Author Topic: Tach reading high amp meter pegged high, no other guages working, regulator?  (Read 3014 times)

Offline cuda346pk

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Tonight I started to go for a drive to a friends house. Early I noticed my dash lights were good and bright, I need to have the dimmer knob rebuilt by the member here that does them, I was like cool, that will look good once the dimmer is done, since I redid the tint for them and made it purple to match the car they are a little dim. Well 2 miles down the road I notice my tach reading just over 4000 RPM at 60 MPH, I know my 3.91 rear is bad but come on that's a little high. Then I looked right and saw the amp meter pegged to C, I have done the amp meter "bypass" so any movement a the meter is unusual, plus the fuel, temp and oil pressure gauges not working. Of course I spun around and headed home. At low rpm close to idle it would dim all lights considerably and the amp meter would go back to middle. Once home I checked and found a blown 60 amp fuse on the amp meter bypass wiring. Replace fuse and check voltage, all good at 12.5 idle up to 13.9 higher rpm's. Shut down and look for a few minutes. Restart and check at idle - at the fuse inlet for the upgraded wiring, volts start climbing to 13.9. Once I blip the throttle I see 17.9 volts before I can get the key turned off. New regulator and alternator from NAPA when I did the bypass wiring. Has been fine for close to 1000 miles. I redid and added a bunch of grounds when I redid the charging. I know my regulator went south but is there anything I need to pay attention for that may have caused the reg to die? Any particular regulator out there better than others?
David - In Georgia

1972 'Cuda In-Violet 340 6 Pack 4 Speed 3.91 Sure Grip - Finally, after 27 years of waiting and dreaming it is real. Now the fun begins!




Offline Chryco Psycho

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #1 on: September 08, 2012 - 12:55:32 PM »
sounds like the reg failed , could be the alt too though .

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Offline MEK-Dangerfield

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #2 on: September 08, 2012 - 03:00:16 PM »
The regulator is the cheapest link in the chain, so I would start there. The regulator had to be grounded well, otherwise it wouldn't have been able to send out a "charge at full blast" signal.

I had the same experience with an 86' Pontiac I once owned. I noticed my dash lights nice and bright, then looked down at my gauges and    :22yikes:

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Offline cuda346pk

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #3 on: September 08, 2012 - 04:28:00 PM »
The regulator is the cheapest link in the chain, so I would start there. The regulator had to be grounded well, otherwise it wouldn't have been able to send out a "charge at full blast" signal.

I had the same experience with an 86' Pontiac I once owned. I noticed my dash lights nice and bright, then looked down at my gauges and    :22yikes:

Yea definately grounded well, I had redone all grounds with multiple star washers and added extras too. Oh yea the dash lights were good and bright, that was nice.

sounds like the reg failed , could be the alt too though .
How would the alternator do it? Sending out too high voltage that the reg can't handle? Today I will swap back to my old reg to test but wanted to make sure if I needed to pay attention to anything else, especially with the bypass wiring.
David - In Georgia

1972 'Cuda In-Violet 340 6 Pack 4 Speed 3.91 Sure Grip - Finally, after 27 years of waiting and dreaming it is real. Now the fun begins!

Offline Chryco Psycho

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #4 on: September 08, 2012 - 04:31:29 PM »
failed diode

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Offline cuda346pk

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #5 on: September 08, 2012 - 07:32:37 PM »
failed diode

Ok - after thinkg about it some more the regulator regulates the voltage by cycling the fields in the alternator thereby regulating the voltage before it is made and outputted by the alternator. I was thinking more along the lines of it regulating it after it left the alternator but now that I consider how it is wired it makes more sense - duh :banghead:
But not knowing the specifics of the setup inside the alternator and for curiosity of knowledge sake, how exactly does a failed diode come into play with over voltage? Is the diode in the circuit such that it would allow the fields to stay energized causing the over voltage even if the regulator is trying to control it?
David - In Georgia

1972 'Cuda In-Violet 340 6 Pack 4 Speed 3.91 Sure Grip - Finally, after 27 years of waiting and dreaming it is real. Now the fun begins!

Offline Super Blue 72

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #6 on: September 08, 2012 - 08:03:26 PM »
Hmmm...I'm not electrical expert but I think the diode rectifier bridge has 3 diodes and  it rectifies the voltage from AC to DC.  If a diode id bad, you'll have decrease voltage I think, not increased....if one is bad then you'll be down to 2/3s voltage... could be very wrong...  :dunno:
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Offline cuda346pk

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Re: Tach reading high amp meter pegged high, no other guages working, regulator?
« Reply #7 on: September 08, 2012 - 11:08:16 PM »
Hmmm...I'm not electrical expert but I think the diode rectifier bridge has 3 diodes and  it rectifies the voltage from AC to DC.  If a diode id bad, you'll have decrease voltage I think, not increased....if one is bad then you'll be down to 2/3s voltage... could be very wrong...  :dunno:

Sounds logical, but I am not electrical expert either. I am a refrigeration technician and deal with AC electrical with all kinds of relays, controls and motors but after all these years I have never torn apart an alternator and looked. So come on Chryco, enlighten us with your wisdom, please. I bet a few here would like a good read on a breakdown on the specifics of how our old school charging systems work. Plus I want to know how to isolate my problem.
Tonight I swapped to my old, good regulator, to test. Running 12.7-13 at idle, 14.6- 14.9 at 2,000 but revving it would randomly cause it to jump up to 15. and even saw 16 once before I shut it down. So sounds like maybe it is the alternator. Other than pulling it and taking into NAPA to test it on their machine how can I test it first?
Thanks
David - In Georgia

1972 'Cuda In-Violet 340 6 Pack 4 Speed 3.91 Sure Grip - Finally, after 27 years of waiting and dreaming it is real. Now the fun begins!