Excessive Parasitic Current Draw
June 30th, 2011, 9:36 PM
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Excessive Parasitic Current Draw
I am trying to repair a problem on my elderly fathers Suburban. It is a 1999 1500 SLT with the 5.7 gasoline engine. Even with a new battery -- after it sits for several days the battery is drained to where it will no longer operate the starting motor. The alternator puts out a good 14 plus volts when running. I installed an accurate ammeter in series with the battery and something is drawing around 900 milliamps (0.9 amps) while the vehicle is parked. Obviously this is way more than it should be (50 milliamps or so). I disconnected the alternator and the current draw didn't change. I've disconnected the glove box light and the light under the hood. At nighttime I've checked for any light that is on. Nothing. I then individually removed each of the fuses in the interior fuse panel at the end of the dash. No change in the current draw. I then removed each of the relays, circuit breakers and fuses in the flat fuse box in the engine compartment by the master cylinder. Only when I removed a 50 amp fuse labeled 'BATT' did the current draw go completely away. This fuse is between a 50 amp fuse labeled 'LIGHTING' and a 40 amp fuse labeled 'IGN A'.
I'm wondering if anyone has an accurate electrical schematic on this vehicle and can tell me what this 'BATT' fuse supplies and therefore what could be possibly causing the excessive current draw. I will very much appreciate any help that can be provided (and so will Dad). He is 84 years old and he bought the thing new back when mom was still alive and they used to haul the grand kids around in it camping etc.. Now the grand kids all have cars of their own.
I'm wondering if anyone has an accurate electrical schematic on this vehicle and can tell me what this 'BATT' fuse supplies and therefore what could be possibly causing the excessive current draw. I will very much appreciate any help that can be provided (and so will Dad). He is 84 years old and he bought the thing new back when mom was still alive and they used to haul the grand kids around in it camping etc.. Now the grand kids all have cars of their own.
Last edited by Chuck D.; June 30th, 2011 at 9:43 PM.
June 30th, 2011, 9:44 PM
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Welcome to the forum Chuck.
I will take a look at the info I have and see what I can come up with.
Be sure to check the visor vanity mirrors, they are notorious for being on.
I will take a look at the info I have and see what I can come up with.
Be sure to check the visor vanity mirrors, they are notorious for being on.
January 25th, 2012, 7:52 PM
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Any word on this here? I have the same problem in my 1993 Burb. But thing is mine is a Cheyenne so it is a base model, with not much electrical accessories in the passenger area. I get .05A with the amp but Head Unit removed. Remove power lead to amp and I get 0.04A. Remove power to sirens(former cop car) and my draw goes to .03-.04A. This isnt a lot but I m going to reinstall the head unit tomorrow and I d like to know what to expect. My problem is the new battery is too weak to start after about 2 days sitting. What is sleep draw? 0.02A? I thought 0.05A was too much but other sources say that is the max norm limit. But who knows when I reinstall the radio?
August 12th, 2012, 7:50 AM
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August 13th, 2012, 10:20 PM
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Hi,
I have been working on a 1993 Chevy Cheyenne truck.
Removed neg. terminal.
Put in test lamp.
Fairly bright.
When I removed the STOP light fuse, the light was very very dim.
Put stop light fuse back in - light come back on..
So, I need to figure out if the last owner of the truck attached an aftermarket radio to the brake light fuse.
If you look at where the brake light fuse power goes - it goes all over the place - to the turn signal switch and to the 4 ways too.
Measured current draw with stop light fuse in - .04 amp or 40ma.
That seems like too much.
Was googling and this math is interesting.
Says average car battery is about 50 amp hours.
That means at the draw of 1 amp the battery will run 50 hours.
So, if we take 1 amp and divide by .04 amps = 25
25 times 50 = 1250 hours.
1250 hours / 24 hours per day = 52 days until battery needs a good recharge.
So, at .04 amp draw, a healthy fully charged battery should last a month.
That's still not good.
I have been working on a 1993 Chevy Cheyenne truck.
Removed neg. terminal.
Put in test lamp.
Fairly bright.
When I removed the STOP light fuse, the light was very very dim.
Put stop light fuse back in - light come back on..
So, I need to figure out if the last owner of the truck attached an aftermarket radio to the brake light fuse.
If you look at where the brake light fuse power goes - it goes all over the place - to the turn signal switch and to the 4 ways too.
Measured current draw with stop light fuse in - .04 amp or 40ma.
That seems like too much.
Was googling and this math is interesting.
Says average car battery is about 50 amp hours.
That means at the draw of 1 amp the battery will run 50 hours.
So, if we take 1 amp and divide by .04 amps = 25
25 times 50 = 1250 hours.
1250 hours / 24 hours per day = 52 days until battery needs a good recharge.
So, at .04 amp draw, a healthy fully charged battery should last a month.
That's still not good.
