Coil rebuilding question

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Model T Ford Forum: Forum 2012: Coil rebuilding question
Top of pagePrevious messageNext messageBottom of page Link to this message  By Will Copeland - Evans Mills NY on Friday, November 02, 2012 - 07:51 pm:

we are using a strobo-spark to setup a coil without any luck...

Coil has new points and cap. Resistance from the primary to the core is 5Mohms, primary to secondary is 80Mohms (tested with a megger).
resistance of the primary is about 10 ohms but its hard to measure that on our meter. The secondary measures 3Kohms.

We installed new points and set the gap to 0.030". when we first put the coil in the strobo-spark we had a few intermittent sparks and a large amount of current. we reduced the tension of the lower point to reduce the current to 1.3Amps but now we have no spark on the strobo-spark. The points are buzzing but here we are...

(the measurements we took above were done after we tried to setup the coil on the strobo-spark)

Any help or tips on getting this one set up would be appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Friday, November 02, 2012 - 08:02 pm:

Check your connections. Clean the points in lacquer thinner or alcohol. Are you measuring the gap with the vibrator down from the bridge or tight against it? Some point just seem to want less gap then others. Are you setting the tension by the lower contact or the bridge?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Vaughn on Friday, November 02, 2012 - 08:23 pm:

Sometimes you will find a coil that measures good resistance but you actually have an open in the secondary windings and your spark is lost to ground internally within the coil. It will still buzz and sometimes you will actually see a spark in the strobo spark tester. You might not see all three only one or two because the coil is intermittently grounding within.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Friday, November 02, 2012 - 08:43 pm:

And some times just putting the hot tar back in kills them :-(


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Friday, November 02, 2012 - 09:16 pm:

Will: try adding some tension to the vibrator. then add some tension to the cushion spring to balance out the vibrator tension


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Friday, November 02, 2012 - 09:18 pm:

I have a HCCT to calibrate coils. E-Mail if you need help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Friday, November 02, 2012 - 09:26 pm:

It helps to have the proper point orientation, do you need shims under the bridge cylinders to raise the bridge due to compressed wood ???


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, November 03, 2012 - 12:52 am:

My guess is that the coil is arcing internally. The Strobo-Spark is set up with an exact gap of 1/4". I suspect if you reduce the gap you will then get the coil to arc external to it rather than internal but that is not a "fix". If a coil will not arc at a gap of 1/4" then it is defective and you cannot "repair" it by reducing the gap that it has to jump as a means of preventing it from arcing internally. If you have any sort of other tester with a narrower gap such as an HCCT you can then prove this is the case or not by reducing the HCCT gap to say 1/8" or so and then increasing it to 5/16" and see if the spark will jump the wider gap or not. I suspect it will jump the 1/8" gap just fine but not the wider gap. This is often caused by someone powering up the coil without a suitable gap of 1/4" or less for the spark to jump so it then jumps somewhere inside the coil and lays down a carbon trail inside the coil or its windings. Unfortunately that is all too common.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Barker, Somerset, England on Saturday, November 03, 2012 - 04:55 am:

I have found several coils which appear to be 'right' in every way - points clean, gaps set, cushion spring working, resistances OK, and capacitor not leaking but has uf etc, but they won't show 3 good sparks on my Strobo-Spark.
But they all had non-original capacitors - usually pale green or yellow in colour. As soon as these were replaced by the correct orange-coloured type, all was fine.
The experts are right - the capacitor has to be to the correct spec - notably a property called dv/dt. Other caps may work for a while but they don't last long.
But John Regan's suggestion is the likely one if your capacitors are OK.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, November 03, 2012 - 11:17 am:

With regard to the "orange colored" or "orange drop" type of capacitor. I find it very worrisome that most of us have named the "correct" capacitor as the "orange drop" type. The term "orange drop" defines a type of housing that MANY different capacitors use. It does not define the correct type of capacitor. The company that currently makes the "orange drop" capacitors that work for our coils just fine also makes some other capacitors in this exact same package that will NOT work just fine so make sure you have the right part and of course as you might expect, the wrong part is way cheaper. The correct part must be a film/foil type of capacitor with a high dV/dT rating or it will not last more than a few miles in a T coil application. I have been guilty of using the term "orange drop" capacitor myself but just make sure you are getting the right type of capacitor. Ask your vendor if the capacitor is the high dV/dT version of the orange drop cap. A higher working voltage than 400V does not mean it is a high dV/dT capacitor and a 600V part will fail just as quickly as a 400V part if the part is the wrong type.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Saturday, November 03, 2012 - 11:21 am:

I have found coils with no sparks that had to be set to a rough adjustment with a HCCT before they could be fine tuned with a StroboSpark tester for great sparks.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Saturday, November 03, 2012 - 12:03 pm:

One thing I don't recall anyone talking about is doing a hot test. Heating the coils to as I recall 150 to 200 degrees and checking them. I got this suggestion in my magneto repair book.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Saturday, November 03, 2012 - 01:29 pm:

One more thing that should be mentioned, after John Regan reminded me that it was important, is that the StroboSpark is set for a 1/4 inch spark gap.

