max output voltage on a stock alt. " REGULATOR UPDATED "

[Highbanked Hauler]

   What is the max voltage on a stock alternator ? I had a points ignition and had to get a replacement alt. on the road last fall and got the stock single field unit. Started the car with a points regulator and the volt meter needle was jumping so fast you couldn't see it. I put in the blue MP spare that I had  and started it up and it jumped to 15.5 volts. I checked it with the volt meter I have with and thats what it was. Cold start next day and it doesn't go above the voltage in the battery at 12.5,went for a short drive with the lights on and when it got warm it goes up to  15 + again .   The regulator in new, and the alternator has about 20 miles on it and I swapped in another  good battery so what is screwed up ? I am planning on getting a "new" alternator if this one is fugged. Also put in a new electronic ignition.

     For years I have had a NEW   P - 3690732  blue regulator under the seat for a spare  so when the alternator quit and I put the rebuilt in and the  volt meter needle was jumping so fast I put the "spare" in and then started the above story. I switched in a good alternator and same problem so I put in  ANOTHER blue reg. and we had charging so my new spare under the seat was junk even being new.
    So is there a regulator that will  work  with electronic ignition for 69 and back ??  Thanks.

[Pete in NH]

Hi,

Those Blue MP regulators are made for "race" applications and provide a high constant output voltage. In a street car they run too high an output voltage and will fry the battery. Just get a stock replacement regulator for your year car. Most of the replacement regulators for the older single field wire alternators are electronic types made to look like the old mechanical points type.

Normal system voltage should be 14.4 to 14.8 volts or so. 15.5 volts long term is too high.

[John_Kunkel]

On a single-field alternator, the only way it can achieve 15+ volts output is if it is full-fielded (regulator is sending battery voltage to the field) or there is heavy load in the system that is demanding full output from the alternator.

[Highbanked Hauler]

Hi,

Those Blue MP regulators are made for "race" applications and provide a high constant output voltage. In a street car they run too high an output voltage and will fry the battery. Just get a stock replacement regulator for your year car. Most of the replacement regulators for the older single field wire alternators are electronic types made to look like the old mechanical points type.

Normal system voltage should be 14.4 to 14.8 volts or so. 15.5 volts long term is too high.

I thought the "blue" regulators were 13.5  constant volts ?? No ??


My understanding of electrical is minimal.  How can a regulator feed voltage back to the alternator unless battery voltage is a lot higher ?

[Pete in NH]

Hi,

You're absolutely right those blue regulators are 13.5 volts I just looked them up. I had it in my mind they were 15.5 volts. I should know better than to trust my memory and look things up as  I'm getting older and the memory isn't as good as it once was.

John is right it sounds like the regulator letting the alternator run wide open. Either the regulator is bad, not grounded well or there is a big voltage drop between the regulator blue wire and the positive battery terminal.

[b5blue]

  I'd go through all the connections if the car has been sitting mostly. I've a ground strap from the block to the mounting bolt for the regulator/firewall, don't know if that's quite factory but helps insure grounding of the case. My battery just started acting up so I'll be starting to check all connections myself this week.