The solenoid in your golf car is the main electrical contactor (switch)
that allows battery current to flow to the starter/generator (on gas cars to crank the
engine) or to the traction motor (on electric cars). It is a critical component for both gas
and electric cars and it is prone to failure because it works so hard, especially in battery
powered golf cars. Unlike the starter solenoid in your automobile, which works only as you
start the engine, a golf car solenoid must work the entire time the pedal is down. Each time
you stop and then restart your golf car the solenoid must also stop working and then start
working again. Throughout a busy golf day, the stops and starts can number 1200-1500 per
day. These nifty little switches will work for years conducting up to 300 plus amps per use
in electric golf cars.
Oddly enough, to reliably conduct all this current and continue to function thousands
and thousands of times, most solenoids have a relatively simple design. A steel plunger
with a thick plate on one end is surrounded by a coil of thin wire wrapped many times,
kind of like a fat spool of thread. When a small amount of battery juice is put across
the thin wire, the magnetic field created by the coil throws the steel plunger and plate
into two large bolts that stick out of the side of the solenoid case. The two large
bolts, or steel studs, and the plate conduct the high current needed to power the
starter or golf car motor.
The great advantage to this high amp switch is the plate throws very quickly against the
large studs, thereby minimizing the electrical arcing created when connecting high
amperage. Picture when you pull a plug out of the wall when the appliance is still on.
You see a spark at the wall receptacle. Inside a golf car solenoid this arcing occurs
every time the car is stopped and started. It's easy to see why solenoids are the #1
problem in electric cars.
In the early years of golf cars, there were all kinds and designs of multi-solenoid
speed controllers. Reliably switching all the battery current required in those early
years gave the manufacturers fits. Modern golf cars still have solenoids, but with the
advent of electronic speed controllers and regen motors, it seems as though the
solenoids do a little better these days. Today, new demands are placed on the solenoid
because folks are lifting their golf cars with larger diameter tires and installing
larger motors and controllers. This effectively creates the need for greater amperage
draw to start the electric vehicle, to overcome inertia. These high currents also take a
toll on the Forward & Reverse switch, which is designed to handle 300 amps, more or
less.
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Regen motor controllers now effectively function as F&R switches by electronically
directing the high amperage. The regen controller needs only a low amp signal from a
dash mounted F&R toggle switch to correctly switch forward or reverse. Non-regen cars do
not have this function so high amperage put through to the F&R switch can create
problems. In some cases, installing larger power cables in the car can alleviate F&R
problems. Standard battery cable is #6. Installing #4 cable and ends can help. In severe
case, a multi-solenoid F&R switch can be installed in your car to replace the mechanical
rotary switch. Multi-solenoid F&R switches were common in Harleys, Columbias, Pargos,
Yamahas and other early electric and gas cars. They all used a key to change directions.
That's because a key switch can handle the small amount of current needed to throw a
solenoid. The solenoid does the heavy lifting, so to speak.
The 4-terminal solenoid shown here is typical of many used in the industry. Club Car
uses one that looks different but functions the same. Forward and reverse switching two
6-terminal solenoids must be employed along with a 3-way (reverse, neutral, forward) 10
amp minimal key switch. To understand 6-terminal solenoids, you have to realize that 2
of the 4 large studs are connected when there is not current acting on the coil. This is
called the NC (normal closed) side. When current is applied to the solenoid coil these
same two studs then become disconnected. The other two large studs are not connected
when there is no current on the coil. This is the NO (normal open) side. When the coil
is energized, the plunger throws causing these two studs to then become connected
through the plate. As these two studs connect, the other two normal closed ends
disconnect. Remember, closed means working (circuit is continuous), while open means not
working in electrical jargon.
In this design, one solenoid becomes the Forward solenoid and the other becomes the
Reverse solenoid. A 10 amp, 3 way key switch controls which solenoid energizes.