If the HCCT has a spark gap set at less than the 1/4th inch specified, a smaller voltage and/or current will be required to make a spark jump and the HCCT might produce sparks while the StroboSpark will not show any sparks.

My HCCT that I had been using had a slightly smaller spark gap and was adjusted to the correct 1/4th inch. Then the readings compared better with the Strobospark.

Sometimes when the Strobospark shows no sparks, all that is required is to adjust the HCCT coil under test to make the meter read 1.5 Amps. The extra current will then also produce StroboScope sparks and the fine adjustment can be completed.

Another early book I have notes that the spark can be set anywhere between 1.2 and 1.6 Amps.

Well, it works for me anyway, but a second opinion is always great to have here.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, November 03, 2012 - 03:12 pm:

Most good Ford or KW coils with good capacitors will easily produce a 1/4" spark on as little as 1 amp. I am probably uncomfortable with a coil that needs to be set higher than the 1.3 amps in order for it to work properly in a Strobo-Spark. The SS is a fussy tester and you must PROVE the coil is good or it will flunk it with one of its various tests. This can be aggravating until you are on a week long tour and your car is running on Friday just as good as on Monday.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Saturday, November 03, 2012 - 04:47 pm:

Will Rogers once said, “all I know is what I read in the papers.”

I only went to night school and don’t read too good in the daytime, but I though I understood this note on Page 47 of Repairing and Restoring the Model T Ford, The Electrical System, © 1988, 1991, 1997, 2008

“The exact current is not critical – anywhere from 1.25 to 1.75 is OK but try for 1.5 amperes. If the current draw is too high, it will be difficult to start on “mag”, and if too low, the spark will be weak. If you are running on “battery” (your magneto does not work), set the current higher for better high speed operation, (Battery operation is never as good as magneto; the points wear faster, and the spark is weaker at driving speeds.)

When properly adjusted, the coils should put out a spark that will jump about 3/8”. Each coil should draw the same current.”


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Saturday, November 03, 2012 - 05:31 pm:

James:

All I know is what I have learned in my own lab with my own equipment. 1.3 amps is the ideal current. More than that just adds heat. I have found through experience that the hobby is plagued by the "more is better" syndrome and just because something is in print doesn't make it a fact. If you tell someone that 4 amps of charge is max for a cutout equipped generator, someone will post that they set it to 5 amps and the next will say 6 is better....

The spark will not be weak at 1.3. Whether properly adjusted or not if you test your spark at 3/8" you will encourage an internal spark inside the coil since there are parts in there that are just barely 3/8" apart. I have watched T guys impress people with wide spark gap testing and it proves nothing but risks everything. Since the current is what controls the spark intensity there is no difference between spark intensity when the coil fires just the speed with which it ramps up to fire. This is based upon the still accurate physics concept that magnetism is determined by amp-turns and it matters not the voltage since once there is enough current in the primary to create enough magnetism to pull the points open - the coil fires. Battery performance is not the same for 6V as for 12V battery and if you increase the current of the coil when using 6V you will make the car run much worse since it will take just that much longer for the coil to ramp up and fire. 12V performance is fine at 1.3 and setting the current higher is just creating more heat and setting the current higher when running on battery to increase high speed performance is backward from the truth. There is no author cited in the article you cited but it is simply wrong on some points. As for the 3/8" testing of your coils - well - since I make and sell coils it would be certainly in my best interest for folks to in fact test their coils at 3/8" and in the interest of "more is better" then maybe they should test them at 1/2" or even 1". 3/8" in free air is the equal of a plug gapped at 3/32" under 4 to 1 compression and that would be a wide gap indeed and thus the coil is being tested way beyond normal operation.

