Problem With Power Outlet

Yes, it could be a bad ground. However, if the voltage read low this
way you would KNOW it was either the wiring or the body ground.

 

OK, under load you have 1.1 volts drop in the wiring to the front
socket. This is DEFINITELY excessive.

Again, you have 1 volt drop with the inverter and charger connected,
and the laptop not running. This id definitely excessive.

I would suggest you connect the voltmeter to the battery negative
post, and a clean bright ground on the body and turn on the headlights
and heater fan. You will likely have to set the voltmeter to 2vdc to
get an accurate reading, but start on a range above 12 volts, to be
safe. I suspect you will read over 1 volt drop, in which case you need
to repair the body ground.

 

I mean retest the inverter problem.

 

We KNOW the battery voltage

Yes, but we KNOW the battery is not the problem. At least I'm
confident from the information supplied and 40 years experience.

 

No, but I have a 2004 Pontiac Trans Sport. When it stops raining I'll
connect my 300 watt invereter and my Thinkpad 770 to the rear power
outlet and give you all a voltage reading.

 

I've had batteries go bad at 3 months, and I've had them last 10
years.

 

AVERAGE is the important word here - and a LOT of batteries don't last
2 years. Discounting "infant mortality" average battery lifespan is
closer to 5 years. Not counting those undersized Delco Freedom
batteries of a few years back.

 

Max,
Nobody said anything less than 13.2 was a bad battery. All I said was
MAXIMUM FULL CHARGED VOLTAGE of a lead acid battery is 2.2. volrs per
cell. When surface charge has been drained it will be NO MORE THAN 2.2
volts per cell. VS your 14.3 , which is 2.38 volts per cell.

A battery coming off charge at 12.8 (as reported by the OP) IS fully
charged.

 

A diehard isn't a battery to start with - it's a poor warranty
attatched to a plastic box of lead and acid.

 

Not sure if I did this correctly, but I didn't see any drop. I placed the
black lead on the negative battery post and touched the red lead to a clean,
shiny area of metal on the outside of the car. I set the VM to 20V and
turned the key a little, and then turned the heater on full and the
headlights on. No change. VM read zero.

I then did the same with the VM set to 2000 mV and 200 mV. Again, VM read
zero both times.

 

Hi Clare...

With all due respect, a fully charged lead acid cell will read
a tiny smidgeon over 2 volts... If I recall correctly 2.04v,
for a total of 12.24 volts

Anything over that is surface. They don't call 'em 12 volt
batteries for nothing

Take care.

Ken

 

OK, I just went out to my 350,000km 1984 Pontiac TransSport Van
(closest I have to a '93 Caravan) with a 540 cranking amp Interstate
Megatron battery, about 9 months old, and an alternator and regulator
about 3 years old.

I tested with a cheap digital VOM, a 400 watt Coleman inverter, and a
Thinkpad 770 laptop, the adapter for wich says Input 100-240 VAC 1.0
amp.

After sitting for 3 hours, battery voltage, measured at the battery,
and at each outlet, was 12.18 volts.
I started the van and let it run at idle with low beams and heater fan
on, and voltage was 13.2 At 3000 RPM voltage rose to13.98, and dropped
to 13.8 when I stepped on the brake. At 4000 RPM it reached 14.02
volts.
Returning to idle, voltage sat at 13.92, with loads on, 13.4, and with
brake depressed, 13.19, in gear, 13.10

I shut down for 1 minute and voltage read 13.0.
I turned low beam headlights on for 1 minute, and voltage sagged to
12.2.
When I turned the lights off and waited a minute, voltage recovered to
12.62

I then got the inverter and laptop and plugged them in.

My open circuit voltage was12.47 volts with the interior light on
(door open) and with the inverter plugged in and turned on, it dropped
to 12.38 volts.

I turned on the computer and voltage dropped to 12.9 - after 3 minutes
it was 11.9 and battery terminal voltage was 12.29

Plugged into the rear plug, inverter (power outlet) voltage was 11.75.

SO on my Trans Sport, I have a 0.39 volt drop in my front outlet
circuit, and a .54 volt drop in my rear plug circuit.

This is a 12 year old GM vehicle with over 300,000 hard KM on it, so
in all likelihood has more voltage drop than it left the factory with.
It is definitely more than I would prefer to see - I know the inflator
compressor runs significantly slower from the rear plug than from the
front.

The front plug is fused at 20 amps, and according to the owner's
manual, the rear plug runs on the same fuse.

If the adapter takes 1 amp at 120 volts, the inverter draws a minimum
of 10 amps to supply the adapter. It (the adapter) likely draws less
than 1 amp from the 110 volt plug.
IF it draws 1 amp, the rear circuit has a (.54/10).054 ohm resistance,
and the front has a (.39/10)) 0.039 ohm resistance.

Resistance of a 20 amp ATO fuse in the panel is roughly .0025 ohms. A
good fuse connection adds about the same resistance, for a total of
..005 ohms, which means .05 volt drop in the fuse panel
A fuse holder can introduce 30mv drop PER CONNECTION to a 20 amp
circuit according to several auto sound sites (which quoted Littlefuse
re: ato fuses), and this checks out with the previous estimate pretty
closely. This was cited in explaining fuse blow times.

My rule of thumb has always been a properly designed circuit should
not drop more than 0.10 volts in a 12 volt system, so my old Pontiac
is shedding 4 times as much in the front circuit, and 5 times as much
in the rear circuit as I would LIKE to see. Likely due in part to some
pretty scabby connections at both body ground and the "booster post"
as well as some corrosion in the 12 year old battery cables
themselves.



