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Topic: Current Drain

in Forum: C3 Electrical


Current Drain

Posted: 6/29/05 7:19am Message 1 of 13
Former Member
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Columbus, OH - USA
Joined: 11/13/2003
Posts: 30
Vette(s): 1980 Coupe T-Top

I have a 1980 Corvette and last Saturday my battery was completely dead.  The battery is less than a year old and I had just driven the car a week earlier and the battery was fine.  I doubt the problem is in the charging circuit.  The battery took and is holding a charge but I have disconnected it from the system.  Apparently something is draining the current out of it at a fairly rapid rate when the car is just sitting.

 

How do I measure for this and what components are the most likely cause?  I have a very good Multimeter that I can measure both ohms and current with but don’t really know how to use it for this or where to begin.

Herb




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Current Drain

Posted: 6/29/05 10:22am Message 2 of 13
Former Member
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Virginia City, NV - USA
Joined: 1/19/2005
Posts: 314
Vette(s): 1979 Coupe, white in color
Herb, The only method I've ever used was to hook up a meter (amp) and note the current drain. Then one by one, pull the fuses out of the fuse box, check the meter and replace the fuse. Keep doin it till you've checked all the fuses. When the draw goes away, you've narrowed it down to the systems protected by the fuse. Then it's a hunt to see what it may be that's fused from that one. That's the way I've done it, but I'm an old goat and perhaps there's a newer more efficent way.


Current Drain

Posted: 6/29/05 10:59am Message 3 of 13
Former Member
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Columbus, OH - USA
Joined: 11/13/2003
Posts: 30
Vette(s): 1980 Coupe T-Top

It works for me.  I am an old guy too.  Stupid queston but how to you test for current drain?  Set the multimeter on ohms and touch red to hot and black to ground or set it on current and do the same?  Its a great meter but this is one function I have never used.

 




Current Drain

Posted: 6/29/05 3:39pm Message 4 of 13
Former Member
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Virginia City, NV - USA
Joined: 1/19/2005
Posts: 314
Vette(s): 1979 Coupe, white in color
Put it on amps and connect it between the neg post and cable


Current Drain

Posted: 6/29/05 5:59pm Message 5 of 13
Former Member
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Columbus, OH - USA
Joined: 11/13/2003
Posts: 30
Vette(s): 1980 Coupe T-Top

David - Thanks for the info.  I think I am a bit of slow learner here and it has been many years since I had any schooling in electricity.  (High School Physics?).  I assume when you say put it on amps that is "current" on my meter which will read up to 10 amps on the basic setting and 20 if I am quick to disconnect it.  If I put the red probe on the postive cable and the black one on the negative battery post (I assume that is what you meant) with everything off in the car the meter should read "zero" if I have no problems and something more than that if I have a current draining "short".  If I do show some current then I start disconnecting fuses till it goes away and that will be my problem circuit.  Then go from there to isolate what it is in the circuit.

Sounds pretty straight forward but I just don't want to do something stupid and either fry my meter or something in the car.

Thanks again,

Herb

 

 

 

 




Current Drain

Posted: 6/30/05 3:43pm Message 6 of 13
Former Member
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Joined: 3/22/2004
Posts: 179
Vette(s): 1982 COLLECTOR EDITION
Herb,What Pumps is saying is to disconnect the negative cable,then place your pos.(+) meter lead on the disconnected negative cable,and the neg.(-) meter lead on the negative battery post.If current IS flowing with every thing off(doors shut so the courtesy lights are off) you have a draw on the battery.Your meter will be o.k. as long as the draw is less than the 10 amps your meter can handle.A lot of less expensive meters can only handle milliamps.Make sure your meter actually can handle 10 amps and not milliamps.If your in doubt,you can hook a 12 volt test light the same way as the meter and watch for the bulb filiment to light.It can light dimly to bright depending on the severity of the draw and you can proceed to pull fuses one at the time like Pumps suggested.


Current Drain

Posted: 6/30/05 5:28pm Message 7 of 13
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Saxonburg, PA - USA
Joined: 11/14/2003
Posts: 143
Vette(s): 1982 Black over red, doing a resto.

82 collectorshark is right, a test light is a good tool. It should not light if you don't have a draw. Make sure you pull the fuse for interior lights, makes it easier then trying to hold the door switch.

Denny




Current Drain

Posted: 6/30/05 5:39pm Message 8 of 13
Former Member
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Columbus, OH - USA
Joined: 11/13/2003
Posts: 30
Vette(s): 1980 Coupe T-Top

Thanks guys.  Placing the meter in line to measure current makes sense.  I took a long look at the rather cryptic diagram that came with my meter and that was what it showed but it was sure not obvious the first time.  It has been a long time since I learned about electricity and all I have ever really done is to measure voltage and resistance (basically just continuity). 

My meter has two setting 320ma and 10amp which is fused to 20 if it is brief so I should be fine. Now all I have to do is find the problem.

Looks like I have my weekend project.

Herb H




Current Drain

Posted: 6/30/05 9:47pm Message 9 of 13
Former Member
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sonoma, CA - USA
Joined: 8/9/2002
Posts: 784
Vette(s): 72 LT-1 AC coupe,69 l-36 coupe
If you don't find a draw somewhere, and your battery is good,and one day its up and the next day its dead take a look at the generator, a bad diode trio will kill a battery in quick fashion.


Current Drain

Posted: 7/4/05 8:18am Message 10 of 13
Former Member
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Columbus, OH - USA
Joined: 11/13/2003
Posts: 30
Vette(s): 1980 Coupe T-Top

Thanks everybody.  I found the current drain. The relay from the anti-theft system decided to start working again after many years of most of the system being disconnected.  It was sucking up about .17 amps all the time.  I unplugged it and WOW - no more current drain.

Herb H




in Forum: C3 Electrical


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