Technical Generator charges good at idle and low RPM but not so good at higher RPM

This is in my hot rod a 29 Ford Roadster with a 347 Pontiac in it with the stock GM Pontiac generator. I can't remember if I got this thing rebuilt when I built the car about 15 years ago but here's the problem. When I first fired up it takes a few minutes to charge up to 13-14 volts but no big deal. I can cruise for a while maybe a half hour and then it starts dropping to about just over 12 volts. If I come to a stop and it's idling it'll start creeping back up. This is been happening for over a year and I just haven't messed with it yet as it's always gotten me home. I do have another generator I can toss on to see if it's the generators problem or not. Note I have no accessories on the car like an electric fan or anything like that just a small fuel pump that pulls a couple amps. Anybody have any ideas to look for anything as I'm going to mess with it this weekend thanks

 

Does the cranking speed differ from first start and others throughout the day?. It sounds like the regulator is doing it's job. You really need to check it with a tester while it's running and then you can put a load on the system and watch the regulator work.

You can full field the generator and find out what the max amps and voltage are, but that;s just telling you if the generator is working or not. The regulator is the one the adjusts the current to meet the needs of the system.

 

Out of round commentator or sticking brushes.

 

don't fix it if it ain't broke?

Have you checked the volt meter for accuracy? and thought about where it's connected? Might be that it's working fine. Or the regulator might need adjustment. But since it always gets you home....

Might compare the reading on the gauge, to a good digital voltmeter connected to the battery, when it's sitting running after a drive.

 

Tighten and/or change your belt.

 

All good stuff to check. I'll get into it tomorrow. The belt is new and is snug enough. A close up picture just because

 

recheck wiring - no corrosion under wire covering, wire ends soldered & not lose, etc

 

It looks like it is riding low in the pulley. Could it be bottoming out? The belt needs good grip on both sides to work properly. You might need a wider belt.

Back when I was in tech school, I pulled my 65 Galaxie in to check the charging system. I was probably using a Sun VAT28 to check it. On the VAT 28 you could load the system with a carbon pile to check maximum output. Every time I would apply the load, the amperage would go up like it should and then drop way off. I called my instructor over and showed him what was happening. He laughed and said, "tighten the belt". I didn't believe him, but he was right; never forgot that. In that case the alternator would charge at idle, but not at higher engine speed much like your vehicle.

 

Huh, I'm starting to remember that I did have it rebuilt because when I first put the car together I tightened it like an alternator that has bearings and this has bushings and I wasted the bushings. I did replace the belt maybe a year ago or so. I'll look into it in a little while as it's kind of rainy here and the neighborhood is still asleep so I don't want to fire the car up yet

 

Definitely agree that it gets dirty as I used to live on a dirt road. And it does hang out in the Wind. Was just checking the pulley and it is worn a lot and the belt is sitting way deep in it. The crank and water pump pulley are great. The spare generators that I have have good pulleys so I'm going to swap that and check connections and see what's up

 

So I swapped the pulleys out and this one is riding perfectly where it should and i tightened up the belt a bit. Undid all the connections and cleaned them up a bit. Checked voltage everywhere and it's all the same everywhere so no voltage drop. Fired it up and had it idling and it went up to 13 very fast and then about 20 seconds up to 14. Hasn't done that in a million years haha. Going to go drive it around the neighborhood and see how it does

 

You fired it up before checking for voltage drop, right? You only get voltage drop at bad connections when there's current running through it.

 

I checked it before running and after running. Even at the gauge itself. I figured running or not if you've got a bad wire or ground problem the voltage won't be the same right? Well it started raining so I can't drive it around right now maybe tomorrow

 

Not right, you can only check for voltage drop when you have current flowing. Checking statically you will find the same voltage everywhere. It's not until you have current flowing that you will find voltage drops.

 

Got it, well when I checked it while running everything was the same at every point you know give or take a tiniest bit so that's all good

 

It would be a good idea to remove the generator and run every part that touches the engine with your bench wire wheel. Same with the voltage regulator.

 

I 100% agree with that. But a wire brush will have to work as I don't have a bench grinder haha

 

Everything's been working good so far. Ran it up to the RPM Nationals and back no problem and charging perfectly. Even had to jump start a couple cars, good thing I got it charging right.

 

In or about 1957, my new boss enlightened me by adjusting the voltage regulator on my Mom's '48 Cad.
I just loved how simple he made things look.
A week later, he hired me. I was 15, no drivers license yet, but he put me right to work removing the transmission from a '52 Ford step van. He was surprised to watch me tear the tranny apart, dropping the cluster to get the main drive out... "Where'd you learn this, Son?"
"We have hot rods we're building," I told him. Then, "Can you explain a little about that generator and regulator, Red?"
That was the REAL mystery. But he cleared it up.