60 MV drop at 20 amps is .006 ohms, or .003 per connection

 

You do NOT need to "test" the battery -- all you need to do is check
the VOLTAGE of the battery (which IS the voltage at the power plug
with no load) and check the battery voltage at the battery with the
circuit under the "test" load - which in this case is the
inverter/adapter. This allows you to CALCULATE voltage drop.

Or, you can just measure the voltage drop directly, and the battery
voltage itself doesn't mean a thing, as long as the load voltage is
within a few volts of spec.


See ACTUAL VOLTAGE MEASUREMENTS posted my me a few minutes ago.

 

Actually, what was posted - 2.2.volts per cell MAXIMUM is correct.
Actual voltage varies according to acid density, which varries from
place to place around the world, and from battery application to
battery application. In warm climates, battery SG is lower, and
therefore battery terminal voltage is lower, to reduce self discharge.

AVERAGE north american battery terminal voltage is 2.1 per cell, for
12.6 volts. I have some batteries that will never go above 12.13 volts
(2.02 volts per cell) that work perfectly (AGM batteries).

Anything over 12.45 volts open circuit is considered to be a fully
charged battery.

 

LOL, unless he has a shorted cell, the voltage while running is dependent on
the regulator, not the battery.

 

That would be correct procedure if the clean, shiny area of metal on the
outside of the car happened to be the location where the power outlet gets
its ground. Otherwise, no.

 

How would I determine where the power outlet gets its ground?

 

here.

I would hold off on the Dipshit comments if I were you. Please show me one
battery that is rated for 628 CCA, don't worry, I'll wait. A modern load
tester can estimate the actual CCA of the battery it is testing. It is
probably a 700 CCA battery that is now down to 628 CCA from age and wear but
is still more than capable of operating his inverter for hours.
As for you 1000 CCA comment, all that does is clearly demonstrate that you
don't know WTF you are talking about because no matter how high the CCA is,
it will have no effect on a voltage drop due to wiring.

Says who on a 3 year old battery?

Yea, after your other bullshit and what exactly do you mean by acting
accordingly, especially when speaking to an obvious electrical novice?

 

Ted, comparing two different DC systems that rely on battery power is less
than informative. Sure, it'll show him what the other truck is doing, but it
won't have the power inverter.

Fact is, most of these guys have assumed hte problem is not the truck, but
the port itself somehow.

First fact that I picked up was,
cars (a GMC Jimmy and a Chevy Cavalier), I've plugged an AC inverter into
the cigarette lighter/power outlet, and then plugged my laptop computer into
the inverter to charge and run it, without any problems. <<<

This tells me the device is not the problem.

Next, he says the device exhibits a specific event, and why that event
occurs:
new car, the inverter shuts down, indicating it's not getting enough power
(it automatically shuts down at 10.5V).<<<

He then qualifies this event, by defining conditions under which the event
occurs:
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.<<<

This infomation combines and tells me that the system voltage drops below
10.5v at the power port. We KNOW the device functioned fine in other cars.
We KNOW it works well while the engine is running. We KNOW it functions as
though a drop in voltage has occurred while the engine is not running. We
KNOW from all this that the port in question probably isn't supplying enough
voltage.

As such, another vehicle isn't going to exhibit the same events unless the
same device is plugged into it.
everything tested fine, and the battery was at 12.8V.<<<

We know from this that the battery is a bit on the low side for having just
been charging. We know from general information that the charging system
runs at about 13.5-14.5 volts. The OP does not mention any DTC's, which
would indicate low or high voltages in the system while running.
there. He said he thought it would be the battery, as it's the original
manufacturer battery and has 45K miles on it. (I told him about the AutoZone
test, and he said that that test isn't conclusive, that I could have a bad
cell in the battery, and so forth.)<<<

We know from this that the battery is original, and thus is three years old,
an average lifetime for a factory installed battery. His mechanic agrees
with that statement.
right up, without any hesitation, and it seems to me that if the battery was
so low that it couldn't provide at least 10.5V, that there would be some
hesitation when the car was started.<<<

The OP is reasonably correct here, although batteries do work "well" until
you replace them, and find that a new battery does so much better.
if anyone had any other ideas about what this might be. The specs for the
power inverter and for the laptop charger are below.<<<

The OP clearly has not ruled out the battery. So I'll again state the
obvious:

1) Load test the battery to see if it will hold voltage above 10.5v while
under load.
If no) replace battery.
If yes) go to step 2
2) Test battery voltage with a VM while battery is "at rest".
3) Immediately test port voltage with a VM as comparison.
4) Get in the device, and use the port it has as a "pass through" (saw that
somewhere in this mess) and while plugging it in, monitor voltage at the
port. THat will show the problem, without a doubt.

There are those that will argue to do it differently, but the KNOWN facts
indicate a battery problem, or a port voltage problem. To fix the battery,
you replace it at a cost of $60 or so. To fix the port, should all else be
confirmed good, will cost $60 AN HOUR to rewire the port with larger guage
wire.

All that testing above costs about $25 for the VM, and takes about ten
minutes. IOW, far less time than listening to these idiots play games with
how much testing and diagnosis cost and how much should be done to achieve a
solution.


--
Max

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)

 

LOL, unless he has a shorted cell, the voltage while running is dependent

Very true. However, if you read the OP, the problem is while the engine is
not running.

--
Max

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)