Using a handheld voltmeter, at the battery on my car, I get
a reading of around 12.5 volts. When I use the same
voltmeter at the cigarette lighter socket and at the
accessory outlet, I get a reading of only around 4.5 volts.
(The latter reading jumps about a volt if the engine is
running.) Why aren't the readings on the cigarette lighter
socket and the accessory outlet pretty much the same as at
the battery? (Both the cigarette lighter socket and the
accessory outlet work just fine to recharge my laptop
Former slayer of dragons; practice now limited to sacred
Assuming the sockets work as you say, you may have a bad connection of your
voltmeter test probes at the point you are trying to measure. The voltage
should jump a volt or two with the motor running as it takes more voltage to
charge the battery than what it is normally.
I have also seen bad connections on the wiring that measured the normal
voltage, but under load the voltage would drop. That is not your case.
If it's the same with two jacks, it must be the ground. I'll bet if the
OP measured between the point he thought was ground and the negative
terminal of the battery, he would find approximately twice the
resistance of his meter.
When humidity is low, clothing rubbing against car seats can cause
static shocks when a person touches grounded metal. If the car
manufacturer puts some megohms between that metal and ground, touching
it will drain the charge painlessly.
Actually the car metal does not have to be grounded. As the car is a large
mass of metal it will have a differance of potential from the person that
slides across the seat.
PUtting a resistor between the car and ground will do nothing for this
Years ago some gas trucks would drag a chain to ground the truck. This was
thought to drain off any static charge the truck would have so the gas would
not blow up when the hose was used to transfer the gas. A spark could jump
from the end of the hose to the storage tank.
Fuel trucks still use static dissipation devices.
Instead of chains there are conductive straps
that are less likely to cause a spark when dragged
across metal. The straps are used on cars, trucks
and motor cycles. Sometimes the chains you may see
under a truck could be automatic snow chains. It's
some interesting stuff.
Check out #9
Looking at that automatic tire chain sitting so close to the ground
got me to wondering.
If he ran over a piece of tire debris and knocked it loose, that could
cause some serious damage to his truck.
Not exactly my field, but I have read that modern car tires have enough
carbon in them to be a ground path. Might be high resistance?
I agree with other that the OP probably does not have a good connection.
~10 years ago, when 3M still made the "touch me first" anti-static strips
for computer keyboards, I took one and stuck it to the armrest/door handle
of my car then ran the wire in behind the trim and attached the wire to some
point on the body. It worked great. Wish I could still get them!
Window glass typically has the right amount of resistance to drain
static safely. If you could pick up static at the arm rest and carry it
to a conductor that brushed against the glass, that should work.
Another trick is to wipe an insulating surface, such upholstery or an
arm rest, with a soapy wash cloth. The soap film will allow static to
bleed across the surface to a ground.
Polyurethane soles, which are very common these days, insulate so well
that static can build. If I start getting shocks, I use a soapy cloth
to wipe the edges of my soles. I wish I knew something that wouldn't
wash off the first time I walked on wet grass!
Static electricity.... The local walmart got all new shopping carts
(buggies down south). They are painted with a fairly thick coat of
paint. If your hands are on the painted surface, or even the plastic
handle, as you stroll along you keep getting zapped with static shocks.
They also got some electric cart pushers with a remote so that one
person can move a loooong line of carts. They stand up front and steer
the first cart and the electric one is in the rear pushing, operated by
remote control. The first thing they tried to fix the static was to
hang chains from the remote cart pusher but that didn't do a thing. I
think they have been using anti-static spray on the hard rubber wheels
and that lasts for a little while. Even all summer although humid
outside it's air conditioned enough inside so you get the shocks all
The cigarette lighter should be about the same as the battery. This would be
measuring DC volts with the multimeter.
1. Does the ignition switch need to be on for this to work? Also be sure you
are measuring directly to the socket itself and not through any plug-in
device (which could change the voltage).
2. The problem could be with the +12 volts which would be the center of the
socket, or the ground which would be the round metal. Get a long wire or
jumper cable and connect it to the + of the battery, then measure from that
to the ground of the lighter socket (this tests the ground). Then switch the
cable to the ground on the battery and measure from that to the +12 center
connection on the socket (this tests the +12).
If the ground is bad, check the ground connection to the socket.
If the +12 is bad, check the fuse and measure for +12 at the fuse. If +12
good at fuse, but not at socket, then problem with the wire or connectors
between the two.
If the +12 is not good at the fuse (you would probably be having problems
with starting your car in this case), check all main electrical connections
How to test automotive fuses...
"CWLee" wrote in message
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.