15.5 Volts coming off the alternator

[cudajim]

On my 67 Fish car I am getting 15.5 Volts coming off the alternator; it seems a bit high from everything I've been reading. The solid state blue regulator I had was acting strange (working then not working) which prompted me to start measuring voltages. I'm running an old style single field alternator. Just for fun I replaced the regulator with a good mechanical one I had lying around and I still get 15.5 volts coming out and working properly (except for the high voltage). I made sure the regulator is grounded well and all wiring appears good. Any ideas?

 

[67Dart273]

Four reasons for high charging voltage

1 Bad/ maladjusted regulator

2 Bad ground to regulator and by that I mean the BATTERY NEGATIVE POST is not the same voltage potential as the regulator case

3 Voltage drop on the positive feed from the battery---through the bulkhead--to the ign switch connector--through the switch contacts--back out the ign switch connector--back out the bulkhead connector--and to the IGN terminal on the regulator

4 In rare cases on the newer isolated field systems, either a grounded rotor "in the right spot" or a grounded brush (blame the rebuilders) can cause a "full field" condition.

TO CHECK voltage drop, check the battery, make sure the cells are OK, Run the engine to simulate "low to medium cruise" with all accessories off, then re--test with heater, headlights on

Take your digi meter and stab a probe directly onto the battery negative post, the other probe directly onto the regulator case

On the positive side of things, stab your probe directly onto the battery positive post, the other as close as you can get to the regulator IGN terminal. On 69/ earlier, directly onto the regulator. On 70/ later, probably the blue ign feed to the ballast

IN BOTH CASES you are looking for a really low reading, the lower the better, zero volts would be perfect. Anything over .2V (two TENTHS of a volt is too much) and indicates a problem

 

[cudajim]

I did check for a voltage drop on the ground side and it was fine. I did not however check the positive side but I will tonight when I get home. Both regulators gave me the same voltage output so I do not suspect the regulator itself. I'll report tomorrow.
Thanks.

 

[RedFish]

Another member recently found a fault in horn relay or wiring to it. So I guess I'm asking if the horn works. Better yet, What does work and what doesn't ?
Check the ground between firewall and engine block too since that is the ground path for the regulator.

 

[cudajim]

The horn does work just fine and the ground strap from engine to firewall is in place. I also have an additional ground strap direct from the battery to the radiator support (about 8" away). I'm guessing it'll turn out to be a positive voltage drop.

 

[cudajim]

I got the old voltmeter out last night and checked it out. The ground drop at the regulator was negligible but I have a .4v drop on the positive side. Jumping it did little to alleviate the problem at the output of the alternator. I then decided to swap batteries with a newer one and it solved the problem. So the bottom line is that I had a bad battery; probably a low resistance path internal to the battery I assume.