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Old 11-11-2009, 05:00 PM
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Battery drain issues '84 300D - what is quiescent current drain?

Hi all,

My car was getting hard to start as soon as it started raining a lot here in Portland, OR. Then during the heaviest rains, it wouldn't start at all. All the dash lights would fade and the engine wouldn't turn over. A jump start got me going, and I put the battery on a charger all night.

I disconnected the ground terminal from the battery and attached an ammeter in series. It read 25mA. Is that a normal quiescent load for the car when it's off?

I reconnected the battery and started going through fuses that control things that work when the ignition is off. Bada-bing! Fuse #2 (clock, trunk light, diagnostic, switch-over valve seat back arrester [for a coupe?], roof light front + rear, hazard warning system, automatic antenna, illuminated vanity mirror, warning monitor term. 5, electronic radio) gives a load of 25mA.

So if 25mA is not a normal quiescent load for the car through that fuse (like does the clock use that much current?), are any of those others known problem areas?

I did have a problem where I tried to put on the hazard blinkers the other day during the rain storm and there was just a loud buzzing from the switch. I tried it again a few times and it started working again. Also, the bulb in my transmission selector went out.

Thanks!
Aaron

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Old 11-11-2009, 05:47 PM
aaa aaa is offline
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25ma is insignificant. Sounds like the clock all right.

Since there's only 25ma I don't think there's a battery drain at all. Try checking the alternator, also how old is the battery?
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Old 11-15-2009, 05:25 PM
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The battery is at least 4-5 years old. I remember replacing it around that time.

I believe my alternator was replaced within the past 18-24 months.

Battery voltage is 12.48 when the car is off, 14.08 when the engine is running.

Any thoughts?
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Old 11-15-2009, 06:38 PM
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What kind of radio is in the car?
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

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  #5  
Old 11-15-2009, 06:50 PM
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Location: Middle TN
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Quote:
Originally Posted by MonsieurBon View Post
The battery is at least 4-5 years old. I remember replacing it around that time.

I believe my alternator was replaced within the past 18-24 months.

Battery voltage is 12.48 when the car is off, 14.08 when the engine is running.

Any thoughts?
I had similar situation and it turned out to be the battery but something like alternator diodes could cause intermittent charging. Measure battery voltage with cables disconnected. Also, put 1 lead in cell 1 the other in cell 2. Note voltage. Move lead from cell 2 to cell 3. Note voltage each time. It should increase 1/6 with each cell. Repeat after battery sits over night. You could also load test battery by connecting volt meter & cranking engine. Also take to idiot at the chain parts store & have them test charging system and battery.
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  #6  
Old 11-15-2009, 07:00 PM
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Had a similar problem in my 300SD. Turned out to be the power antenna.

Sincerely,
Brian
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'94 E420 - 99K
'12 C300 4 Matic

Previously owned:
'06 CLK 500K Cabriolet
'85 300SD (Old Smokey)
2002 Boxster
2002 C320 (The five-pointed star Mercedes)
1993 300E 3.2 (Dealership's cash cow)
1979 300SD (Chrome beauty)
1983 300D (Old faithful)
1983 240D (Right lane cruiser)
1977 240D (Miracle of bondo)
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Old 11-15-2009, 07:04 PM
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This is one of my biggest pet peeves with these cars. Putting a bunch of accessories on one fuse is probably the dumbest thing I have ever seen.

I kept blowing fuse 2 when I pulled my car out of storage. It ended up being the power antenna, but it honestly can be any one of those accessories.

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