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09-17-2003, 06:24 AM
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CC Member
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Join Date: Dec 2001
Location: Augusta, GA,
Posts: 253
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Not Ranked
Ampmeter/Alternator question
I have an ampmeter on my car that I need some help with. First let me say that I have never had a dead battery, so I don't think charging is an issue. When the car is idling the ampmeter reads 0. When I am at speed, it may read around 30. At night when idling, the headlights dim, and if I turn on the fans or lights at idle, the ampmeter goes below 0.
Is this normal? Do I need a larger alternator? Do I have a bad ground strap somewhere? Any suggestions appreciated.
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09-17-2003, 08:05 AM
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CC Member
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Join Date: Mar 2002
Location: so cal,
Cal
Cobra Make, Engine: I used to fix them for a living
Posts: 2,563
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Not Ranked
normal to see the needle go in both directions. How far into the negative will determine whether you need a higher output alternator, you say you have never had a dead attery.
__________________
In a fit of 16 year old genius, I looked down through the carb while cranking it to see if fuel was flowing, and it was. Flowing straight up in a vapor cloud, around my head, on fire.
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09-17-2003, 09:17 AM
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CC Member
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Join Date: Mar 2001
Location: Indianapolis, Indiana, U.S.A.,
IN
Cobra Make, Engine: Home built, supercharged 544cu/in automatic
Posts: 924
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Not Ranked
I've allways used a voltmeter gauge instead of a amp gauge. It takes you a while to learn how to read them, but they tell you MUCH more about what's going on.
I concour with Mr. Fixit. If you've had no problem with low batterys- then nothings broke. Tis time to worry about something else.
cobrashock
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Ron Shockley
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09-17-2003, 10:09 AM
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CC Member
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Join Date: Feb 1999
Location: Kansas City,
MO
Cobra Make, Engine: CRL, 351W, Tremec TKO
Posts: 2,299
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Not Ranked
If the ammeter is reading + numbers then the altenator is putting out more current than is being used by the electrical "stuff" and the excess is charging the battery.
If the ammeter is reading 0 then the altenator is putting out just the right amount of current for the electrical "stuff" and the battery is fully charged.
If the ammeter is reading -- then the electrical "stuff" (fan, fuel pump, spark box, radio, etc) is using more current than the altenator can provide while still keeping the battery charged.
Fundamentally.... don't worry 'bout it unless the ammeter is always reading negative numbers.
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Pete K.
Who is John Galt?
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09-17-2003, 10:15 AM
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Member of the north
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Join Date: May 2003
Cobra Make, Engine: A Cobra
Posts: 11,207
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Not Ranked
unless
You say the amp meter goes negative at night when the lights are on?
You may want to up the output current of your alternator to handle this better.
It sounds like your meter is working correctly.
Just added comentary.
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09-17-2003, 12:19 PM
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CC Member
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Join Date: Dec 2001
Location: Augusta, GA,
Posts: 253
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Thankyou, thankyou, thankyou, and thankyou. I wondered about this for the last year or so, and since I recently have been redoing wiring in the car, I wanted to take care of it now.
What about the dimming headlights, just put up with it? or do I need one of those 100amp alternators?
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09-17-2003, 12:46 PM
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CC Member
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Join Date: Mar 2002
Location: so cal,
Cal
Cobra Make, Engine: I used to fix them for a living
Posts: 2,563
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Cobras are not known for their high intensity headlights. I believe there are better ones available on the market. How bright do they need to be at idle? This is one of those qualitative areas that is hard to quantify.
__________________
In a fit of 16 year old genius, I looked down through the carb while cranking it to see if fuel was flowing, and it was. Flowing straight up in a vapor cloud, around my head, on fire.
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09-17-2003, 01:01 PM
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CC Member
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Join Date: Jun 2003
Location: Modesto,
CA
Cobra Make, Engine: Heritage body, built the rest..460 Toploader..9"
Posts: 165
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I had a problem with mine doing the same thing until I realized I was using a pully that was just slightly too large. Changing to a smaller pully cured all my charging probs even at nite with everything on. John
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6year Heritage A&F
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1969 Hurst SC/Rambler(only 1,512 made) in the middle of restoration.
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