Solenoids come in lots of designs with different metals used for the terminal studs
and plate. Most common is copper, but years ago silver and silver plate was common.
They also come in many different amperage ratings and voltage requirements needed to
properly energize the coil so it functions as intended. Some solenoids are designed
to work for short periods of time such as the starter solenoid in your automobile.
These are intermittent duty solenoids. Golf cars require "continuous duty" solenoids
because they are energized the entire time the car is under power. Auto style
solenoids will work as a "continuous duty" solenoid for a while but they will
prematurely fail.
Lots of things go wrong with these switches. Obviously, the high amps create a lot
of arcing at the stud/plate interface inside the solenoid. Even though the plate is
designed to slightly rotate with each throw, eventually the stud/plate connection
deteriorates, sometimes to the point where it breaks down completely. This is
evidenced by the solenoid clicking and sometimes working (car moves), and sometimes
not working. Complete failure is around the corner though.
Electric cars are funny. Sometimes when there is a problem here, the failure shows
up over there. Loose connections anywhere the heavy battery cables attach (i.e. –the
speed switch, the motor, the batteries, F&R switch, even on the solenoids itself)
creates a lot of heat build up and, if loose enough, arcing. Remember DC current is
what welders use. When a sufficient air gap is established the DC arc melts steel.
Solenoids and lead battery posts don't stand chance. Keep all cable connections in
the car clean and tight. Inspect them at least once a year. Tightness is not as
critical with the small control wires, the control circuit as it is called.
Nevertheless, these connections must also be clean and tight.
Another reason solenoids don't work is because the energizing current just doesn't
get to the coil. In order that electricity gets to the solenoid winding, it must
first pass through the key switch and usually several small micro (or limit)
switches often found on the F&R switch and on the accelerator linkage. If any of
these switches have failed or if the wires interlinking them have broken or are
loose, then current cannot get to the solenoid. Some of these switches are position
sensitive. If one gets out of adjustment, even though it works ok, it cannot
function.
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Another cause of a solenoid not working is there is not enough battery voltage to throw
the solenoid. The voltage rating on the solenoid, say 36 volts, is required for that
solenoid to work correctly. Batteries can "self" discharge for various reasons. The
modern regen cars must be turned off at a special tow switch. If the car is not turned
off, the battery pack will self discharge in three to six weeks. Actually, the regen
controller's capacitors use the battery pack to stay charged, eventually draining them.
Non-regen cars do not have a main cutoff switch for the batteries, but unless there are
live accessories, such as a radio with memory, a clock, or a charge indicator or gas
gauge constantly on, a fully charged battery pack will maintain a charge for months.
Constantly "on" accessories are okay if the car is used frequently but they will
discharge the batteries to which they are connected if left uncharged for several weeks.
Monthly "catch-up" charges are suggested but not always feasible. We don't recommend
disconnecting battery cables because the regen controllers have a particular sequence
for disconnect and reconnect. Besides, it usually leads to more problems than it solves,
if seasonal storage procedures are carefully followed. Don't forget, discharged
batteries can freeze and burst their cases when temperatures drop below 32 degrees
Fahrenheit. Fully charged batteries can withstand 40-60 degrees below zero.
The last type of solenoid failure results when the internal plate and studs freeze
to each other. In other words, the solenoid works ok, but doesn't stop working when
the pedal is released. This results in the car creeping on its own when the shifter
is in F or R. Sticky solenoids are more common in the older resistor style cars, but
this condition, if not recognized and repaired, can be a fire hazard and at a
minimum, cause the battery pack to drain. Lots of folks have seen the result of a
sticky solenoid. The resistor coils glow red hot, hence the fire hazard, and why
this glowing condition drains the batteries. If this situation happens to you, just
shift into neutral each time you stop. Get it fixed right away! Remember that arcing
we mentioned earlier? Now that arcing is occurring at the F&R switch, not the
solenoid. The F&R is not designed to handle this condition.