My name is scott and I'm having a charging issue with my
56 f100 12 volt generator. I've looked at the voltage regulator and it looks
Good the contacts are clean with no corrosion. I have tested the voltage
From the generator and I get 13 volts at idle but when I rev the motor up
It stops charging and my batt light comes on. I jumped the field contact to
The battery contact and the generator says it's putting out only 9 volts while revved up . I pulled
The gen and cleaned the brushes and everything looks to be good inside.the wires look to be correct. So
I guess I just have a bad generator . Should I be checking anything else before
I replace it? My battery was pretty dead. Any help would be appreciated!

 

Ummm, belt loose?

 

Brushes may be lifting off the armature, especially if they are broken or weak.
This is something I found that may be helpfull

IN MOST OLDER CAR APPLICATIONS, THE GENERATOR ARMATURE
TURNS ABOUT TWICE FOR EVERY RPM THE ENGINE TURNS.
When a generator spins at high speeds (above 3500 rpm engine speed) the output
of the generator will actually drop off quite a bit, as the brushes are lifted off of the armature
by centrifugal force. If heavier brush springs were used (a great idea), it would cause
excessive brush wear at the slow speeds.
An interesting note: Did you ever wonder why over the road trucks get such long
life out of their generator brushes as compared to a car? Here are the reasons. One is the
constant rpm that make it easy to match the correct engine to generator speed.
The other factor is called air gap. This is when the brushes lift off of the commutator
just slightly due to the centrifugal force. The brushes will then experience minimum wear
because the brushes are not physically touching the commutator and the loss in output will
be slight.
Cars driven in town will wear out generator brushes at a much faster rate than those
that spend their life traveling up and down the highway. The same principle applies

 

The belt is good. I might try new springs and brushes first. Thanks guys

 

Just got my new brushes and springs in the mail from
C & G ford parts very fast shipping I would recommend
Them. As soon as I get them installed I will post if it fixed
My issue.

 

The brushes aren't spinning, I don't see how centrifugal force could be at play. Any out-of-round condition on the armature could knock the brushes back. A bad bushing or bearing could also.

Also surprising the gen is putting out at idle.

 

I wondered about the mention in the article about centrifugal force also. I figured he was talking about the brushes bouncing over the armature and then not re-seating quickly enough ( similar to valve float). He just didn't state it that way in the article.

 

I'm leaning more to the armature being worn out. It looks like my bearings are new, so I think the previous owner may have had charging issues also. Just thought the springs and brushes were so cheap it was worth a try before buying a new armature section. Also I was surprised with it charging at idle made me think someone had wired it wrong. It's working the opposite that it's supposed to. I've had generators on my VW sand rails and they only charged at fast rpm's. The field coils still looked nice and wrapped so I don't think they are bad. Have a great thanksgiving everyone!!!

 

We'll I installed the new brushes and it didn't change much. I used my old springs cause the new ones I bought had less spring pressure than the old ones I bought. The generator seems to charge if u rev the engine very slowly but if u rev fast it stops charging. So I will be getting a new armature section and maybe new bearing. Seems the brushes won't stay in good contact during med to higher revs. So I guess I have some vibration causing this. I'll update when I get the new parts in.

 

At night or in a reasonably dark garage, you'll see all kinds of sparks at the brushes if they aren't making good contact. Keep in mind, if the battery is charged up, it won't put out. Turn on the headlights to put a load on it. The workshop manual has excellent procedures to identify problems. A generator shop can test all the components quickly, may save you money from buying unnecessary parts.

 

I like Ross's idea about taking it to a shop. I once had a fancy 12v alternator that lost output at higher rpms. It turned out that the shop discovered that the new belt was slipping on the new polished pulley. I roughed up the interior surface of the pulley and that cured the problem. Last year my 6v starter began to intermittently refuse to start. (Starters are very similar to generators in their parts makeup.) It turned out that the armature was out of round. The generator repair shop trued it up, replaced the brushes and painted the exterior for $40. My guess is that the armature might throw the brushes away from the surface it is out of round. Good luck, Jag

 

We'll I finally got it fixed!!!! I want to thank everyone for there help! I took my generator to a shop and they tested it and it was discharging instead of charging. They said my armature was bad. So I ordered one from C&G parts on the internet, it was only $25 plus shipping. Just installed it and everything is working great!!!

 

Congratulations 50!!
It's nice when you finally figure it out & it works!

Looking good up there in Oklahoma. Nice truck.

Ben in Austin
1950 F1

 

Did the shop offer to repair the generator? How much did they want? Glad you got it going. Jag