Maneto Coil pack seems to be bad

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Model T Ford Forum: Forum 2012: Maneto Coil pack seems to be bad
Top of pagePrevious messageNext messageBottom of page Link to this message  By Steven Thum on Sunday, November 04, 2012 - 05:33 pm:

I replaced the mag ring in my 25 tudor, recharged the magnets, leveled everything and set up the magnets to 30 thousands all around. Mag output zero. This is before I connected the mag wire so I did not get a voltage to the mag. This is checked with the magneto voltage meter sold by Lang's and the meter was checked on another car. The mag post was replace and that did not fix the problem.

Has any one had any problem with a bad mag coil ring that has been rebuilt?

I have done about 10 of these so far and have not had this problem before.

Thanks
Steven


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Sunday, November 04, 2012 - 06:56 pm:

Steve
Does the car have a outside oil line from the magneto post to the front of the engine?
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steven Thum on Sunday, November 04, 2012 - 06:59 pm:

No, it has a high capacity oiler and a Model A crank with a regular mag post.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Sunday, November 04, 2012 - 07:12 pm:

Steve
I assume you are using the St Louis magneto tester?
When testing , take the magneto post out, point your meter test lead firmly down onto the solder pile of the field winding and wrap a rag around magneto post hole.
Take the readings again and let us know.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steven Thum on Sunday, November 04, 2012 - 07:54 pm:

I am using Lang's part number A-MAGM Magneto Meter. It shows 26 volts on my Touring. I have used 2 different mag posts, one off of a working car. I show continuity to ground when testing with a volt ohm meter. zero voltage output.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, November 04, 2012 - 08:59 pm:

The magneto meter is just an AC voltmeter. Since you have continuity to ground then either you have a shorted magneto post or else there is a short to ground in the coil itself.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steven Thum on Sunday, November 04, 2012 - 09:36 pm:

I am thinking short to ground on the coil. So, has anyone else had a bad newly rewound coil?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Sunday, November 04, 2012 - 09:50 pm:

I've never tested a mag with the post removed. I'd be afraid of having oil all over the place. But I guess you could use a grommet or rag around the test probe. I would at least test the mag post for a short to ground.

We're assuming you assembled the magnets correctly (NN-SS-NN, etc.) but follow the setup directions for In-car charging of the magnets using a compass. Have someone crank the engine slowly and verify that the poles change through a complete revolution.

Won't the mag coils always show continuity to ground. The other end of the coil series is connected to ground.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jack Putnam, Bluffton, Ohio on Sunday, November 04, 2012 - 09:56 pm:

Yes, the mag coils always show continuity to ground. Ken is correct. I you remove the end connection you could then test for continuity which should then show an open circuit. Impossible to do with the coil in the engine.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Sunday, November 04, 2012 - 10:20 pm:

If someone has ever determined the cross-section area of the mag wire, you could check it with an accurate VOM. I'm only guessing based on unconfirmed specs but it would be somewhere around .5 ohms.

I can't see how a new/rebuilt mag ring could be shorted to ground. That's not likely given how they're wrapped and sealed. (or should be) Unless, of course, you damaged it during installation of the starter with the bendix installed. A more likely problem would be an open circuit if one of the coils had a broken/cold solder joint.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, November 04, 2012 - 11:41 pm:

One end of the coils is connected to the output terminal post and the other end is connected to the coil ring, thus is grounded.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Monday, November 05, 2012 - 12:01 am:

I once measured 4 new rebuilt magneto coils done by Leo Musch. I used the voltage drop method of putting exactly 1.000 Amps of DC current through the thing and then measuring the voltage across the coil from magneto solder pile on top to frame. I then calculated the resistance and they varied from .25 ohms to .28 ohms total series resistance. You really cannot measure this amount of resistance reliably using a common ohm meter set to the resistance scale since the probe contact resistance will vary enough to give you half or double the actual resistance reading. It is rather difficult to attempt to do anything meaningful with the DC resistance measurement as a diagnostic tool beyond telling if the winding is open or not. The winding could be shorted to ground right at the solder pile and it wouldn't look a whole lot different than a good mag coil with regard to a resistance reading. I think the best way to test a mag coil ring is running a controlled amount of DC current through the mag ring BEFORE you put it onto the block and then checking to see that there is magnetic pull on each of the magnet cores that is equal. A hack saw blade laid flat on each magnet center in turn makes a good probe to check for this magnetism. There should be an equal pull on each of them.


