Generator hot to the touch

Larry in Ark.

Larry in Ark.

Junior Member
Working on '31 generator, replaced field windings, bushings, bearings, brushes, etc. except armature which checked out good. Bench test 8-10 volts on volt meter but it really gets hot to the touch. Could the motor be turning the generator too many RPM's? Brushes make a noise sometimes like there's a load on them. I went to "professional" electric shop and he was no help.
 
Paul -- everything turns free and easy. No binding.

One thing I did notice was I have fire under 3rd brush but not under main brush. Could it be a short?
 
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What was the current output on your "bench test"? You must set the current within spec or the generator will cook itself. I suspect it's too high.
Also, the brush spring(s) might be weak. Use the eraser end of a pencil and press down on the back of the brush to see if the sparking goes away. If it does, replace the springs. But first check the current output. Knowing the voltage is not enough.
 
How hot is it actually?

Many Ford Barn threads are concerned with the temperature of various automotive components: A generator or carburetor or radiator is too hot.

How hot is too hot?

It might be helpful to provide actual temperature readings with the use of an infrared thermometer. These divices are inexpensive and accurate enough for such purposes.

Here is one example.
 
CCWKEN - How would you measure the current and adjust it?

Mike -- I'm just spinning it without a load and checking voltage.

I appreciate your responses.
 
Larry in Ark. said:
Working on '31 generator, replaced field windings, bushings, bearings, brushes, etc. except armature which checked out good. Bench test 8-10 volts on volt meter but it really gets hot to the touch. Could the motor be turning the generator too many RPM's? Brushes make a noise sometimes like there's a load on them. I went to "professional" electric shop and he was no help.
Click to expand...

The only way the motor could be turning to generator too many RPM's would be if you (or someone else) changed some of the pulleys. Have the pulleys been changed?

Charlie Stephens
 
Larry in Ark. said:
Working on '31 generator, replaced field windings, bushings, bearings, brushes, etc. except armature which checked out good. Bench test 8-10 volts on volt meter but it really gets hot to the touch. Could the motor be turning the generator too many RPM's? Brushes make a noise sometimes like there's a load on them. I went to "professional" electric shop and he was no help.
Click to expand...

Could it be that the field wire is crossed with another? Sounds to me like it is very possible.


Tom W on FB
Generator work gone bad!
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I just opened a box with a generator sent to me for work. As soon as I opened the box I could smell trouble. As soon as I removed the band I could see what caused the trouble. Someone had worked on this generator and had the field wire going to the output brush, and they had the output wire going to the adjustable field brush. This mistake cooked the generator, so it now needs an armature.
The adjustable brush is thinner than the other 2 brushes. If you have any doubts about which wire is which, just connect an ohm meter, or continuity tester to the generator output stud and each of the 2 wires. The wire that shows continuity is the output wire and goes to the THICKER output brush, which is 180* from the ground brush.
To check the field you can connect a 6 volt battery charger + lead to the case and the NEGATIVE lead to the field wire. The battery charger should show about 4 amps if the windings are good.
I don't know who did the work on this generator, but I had to fix 2 generators about 2 years ago for the same problem and both of them were worked on at a professonal generator shop.
 
My newly rebuilt generator likewise ran really, really hot after my 1st drive around the block after a years-long restoration. I discovered it when I raised the hood and saw the grease melting out of the rear bearing, and when I touched it, it was extremely HOT. It also was showing no charge when the engine was running and revved up, but would show a discharge when the lights were turned on. I conferred with Forbarn folks and got lots of ideas, but I simply changed the cut-out to one that was working fine on another car of mine. The generator now works fine, stays cool and shows appropiate charge when the engine is sped up. It seems the diode cut-out that I ordered from Bratton's was bad.

Maybe you could get as lucky as I did.
 
Running it without load is why it is getting hot. If you continue you will fry it. Don't ask me how I know. Hook it up to a battery and a light.
 
30Tudor,

I'm curious why no load on the generator would get hot ? The heat from the generator due to current flow losses in the copper is zero with no load.

Marc
 
Larry in Ark. said:
CCWKEN - How would you measure the current and adjust it?

