So, I am in the middle of salvaging a spare 1915 engine that is in fantastic condition internally and actually appears to have been freshly overhauled shortly before being removed and never run again. In any event, the Magneto ring has now been removed and it is the later ring with the starter notch, so clearly it was replaced. I carefully cleaned it in new mineral spirits and the oil rinsed away revealing what appears to be an NOS mag ring, or one that was freshly rebuilt back in the day. Even the black protective coating that was applied looks fresh and the insulation is perfect.
So, the million dollar question is; How do I test this thing on the bench? I'm an optics guy... I work with photons... not electrons.
Anyway, with this ring looking new, it just seems a shame to rewind it simply because "that's what you do". Especially if it can be used as is in a power plant or something low budget. Thanks in advance.
Here's a previous thread describing the hacksaw blade test and the compass test
I'm surprised to find that The electrical System tells how to rewind a field coil, but not how to test it. Fortunately that's in the Ford shop manual, beginning on Page 235.
I had a original ring in my 24 Coupe that I used electrical insulating varnish on years ago. It worked and the car ran good on mag.
When I finally gave the engine a complete rebuild when I restored the car it "looked ok" but when tareing the engine down flakes of the insulation came off in small pieces. The varnish had held together the detorating insulation.
I wouldn't put together an engine again with an original 'Good' ring. If you know for sure the ring was replaced or rewound that might be OK.
But building an engine and 3 months later finding out that the mag ring is shorting out would be a BIG letdown and headache knowing that I could have put in a new one to begin with.
John... Yes, I understand all that. That's why I said I'd keep it for a powerplant or some low-budget project. Besides, my 25 coupe has had a bad mag for over 50 years and it runs fine off the battery/generator. So this wouldn't be put in anything that would be upsetting if it failed. All that considered, it's too new looking to just discard as a core. At worst, it will become a wall-hanger. But either way, I want to know if it is good.
I use a old toy train transformer DC side cause a can reduce the voltage
Hook one to the ring others touch to the mag post
I use a piece of steel across the contacts and touch the the mag post yes this creates a short but also magnetized the posts feel the pull just few seconds check each post all the way around if one poor or shorted you won't get the magnetic affect
May not be right but it works
If I remember, the way I checked my old original coil ring years ago was with a volt ohm meter. Maybe it was a continuity checker I used.
If it was with the continuity checker you could determine if there was a dead short between the cast iron and the copper coil rings.
That's a simple way but maybe not the best.
If the copper coil windings have nice insulation on them like you say its probably a good mag ring.
The old mag ring in my Coupe had missing insulation on it but wasn't shorted out to the iron ring and it was a good ring. I just sprayed on the insulation varnish. As it turned out the flywheel magnets was the reason it wouldn't run on mag. After I charged them it ran fine.
Ok, Bit are you supposed to touch the power supply to the contacts each time you check each individual coil? Because I touched a 12 volt source to the mag post and the mag frame just once for a second or so, and it magnitized each coil.
I think I would contact R.V. Anderson. He rebuilds coil rings. I believe he posts on the forum time to time.
I bet he would know for sure and would probably give you a good answer to check it correctly.
Very little power is needed to check a coil ring. A 6V lantern battery or small trickle charger will do it. Ground wire to one of the mounting bolt bosses and the hot wire to the contact button. Leave it hooked up while you run the entire test. Using a smallish screwdriver, hacksaw blade, or any piece of steel, pass it over each pole face in turn. If you get about the same magnetic pull over each face, you're good. Next, with the power on, pass a compass around the circumference of the field coil. Watch the needle to see if it flips 180 degrees each time you move it to a new winding. It should go N,S,N,S, etc. If in one spot, it doesn't want to flip when you move from one winding to another, the mag is defective in having consecutive windings wound in the same direction. Each should alternate.
Read the linked thread above - it's easy connecting a 12v battery to the magneto ring in series with a 12v bulb to limit the current, then testing each coil for magnetism with a hacksaw blade.
The method described in the service manual is one of few methods in that book I wouldn't recommend - they propose connecting 110 or 220v household current to the mag ring over a soldering iron - shudder, I wouldn't want to play with that kind of voltage for testing.
R.V. Anderson Is right with his talk about the way to test a magneto coil ring. I just willing to add that if the contact is pointing E or W to the coils you have a short between the winding in the coil you are testing and no magnetism is build up.
Correction in my last post :
I Just willing to add that if the contact is .... must be : IF THE COMPASS is pointing....
Here is how I do it:
Hooked up the coil ring on a 12V battery in series with a 21V bulb and check the magnetism.
Guys... Thanks so much for the information.
R.V. - I used a 12V trickle charger and all the coils pull nicely on a small screwdriver blade. Tomorrow, I'll do the compass test. Thanks again.
RE that's were the toy train transformer comes in handy you can really reducen your votage
The one I have fused and reads volts plus on off switch I even use it when an engine on the test stand powers coils as well as a battery
Bob, don't let out all the secrets of us in "that other dying hobby!"
