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  #1  
Old 03-31-2001, 05:16 PM
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What is a normal current draw for a 92 400E? When off, my car draws .75A. Test was conducted with negative battery terminal disconnected and an ammeter in series with the terminal and cable (one probe on the negative battery terminal and the other probe on the disconnected negative cable).
I have recently had battery drain problems. I believe they are now fixed, but need this info to verify.
Thanks!

Ray.
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  #2  
Old 03-31-2001, 06:13 PM
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That would be too much. Proper sleeping current loss should be less than 100ma. (0.100A)

But! I think you may be testing the circuit inappropriately. By installing your meter in series I imagine that you disconnected the circuit. After doing this everything resets itself and some control units don't go back to sleep right away.

MB says to test quiessent current flow by mounting a switch between the battery cable and battery, such that when disconnected the only path becomes your series circuit through the ammeter. This circuit allows all control units to stay engaged and allows true testing of the sleep state.
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  #3  
Old 03-31-2001, 07:49 PM
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An easy way I do this is to put your test lead probe right on the bat terminal[verticle position] , the other clipped to the cable end ,
and remove the bat cable end and slip it up the insulator of the test lead. No interruption of powerand correct reading
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  #4  
Old 03-31-2001, 08:50 PM
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I noticed the power-up draw when connecting my meter; the draw is initially 3.45A while everything re-sets (about 30 seconds)and then drops back to about 0.75A. The trunk lamp is on, but I'm sure that doesn't use 0.65A!

Are there any circuits that are unfused, or fused elsewhere than in the box on the driver's side firewall? It looks like I still have a short somewhere and have been lucky that the battery has lived overnight.

Ray.
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  #5  
Old 03-31-2001, 09:02 PM
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The trunk light is probably more than half of that amount.
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  #6  
Old 03-31-2001, 10:29 PM
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Pull the truck light out and retest the current draw. I would bet that the trunk light is drawing most of the .75 amps.

With a .75 amp draw, you would get about 3 or 4 days before the car might not start. You have to get that current draw down or you'll have trouble if the car sits for a while.

I would pull the truck bulb out until you can get the switch fixed.

Let us know what you find out.

Joe

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  #7  
Old 04-01-2001, 12:41 AM
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A 5 watt trunk lamp will draw .42 Amp at 12 v.
Most trunk lamps are around 5-10 watt.
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  #8  
Old 04-01-2001, 12:34 PM
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Thanks to all who helped! I knew I'd get the hints I needed from this forum.

I can now rest at night knowing the current draw has indeed been fixed. The trunk lamp is 10W (!). Thanks, Arthur - you reminded my of I=P/V. 10W/12.6V = 740mA. Joe - I pulled the lamp and retested just to verify the math and it is right on - the draw after all systems reset and without the trunk lamp on is between 50mA and 90mA.

Interestingly, when the trunk mount CD changer is plugged-in but turned off, there is a small additional current drain of 50mA or so. Anyway - the total current draw is now less than 150mA in all conditions so we've verified that the original problem has been fixed.

Thanks again!

Ray.
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