Problem With Power Outlet

And proper use of a voltmeter is REQUIRED skill for troubleshooting
ANY electrical problem on an automobile. Checking voltage drops is a
skill every mechanic should be taught - until it is second nature.

 

That was pretty sneaky (and dishonest)! Here's the complete sentence,
the beginning of which you conveniently left out: "WHEN THE ENGINE IS
RUNNING [emphasis added], the inverter works fine; but when the engine
is off (with key in accessory position), the inverter will run for a few
seconds, give an error beep, and then shut down."

Well since you misread the OP (and now can't admit that), you need to
read it correctly now and re-think your position. With the engine off,
all bets are off on the inverter running with some finite line drop and
nominal (non-charging) battery voltage. Whether the inverter runs
properly with the engine off should not be a concern.

Not before you applied your sleight-of-hand to the OP's orignal post.

No - you are the first to pretend that it is off when it is in fact
running (in which case the inverter works - according to the OP).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

If the inverter you have has that feature, it's a REAL no-brainer. Not
all do. Mine has exposed "binding post" type connectors that make it
real easy to check as well, but a lot of the sub-150 watt units are
simply hard-wired and no connections are accessible.

 

keep digging, boy

ever heard of a VOLTAGE regulator ?

 

in this case, two full days have been wasted farting around, and 10 minutes
spent replacing the battery (which is alread three years old) would have
given a definitive answer

 

Max, what you are advocating (I hope) is a BATTERY RESERVE TEST.
Simple way to do it, with NO fancy equipment, is to measure open
circuit coltage with the engine shut off (should read above 12 volts -
12.6 is theoretical full charge (2.2 volts per cell)). To stabilize
the battery and draw off the "surface charge" crank the starter for a
couple seconds. and then turn the headlights on low beam for one
minute, and read the battery voltage with the lights on. It should
hold 12 volts.
If you leave the lights on for 3 or more minutes, and the battery
voltage"sags" to 11.6? more or less, you want to do a "recovery test"
which means shut off the lights, wait one minute, and recheck voltage.
It should be back to a minimum of 12 volts.

If it passes these tests, and does not drop below 10.5 volts when
cranking, the battery is functional and is not causing the problem. It
may still not be GOOD, but it is NOT the problem - and since starting
after sitting a couple days isn't a problem either, the battery IS
good.

 

No Max - it is, 99.9% sure, NOT a battery problem. It IS a wiring
problem.
Not knowing the wiring schema on the Caravan intimately, I'd say
either a bad body ground (has been a problem on Chryslers) or a bad
connection in the distribution system, or an undersized wire. All 3
are very possible, and the "booster post" mentioned by another poster
would be the second place to check, if it has one, after the body
ground, from my experience.

 

And, at the risk of sounding ignorant (which I am, but I don't want to sound
that way ), which lead goes to which terminal (or does it matter)?

 

And if that's not the problem he has a good used battery on his hands,
and still no farther ahead. Better to buy a cheap voltmeter, get a
book from the library on how to use it, and test it himself. Learn how
to do his own testing and not be at the mercy of (what seems to be
more commonly) incompetent "technicians"

 

The only indication I have of that is that the inverter shut off the other
day while I was driving the car (and stopped at a red light), while the
computer was OFF (normally both front and rear outlets work with the
computer off, but charging). This was with the rear outlet. So, yes, maybe
the battery was pulling down the alternator. Or maybe the regular
fluctuations of the inverter caused the power to drop enough for it to shut
off. Either way, not good.

 

Actually, Max, would you not check power AT THE OUTLET first, to see
if it is a power problem atall, or a device problem????
I would. If the voltage at the outlet is OK under load, no use going
to the panel. If it is low at the outlet, check at the breaker. If ok
at the breaker, bad wiring, if low at the breaker, check the line side
of the breaker. If ok there, replace the breaker. If low at the line
side, check at the main breaker. If OK there, you have a panel
problem. Always check from the known problem back, not from the known
good forward.

 

Remember, this is MAX speaking. Doesn't have to make sense or be based
on fact.

 

It depends on the outlet design and I haven't looked into one in a
minivan in some time. However, most are similar. Typically, you will
see a contact in the center bottom of the outlet which is typically the
positive (+) terminal and then the outer body of the outlet is the
negative (-) terminal. Take your DVM, multimeter, or voltmeter and
touch the red (+) probe against the contact in the bottom center of the
outlet and then touch the black (-) probe against the shell of the
outlet which is all grounded. This will show the open circuit voltage
of the outlet. To measure the voltage under load, you will need a
splitter as someone else already measured.

Be sure that your meter is set on DC and for the proper range to read
10-14V. Many of the new DVMs are auto ranging so all you have to do is
select the DC range and you are good to go.


Matt

 

That is a cluelss service manager. I've had batteries last less than 3
years and 40,000 miles and I've had batteries last 9 years and over
100,000 miles. You simply can't judge battery condition by age or
mileage alone.


Matt

 

Put the RED lead on the little contact in the middle of the outlet,
and the BLACK lead on the outer contact, or any good chassis ground.
That simple.

 

At idle, with headlights and heater fans running, your battery was
likely close to or below 12.2 volts.

If the lights are flickering, you, 90% or better chance, have a
compromised BODY GROUND. Put a booster cable from the battery negative
to a good clean, bare metal contact on the BODY of the van and retest.

 

Auto Zone and MOST battery retailers use a transconductance tester,
such as a Midtronics tester, to test batteries. MOST battery suppliers
REQUIRE the battery to be tested on one before replacement. It can
test a battery that is 3/4 discharged, accurately. If a Midtronics
tester says the battery is shot, its shot. If it says it's good, 99.9%
of the time its good. The ONLY exception is an intermittent intercel
connector, which may test perfectly good once, and read 100% dead,
even with a voltmeter, the next. I've seen that happen only ONCE.

They are MORE accurate than a load test.

 

Yep, and do you know how they work? They don't hold voltage exactly.

How does the amperage vary if you hold the voltage constant?


Matt

 

Hardly. If the voltage drops much under load, it won't provide enough
current to crank the starter. Do you understand Ohm's law at all?

No, there are many tests that can and should be performed first that
require much less equipment and expense.

I haven't tried to keep track of who said to replace the battery and who
didn't. You just sound like those who have been suggesting that.

The starter doesn't care because a starter is an inanimate object and
can't care, but it does "know" what is going on. If the battery can't
maintain sufficient voltage to drive MANY amps through the starter, it
won't spin the engine to start it.

That isn't the power source. For the OPs inverter, the outlet is the
"power source" in the same sense that your service entrance is the
"power source" for your house. Checking the voltage at the outlet is
the absolute first test he should make, both open circuit and then under
load if possible. That is much easier than running a load test on the
battery and takes much less equipment. Very few of us have battery load
testers in our garage.

It hasn't been worth much to read.


Matt

 

TRANSCONDUCTANCE ???????

surely you jest

Transconductance Transconductance is a measure of the change in plate
current to a change in grid voltage, with plate voltage held constant. The
unit for conductance is the mho (siemens), pronounced "moe."
Transconductance is normally expressed in either micromhos or millimhos.

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