Mike -- I'm just spinning it without a load and checking voltage.
Click to expand...
:eek:That will make it run hot. Without the generator connected to a load, the field coils get full voltage and the generator will attempt to produce full current in an over-run condition. This is enough current to melt the solder out of the commutator segments and possibly burn the windings. It doesn't take long either. A few minutes will do it. It's the quickest way to destroy a generator. That's why they say to never run the engine without the battery lead connected to the cutout. (Or without a battery.)

You need an ammeter, cutout and at least a battery. The battery will act as a load. The ammeter is setup between the battery and cutout. You will need to move the third brush to set the current output while the generator is spinning. If you're using a cutout and not a regulator, this should be no more than a few amps for all day-light driving. If you drive at night or run the lights during the day, set the current at about 7-10 amps. (A little more if you've added additional lighting.) But keep in mind that without lights, this charging rate will destroy a battery on a long trip by boiling the electrolyte out. If you're using a voltage regulator, follow the direction for the regulator--Exactly! A regulator is far better in that it will regulate the charge rate based on battery need. A cutout will not. A cutout will "turn-on" when the engine is running and "turn-off" (hopefully) when the engine is stoped.
 
"That will make it run hot. Without the generator connected to a load, the field coils get full voltage and the generator will attempt to produce full current in an over-run condition. This is enough current to melt the solder out of the commutator segments and possibly burn the windings. It doesn't take long either. A few minutes will do it. It's the quickest way to destroy a generator. That's why they say to never run the engine without the battery lead connected to the cutout. (Or without a battery.)"

Sorry, but I don't understand. If there is no load, then the current from the generator will not flow through anything and therefore there can't be any heat due to the current !

The only heat would be from the field coil.

Marc
 
The generator will still generate when disconnected from a battery. It has an internal load and that being the windings. The field is grounded on one end. The other end goes to the third brush. When the generator is turning, it's producing potential in the armature and this is picked up by the third brush. Without the resistance of the battery, the generator feeds itself voltage. Disconnecting the battery while running on a test stand will almost stall the driving motor while the generator is trying to produce around 30 amps or more. The only way to keep a generator from generating is to ground the output terminal. This has been done in emergencies when a cutout fails. It's a quick fix that will keep the generator from distroying itself if you're out on the road.

You don't need to understand it. Just know that it happens.
 
"You don't need to understand it. Just know that it happens."

Sorry, I can not accept that.

Lets try another idea...Without a load, the generator will produce a much higher voltage than normal..say 20 volts. This high voltage , when applied to the field coil, will overheat the field coil since it's only designed for a nominal value say up to 8 volts.

Does that make sense ? The heat is from the field coil ?

Marc
 
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Marc - CCWKen is right. Les Andrews has an explanation of what happens on pag 4-17 of the "Troubleshooting and Diagnostics" manual. It is counterintuitive but if there is no load on the generator, the third brush collects all the current from the armature and passes it directly to the field coils. This strengths the fields causing the current to further increase which then sets up a bit of a chain reaction. At least this is how I understand it. Think of it this way, the generator is spinning and therefore creating magnetic fields and setting up a current - the energy has to go somewhere. If you ever disconnect your generator and want to run the car, you have to ground the output.

Once on tour, I had an electrical issue which we thought was a short somewhere. I was advised to disconnect my generator. It go hotter and hotter until it completely fried and I was out a generator. Expensive mistake, but now everybody in the club knows not to do it without grounding it.
 
30Tudor and Others,

Yes, I read the section in Les Andrews book and as I thought, the lack of a load on the generator causes the voltage to the field winding to increase higher than designed. Then, using ohms law, the current in the coil rises and with IR losses, the heat bakes the coil and heats the generator. Makes sense.

Thanks for the info as today many electical appliances are made "goof proof" where as the Model A generator needed to have a load on it always.

Interesting.....

Marc
 
I've had this car since 1958, drove it as a kid in high school. I put it away and decided I would restore it some day. Some day (30 years later) I finally got around to restoring it and I'm finally about done. I was either lying to myself that I knew a lot about a Model A or I've just forgotten a hell of a lot! I appreciate all your help. It makes sense to me. It runs good with a battery hooked to it. Tomorrow I'll put it to the test on the car and will report what happens (if I remember). lol
 
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