Battery drain - PeachParts Mercedes-Benz Forum

jlw15 · #1 03-16-2012, 01:34 AM

I have an 1987 mercedes 420 sel ---i put a meter on the neg. cable and battery terminal and its shows 0.10 draw on the battery i guess that would be milimeters, is that enough draw to lower my battery that it won't start after a week or so of not being used ??
Thanks
jlw15

JamesDean · #2 03-16-2012, 01:40 AM

It depends on what scale you had your meter set to.

If you had it set to 10A, then that means 100mA.

jlw15 · #3 03-16-2012, 09:40 AM

Quote:

Originally Posted by JamesDean

It depends on what scale you had your meter set to.

If you had it set to 10A, then that means 100mA.

Yes meter is set at 10A

oldsinner111 · #4 03-16-2012, 10:07 AM

when alternator go bad sometimes they will draw power..I had to replace mine

ILUVMILS · #5 03-16-2012, 12:11 PM

A 100mA draw shouldn't kill a healthy battery in just a week. The normal rest current draw for that car is at least 50-60mA so you're only looking for a 40-50mA problem. Star by removing the fuses one at a time while watching the meter.

Adler · #6 03-16-2012, 01:05 PM

Try removing the clock fuse to isolate the leakage . Leaky capacitors in these clocks are common .
good luck

Adler

JamesDean · #7 03-18-2012, 07:01 PM

1.3A draw with doors open sounds correct. I'll check my 420SEL in a bit here and see what the battery drain on it is..

Edit: Here you go. Looks like 20mA is the nominal draw on the battery. You've got something extra pulling power.

jlw15 · #8 03-18-2012, 10:14 PM

Ok---Where do i start looking ?? i pulled all the fuses under hood in fuse box except the square metal ones and nothing changes and even when i pull the clock fuse it don't even change---Help Please

JamesDean · #9 03-19-2012, 02:19 AM

Do you have any wires coming off the positive terminal aside from the factory mercedes ones that are on the connector?

jlw15 · #10 03-19-2012, 08:47 AM

No--Main positive wire and one thinner wire---car is stock---today i pulled the clock fuse and meter read .08 with the fuse in it bounces from .09 to .10 like everytime the second hand moves it goes to .10

Edmund · #11 03-19-2012, 07:12 PM

80mA isn't that bad. That can be a combination of things like the radio,alarm,immob,telephone,clock,etc all drawing a little current adding up to 80mA. Don't worry about it unless you experience trouble. If the battery drains in less than a week something is wrong or the battery is defective. To give you an idea : a standard LED draws about 10mA and can run about 6500hrs(270 days) when connected to the average car battrery(657).

jlw15 · #12 03-19-2012, 07:31 PM

I know when the battery was replaced a couple of years ago i wasn't there and the mechanic did not put the proper battery replacement in---i have had this battery load tested and it shows fine---i only drive this car once every couple of weeks and in that amount of time the battery won't start the car. ----if i disconnect the battery it stays charged with no problem.

JamesDean · #13 03-20-2012, 12:39 AM

You might want to consider trying this. Just below the battery on the firewall closest to front of the car there is a distribution block. If you put your meter in between the positive terminal and each individual wire/wireset (removing them one-by-one) you might find that your drain is coming from the alternator or fuse box or starter. I know when my 190E's alternator went it produced a large draw on the battery.

jlw15 · #14 03-20-2012, 12:23 PM

when i'm checking each wire in block with meter do i leave the battery connected and put my meter on 10A and if i show a draw on a wire thats the problem??
thanks

JamesDean · #15 03-20-2012, 03:18 PM

You should disconnect the main positive battery cable from the battery. Then disconnect the wires from the block and put your meter between the positive post and the wire. It should be fairly visible where each wire goes. One or two should go to the starter, alternator and main car fusebox.

If you show a power drain on the alternator or starter wire set that might be indicative of a problem. If you find no drain on the starter or alternator wire sets thats a good sign that and your drain is elsewhere.