You don't want a reduced voltage. 12V DC is just fine and will not damage the coil. You don't even need a series bulb. Just use 12VDC. The high current will give you a strong magnetic field on each coil and will detect any shorts. The best test for a coil ring. Never use 110VAC
Here's how I test it. I use a jumper cable from a battery and put one lead to the magneto ring which is grounded to one end of the coils. The other cable is used to contact the button. Actually it is easier to leave the cable on the button and use the other cable to touch the frame of the coil ring. Then I use a hack saw blade and go around the ring holding the blade over each pole and touching the battery. The magnetism should draw the blade to the pole. Go all the way around the magneto. If you find the blade is attracted to some of the coils, and then from there on no attraction, the coil is grounded. An internal short is harder to find. It will have a weaker attraction on the coil which is shorted but the others will still attract the blade.
You can also check for polarity by holding a compass near each coil, not directly over lit but hear it. The poles should alternate north to south as you go around the coil ring. If you find two with the same polarity next to each other, one of the coils is wound the wrong direction.
Here is a thread from 2013, www.mtfca.com/discus/messages/331880/386738.html, in which I recounted my experience in 1970, when, as a 16 year old novice, I successfully restored the magneto coil ring from my newly purchased 1926 coupe, when I had no money, resources or forum to drawback on. Back then, we were on my own and had to use common sense, the Model T Service Manual and what resources were at hand in order to complete my 2 year restoration project. Luckily the coil was good, for I did not even know to test it If it had been bad, I would have been up the creek and at a loss for what to do next.
I completed my coupe in October of 1972, just weeks before leaving for Marine Corps bootcamp. Jim Patrick
GEEEZ LOUEZZZZ Glen! Surely you don't mean what you said. Connecting just any 12V source to a mag ring can cause serious damage if that source is not current limited. The entire mag ring has a total resistance of about .25 ohms. Since ohms law states that the current will be then E/R=I then 12/.25 = 48 amps! and power in watts = ExI so 48X12 = 576 watts which can burn up your mag ring and very possibly burn your hands.
Please folks don't use just any 12V source but DO us a bulb in series as Andre V demonstrates. His method is the best test of those mentioned here. A good USA numbered bulb to use is your trusty #1156 bulb that I have recommended is also the correct bulb to use for in the car testing of magneto output when you have no more accurate means of testing your cars magneto. Just remember to follow Andre's pictures and place the bulb IN SERIES with the battery and mag ring. The current flowing will be less than 2 amps and your test will be valid and not harm anything. You must be very careful when using a lead acid battery for your test voltage. If the battery is very small then you may harm the battery since you are placing near a dead short across it when connecting up a mag ring to it for test. A series current limiting device such as a bulb is strongly suggested. Use any 12V bulb you have if indeed your don't have an 1156 handy but 1156 is very common and sold almost anyplace that has car parts.
Thank You John,
I just checked my post and saw my writing. The bulb I use is a 12V 21W bulb .
David D my last piece from massive layout from my days as a youngster to about college girls and model Ts
12VDC such as a car battery with no limiting will quickly identify any shorts, but it can also quickly melt the solder on the joints. The solder on original mags has a low melting point and it won't take much duration of heavy current flow to ruin a mag.
If you use the trickle charger I mentioned, the charger will be the limiting device. Because of the short duration of the test (about 7 seconds) I have also used the typical square 6V flashlight lantern battery without harm.
When I test a rebuilt mag before releasing it for shipment, I use a large heavy duty battery charger/start set to 6V and the lowest (trickle) setting. I have tested more than four thousand of my rebuilt field coils this way with no harm to charger or field coil.
I'm not as dumb as I look. I must admit that I use a battery charger to run the test. But I have also used a 12 volt battery with no ill effects. about one volt is dropped across the battery cables used so the voltage at the coil is 11 volts. Theoretically that would be 44 amps. My volt meter only goes up to 12 amps but the meter pegs softly at the stops so I believe the amps is somewhat less. There is no smoke or fire and no solder melts. The coils produce a good magnetic field and nothing even gets hot. So why all the fuss. Try it , you may like it..
I must also point out that you only need to hook up the coil for about a minute to run the test. Assuming you have 44 amps that's 484 watts divided by 16 coils equals about 30 watts per coil. As I Said the coils don't even get hot after five minutes.
I agree with Glen on this. I've hooked 12 volt batteries up to field coils many, many times and they don't get overly hot. People said the same thing about hooking 48 volts up to the field coil to recharge the magnets. They just don't get as hot in practice as folks seem to think they should get in theory.
Thanks for the support Tom. I am a retired Electrical engineer and do understand ohms law. I also have 80 years of practical experience.
I know folks are going to tell me this flirts with disaster, but Tom Sharpsteen had a set up with multiple batteries in a box (commercial deal) and he would take a flywheel with the magnets on it, set a coil on top and hook up the wires, then flash the coil, everything would jump a bit, repeated 3 times (4 times total) and then we'd need a crowbar to separate them. He had a Ford script gause (sp?) meter, and the magnets then would nearly peg the meter, greater than the "normal" limit on the meter. Made for a great hand-crank start mag.
