Ralph Mowery wrote:
"CWLee" wrote in message
m...
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 computer.)

Enlightenment appreciated.


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.

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.