OK, here are the results of the tests.
With engine running, laptop plugged in and running in the rear outlet:
Rear outlet (feed-through plug): 12.7
Front outlet: 13.5
Same as above, but with heater fan on full and headlights on:
Rear outlet (feed-through plug): 12.5
Front outlet: 13.35
Chassis ground voltage drop test (with everything running as per above two):
With VM connected to battery positive and rear outlet fuse: 0.033
With VM connected to rear outlet fuse and center of inverter feed-through
plug in rear outlet: 0.69
With VM connected to shell of inverter feed-through plug in rear outlet and
body ground: 0.164
So, the results seem to be accurate, since the total of the four tests 0.94, which is the same as the drop from the battery to the rear outlet.
What seemed strange to me, though, is that these tests don't show a big drop
to the front outlet. Yet I have intermittent problems with the inverter
staying on in the front outlet when the engine is off.
Plugging the inverter/laptop combination into the front outlet, with the
same conditions as above, I got:
Inverter feed-through plug: 12.9
So, not as much of a drop as to the rear outlet, but still a drop (though it
didn't show up when I just tested the front outlet without the inverter
Anyway, thanks for your comments regarding the above!
<clare at snyder.on.ca> wrote in message
OK, You have a 0.8 volt drop - which IS excessive.
And your drop increases with other loads by 0.15 volts, which is also
excessive, This is "common" circuit voltage drop - which could be
body ground, or could be between the battery and the fuse.
This indicates roughly 1/3 of this "common" drop is on the body
And 0.030 volt drop is on the live side between the battery and the
Which indicates the wire between the fuse panel and the socket has a
large voltage drop. Either a bad connection on the back of the socket
or severely undersized wire.
And the wire from the socket to ground also has excessive resistance,
for the same reasons.
The drop to the front will only show up with the inverter plugged into
Which indicates a total drop on the front plug of 0.55 volts - which
is still excessive.
Voltage drops ONLY show up under load. The front and rear are separate
I would pull the rear socket and check the connection there, and run
another wire, at least as heavy as the current wire, and preferably
more like a #14 or better wire from the fuse box to the socket, and
from the socket to ground, in parallel with the existing wire.
I would also still put an extra ground from the battery to the body -
#6 preferred - or a standard ground braid if you can find one.
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Thanks for your comments! I assume that this running of the new wire to the
socket is something that I would have a professional do. Is it something
terribly difficult/complicated? Any idea about what it might cost?
When you previously said, "add a new body ground," I thought you meant to
replace the existing one. But here you're saying to add an extra body
ground. So I must have misunderstood.
You note above to run a new wire from the fuse box to the rear outlet. Since
the front outlet also has a drop under load and is on a separate circuit, I
assume I would need to do the same for the front outlet?
Also, as noted previously, the headlights sometimes flicker when in use. You
said previously that that was probably due to a bad body ground. Would
adding the second ground from the battery to the body resolve that, or do I
need to some something else?
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