3 Wire Generator Not Charging

buck36

buck36

Junior Member
I have searched the forum and have not been able to find an answer to my specific generator question. I found the following conditions and need to confirm if they are correct.

Field Wire: 1 wire goes to the 3rd brush and the other end goes thru the rubber grommet and hooks to the generator case at one of the cutout mounting screws.

Armature Brush: + fixed wire to ground attached to generator end cap.

- wire from brush to cutout

This does not seem right to me. Any help would be greatly appreciated.
Thanks
 
Buck;
I'm afraid that I don't know about the 3 wire, but I am using a 2 wire. One to the battery side of the solenoid and one to the coil side from the ignition switch. The second wire is an exciter wire. This may be totally differant from your 3 wire. Do you have any instructions from the manufacturer?
 
Buck, you have it pretty right. There are two main brush holders on the end plate and the third brush (the thin one). The pos + or ground brush holder is not insulated on its mounting pins and has a short copper connecting wire from the screw that holds the carbon brush in its brush holder to the alloy end plate held there with a rivet. The neg - brush holder which has insulated pin mounts has the flexible main charging wire connected one end under the brush retaining screw and then goes through the generator case via the rubber grommet to the cut out GEN terminal. Most important to make sure that these three wires on the brushholders are special VERY FLEXIBLE cable and not just standard plastic automotive cable which is too stiff and will restrict the movement of the brushes pressing down on the commutator. Set your 3rd brush low at about 3amps charge on your ammeter (engine reving) which is actually about 7 amps charge in total allowing for the ignition coil draw. This setting is for daylight running (no lights on) and will not overcharge your battery. The setting sometimes written about of 14 to 19 amps in handbooks is way to high for daylight running and will cook your battery especially on longer runs. This is the standard ford 6 volt system of coarse. Hope this helps you, Regards, Kevin.
 
Buck, I should also mention it is most important to connect the two field coil wires around the right way. If you get them back to front the generator will not charge in its driven direction (clockwise looking at the front of the pulley). It would charge if it was driven anticlockwise which it wont be on the car. Now dont ask me which way the field wires go but generally they will only reach in the correct places unless they have been messed with. The original ford electrical system is POS + to earth (chassis). Good luck, Kevin.
 
If this is correct that means the field is grounded on 1 end at the case and attached to the 3rd brush on the other end. In order to polarize the generator I would need to remove the wire going to the case and apply 6 volts to it for 2 to 3 seconds. Then reattach it back to the case where the cutout mounts. I guess what I am confused about is... does this not ground the field coils and remove the residual magnetisim?
I know this is pretty simple stuff. I just want to have a good understanding of the working principals.
I should also note that when I attach 6 volts to the field and armature wires the generator does motor although it seems slower than I would have thought and has very little torque.
 
Buck, Why would you want to polarize it ? It is probually OK. But if you must all you have to do is connect battery power (neg - on your pos ground system) with a jumper wire onto the generator wire/terminal on the cut out for a second or two and thats it. You do not have to dissconnect any field wires. You have not stated if you generator is on your vehicle or not. Just put it on and start her up and see what happens, easy. You have the fields connected correctly so dont be concerned about residual magnetisum and such. You are reading too many other threads probually and sorry to say but some people who answer them dont know much about automotive electricity and only confuse the issue with their advice. Good luck, regards, Kevin.
 
Kevin, I had the generator off to clean up and put new brushes in. I don't think it has ever worked as long as I've owned the truck. It's been in storage most of that time. I've found several other things that previous owners have done incorrectly and I'm correcting them one by one.
Hope to make some progress on it today.
Thanks for your input and advice, David
 
OK, Let’s clear up some things and hopefully help someone who may have a similar problem.

I removed the Generator again and connected it to a 6 volt battery with the positive wire to the case and the negative wire to the armature wire. The Generator did motor slowly with very little torque. I knew something had to be wrong .

I made some calls and found a guy with the knowledge and equipment to work on these generators. The first thing he did was hook it to a battery with the same results as I had. He confirmed what I had expected. He said the Generator should turn faster with more torque. The next thing he did was pull the Armature and place it on a Armature Tester ( Growler ) and grab a hack saw blade. The blade stuck to the Armature Core in several places as he turned the Armature in the V of the Growler. He said this was a sure sign of a bad or shorted Armature winding. He let me do this as well so I would understand what he was talking about.

Things were now getting good… progress was being made and I was learning something.

As luck would have it he had a NOS Armature as well as the bearings, bushings etc. to rebuild the Generator. Everything but the field coils. Mine checked good reading 1.2 Ohms with a meter thru both coils in series. He said this was correct for the 6 Volt Generator.

After he installed the new parts and hooked it back up to the 6 volt battery the Generator turned 3 times faster with a lot more torque. More torque than I would want to stop with my bare hand.

I put the Generator back on the engine, installed the cutout and polarized the field windings. After starting the truck I saw the points on the cutout close ( I left the cover off ) and checked the voltage with a meter 7.4 -7.6 volts. I then adjusted the 3rd brush for 3-5 amps with the lights off. I will probably fiddle with this some as I continue to work and learn more.

These vehicles and engines have been around longer than some of us. We have no way of knowing who has done what or how well the work was done. I’ve learned not to take anything for granted. With persistence, patience and knowledge you can figure it out. In my case the Generator was not working correctly when I bought the truck.

Sorry for the long post. Hopefully this info will be helpful to others.
 
It's always a good learning situation when you start out with the simplest form of an electromechanical theory. The 3-brush systems having no need for a ******** type regulator made them as simple as it gets for electrical power generation. The only drawback was that they were very limited on output. If you wanted a generator to put out a larger quantity of current flow, it had to be a larger unit. Some of the 3-brush units specially made for higher output for police cars with 2-way radios and other purposes, were so big that they were difficult to get fit to the engine. For this reason they went on to the 2-brush types with external voltage regulators. This allowed peak output from a smaller generator set. Larger output still required a larger unit but not quite as large as for 3-brush units since control was more efficient.

For the generator to even start to function, it has to have some residual magnetism in the field pole shoes or it won't even generate enough to close the cut out points. That's why polarization is important. The magnetic field has to be polarized to the way the battery is connected in to the system (either positive ground or negative ground). DC current passed through a coil is how most fero-magnetic objects are magnetized. To de-mag or remove magnetism you have to pass the same part through a coil with AC current flowing through it.

A generator is most efficient when the wire size used for field & armature windings are of a smaller guage than the average electric motor. To get high torque, a motor needs relatively large wire gauge in it's windings. If you look at a starter you can see this. It draws a lot more current to turn than a fine winding motor but that's the only way it will have enough torque to turn an engine over. Motoring of a generator is why the cut out is on there. It would always have the reverse current acting on it and try to motor which would soon burn the generator up. You can motor them to test but it gets hot quick and can do damage to the windings. Many of the old generators were ruined due to a stuck mechanical cut out unit. The modern diode rectifiers wont stick and will give reliable service if they are quality made. Some have even been converted into solid state voltage regulators for a 2-brush conversion along with a diode for reverse current protection.
 
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