How To Test Voltage Regulator?

Crankster

Crankster

Well-known member
Well today I had (planned) to move the Truck out of the garage, finish filling the bed with some yard waste and make a trip to the city site yadda yadda.

Started the engine and was greeted with a GEN light that wouldn't go out after engine start, regardless of RPM. Not a stuck cutout condition. Polarizing the generator "by the book" had no effect on this condition.

Instead of diving into the troubleshooting phase out of the manual, which aims to determine whether it is the generator or the regulator at fault, I swapped in my spare (script Ford reproduction) regulator. Everything fine with the spare regulator.

So I'm reasonably certain the regulator is at fault. The offending unit is an Autolite service replacement that I bought NOS from the fine folks in Waxahachie that has worked well for quite a while now. I took a peek inside and didn't see anything notably out of whack. At a guess, it seems like the cutout won't cut in, but I didn't messed with it yet.

Ordinarily the cutout should never need re-adjustment. Spec is 1300 RPM, seems kind of high, but I could play with it. I just don't want to bugger it up either. It was a little expensive, but until now I had no issues.

The next thing is I have to wonder if there is some defect in the generator itself that might eventually result in two defective regulators instead of one.

Any ideas from the borderline stubborn knotheads still running generator equipped cars and trucks in 2021?
 
When you say AUTOLITE, is it a FORD AUTOLITE or aftermarket AUTOLITE? (FORD bought AUTOLITE - not all divisions - in 1961 and had to divest in 1972).

You would first establish AMP output from the GEN. It should be described in the WSM. If the points are adjustable and it is built like a GENUINE FORD, you would follow the procedures in the manual to test and adjust. If not FORD and has points, you would have to find the manufacturers procedure I would imagine.
 
I mis-spoke, it is actually a MOTORCRAFT service replacement voltage regulator. I expect it is from sometime in the early 1970s. I don't believe that particularly matters, everything, all the adjustment operating points were dead nuts on accurate right out of the box, one reason I bought it. The modern manufacture generator regulators are kind of sketchy sometimes, from all accounts.

The generator is in excellent shape, though I suppose there's no alternative other than going through the whole enchilada. I'm reasonably certain the fault lays in the regulator given the observations.
 
There is a difference between setting up to adjust a generator control unit and actually troubleshooting a unit with a problem. It can be more complex finding out whether the resistors & pole coils have a problem or not unless a person can find the specifications or compare them to a known good unit.
 
The generator is in excellent shape, though I suppose there's no alternative other than going through the whole enchilada. I'm reasonably certain the fault lays in the regulator ...
Click to expand...

How do you know the GEN is good? Is it the original, a dedicated rebuild or did it come from PEP BOYS as an exchange?

What are you working on? Do you have a WSM and multi-meter?

I am surprised the USUAL SUSPECTS here haven't taken a few random pot shots at it ...:cool:
 
It is a dedicated rebuilt generator purchased a couple years back from a closed down shop, not a pep boys krylon special. It did include a problem with the new brushes that were i installed, they were still squared off. This caused them to rapidly arc, and burn within a few hundred miles. I "assumed" a rebuilt generator was ready to go. Brushes should be sanded so they conform to the commutator surface.

I do have the shop manual and necessary test equipment to measure the amperage and such. The generator itself does (or did) peg exactly at 30 amperes when I got everything setup and performed an output test. It has good bearings and the field winding pack looks clean and unburnt, and isn't oil soaked. I did everything with an eye towards long term reliability.
 
If it's working with the back up regulator, that would be test enough as far as output. Most will put out more then 30-amps if the current is not limited by the control unit but a person wouldn't want to go too far. Just peak check it and it's good to go. The cut out in the modern control units have to have output from the generator to turn the GEN light off.

My tool set for generator includes a growler so I can test the armature. The rest of it is pretty cut and dried. There is not much to them really but what's there has to work.

