Re: Why doesn't my volt meter show more than 12.5v charge?
[Re: A12]
#134721
10/10/08 03:01 PM
10/10/08 03:01 PM
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Joined: Sep 2005
Posts: 12,481
Chino Valley
RodStRace
I Live Here
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I Live Here
Joined: Sep 2005
Posts: 12,481
Chino Valley
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I just put a rebuilt '68 alternator on my 383 RR and was told it put out 58 amps by the shop that rebuilt it. So far, so good. You do realise that it will only do that when needed? So before I put the new alt on I made sure the battery was fully charged and then started the engine... Good, that is required to check charging system issues. However, that also means that the alt. doesn't have to work very hard, since the battery is full. and ran it up to +4000 rpm Ease up there. A good rebuild should be providing full output at 2500 RPM and checked the battery at the terminals with a digital volt meter and it wouldn't read more than 12.5 volts. Okay, the voltage is low. However, you also need to check current output by loading the system. You should put a load tester on and a ammeter. With the engine at idle the meter reads 12.2v-12.3v but that's about what the battery shows with the engine off??????? The dash gauge shows little or no charge at idle to 2000 rpm and barely moves above that. That's pretty normal with little load and a fully charged battery. Turned the lights on high beams and the gauge shows a major discharge at idle and doesn't go beyond center at any rpm. Okay, that's a good replacement for a load tester. It's showing that the system isn't working. So I go to the parts store and get a new voltage regulator and the only one available is listed as 35-46 Ampere and the replacement looks just like the one on the car. Same results with the new volt reg. Do I need the Volt regulator listed as 60 Ampere to get this thing to charge at more than 12.5 volts????????? I doubt it. Remember that the charging system is the following:
Battery - This should be good.
Battery cables - car starts, so let's say they are okay
Battery cable connections - Same as cables, but would not hurt to clean.
Alt. case ground - this is the bracket, bolt spacer and alt. case. the ground side must be good too. Fresh pait? Sitting a long time? Clean to bare shiny metal.
Alt. - I've had bad new parts, but let's assume this one is good.
Wiring - this is where a lot of problems are found. Check the entire circuit between the alt, regulator, bulkhead, amp gauge, bulkhead, solenoid and battery.
http://www.mymopar.com/downloads/1968/68BelvedereGTXSatelliteRoadRunnerB.JPG
Regulator - part may be bad, but check the rest first.
Amp gauge - If the car starts, the connection will flow current.
Voltmeter - I've seen some that will show low voltages. It will make you pull your hair out. Try another meter, and read up on checking voltage drops.
http://www.engine-light-help.com/voltage-drop.html
Last edited by RodStRace; 10/10/08 03:48 PM.
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Re: Why doesn't my volt meter show more than 12.5v charge?
[Re: gtsuperbee]
#134724
10/12/08 02:29 AM
10/12/08 02:29 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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I had a similar problem on my 70 cuda one time, driving along, suddenly it was discharging instead of holding steady or charging.
figure my VR is bad. $15 later, still no good.
Took the alternator in to be tested...they said it tested bad...ok good! problem solved! new alternator installed...still no charge!
I untimatly found that I had a bad connection going from the body to the battery.
engine ground was working fine, and the body ground was working well enough for all my lights to work, radio worked, etc...but for some reason, when I re-did the body ground wire, my problem went away.
check your grounds...all of them.
**Photobucket sucks**
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Re: Why doesn't my volt meter show more than 12.5v charge?
[Re: gtx6970]
#134727
10/12/08 11:16 AM
10/12/08 11:16 AM
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Joined: Jun 2006
Posts: 824
NH
72challorange
He's Game
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He's Game
Joined: Jun 2006
Posts: 824
NH
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I added/moved the battery to chassis ground to a welded in lug on the rad support. Never liked the top of support nut and bolt I normally see. I just swapped out the bolt holding the battery tray with a longer one and added another nut on the end for the lighting grounds. Tom  By tdavist, shot with DSC-P72 at 2008-03-22  By tdavist, shot with DSC-P72 at 2008-03-22
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Re: Why doesn't my volt meter show more than 12.5v charge?
[Re: 72challorange]
#134728
10/13/08 01:32 AM
10/13/08 01:32 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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not sure that mine is original, in fact, I doubt that it is, but that's how it was when I got it, there's a little pig tail that goes from the radiator support to the negative terminal on the battery, using like an 8Ga wire, then the big ground went from the engine block to the battery...actually, I think it was a head, but whats the difference!
**Photobucket sucks**
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would be your problem is elsewhere.. did you have the parts store check your old alternator to see if it was bad?
Thanks!
