, AND TERMINALS. Wire and cable used in an EV should be sized to safely handle the current being carried without overheating. Undersized wire can get hot or even catch fire. Manufacturers' amp capacity tables should be referred to when deciding which size wire to use. Use wire that has thicker insulation to maximize abrasion resistance in EV applications. When running heavy-duty cable underneath a vehicle, add abrasion resistance to the cable by enclosing it in PVC conduit or rubber heater hose. Put extra covering on wires that are routed through sheet metal with potentially sharp edges. Use copper wire, never aluminum. The debate on whether to crimp or solder terminal lugs onto heavy-duty cable ends may go on forever. Basically speaking, all lugs should be crimped onto wire ends using a proper crimping tool. Solder them too, if you like, but do crimp them. If a cable lug secured to a battery terminal ever becomes loose, it can become hot enough to melt the solder and separate. A crimped lug will hold to the cable because of its mechanical bond. Check all battery terminal hardware at least once per month and retighten as required.
(5) BATTERIES. Batteries, of course, should be securely fastened from moving around in an EV. The most common type used today for EV applications is the flooded-cell lead-acid battery. These have a liquid electrolyte and are unsealed. During approximately the last 20% of their recharge cycle they will produce a significant amount of hydrogen gas. Allow adequate ventilation for the hydrogen so that it doesn't collect and present an explosion hazard. Hydrogen ventilation can be assisted by using small fans. Never use a DC brush type fan in this application because commutation sparks can ignite the hydrogen. Always use brushless DC or AC fans. Also, when handling or working around batteries, always: (a) wear heavy-duty shoes to protect your feet and heavy-duty gloves to protect your hands and fingers (b) wear a face shield to protect your face and eyes in the event of an explosion (c) tape the unused ends of wrenches which are to be used for removing, installing, and/or tightening battery terminal bolts and nuts (d) place an insulating cover over all batteries which are adjacent to others being installed, removed, or serviced. A sheet of plywood will work fine.
(6) MOTORS AND MOTOR INSULATION. Use motors that are heavy-duty enough for your application. Don't try to use a 4 HP motor when a 10 HP unit is required, Motors that are undersized for an application will overheat and can eventually burn-up. Never use a motor that has an inferior insulation system or is constructed from inferior materials. Insulation systems are rated by 'letter' according to their temperature value. Use motors that are rated class 'F' (155 deg. C), or 'H' (180 deg. C). Better materials may cost more money but the added price is worth it.
One formerly-popular motor manufacturer used class 'B' (130 deg. C) insulation in his motors to save money. Because of inferior insulation, the armatures in nearly all of his motors eventually overheated and shorted out in electric car applications.
(7) FLOATING GROUND SYSTEM. For maximum safety, no part of the propulsion system should be connected to any part of the vehicle frame. Isolating the propulsion system from the frame will minimize the possibility of being shocked when touching a connection point such as a battery terminal and any part of the body or frame. It also minimizes the chance of having a short circuit to the frame if wire insulation becomes frayed and touches metal.
(8) FRAME GROUNDING AND BATTERY CHARGERS. In most EV-conversions, the frame and metallic body structure of the vehicle will carry the circuit return path for the 12-volt auxiliary power system (for lights, horn, radio, etc.). As mentioned in step (7) above, the frame shouldn't be connected to the propulsion system--but it can and should be used as part of the 12-volt auxiliary system. However, the frame and body should also be connected to the third-wire mechanical ground of the AC input power (green wire) whenever battery charger power is connected to the vehicle. Battery charger power connected to the vehicle can be DC, in the case of off-board chargers, or it can be AC, as in the case of on-board chargers. Making this third-wire mechanical ground connection will prevent potential shock hazards when the vehicle frame or body are touching and while the batteries are being charged. Transformer-type chargers, in and of themselves, do not always insure against frame and body shock hazards. Chargers without transformers should always have a ground fault interrupter (GFI) installed on their AC inputs, preferably ones that are UL listed or approved.