I assume the generator system involved is in the OP's avitar photo. That would put it in the category of the units made near the end of the use of generators. It's a good idea to mention what year and model the questions are about so we know what we are discussing.
 
rotorwrench said:
Most will put out more then 30-amps if the current is not limited by the control unit but a person wouldn't want to go too far. Just peak check it and it's good to go. The cut out in the modern control units have to have output from the generator to turn the GEN light off.
Click to expand...

Yeah '64 was probably the very last year for generators. I can't recall without looking in the manual the specific connections for a generator output test, but I was able to do the test because I also have an analog ammeter on an old SUN portable unit capable of measuring up to 50 amps.

The only "testing" done so far is swapping out regulators. The fact that the GEN light isn't illuminated with the spare regulator doesn't necessarily prove out anything 100%, but, whenever a GEN light is illuminated there is always going to be a charging problem.

That's kind of what has me puzzled, assuming the generator itself is serviceable and working as advertised, can't really see how the regulator cutout (for example) could get itself out of adjustment. All the connections and grounds and wiring &c are clean and tight and low resistance. I'll have to get in there and do some actual testing.
 
Maybe? The suddenness of the fault coming on doesn't point in that direction to my way of thinking.

I've only seen the cutouts fail in the "stuck" position, but I'm definitely not a generator guru. It may not be a fault in the cutout, that's just a guess. One thing is I don't want to otherwise bugger it up finger-faddling around with it either. I'm not poor, but they ain't giving them away in boxes of Wheat Chex.
 
Since I will will be using the same set up my car, and I am NO electrical expert but have you cleaned the points inside the regulator? The only reason I ask is that I opened up a newer one that I got from a donor car (I am guessing 80-90's) and saw the points. In the Model A world that is what we do when the cut out sticks.

Mike
 
1930artdeco said:
Since I will will be using the same set up my car, and I am NO electrical expert but have you cleaned the points inside the regulator?
Click to expand...

Yes, about once a year though being very, very careful. "By the book", because everything in those books was pretty insistent that ham fisted attempts will bugger the unit permanently.

I enjoy obsolete technology, but only to a certain point. I'll have some time today to start running through everything today.

The generator output test Ford outlines involves removing the ARM and FLD wiring at the generator terminals itself and a jumper wire between the terminals. Then connect an ammeter and start the engine. The last time I did this test it pegged exactly 30 amperes on the analog gauge. Voltage output & regulation has always appeared excellent even when loaded down pretty good. I expect circuit resistance (voltage drop testing) will be OK too. I suppose I should take a peek at the brushes.

One thing that was sort of odd in this whole routine, I had just packaged up a replacement generator backing plate w/fresh brushes in a ziplock and put it in the truck for safekeeping, in case of trouble out on the road. The very next time I fired it up, bingo bango get a GEN light. Hm.
 
Since there is no volt meter on many of the Ford vehicles, I generally test for voltage while running directly and the battery posts using a digital multi meter. If it reads battery voltage then something is wrong. It should read close to the 14-volt range for 12-volt vehicles. If the cut out pole contact points are clean then it's likely not the points anyway. All of the pole coils are connected in with the armature terminal on the VR and that is the ground connection with the GEN warning lamp too. As soon as the generator comes on line then the GEN lamp loses it's ground. If the generator doesn't come on line then it could be any one of the coils or the resistors. All of that stuff would have to be checked to find the problem. Isolating things to check them could be problematic depending on how the unit was manufactured. Many were made to be repaired back in the day but that started to change in the 50s.

There could also be a problem with the voltage regulator contact points but be aware that it doesn't take much "cleaning" to affect the voltage output.
 
Last edited:
Yeah, at this point we'll do a quick check and see if the output voltage or charging at the battery is at least in the ballpark with the spare regulator. Then depending on the result, check generator output or, swap the other regulator back in to see if the cutout is working or not.
 
You must log in or register to reply here.
Back
Top