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  #1  
Old 01-20-2013, 11:41 AM
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AMP Meter Reading Vascillating

Getting nowhere trying to use one of those battery quick disconnects to test for parasitic drain, so I decided to test for drain at the fuse box. Pull one fuse at a time and connect VOM +/- probes at each port.

I get a stable reading on fuse 15. Amp setting on 200m - seeing 03.7

When I test fuse 2 - the meter reading is all over the place. Retested that port using 2 different VOMs. Same thing - meter reading jumping around using different VOMs.

Curious as to what would cause all of this vascillation on the meter?

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  #2  
Old 01-20-2013, 12:34 PM
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Some components only draw current when they are "booting -up". After that, they drop down to lower current. The amp meter restricts the amount of current flowing in the test circuit, so it's possible that some device is stuck trying to boot up over and over. Some components draw current all the time, like the remote door locks, theft alarm, clock, and radio. So, some key off current draw is to be expected. In my experience, internal resistance in the battery is usually the cause of a battery going dead while sitting, even over night. (self discharge) It may be difficult to grasp, but Lead acid battries have internal leakage currents, especially as they age. Batteries have a complicated "science" of their own. A battery can show good terminal voltage, but not hold a charge. Just thought of something else.... The capacitors for the air bags have a charging curve too.
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Old 01-20-2013, 12:49 PM
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Battery is brand new - Deka Gold - one of the best in my humble opinion.

OVC reads 12.76 after being idle a number of days and cranks right up. Reason for that is I disconnect the battery with a quick disconnect after driving. Leave it connected and the batteries OCV starts falling of rapidly - battery drain.

Your comments about a component recycling continuosly are well taken. That would explain the vascillation.
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Old 01-20-2013, 02:27 PM
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Have you tried measing current that might be flowing back into the alternator? I've heard accounts of bad voltage regulators causing battery drain. I suppose you'd have to break the connection at the alternator itself. I've never done that. Just a thought.
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Old 01-20-2013, 03:01 PM
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Draw test

The best way to test for the draw would be to hook your amp meter to the negative side of the battery between the terminal and the cable. If the car you are testing is the sel in your sig then the acceptable draw will be about 25 to 30 milliamps after any components that need to energize have done so. The most common component to cause problems on that car would be the automatic antenna. You also want to be sure that your trunk and glove box lights are turning off. About the only thing pulling any juice normally will be the clock in the instrument cluster.
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Old 01-20-2013, 03:28 PM
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Quote:
Originally Posted by Mike Richards View Post
Battery is brand new - Deka Gold - one of the best in my humble opinion.

OVC reads 12.76 after being idle a number of days and cranks right up. Reason for that is I disconnect the battery with a quick disconnect after driving. Leave it connected and the batteries OCV starts falling of rapidly - battery drain.

Your comments about a component recycling continuosly are well taken. That would explain the vascillation.
Bit off topic but since you mentioned your preference - napa batteries are made by deka so you can save a few bucks buying there.
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  #7  
Old 01-20-2013, 10:20 PM
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Appreciate all of the comments/suggestions.

Local Deka retailer was actually cheaper than Napa.
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Old 01-21-2013, 07:41 AM
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Could you list what is powered by fuse 2. I don't have that information. Maybe I could help, I worked on problems like this for many years.
Paul
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Old 01-21-2013, 10:01 AM
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Will list components powered thru the 2 fuses that had measurable readings. Those readings are listed above. Info obtained from data card inside fuse box cover(underhood).

Fuse # 2
diagnostic terminal #6
hazard warning system
clock
front roof light
elect. radio(now an after-market unit)
vanity mirror light
elect. illumination control

fuse #15
roof light rear
trunk light(always cool to the touch whenever trunk is opened)
safety belt handover arm
switch over valves seat back arrester(posts at this forum indicate this is found on an SEC - I have '91 300-SEL)
central locking system(car also equipped with after-market alarm-Clifford-at least 15 yrs old alarm).
door lights
reading lamp-rear area
automatic antenna
control unit seat adjustment memory

With fuses #2 and #15 removed - car starts - so I suppose the Cliffored alarm is not tapped in thru either of these.

Digging thru archives - I see that audio equipment in trunk is interfaced electrically with automatic antenna. In the trunk I have an after-market amp(power booster) and cd player. Have disconnected both of these and still see huge vascillating draw on fuse #2.

Need to disconnect automatic antenna motor and see what things look like after that.

It's Monday A.M - back to work - may be a day or two before I can return to this issue. Will update thread when/if I know more.

Regards.

Last edited by Mike Richards; 01-21-2013 at 12:16 PM.
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  #10  
Old 01-21-2013, 01:58 PM
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Disconnect the Alarm system and the antenna. Test. Disconnect the radio. Test. Let us know.

I suspect the alarm system is the problem so unhook it first.

Paul
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  #11  
Old 01-24-2013, 07:41 PM
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Current drain comes to a halt with fuse #2 out - it's appliances and fuse 15 are listed above.

Only after-market on that fuse is the radio.

Will operate with fuse 2 out 'til I have more time.

Thanks for all of the replies.

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