Alternator Rebuild/Voltage Regulator issues (1 Viewer)

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I just recently had my alternator rebuilt by a pro on an 82 FJ45 with 2F engine. Truck starts and runs fine since replacement but I’m having concerns with the voltage.

I have a digital voltmeter on the dash I just installed and noticed when at idle it’s at 13-14 where it should be but as I drive and RPMs increase, the voltage increases to 15-16 which I think is too high? If I turn the lights and heater fan on it drops them back down to the 13.5-14 zone. Shouldn’t the volts level out at around 14.2 or so when driving for extended periods of time lights on or off? Anyone know why the volts are increasing over 14.3? Is this going to harm my wiring or alternator?

I did put a new voltage regulator as is suggested with a new alternator, I even put the old one in again to test and it does the same thing. I’m I making something out of nothing here or is something not right?
 

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lets see some photos .....

perherhaos the keen eyes of mud can spot a issues , like a mis-matched regulatyor to your new rebuilt unit ?


assuming you have a non-usa 2F

D5FDB1D0-3459-4F74-B81C-1A54BFE0247E.jpeg
 
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Correct, non USA 2F which really is the same thing as US, just mostly desmogged is my understanding. Again, I have the stock rebuilt alternator and currently running the original (I believe voltage regulator) still doing it. New voltage regulator does the same thing so I don’t know if it’s the wrong one, or bad? Isn’t the function of the voltage regulator to back off on charging when the batteries are where they need to be? Thanks

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You mention that you also installed a new digital volt meter. Could it be that the new VM is incorrect? Have you checked the output with a multi-meter? Just a thought...
 
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This is the new voltage regulator. I’ll check the volts with my voltmeter, I think it is working fine though. I did tap into the blue wire to light up some relays does anyone think that could cause my issue? It’s got a 6 wire plug. Maybe someone can confirm a part number I should have on it.

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AFAIK, the VR is supposed to cut the voltage at ~14.xx volts. I think generally about 14.4, but I gather it varies quite a bit from the factory. If you are seeing 16VDC at 2000 RPM, that's probably not great and you can cook you're battery.

There's some service literature on the adjustment of the VR, as outlined here: Voltage Regulator (ext.) / How it works

There is mention of both the 3 and the 6 wire versions there.
 
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AFAIK, the VR is supposed to cut the voltage at ~14.xx volts. I think generally about 14.4, but I gather it varies quite a bit from the factory. If you are seeing 16VDC at 2000 RPM, that's probably not great and you can cook you're battery.

There's some service literature on the adjustment of the VR, as outlined here: Voltage Regulator (ext.) / How it works

There is mention of both the 3 and the 6 wire versions there.


Thanks! I’ll look into that.
 
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Problem solved! That blue wire on the 6 plug for the voltage regulator is not to be utelized for a 12V source :rofl: I was using that (as seen in photo above) to power up some relays so I tried disconnecting that and taking it from somewhere else and my voltage is now a constant 12.3-12.9 regardless of RPM's. Lesson learned. Thanks all, for your input!
 
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That sounds low... A fully charged battery in good condition should be 12.6v with no load, and alternator should get up to 14'ish to charge that.

I'll monitor it, maybe I still need to adjust the voltage regulator. I'm getting a reading of about 50 Amps off the alternator last I checked, so I know its putting out a charge. I have only driven around a few miles so far. I am no longer seeing a swing of 12.5 to 16+ V during normal driving conditions. 2 brand new batteries. Newly rebuilt alternator. Fully charged reads about 12.2 V when I turn key to ACC. When started and driving under normal conditions, the Voltmeter is showing about 12.6-12.8 which tells me its charging at least? What in your opinion should be the constant Volt reading while operating/driving?
 
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I'll monitor it, maybe I still need to adjust the voltage regulator. I'm getting a reading of about 50 Amps off the alternator last I checked, so I know its putting out a charge. I have only driven around a few miles so far. I am no longer seeing a swing of 12.5 to 16+ V during normal driving conditions. 2 brand new batteries. Newly rebuilt alternator. Fully charged reads about 12.2 V when I turn key to ACC. When started and driving under normal conditions, the Voltmeter is showing about 12.6-12.8 which tells me its charging at least? What in your opinion should be the constant Volt reading while operating/driving?
It should be around 14v (13.6 to 14.8 based on this):


12.6v should be a fully charged good condition battery at the battery posts. There will be slight drop across wiring.

If it's near 12.6 with the engine running, it's possible the regulator told the alternator to stop charging. Turn on the headlight, fan and wipers (and anything else, run the winch in and out if you got one) to generate a load and force it to supply power.
 
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It should be around 14v (13.6 to 14.8 based on this):


12.6v should be a fully charged good condition battery at the battery posts. There will be slight drop across wiring.

If it's near 12.6 with the engine running, it's possible the regulator told the alternator to stop charging. Turn on the headlight, fan and wipers (and anything else, run the winch in and out if you got one) to generate a load and force it to supply power.

I swapped my old voltage regulator for the new one I found on ebay and am getting consistent 13.8-14.2 V. Awesome. Will keep an eye on it for the next couple weeks. Haven't had a working charging system on this truck since I bought it. Glad to finally have it sorted out I think? Thanks again
 

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