Hello,

I have an 89' that is cooking the battery, it is putting out from around 14v at idle to over 18v at higher rpm. I had a voltage spike take out my high beams one night, and then it would not charge at all. I then cleaned all the grounds and put the good regulator from napa on it and then it would charge at 15v at higher rpms.
After a longer trip with my trailer at night, I noticed my battery boiling when I shut it down, and this is when I noticed the high voltage reading. I have rechecked my grounds again, and jumped the reg case straight to the - of the battery with no difference. I also checked the green wire and it has continuity from reg to alt. The blue (ign. on) is also getting full battery voltage, but when I check to see if it is grounding out I get about 3.4 ohms of resistance, I am not sure if this is because there are other things on this circuit as well.
I have always had a pulsing of the lights of the truck that is quicker with higher rpms.
Should I run 12v from the battery to the field + terminal of the reg.( where the blue wire normally goes ) to eliminate any issues I may have with the ign. on power source?
I also notice I have continuity on the battery wire where is connects to the alt. through the battery clamp end with the battery disconnected. When I connect the battery it has like 10 ohms resistance.
I feel like I am missing something and just replacing the reg may not be it but I may give it another try.
Thanks for any insight into this.

 

I had a gasser do this and it was a bad alternator.

 

Thanks for the reply, I was hoping it was some thing cheap, the alternator does not have many miles on it but it may have been abused by a bad ground along the way.

 

Nah, the problem would be an internal ground to the field circuit. Could be just a misplaced wire in assembly, or a short in the rotor. Easy to check out.

Circuit goes in a terminal, through a brush, through the rotor, through the other brush, and out the other terminal. Shouldn't be grounded anywhere.

 

have the parts store check it to rule it out.

 

I just checked the alt. from case ground to green wire terminal 9.5 ohms, and from case to blue wire terminal 4.2 ohms. This is with the reg and battery disconnected.

 

That appears to be a short to ground in the armature. It would nearly full field the alternator. If true, it should (over)charge with just the 12V field (ASR) wire connected and the VR disconnected.

Bottom line, bad alternator.

Clown auto test is full field, see if it puts out. It would pass.

 

I did try it with the reg. disconnected and it would not charge.
I put a new reg. on today and it now charges at 13.7 v at low idle to 14.8 v at 1200 rpm and does not go higher than that at higher rpms.
It still has a slight pulse between 800 - 1400 rpms.

When I first start it up and let it run at low idle it goes to 12.5 or so volts and slowly climbs to a little over 13 v. If I rev it up it will climb quick and then stay around that 13.7v at idle.

I am still not sure that the alt. is not starting to go.
I put a voltage gauge in the dash so that I can keep a better eye on things - Dodge and their iffy electronics...

I think I will call it good for now. Thanks.

 

When you start the truck, you partially discharge the battery, so the voltage will be lower till it charges up.

The battery voltage depends on:
1. The charge condition of the battery.
2. The charging or discharging current
3. The internal resistance of the battery (goes up with age)
4. The temperature.

A partially discharged battery will charge at 50 amps, holding it down to 12.0 or 12.5 volts. The same battery fully charged, and being fed 50 amps, will boil like the soup pot on the stove and voltage will go 15V or more. If the supply voltage is held to 14V or so, it will draw very little current. The function of the voltage regulator is to limit the voltage, and thus the current to a fully charged battery, while allowing charging current up to the capacity of the supply (alternator) depending on battery condition.

The alternator is capable of supplying full rated current at 50V or more at top engine rpm. Without regulation, it doesn't even strain to blow up a battery.

So the numbers aren't "this is good, that's bad." you have to consider the circumstances.

 

Thanks for your help with this, hopefully my battery did not boil like a tea kettle too long before I put the second regulator on and it will be OK for a few years at least now.