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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

Replacing primary and secondary coil


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  #1  
Old 01-06-2015, 08:08:36 AM
AussieIron AussieIron is offline
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Default Replacing primary and secondary coil

First off, I have only a little knowledge of coils. I've got a New Way buzz coil with a faulty secondary coil. (it works but it sparks also across coil inside box. I want to keep the coil , so has anyone tried to put a good T Model type , (or a modern replacement) secondary/primary coil assembly into a similar coil box like the New Way one? Looking at a T Model assy. it is about the right size to fit. Hope someone can help.--cheers.
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Old 01-07-2015, 06:02:57 AM
Combustor Combustor is offline
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Default Re: relpacing primary and secondary coil

Hello AussieIron,
Sounds like your coil is still making HT voltage OK. As long as the secondary has continuity, can you scrape away any carbon tracking where it jumps across, and/or increase the distance to earth where it jumps? If you can clean any burned insulation without winding damage you may be able to apply elecrical spray varnish or even nail polish to effect a repair. Anything is worth a try if there is nothing to lose. Someone more familiar with your particular coil may have a better suggestion. Will see what turns up. Regards,
Combustor.
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  #3  
Old 01-07-2015, 06:25:40 AM
AussieIron AussieIron is offline
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Default Re: relpacing primary and secondary coil

Combustor, thanks for reply. Yes, I have nothing to loose by cleaning or gently melting the brown resin ( not tar in this New Way coil), to expose the windings and reinsulate with electrical varnish. If that doesn't work I'll go ahead and try replace whole windings with a T model coil unit. I just thought someone else may have already done something similar and know if that the wiring is the same between the two coil units. Thanks again-appreciated.
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  #4  
Old 01-07-2015, 07:12:41 AM
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Elden DuRand Elden DuRand is offline
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Default Re: relpacing primary and secondary coil

It could be that the New Way coil was made by the same people who made Model T coils. It could be that they are internally identical.

The only question is, if the finished coils were made by the same company, why they didn't use the same tar for potting.

In any case, just wire the new coil like the old one was.

You might want to replace the original condenser while you have the parts out of the case. A modern rplacement should be readily available. You can get a (non-electrolytic) 0.22 microfarad capacitor rated at around 640 volts at an electronics supply house that will work fine. A further benefit is that it will be smaller than the original so it will easily fit into the coil box.
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Old 01-07-2015, 05:55:41 PM
AussieIron AussieIron is offline
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Default Re: relpacing primary and secondary coil

Thanks Elden,
The "T" type coil set up is a very similar size to this coil. I can't see at the moment but I would bet the wiring connections would be the same too. I'll see if a bit of re insulation works, if not I have a few good "T" coils I could take a unit from. (Does anyone supply new primary/secondary units?). Getting the tar off will take a bit of thinking out. A heat gun may work? Nothing to loose if I take my time! The reason I'm doing this is to keep the original box. -- Cheers
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Old 01-09-2015, 01:03:24 AM
piewagon piewagon is offline
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Default Re: relpacing primary and secondary coil

Eldon I really hate to have to disagree or at least warn that very often, in fact most of the time, the capacitors purchased at an electronic store with specs like .22uf and 630V will yes get you a nice small capacitor but it will NOT work for more than a few minutes in service because that is an incomplete specification. I have unpotted now over 2500 original Model T coils and repotted them in new hard maple T coil boxes with a correct capacitor and have not had any failures but I test the coil windings very carefully . Also I also use the correct type of capacitor. There are many ratings that different types of capacitors have besides the usual capacitor value (.22uf?) and working voltage (630V?). The simple thing I warn folks about is if a capacitor of correct value and voltage fits easily inside a T coil then you have bought the wrong type. The rating that you are missing is actually a peak current rating that has to do with the ability of the capacitor to handle very high peak charge and discharge currents. The rating is basically a safe rate at which a capacitor can be charge up and discharged and is usually expressed in Volts/uSec and referred to as its dV /dT rating which is rate of charge per unit of time. in Volts/Microsecond. The minimum rating needed for a typical ignition coil is about 300V/uSec and is not a spec printed on the cap nor is it commonly advertised in the catalog. Ignition coil capacitors across the points need to be a film/foil constructed capacitor and not a Metalized type. If the description of the capacitor says it is of metalized type then it will be physically small and its dV/dT rating will be likely less than 30V/usec and will quickly fail. There are hundreds of companies making capacitors but only a few that still offer full film/foil type. I sell capacitors for this application and had some made up to fit inside a T coil a bit easier since they are flat. Just about any value from .22uF to .47 uF will work and you really only need 400V rating as far as working voltage or even less on some coils. The capacitors I sell have a rating of 1700V/usec and an epoxy coating so you can bury them inside hot tar or sealing wax. I don't care where you buy them but make sure you know the ones you install are the correct type or all of your hard work will be for nothing. Also you might want to make a good wiring diagram of your coil before you melt out the tar or wax since things might short out inside once you start that process. If you could post a picture of it and we could identify the terminals then you would know how it is wired up and that would save a lot of headaches later too. Read the info at this link.

http://www.funprojects.com/products/5007CAP-HiD.aspx

If you were nearby I would melt the old winding out for you and put a new winding in and pot it since I do that every day during the winter months but I think you are in OZ so not much I can help you with. A coil point type capacitor for ignition might be a film/foil type but it also might be a different type with a lower dV/dT rating that will work OK with a modern ignition coil but might be a bit marginal for use with a T coil winding.

hope this helps.
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  #7  
Old 01-09-2015, 08:06:27 AM
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Default Re: relpacing primary and secondary coil

Piewagon:

No problem here with disagreement. I didn't specify foil type. My bad.

