Quote:
Originally Posted by Hib Halverson
If you connect an amp meter between the battery and ground you'll read current flow. There should be only a few hundred milamps.
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Ah, Hib... I believe you meant to say putting an ammeter in series between the battery post and that post's cable connector (have to disconnect the cable from the battery post to do the test). measuring current between the battery (positive) and ground creates a near dead short with the meter in the middle. If yer lucky, all it does is blow a fuse in the meter.
Robert-
because there is a path to ground through the radio and the ECM, etc that keeps the presets, clock, and memory alive, pulling the cable off the battery and then reading voltage will result in a voltage reading equal to battery voltage. If you were to disconnect the pos cable from the battery, and measure resistance between the positive connector and the negative terminal of the battery or to ground, you will see a few hundred ohms, but NOT infinity as there is a closed circuit even with the key off. (Somewhere between 240Ω and 1.2k Ω, after it settles, is normal.)
Back to the ammeter: Reading current between the positive terminal of the battery, and the positive cable connector (removed from the battery) you should have no more than 50mA (GM spec) , and typically 25mA or less. (Also note that when you first make the connection, the current will be considerably higher than that. That is normal. But, as the various capacitors in the electronics charge up (through the meter), the current draw will trickle down to its normal 10-50mA range before leveling off - usually after only 2-4 seconds or so. Once the reading settles, you can assess the normal "at rest" current draw, due to the "always on" stuff.)
The ammeter feature requires some special consideration: Move the read lead to the "10A" port on the DVM and select "A" on the meter BEFORE making connection between the battery post and the cable connector. To make the connections and then sweep the meter selector knob through the various ranges and such will more than likely damage the meter.
And! It is a good practice, once done makeing a current reading, to remove the test lead from the "10A" port on the meter and return it to the normal port. Otherwise you might do what I did yesterday
. I forgot to move the red lead back to the normal setting before setting the meter aside. When I picked it up again to this time make a voltage measurement, I didn't notice the mixup until it was too late - and popped the fuse in the meter!
You may already know all dis chit, but I can testify that even if you've been doing "lectric chit" forever, it is easy to have a brain fart and forget to do something a pop a fuse...
ask HIB and me how we know!!
P.