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  #1  
Old 03-19-2013, 07:46 PM
Redefining normal daily
 
Join Date: Jul 2004
Location: Frederick, MD
Posts: 445
Dark current question

Dear old Gustav (72 280 SE 4.5 with something north of 350k miles) sat all winter, battery on the back porch (charged when pulled ~ 4 months ago).

Dropped the battery in last Monday, drove him to & from work (two ~30 mile trips). Parked him in the driveway, and he sat idle until today.

Darling Wife went to take him out, and.... nothing. Not so much as a click. I get home from work, confirm the battery is flat out totally dead. 0.4 VDC.

Swap out the battery from Katz (who's up on blocks waiting for a new caliper!), and start hunting for dark voltages.

0.70 amps draw with the door open, house lights on. Close the door, and get 0.35 amps with, in theory, everything off.

Pull fuse #1 (parking light, clock (which is non-op), passing signal light, map light, glove compartment light, dome light, and hazard warning light) and the draw drops to 0.01 amps.

Put the fuse back in, and confirmed none of the above lights are on with the door closed.

Question One: is 0.35 amps enough draw to worry about? Seems a bit high based on my Miata experience, but not oh-my-goodness-no-wonder-your-battery-is-dead high.

Question Two: if none of the items listed for fuse #1 are on, where might the source of the current draw be?
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1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man
1980 Redhead: Darling Wife
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  #2  
Old 03-19-2013, 08:45 PM
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Join Date: Jan 2006
Location: Tucson, AZ
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Have you considered the possibility of the battery not being charged?

What's the voltage output when the car is running?

Batteries DO go bad you know.

Jim, you're old enough to not believe the idiot light. Get the voltmeter out and check it out.
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Old 03-19-2013, 09:59 PM
Redefining normal daily
 
Join Date: Jul 2004
Location: Frederick, MD
Posts: 445
Quote:
Originally Posted by Mike D View Post
Have you considered the possibility of the battery not being charged?

What's the voltage output when the car is running?

Batteries DO go bad you know.

Jim, you're old enough to not believe the idiot light. Get the voltmeter out and check it out.
Which part of my post suggest the voltmeter wasn't employed?

Battery is ~ 2 years old. May well be the weak link.... was looking for inputs related to the current draw and whether or not the recorded level is a concern.
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1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man
1980 Redhead: Darling Wife
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  #4  
Old 03-19-2013, 10:19 PM
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Join Date: Jan 2006
Location: Tucson, AZ
Posts: 4,550
Ummm, the part where you never mentioned what the alternator was outputting when the engine was running?

A .035A draw is nothing considering your battery is probably at a minimum of 650 CCA.

I suggested the voltage output because the 4.5 does have an electric fuel pump which will drain the battery fairly quickly if the alternator isn't properly charging.

Just trying to help.

*edit* (Oops! I mis-stated the amp draw by adding an extra decimal place. It should have been a ".35 amp draw" instead of ".035".)
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Last edited by Mike D; 03-20-2013 at 01:32 PM.
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  #5  
Old 03-20-2013, 12:13 AM
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Join Date: Dec 2011
Location: Honolulu, HI
Posts: 475
Check the trunk light switch.

I just went through this exact same deal over the past few weeks. I'll save you the long story, but it turned out to be the trunk light, which is also on fuse 1, but not on your list.

Mine would work (ie turn off when supposed to, as verified with a phone shooting video as I closed the trunk) then not work randomly, leaving the light on. Over a 5 day period, with a new battery with 790-800CCA, it was enough to get the battery down to 0.3V (I believe CCA are irrelevant in a long-duration/small-draw situation like this. It is a death by a thousand individual milliamperes )
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  #6  
Old 03-20-2013, 12:45 PM
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Join Date: Apr 2009
Location: Los Angeles (Altadena)
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I vote for the battery itself of the voltage regulator. Check battery voltage with car off. About 12.4? Check battery voltage with car on. About 13.8? If not, then you aren't charging. If it IS charging, then battery isn't holding a charge very well. Take battery out and have it tested at local auto store - they can tell you if it is not holding charge. I recently returned a 2 year old battery for free replacement. And it was a top of the line battery.
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  #7  
Old 03-20-2013, 01:06 PM
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Join Date: Aug 2011
Posts: 108
I think car batteries have about 60 amp hours. Palolo is corect that CCA are irelavant.
I am not positive how battery amp hour rating work, but I think it is a matter of simple division. 60/.35=171/24= 7. Seven days or about a week before it completly killed your battery.

That is assuming my estimate of 60 amp hours for a car battery is correct and that my math is correct.

You should not have any draw with everything off. On a 40 year old car the draw is probably comming from a corroded wire or connection causing a slow short/drain. .35 amps is about what one of the dash lights in your instrument cluster draws, but less than a dome light or the trunk light will draw. Pull every light on the circuit and use electronic cleaner on the sockets. If you can disconect sections of the circuit and check your draw again. As an example you can unplug the instrument cluster and see if it might be the inop clock or another short within the instrument cluster. Inspect every connection and clean it with electronics cleaner.
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