I have used metalized Mylar caps on occasion and don't recall any failures but it's a good idea to go with the best spec. if you're potting them.
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Old 01-09-2015, 07:07:48 PM
AussieIron AussieIron is offline
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Default Re: relpacing primary and secondary coil

Piewagon, thanks for that info. Good idea about taking photos when I get the resin out. I think the basic wiring of the "T" model and the "New Way" coils seems to be adaptable. Do you use heat gun to remove tar? or is there a simpler way? The New Way coil has brown resin rather than tar. These coils would have been made by some large coil manufacturer and rebadged New Way. Thanks to all repliers for their help. Neil.
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Old 01-10-2015, 02:19:11 AM
piewagon piewagon is offline
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Default Re: relpacing primary and secondary coil

I actually bake the coils in a low heat oven and let it flow out but since I am extracting coil windings from junk wood boxes that I will toss - I don't care about damage to the coil box and in fact I strip away 3 sides of the old box coil so that only the top, bottom, and terminal side of the coil is not physically removed before I pop the unit in the oven. I place the coil on its side so that the tar has maximum size hole to flow out of. I elevate it with small pan that suspends the coil box wood by its edges and then set the temperature about 250 F and it takes a couple hours. I am careful not to get the thing any hotter than that since some tar has a somewhat low flashover point and can catch fire. I would recommend this be done outdoors. Your sealing agent is not tar and probably is either beeswax or sealing wax. Sealing wax is more reddish and very hard finish while beeswax is softer and you can dig your fingernail into it. If the box is falling apart at its joints you might be better off to disassemble it completely and reglue it and then repot it with tar since hot tar drives out all of the moisture as well as the air. Of course melting sealing wax or beeswax may do that too. I have used beeswax but not sealing wax when refilling a coil but on my reproduction coils I generally use high melting point roofing tar which you can get from most any roofing company if that is used in your land. The stuff to ask for is in the USA is called Type 3 steep roof asphalt and is rather inexpensive if you buy a whole KEG of it which is about 100 lbs. You won't need near that much but be careful since if you get it on you it really burns. Keep bucket of cold water handy as well as a fire extinguisher in case of flashover. I heat up the tar in a tin coffee can and use a pair or pliers for a handle. Old cast iron ladle is best is you have one. Take the same care as you would casting metals and you should be OK. I have done it more than 2500 times.

---------- Post added at 12:19 AM ---------- Previous post was at 12:05 AM ----------

Elden:

I wished to respond to the capacitor type issue by saying that it is very likely you may not have noticed that the capacitor is failing. If a metalized foil type of capacitor has it dV/dT rating exceeded which is a certainty when used with a T ignition coil, the capacitor does not short out nor does it fail catastrophically. What happens is that the sudden charge rate excursion beyond the dV/dT rating causes damage to the metal layer of the capacitor and blows a hole in it. It then self heals rather than shorts out but the capacitor value is just a wee bit less since some of one of the layers is now no longer metalic. This continues to happen slowly or quickly depending on the amount of the dV/dT being forced on the capacitor which metalized capacitors clearly cannot handle. Think of a tin plate being attacked with an ice pick. Eventually it is so full of holes as to hardly work. If you measure the value of the cap when new and it is in fact failing you will start to notice that the capacitor is losing capacity. A .47uF cap might measure .3uF for awhile and then .1 and later .05...until finally it is just an empty shell. This can sometimes be noticed by an increase in sparking at the points as the capacitor is ceasing to suppress the arc there since the capacitor is kaput
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Old 01-10-2015, 07:26:04 AM
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Default Re: relpacing primary and secondary coil

Piewagon:

I believe the weakness is the thinness of the metalization. I guess it can't take the heat generated with the change of potential. The heat would cause weak areas of the metalization to vaporize.

It would be made worse by the current through the increased ESR in the film.

Then, there's the fact that I don't use buzz coils much and build electronic "single-spark"* coil drivers. The repetitive stress from the much lower rep rate of a non-"buzz" coil would be much less and it would take a lot longer for the capacitor to fail.

*: it's not actually a single spark but a series of three or more sparks caused by the damped oscillation in the series resonant circuit formed by the coil primary and the capacitor. I did an Oscilloscope study of this, which is on my web page under "Otherstuff" a few years ago.

This is probably more than Aussieiron wanted to know on the subject.
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Old 01-10-2015, 11:21:13 AM
piewagon piewagon is offline
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Default Re: relpacing primary and secondary coil

Yes that is exactly the issue. The metalized type capacitor is essentially like metal spray paint compared to actual metal foil. This is why the metalized type part is so much smaller than the film/foil part. I agree that the reason you may not see this failure right away is because even though it is damaged likely on each firing of the coil, it would take longer to erode the capacitor than in a motor running at higher RPM. In an actual model T the time is very short and it is a very common problem with new folks rebuilding their own coils. It is very discouraging to dig out the old capacitor and buy new points and do all of the work of repotting then only to have it fail.
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Old 01-10-2015, 06:18:13 PM
AussieIron AussieIron is offline
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Default Re: relpacing primary and secondary coil

Thanks both Piewagon and Eldon, nice of you to take time to share your experience.
Your way of removing the tar will help a lot of other Stakkers as well as me.
Cheers to you both--Neil.
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