Hit or miss engine igniter

[dkwflight]

Hi I am thinking about starting an engine with an igniter.
The mechanical switch in the cylinder is fairly simple.
Does any one have guidance or plans for the inductor coil.
THe coils I read about call for soft iron. Will some of the leaded steels be soft enough or do I have to hunt up some wrought iron? 1018 good enough?

 

[aka9950202]

A suitable source of soft iron is from transformers. The steel will work but not as well as soft iron.

Cheers,

Andrew in Melbourne

 

[rickhann]

When I made a low tension coil for my Galloway ignitor, I simply used pieces of tie (bailing wire) cut from a roll of wire I had bought at a farm supply store. I made a bundle of wire {4-1/2" L x 5/8" D) and stuffed them as tight as I could in a piece of clear plastic tubing. Before bundling I varnished each pice of wire to insulate them. I had read somewhere this would improve performance. I have attached a picture of my coil. It works very well. Coil was wound using wire salvaged from an old automotive air conditioner clutch. Good luck

 

[Caster]

I have several engines with ignitors and use a 58watt choke from a fluorecent light fitting, works a treat.

 

[dkwflight]

I have some cast iron rod 5 1/2 x .840 diameter.

What wire size do you think for the coil. I know too thin is hard to handle
I have previously wound some coils on my mini lathe. It will spin slow and steady.
THanks
Dennis

 

[rickhann]

The low tension coil should have an internal resistance of 3-6 ohms. So you need to calculate the resistance by first knowing the wire gage , then you can determine how many feet will be required. There are numerous calculators on line. In my case, I had approximately 250 feet of 22 gage copper wire which resulted in an internal resistance of approximately 4 ohms. Different gage wires will give different outcomes. There is no one answer. this type of ignition is very forgiving. Keep within the parameters of an internal resistance of between 3 to 6 ohms and you should be OK. I would not use a solid core. Coat hanger wire has been suggested by some. I had good luck with tie wire. As has been previously suggested, there are a multitude of options for the coil, but I found it to be satisfying to build my own and see it work. As I alluded to earlier, the core components should be individually insulated from each other (varnish).
Rick

 

[rutzen]

Hi, I would like to know more about this. How does an ignitor work?

 

[dkwflight]

Hi
Back emf. which is why a capacitor is needed in a points high tension ignition system.
I remember the old days when a car would need new points when they got eroded from arcing when a cap went bad.
Probably the points in a igniter could benefit from a cover bead of silver solder since sparking at the igniter point is encouraged.
Dennis

 

[DKGrimm]

Hi, I would like to know more about this. How does an ignitor work?

Good Morning!

I've had really good luck with ignitors in model hit-and-miss engines. It's pretty simple if you think of it in terms of energy. Running a current through a coil creates a magnetic field. That field has energy. When you try to open the circuit with the ignitor points the current has nowhere to go, and the energy in the coil drives up the voltage at the opening points until it arcs over. The energy in the coil is dumped into the arc until the current finally decays to zero.

"rickhann" posted about the coil resistance. His numbers look good to me. You want as much current as it takes to get a good spark, but you don't want to burn up the points with too much current.

By the way, it's important to have an ignitor design that snaps the points open quickly. If they open slowly the coil energy gets used up before they get open wide enough to light the mixture.

Don

 

[dkwflight]

Hi
Hank you .
I think I have enough info to start a coil.
Dennis

 

[baldavengre]

I have made coils with a solid core, they work. I couldn't really tell any difference.

 

[propclock]

I recently completed a Red Devil with an ignitor and played with point and coil combinations.
I recommend tungsten points and fluorescent lamp ballast/s. I ended up with 3 in parallel for ~10 ohm resistance.
The ultra low coils did not work well nor did the normal ignition coil primary trick. Steel points make a good spark but erode too fast and the slag? goes into your engine, not good. I also have an Aermotor 8 cycle
using a 277 volt ballast pulled from the dumpster. They were replacing all the magnetic ballasts with electronic.
I should have taken more than 1 . The dumpster was 1/2 full. Oh well. Just for what it is worth, 1.414 cents at least.

 

[DKGrimm]

I've use nickel points -- 99% Ni from a stick welding rod for cast iron. I've got maybe 500 hours run time on my Red Wing 1/4 scale with home-brew ignitor. It runs pretty much full time at all shows, with no maintenance other than a cleanup after each show.

 

[rickhann]

It never ceases to amaze how these threads seem to drift from the original posted question. As I read it, the original query was about "constructing" a coil for an ignitor. In my first post I acknowledged the there are many ways to "skin a cat". Admittedly, a commercially constructed coil would outperform a homemade coil, but the "I did it and it worked" factor is missing. Constructing a model of an old hit and miss is an accomplishment. Getting one to run using old technology is more satisfying (at least to me). If I were to just want performance, I certainly would not build an ignitor. I would use a spark plug with a hall effect timer an hit the plug with 30,000 volts instead of the paltry output of a low tension coil. As an aside, ignitors are not all that simple to construct. End of rant! Rick

 

[DKGrimm]

As I read it, the original query was about "constructing" a coil for an ignitor.

Good point. One way NOT to construct a coil is to wind it on a brass tube bobbin (as some have tried). The metal tube constitutes very effective shorted turn and kills the coil more or less completely. To some extent a solid iron core does some of the same thing (eddy currents in the core itself) so while it can work OK, it's not as good. For what it's worth, I have tried bundles of mechanic's wire for a core also (without coating the wire) but that gave kind of a lossy core for me. Varnishing the wire before bundling may help a bunch, as rickhann has suggested.

 

[dkwflight]

Hi
My start on a coil for an igniter.
I had some brass and a length of cast iron rod.
After silver solder to hold the brass to the cast rod and truing up the brass I coated the cast rod and brass with some epoxy to insulate the enameled wire.
The epoxy is hardening on the wire while I took this pic. I Left the lathe running at a slow speed to prevent runs and drips.
I don't know the resistance of the coil as wound.
fingers crossed.
Dennis
An article on igniters and magnetos, etc

 

[dkwflight]

https://www.old-engine.com/magign.h...ly that PROTRUDES INTO the combustion chamber.

 

[dkwflight]

The coil I just built measured 7 ohms
I will try to see what kind of sparks it generates.
Dennis

 

[wgpeters]

Hi
Back emf. which is why a capacitor is needed in a points high tension ignition system.
...

The combination of the capacitance of the condenser and the inductance of the coil make a tuned circuit. When the points open, the tuned circuit oscillates, producing a longer spark time. Also, since the output voltage is now AC instead of 1 DC pulse, the metal pulled from one side of the points is redeposited when the polarity reverses, reducing the wear of the points surfaces.

 

[dkwflight]

Hi
Does this look normal for these coils?