If we don't share what we have learned then what is the point. It is none of my business how anyone wishes to test their coils - I simply would like folks to know that in my opinion there is unnecessary risk being taken by doing things a certain way. Those who wish to disagree are certainly free to do so but the laws of physics don't change according to someones opinion. A coil set to a higher operate current is a slower coil. A coil operated at 6V is slower than a coil operated at 12V. All of the HCCT devices show the long ago arrived at optimum coil current of 1.3 amps but it would seem that the "more is better" concept was alive and well even in the T era since many of the earlier "pre T" coils had a recommended set current of about 1 amp. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Saturday, November 03, 2012 - 05:57 pm:

John, there are a lot of people, like myself, that do not know what is right and are still trying to learn.

That book I quoted is widely read and perhaps misled for some. That may have been just one person's opinion.

My real point in the posting was to suggest, if that is an error, it should be corrected in the next revision.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Sunday, November 04, 2012 - 01:20 am:

I totally agree with John Regan's points about "more is better", or rather that it is not always better. I worked for many years in electronics and communication systems. I have a lot of experience repairing systems and equipment that were "under-built". Trying to push the current loads higher through coils more than they were intended for is just as bad as using the smallest component you think can survive in a circuit. Would you like to see some fire alarm panels that set the building on fire? I saw a dozen of them. All because someone wanted to save a penny per unit by using the smallest diode they could.
Opinions abound. And many of our coils are approaching a hundred years old. Testing our old coils by trying a much wider gap than they are intended for will lead to one certainty. Failure of coils by arcing internally. As for that feeling of reliability because it "passed the test"? Final failure could occur a thousand miles later. Once a carbon track is formed, they tend to grow. Eventually, till they fail. Spark always takes the path of least resistance.
Drive carefully, and enjoy, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, November 04, 2012 - 01:08 am:

James and Wayne:

I confess I never read page 47 or that article before and agree with James that perhaps it ought to be redone purely in the interest of preserving good coils from abuse since a lot of that info in there is not very accurate. It probably is not super death to the unwary but there are a few blatant errors that can do harm.

I worked at Bell Labs for awhile right out of tech school in the late 60's and those guys were always creating projects that they placed on peoples desks to then watch the fun. They were always labeled as "Little Gem" products. One was a device in a grey metal box. It plugged into the wall AC outlet and had a place to put a glass fuse in fuse clips and then an interlock door cover over the fuse itself to prevent the device from being powered by its on/off switch unless the cover over the fuse was closed. The device was labeled as "Little Gem Fuse Tester". It was on my desk along with a small bag of glass AGC fuses. I was curious as to what exactly it would do so I took a fuse out of the bag and placed it into the clips so it was connected and ready for test. I then closed the door over the fuse, plugged the device into the wall and turn the switch on. The moment I did that the fuse flashed and a small digital read out came on and said "it WAS good". The thing simply connected the fuse across the AC plug which destroyed it and this removed the short across the LED read out. I did what everyone else did and removed the burned out fuse. I then placed the bag of remaining fuses and the Little Gem tester on the desk of the fellow across the hall when nobody was looking. There were various Little Gem products that made the rounds. I never knew who exactly built what but they were a good laugh and actually were rather clever designs.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Barker, Somerset, England on Sunday, November 04, 2012 - 06:11 am:

John,
my apologies. 'Correct orange-coloured' was just my shorthand for a capacitor which has the right specification, based on the fact that one of the capacitors commonly used nowadays, and which works, happen to be orange. I know that there are others which will do the job - I believe a red one is now on sale.
And it's pure chance that all the failed ones I found (of different types) happened to be pale yellow/green!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Will Copeland - Evans Mills NY on Sunday, November 04, 2012 - 08:55 am:

Good morning everyone,,,Sorry for not getting right back, The coils had to be put on the back burner for a bit while I helped clear some downed trees. I have come to the conclusion that I had done everything right as to what was suggested here. I had installed the new type of cap and points from Langs. I had also raised the top points with plastic washers to level things out and made sure of proper aliment and adjustments. As a test control I took the cap and point from the non working coil and placed them into a known working coil and it worked flawless. My conclusion is what Mr Regan mentioned that the coil was shorting inside the windings. The unanswered question is why the Megger test did not pick that up. Should I assume that when I get a coil that does not fire all three points on the Strob Spark that it is shorting inside the windings and needs to be used for just parts? Thanks for everyone's help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Sunday, November 04, 2012 - 09:09 am:

Will, your Megger might be operating with 1,500 to 2,000 volts, which was not enough to jump the gap.