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Monday, November 05, 2012 - 09:48 am:

Steven you did'nt say how you did the magnet recharge, KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steven Thum on Monday, November 05, 2012 - 10:15 am:

I own a recharger. All magnets picked up a Model T piston after being recharged. As I said before, this is not the first one I have done. This is the first one with zero output.

John, I will probably do the test you described before I install any more.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, November 05, 2012 - 11:10 am:

Steven,
Was the continuity to ground test done with the magneto contact in place, or was it done through the solder button inside? Sometimes the contact does not make a good connection with the solder button. If the continuity to ground was made with the contact in place, then the contact itself could be grounded. However you said you replaced the contact, so it is not likely. I would say that you either have a coil grounded somewhere in the ring, most likely close to the button. Or your magnets are either not charged or they are not placed in the proper order.

Sorry, this is not good news. The magnets can be charged in the car. The contact can be repaired or replaced. But either of the other problems would require pulling the engine to find or fix.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd on Monday, November 05, 2012 - 11:58 am:

I test magneto coil rings as John R. described. I found one rewound one that had one dead pole in it, the rest of the poles were good. The rewinder exchanged the bad coil ring for another one which tested out OK.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steven Thum on Monday, November 05, 2012 - 01:00 pm:

I called Lang's and talked to Steve. The great way I was treated is why I will continue to do business there. Steve did confirm that once in a while a magneto coil pack does have a short. A new one and the gaskets needed are on their way to me.
In the future I will test all coils in the way John Regan suggested. It is better to find a problem before the engine is back in the car.
So now, back to work, gotta pull this engine again.

Steven


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor on Monday, November 05, 2012 - 01:35 pm:

A while back, I had inquired if anyone had tried measuring or using magneto coil inductance as an indicator of coil integrity as opposed to DC resistance for the reasons cited. The inductance of the magneto coil is a function of the total number of turns of wire used on all 16 coils. I believe a single shorted coil or a coil shorted to ground would cause a significant change in inductance compared with a good magneto coil and would be a good test provided all magneto coils were built with approximately the same number of total turns. I did not receive much input from anyone about magneto coil inductance data or variation in number of turns so I contacted a coil rebuilder to see if there was any interest in characterizing the various good magneto coils to test the theory but unfortunately the answer was; NO! Perhaps a future project.....


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthonie Boer on Monday, November 05, 2012 - 02:51 pm:

Steven : I always test the coil ring and mag before put the engine together . as soon as the crankshaft,coil ring and flywheel are mounted then I put a crank handel on the shaft , and turn as fast as I can I need then 4-5 AC volt , and know that all is OK .At that time I had an AC volt meter, Now I have an Magneto output tester !!!!!Thanks
209R
211R
Toon


Top of pagePrevious messageNext messageBottom of page Link to this message  By R.V. Anderson on Monday, November 05, 2012 - 06:39 pm:

Often the trouble in a rebuilt engine isn't the mag per se but a bit of broken wire or cotter pin that is picked up by the magnets and either jabbed into the field coil or hung up around the contact. Either way, it's a short to ground that will stop or greatly reduce the output. It's way more frequent in rebuilds than in seasoned engines.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd on Tuesday, November 06, 2012 - 10:51 am:

Besides the test that John R. recommended, another test that can (should?) be done on a coil ring before installing it is to apply low voltage, low current DC to it and check that the poles all have alternating polarity, that is; N-S-N-S-N-S etc.


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