Parasitic Draw

[Sigi]

I noticed my batteries were down a bit after sitting for a few days. Pulled out the multimeter and it turns out I have a 0.8 amp parasitic draw with everything off and waiting a couple of minutes. On a car I'd expect less than 0.03 amps. Standard 1123 truck with no add-ons (yet).

0.8 amps is way too much, almost 20W. Does the truck go to sleep after a while? I did not think the electronics were that sophisticated. The only things pulling some power should be the TCM and the start box. Has anyone measured their parasitic current draw?

 

[NDT]

No magic on HMMWVs. Start unplugging stuff until you isolate it. Likely culprit start box..

 

[Milcommoguy]

I noticed my batteries were down a bit after sitting for a few days. Pulled out the multimeter and it turns out I have a 0.8 amp parasitic draw with everything off and waiting a couple of minutes. On a car I'd expect less than 0.03 amps. Standard 1123 truck with no add-ons (yet).

0.8 amps is way too much, almost 20W. Does the truck go to sleep after a while? I did not think the electronics were that sophisticated. The only things pulling some power should be the TCM and the start box. Has anyone measured their parasitic current draw?

800 ma is HUGE.. Might try and isolate it at the 12 volts feed to the TCM / transmission connection (battery center tap) OR take a look on the 24 Volt side of things. Right there in the battery box to figure which direction to head. The smart / dumb box does have a "keep alive" but very small -2 ma draw.

All 24 volt feeds to accessories go thru it, making it a little bit of a brain tease to work out. Sounds like your up to that challenge. Leaky diodes in the alternator can be suspect too on 200 Amp units. Regulator look there too. (not so much on 60 Amp systems)

Good luck probing around, CAMO

 

[osteo16]

Definitely second the possibility of your generator pulling that power out as CAMO said... Id look hard there ..

 

[86humv]

The relay behind the front right seat will sometimes be stuck on with ignition off.
If stuck on...it powers the trans computer.

 

[Milcommoguy]

The relay behind the front right seat will sometimes be stuck on with ignition off.
If stuck on...it powers the trans computer.

Good catch 86humv... points to another gremlin to slay. (I have the simple 3 speed transmission, no relay control.)

Check check and double check, CAMO

 

[cwc]

I have had a parasitic draw within the light switch also.

 

[Sigi]

I measured the 0.8 amps with the ammeter in series. Looks like putting the meter into the circuit woke something up and I did not wait long enough to have it go back to sleep.

This time I measured with with a Fluke DC clamp meter not disturbing the battery connection and did not detect any current. Of course, the clamp meters are not very precise at low currents but it would have detected half an amp or more.

Next time I'll bring some croc clips to keep the ammeter in series for half an hour or so. This should provide the definitive answer.