I bought new coils about 30 years ago that would work OK on Bat and make all kinds of trouble on Mag. I learned that the extra spark voltage available on Mag was sharing sparks with the adjacent spark plug terminals through the black paint, which contained lead and carbon, that I had foolishly painted the coil box wood with to make it look better. The original wood was only stained and that caused no problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Sunday, November 04, 2012 - 09:38 am:

A typical megger operates between 500 and 1000 volts depending on make and model. In your coil Will this voltage may not be enough to jump a defective point internally, however the coils much higher secondary voltage when operating would be able to do so. The megger test does not guarantee the condition of the coil ... it's just another tool to help you decide if the coil warrants rebuilding.

Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, November 04, 2012 - 11:40 am:

To all:

You have it correct that the megger test will help you find an internal short or leakage between core and winding or between windings but it will not show you an arc of 1/4" to thus prevent you from rebuilding a coil that is going to flunk at the "finish line".

If a spark is intermittently sparking at the spark wheel of a strobo-spark that may point to a defective set of points or misadjustment because the arcing inside of a coil generally is full time at a carbonized path in there to thus give you near zero sparks at the strobo-wheel at all times.
The coils that I have seen that have this problem will randomly produce a spark here and there at the wheel if you test it long enough but you can't get the coil to work properly and it is a lost cause. For this reason I would leave the capacitor leads a bit long when putting a cap into a coil so you can salvage it back out. Don't pour in the hot tar until you have at least checked the coil for sparking at the strobo-wheel. At this preliminary step you can ignore double sparking since that is most definitely a coil point adjustment issue. Failure to spark at the strobo-wheel when the operate current is anywhere near correct is almost always an internal arc - sorry. If you previously purchased a buzz box tester then you can set its gap to 1/8" or so and put your suspect coil into it and if it seems to buzz with a healthy spark across that narrower gap you will have confirmed that is what is going on and know there is no point in further work on that coil. You now know it is going to missfire when presented with a normal spark gap situation.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Will Copeland - Evans Mills NY on Sunday, November 04, 2012 - 02:23 pm:

Thanks Mr. Regan... Im still new at making old coils new but I'm learning....


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Sunday, November 04, 2012 - 07:15 pm:

The "more is better" syndrome is alive and well in the Model T world, not just in the case of putting 12V into 6V starter motors, but demonstrating coils producing 1" sparks.
I find it interesting to examine coils brought to me for rebuilding before I pull them apart, just to see what the owner has been driving around with.
Invariably, not only are the adjustments all over the place with wildly varying currents, but the currents are often excessive; eg. 2.5A on their 12V battery. Usually, the points have to replaced after such treatment.
Setting up is often done by trial and error, sometimes by setting by the 'musical note' of the buzz. More advanced types at least progress to a rudimentary buzz box with a meter of non descript calibration. Problem here is that as most use such devices with a 12V battery, the coil gets set to 1.3A. What is often misunderstood is that a coil set for the recommended 1.3A is done on 6V, and the current actually falls when the coil is used on 12V. There are also variations in readings as to what kind of meter is used and whether the buzz box is fed from AC or DC.
Sometimes increasing the current is used to try and compensate for a failing capacitor.
Other times it's seen that the wider the gap you can make the spark jump across, "the better the coil is". Rather than be impressed by such demonstrations, I'm having mental images of arcing between the windings, hoping that the insulation can survive until the demonstration is complete. Then there's the type that likes to use an unloaded Ford coil to electrify a fence, etc.
Regarding that quote from the Restoring the Electrical System Handbook, having had considerable experience with 6V battery operation of coils, I can say that less current is better than more. While the spark appears more intense with higher current, the coil fires more slowly; the end result is top speed is not as high as it can be. Reducing the current to 1.2, or even 1.1A providing firing is reliable, makes a big difference. Not just in driving the car, but the advance in firing time is clearly visible on an oscilloscope.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, November 04, 2012 - 07:51 pm:

John H. YOU HAVE IT TOTALLY CORRECT. What a refreshing post to read. That is not to be at all critical of others since I sincerely believe all of us are looking for the truth and not BS which is often sold as the truth but sold at a very high price tag. Keep the faith guys. As Ron Patterson points out - Ford did not ship 15 million cars with defective ignition systems. Those who make fun of the T approach are now having to explain why modern cars have returned to the "one coil per cylinder" design. All designs that work are typically trade offs from previous designs with an idea that the newer way to do something is better in some way. Sometimes it isn't. Sometimes it is just a company wanting to make some money by convincing us that something is better when in truth it is just different.


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