I would think you want to test the insulation on the coils as well. I use a megger (Electrical Insulation and Leakage Tester).
Here is a example,
You don't need a meggar to test the outer insulation. A good visual inspection will do. make sure that all of the insulation is in place with no bare spots, then clean the insulation with gasoline or other solvent and coat the coils with red varnish or other insulating finish that will stand up to the oil. This will seal the insulation and help prevent further deterioration.
Don't use a really hot solvent such as Lacquer thinner, MEK, or Xylene, as they will attack the insulation coating the flat coil wire windings. Gasoline is a good solvent that will clean out the oil and won't attack the coil wire insulation, but it is so dang dangerous that I quit using it as a parts cleaner decades ago. Mineral Spirits or Naptha are good, mild, relatively safe solvents, that dissolve the oil and will not attack the insulation coating the flat coil wire and do not leave a residue. Soak and change the solvent when it becomes black, until the solvent remains clear. Stir and agitate the solution to dislodge the caked on oil and gently stroke the coils and coil ring with a soft paint brush. Be careful not to scrape off what cloth insulation remains and be especially careful not to scratch the insulation coating the underlying coil windings.
For insulating the coils, the professionals use "Glyptal" insulating varnish, which comes in a dark red color or clear. Wally uses the clear, but I prefer the red. Great stuff! Impervious to oil and high temperature. In 2010, I not only insulated my magneto coil with it, I coated the interior of my engine pan as well as the crankcase of my engine with it and 6 years later, the interior is still bright and clean and there are no red flakes in my oil. Jim Patrick
Rolls Royce used Glyptal to seal the insides of their aluminum crankcases. The stuff works & stays put!
I think we are loosing the original of this discussion: The test of a magneto coil loop out of the engine.
Whatever you use to set DC current over the coil loop and how much tension you use isn't that important.
The important is you have magnetism on each coil and the magnetism alternate N-S between every coil.
I use a lightbulb 12V 21W in series with the coil ring and a 12V starter jumper box. This worked well for me in the past and I will stay on it.
I withdraw my opinion and leave you all to those more learned and with more experience than I have. My apologies.
John, Your opinions are always valued and that is the real reason for the forum. There are some on here that only want to criticize and never offer an opinion or good advise. I can do without those guys. But you and many others always give good advise. We may not always agree but we can all learn from the experience of others and that is a good thing..
What Glen said; so well too!
Thank you David. John and RV'S comments are always good and they usually are right. I wish that more people would get on and share their experience in a helpful way. Those who just get on to argue and run down someone else's comments are not helpful and just drive new comers who really need the help away. That is not what the forum is for.
If we carelessly drive away the true experts who have devoted their lives to learning about all aspects of the T and passing on what they have learned, to us, the forum will consist only of mere forum members doling out useless advice with answers that, at best, are guesses. Jim Patrick
Jim. I agree Glen
Well, I'm curious. Has anyone tried straight 12 volts yet?
I did it like R.V Anderson suggested, using a 6V trickle charger. It worked perfectly and the Mag ring checked good.
Glen, I've tried 12 volts just to see how long it took to get very hot. It really never did for as long as I felt like watching it. I used regular starter cables to lessen the current drop. I hooked up my Hall-effect amp probe and determined that the particular coil I was experimenting with drew 19 amps. The battery was putting out about 13 volts, so that is 247 watts.
Now, having said that I agreed with Glen, I might have put in with John if he had said something a little different. The Geez Louezzz stuff about ruining a good field coil with a 12 volt battery is just plain wrong, however, I think it is a good idea to use a current limiter, at least at first. This is because the field coil could have any number of coils shorted to ground. If enough of them are (like all of them) you could have a dead short. That could cause some sparks to fly if someone were not careful.
I agree totally Tom. A little current limiting wont hurt as long as you are drawing enough current to detect shorts. Assuming there are no shorts to ground the magnetic field test of each coil will determine if there are any shorted coils which is doubtful. Then if the fabric insulation is still good, you are good to go. Thanks for all the good inputs.
Glen, Tom, James and all the others,
There are a few good reasons why you should limit the current on an old coil loop that came out of an engine.
- A visual inspection don't tell you if the loop have shorts and where the shorts are, are they to the ground or are they just internal.
A short to the ground in the first coil in the loop will be different in current as a short to the ground in the 15th coil.
- Using a 12V 21W bulb in series with the loop will limit the current to 1.75A. This is enough to build up a magnetism in each coil.
With the limit current and an internal short in a coil, the magnetism in that coil will be weaker or none and your compass will point to the two coils just next of the short coil. (Didn't see this on a single stack coil loop jet but have seen this a few times on double stack coil loops.) By using just a 12V battery and no current limit, the magnetism will be higher and the compass may give you N or S and the test has failed. By reusing this loop in the engine the magneto will be weak or not working. All the work for nothing.
Just why I use the bulb in my coil loop tests.