Low tension ignition inductor

[duke37]

I am looking for details of the inductor used in the low tension ignition of cars made about 1900. This is used to create a drawn out spark when the contact is opened.

I would like size, number of turns, resistance,inductance, energy storage and core type if any.
There seems to be no hard data on the net.

 

[hevans1944]

Are you restoring an automobile or internal combustion engine from this era? Low-tension coils are not hard to make. You can "guesstimate" the inductance by using an ordinary inductor in place of the "real deal" until you obtain an acceptable spark. I would start with something on the order of 1 to 10 Hy with no more than a few hundred ohms resistance. Then wind a coil with similar inductance and resistance for whatever battery voltage you will use. You are right about the dearth of factual electrical data on the Internet, but I did find some interesting sites such as this Wikipedia reference and this ancient engines site. You might want to write to the owner of the latter site and ask for more information, perhaps search eBay for used coils. Even if a used coil is defective, you could cut it open and count turns and measure wire size to attempt to repair or make another coil. If you want to start from scratch, you need some soft-iron wire for the core. I recommend using green-painted florist wire.

I can remember drawing large, fat, hissing arcs from a low-voltage power supply connected to the field coil of a loudspeaker while still in my youth. Fascinating, as Mr. Spock would say. My first practical experience working with inductors. The loudspeaker field coil was used in lieu of a permanent magnet and was also the input choke for the plate power supply of a tall "living room" radio. So maybe "low voltage" is not exactly correct, but I have drawn sparks from a 10 Hy inductor "powered" with just a 1.5 V D-cell. A science fair project I often recommend to youngsters is a neon-lamp wired across a small inductor with a push-button switch in series with a 9 V battery and the inductor. Press the switch and nothing happens. Release the switch and the lamp flashes. Explain on a large poster board what is going on. Maybe wire up a circuit with a small incandescent lamp or LED for comparison. Requires the child to do some serious research and thus paves the way for an exciting and well-paying career in Science or Engineering. Ahem. Well, it's a cheap Science Fair Project anyway.

Hop

 

[duke37]

I have been asked to wind a coil since I have most of an AVO coil winder. The chappy with the engine has made some parts for it so I am winning at the moment.
Some calcs I have made
Length 67mm
OD 33mm
ID 15mm
Wire 0.686mm
No layers 13
Turns/layer 98
Turns 1274
L (no core) 3.04mH
R 3.9Ω
V 12V giving 3.08A
Energy 14.4J
Time constant 11.8ms

Doubtless a few experiments will be necessary and will give me some experience with winding a good coil and finding the effect of the core.
The core will probably be taken from a high tension coil.
The device will be used on a three litre four cylinder engine and will only be used for starting, later switching to a magneto.

When I was young we had an Amanco engine with a magneto, that was small enough to crank at a reasonable speed. My grandfather used to get into trouble since he found a hen's nest and boiled an egg in the engine. Then he wouldn't eat his dinner.

Thanks for the links, I had seen the Wikipedia one.

Trevor

 

[hevans1944]

Trevor, my "gut" feeling is you have the dimensions, turns, wire gauge, ID, OD, winding resistance, and battery voltage close to what you need, but the inductance "L (no core) 3.04mH" seems to be way too small, and it does not agree with your calculated energy stored in the magnetic field. If the inductance was 3.04 H it would. So, maybe just add a core to get the inductance you need to store enough energy for a decent spark. How did you arrive at 3.04 mH for the inductance of the coil? I assume that is the calculated air-core inductance. Will it increase by a factor of 1000 when you insert a soft iron core?

A three litre four-cylinder engine? My 2002 Ford Ranger truck uses a three-litre V-6 engine. I wonder how the power outputs compare... is this a stationary engine, or does it drive the wheels on a vehicle?

I love 19th century and early 20th century small engines. When I was a lot younger I used to visit local country fairs that exhibited them, along with steam engines used for farm tractors and wheat threshers. There is something wonderful about a one-cylinder hit-and-miss engine that just sits there and chug... chug... chugs along, slow enough to allow you see how everything works, and yet powerful enough to do useful work like pumping water or perhaps sawing wood.

Sounds like a fun project. Here is another link you might like. And maybe this one too.

Hop

 

[duke37]

Hop
The calculations could be wrong. The inductance equation uses inches and I converted to mm. Perhaps I got a 25.4 in a twist or perhaps I multiplied by N rather than N^2, will have to check.
The engine is out of a car. I have not seen the engine or the car.
I would doubt that the inductance will go up by 1000 when a core is used due to the large air path, but we shall see.
Modern vehicles seem to be way overpowered. I passed my driving test using a Jowett Bradford van, two cylinders producing the massive power of 12HP. This was adequate for local travel and the lack of synchromesh taught me how to drive correctly.

Thank you for the links, I will keep an eye on the Cheshire site, I often go to Cheshire to see relations and sometimes visit the secret nuclear bunker if there is a ham event there.

Trevor