A Generator Field Coil Issue

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Model T Ford Forum: Forum 2014: A Generator Field Coil Issue
Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Wednesday, January 22, 2014 - 11:16 am:

A few years ago, I obtained a new generator field coil without knowing the screws were impossible to remove from the pole pieces. Rom Patterson agreed to install the field coils at no charge, so I mailed him the case and coils.

Recently, I found a rebuilt armature and decided to try to rebuild a generator and change those field coil screws myself, as I could see that they had been removed and replaced, so I suspected they screws might not be as tight.

The new field coil assembly that I purchased for that repair was easily installed, but with less than satisfactory results.

The MTFCA Electrical System manual was some help, but the first step to set the end plate did not work. The second step to apply 6 volts to the generator and insure the shaft turns did not work either. This generator that was assembled with the case containing the new field coils did nothing in the way of turning the armature, which turned freely by hand and had new sealed ball bearings on each end.

The MTFCA Electrical System manual also notes on Page 7 that you should ensure the shaft turns properly, but neglects to mention that properly is in a clockwise direction and in some cases those field winding wires have to be uncrossed to get the proper clockwise rotation, when looking from the front.

The next trouble repair test for a proper set of field coils should have been performed first.

Looking at Page 22, top left of the MTFCA Electrical System manual, it shows applying 6 Volts to the Starter Leads, which will give max sparks and may actually explode the battery that is providing the 6 Volts for that test, so it is rather dangerous to try, unless you notice that is really a generator drawing in the wrong section. That fact was discovered the hard way last month when a starter repair was attempted. While that chart is correct and normally works as drawn for generators, it did not work for that generator with the new field coils installed. It did work for another generator case. The compass did not read North – South – North – South as shown in the diagram, but it did read North – East – East – South which kind of identified a problem with the new field coils.

The generator was disassembled and the new field coils were removed, then laid out in a row with the pole piece installed and 6 Volts was applied to each end terminal, as suggested and shown on Page 13 in the same manual. A compass was placed near each pole to verify the polarity and the readings and they were North – South – South – North from left to right across the row. The correct readings would have to be North – South –North – South to align with the test diagram on Page 22, which is correct for a generator.

image{Coils}

What this suggests to me is that two of those field coils will have to be reversed to make the generator work properly and that was not an easy task that I could perform. A replacement field coil assembly was promptly shipped to me and the defective set was returned.

My point here is that if you buy spare parts like I do to have them in stock for a quick repair, you should check you field coils when you get them. I just did not have a new set available at the time, as that is a repair that I have seldom attempted.

This may not be a common and know problem and could be a first time ever event for me.

A more import point is the electrical manual should be corrected before some do-it-yourself type, like me, is seriously injured by an exploding battery while checking the started field coils.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Wednesday, January 22, 2014 - 11:18 am:

The missing photo.

coils

That first character is important!


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Wednesday, January 22, 2014 - 11:57 am:

A small correction could avoid a large explosion.

Field Coil Drawing


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Wednesday, January 22, 2014 - 01:11 pm:

Since factory drawings are available the first question I think someone should ask any source is "are these field windings made exactly to Ford drawings that the vendor has in his possession?" Copies of copies seem to be tolerated and shouldn't be. Look at the money wasted in shipping back and forth and assembly time wasted and sometimes other good parts ruined in the "double" rebuild job - once to do it and again to get correctly made parts to do it over. I can feel your frustration Jim and I don't personally think that any rebuild manual should attempt to show someone how to install poorly made or incorrectly made items since that just encourages more junk parts being made and lets the vendor off the hook for incorrectly made parts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Wednesday, January 22, 2014 - 07:27 pm:

My first question would be, why if the field coils are that new are you replacing them?


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Wednesday, January 22, 2014 - 09:23 pm:

Mark, I am replacing those new field coils because they are wired backwards and do not develop the magnetic fields required to make any electricity.

The original coils were burned up, due to a bad cutout not passing on the current. When that happens, all the current goes through the field coils and makes more electricity that the wires can tolerate.

That is why the Fun Projects diode cutout and current regulator is such a great insurance policy, it save the problem I found on this generator.

Actually two of those coils are wired correct and the other two might work if they were reversed in position, but one has two short leads and the other one has a short lead and the pigtail lead.

If the compass had read North - North - South -South, I could have reversed the two inside ones that were the same with short leads on both sides and had a working set of field coils.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Wednesday, January 22, 2014 - 10:20 pm:

While I understand the meat of the conversation, I am lost on which set was bad, the one Ron installed or the one you installed. Or is it both the same set?
Do you have a pole shoe expander, home made or other?


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 23, 2014 - 11:12 am:

Sorry for the confusion here.

The case Ron installed a field winding set in was great and originally in this totally rebuilt spare generator.

I borrowed the case from that generator to repair another generator, as I knew it was good and I did not have a spare.

It was also removed to perform the compass test and prove the new field winding set was defective.

Ron always does top quality work!

I primarily borrowed that one for a test and quick fix.

The defective new field winding set was purchased to repair the defective case field winding that was beyond repair and replaced.

That generator had been previously rebuilt and the rebuilt armature was still good, along with all the other parts, so it was a quick fix, as planned.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 23, 2014 - 01:19 pm:

A new set of field coil windings arrived today.

They were tested right away.

The results do not match the diagram in the book.

This time the coils were sealed in a standard white plastic bag with the Ford logo attached.

The defective coil came in a clear plastic zip-lock baggie and suggests that someone had already returned it and it was just put back in stock, as it still looked new.

If any two of the opposite side coil compass diagrams were swapped, then the readings would match the diagram.

In either situation, I am not sure which is right, the diagram or the coils, but I would vote for these coils being correct.

This time the readings were South - South - North - North. In this case go clockwise from the lower left coil to read the 1 2 3 4 photo numbers.

Coil 1

Coil 2

Coil 3

Coil 4


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 23, 2014 - 04:42 pm:

Ron Patterson called me and told me that my test procedure was flawed. He said the pole pieces had to be vertical, like they were in the generator for a valid test and asked me to place them in that position, cross the wires and apply the + voltage to the proper wire, which was on the left as shown above after the coils were positioned vertical and the wires crossed, as shown in the above diagram from Page 22.

Then the results were different and correct!

Coil 1A


Coil 2A


Coil 3A


Coil 4A


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 23, 2014 - 05:17 pm:

Note in the above photo that the wires are crossed to aline the photo with the diagram on Page 22 and the black - clip lead is on the right and the red + lead is on the left.

The can is a Never-Dull can and just right in size and height.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Zahorik on Thursday, January 23, 2014 - 07:58 pm:

James, your first test where you have the field coil laid out on a board would work, but you have the compass in the wrong place. Think each coil as a donut and the iron pole piece is in the donut hole. The magnetic flux that the coil makes goes through the donut hole and the pole piece. You need to place the compass perpendicular to the iron pole piece and you should get the proper polarity. If you look at the second set up, the one that Ron told you to do. The compass is perpendicular to the pole piece and that is why it worked and your first set up did not. In the first setup your compass was not in the line of magnetic flux.
Mike


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Thursday, January 23, 2014 - 11:32 pm:

Mike
I had a similar conversation with Jim today.
In simply I reminded him of the "right hand thumb rule" he forgot from Electricity 101.
Ron the Coilman


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