From: tylerh@cco.caltech.edu (Tyler R. Holcomb)
Subject: Electric vehical safety recommentdations
Summary: news from GM about electric vehicles
Keywords: impact electric vehilce. 
Organization: California Institute of Technology, Pasadena
Date: Sat, 22 Aug 1992 23:41:52 GMT



           SAFETY RECOMMENDATIONS FOR ELECTRIC VEHICLE CONVERSIONS
                          by Ken Koch - KTA Services

INTEGRITY OF BODY, BRAKES, WHEEL BEARINGS

        Most EV conversions wind up being from 400 to 1200 lbs. 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 eventually could 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

        As much as possible, try to distribute battery weight throughout the
vehicle for better handling. Too much weight in the back of the car can cause
oversteer with a sensation that the vehicle is too responsive to any change of
steering wheel position.  If there is too much weight over the front wheels,
the understeer 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
'dumbell' 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, and, 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 passengers seat next to him.  He was able
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, even if
some seem redundant. the safer your vehicle will be in the event of some
emergency condition.

(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 Bussman KAA-400
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 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 keyswitch. 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 also should be fitted with magnetic blowouts.

(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. In EV applications, use wire
that has thicker insulation to maximize abrasion resistance. 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 and
retighten as required all battery terminal hardware at least once per month.

(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; and, (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 eventually can
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 offboard chargers, or it can be AC, as in the case of onboard
chargers. To make this third-wire mechanical ground connection will prevent
potential shock hazards when the vehicle frame or body are touched while the
batteries are being charged. Transformer-type chargers, in and of themselves,
do not always insure against frame and body shock hazards. Transformerless
chargers should always have a ground fault interrupter (GFI) installed on their
AC inputs, preferably ones that are UL listed or approved.

-- 
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Tyler Holcomb   *   "Remember, one treats others with courtesy and repsect *
tylerh@juliet   *   not because they are gentlemen or gentlewomen, but     *
  caltech.edu   *   because you are."  - paraphrased from Garth Henrichs   *
From: walt@hpwrce.mayfield.hp.com (Walt Boeninger)
Date: Fri, 14 Aug 1992 18:18:47 GMT
Subject: Re: Post office and DMV
Organization: the Hewlett Packard Response Center