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Do-it-yourself transistorized ignition?


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  #1  
Old 01-29-2009, 12:41:03 AM
grey grey is offline
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Default Do-it-yourself transistorized ignition?

This is a question, really. I am thinking about up-grading the ignitions on some Kohler K301's I want a power transistor between the points and coil. These are conventional ignitions with battery, coil, points and condenser.

My question is this: What type of transistor do I need? NPN or PNP, ect.? I want to salvage some from the automobile junkyard. I have read and studied until my head hurts and still cant figure it out. I have a lot to learn about electronics.

I was able to find these transistors for sale on the internet, but they cost $25. (That is $24.99 more than I have to spend.)

With a little help from someone with experience, I will be on my way to a much needed repair. Thank you very much.
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Old 01-29-2009, 10:44:24 AM
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Elden DuRand Elden DuRand is offline
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Default Re: Do-it-yourself transistorized ignition?

Grey:

Your best bet all around would be to purchase one of those little modules that replace the points and condenser. They're cheap and if your engine is the right type, work very well.

I don't think I could build one for what they sell for.

I think you could find them at a small engine repair shop or from one of Harry's Sponsors.

Take care - Elden
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Old 01-29-2009, 11:02:00 AM
K D Redd K D Redd is offline
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Default Re: Do-it-yourself transistorized ignition?

Elden,

Those little modules WILL NOT work with battery igniton. MAGNETO ONLY

Kent
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Old 01-29-2009, 11:08:24 AM
makoman1860 makoman1860 is offline
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Default Re: Do-it-yourself transistorized ignition?

They dont even work that well on magnetos. Normally points open anywhere from 5 to 10 degrees after magnetic neutral for maximum coil energy.....those modules open the circuit right at magnetic neutal. On a very robust coil like an early briggs you might get away with the lower spark energy, but on more marginal systems like the onld phelon, clinton, and tecumseh coils the engine may get quite fickle.
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Old 01-29-2009, 02:01:30 PM
grey grey is offline
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Default Re: Do-it-yourself transistorized ignition?

Thanks. I should have been more specific.

This is used in conjunction with the points. The points will trigger the transistor which will suppy/break ground to the coil.

Here is a diagram I found on the internet. This shows basicly what I seek, but could be incorrect. (I think this was from a tiny airplane forum)

Now, I have some power transistors from automobiles and diagrams of these cars, but I still have not figured it out. According to my research there are two types, PNP-NPN, identified by symbols. Both types are used in various makes of cars ignitions. I dont recall which type the spares I have are, but I will keep posting. I would like to use junkyard parts if possible.


These transistors are not a new fangled invention. It seems they have been around since the 1940's

The internet seller does not identify the type transistor used.
I can post that link if anyone needs it.
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Old 01-29-2009, 02:13:20 PM
grey grey is offline
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Default Re: Do-it-yourself transistorized ignition?

I will add that when researching this forum I came across a mention of this type setup. But, it was only a mention (or question) on the long thread about using magnetic pickup. I think Honda car was suggested.
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Old 01-29-2009, 05:04:02 PM
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Fred Van Hook Fred Van Hook is offline
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Default Re: Do-it-yourself transistorized ignition?

NTE 2329 is a PNP power amp.

Last edited by Fred Van Hook; 01-29-2009 at 05:04:40 PM. Reason: mispelled
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Old 01-29-2009, 06:34:50 PM
Qurple Qurple is offline
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Default Re: Do-it-yourself transistorized ignition?

This doesn't make any sense. A transistor requires a voltage or current to do its thing. If you're using it in conjunction with the points and coil, then that voltage/current will be supplied by the primary side of the coil when the points close/open. But of course, any voltage produced in the primary is amplified in the secondary resulting in a spark. So what then is the function of the transistor?

Do you have a link or a diagram that explains this because I really don't get it...
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Old 01-29-2009, 07:41:42 PM
Qurple Qurple is offline
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Smile Re: Do-it-yourself transistorized ignition?

Ok I looked at you diagram and I understand it. You're going to need a 12 volt source to rig up what you have shown in the diagram, probably a battery. If you hook the battery up as normal (negative ground) you need a PNP transistor. However, if all you have is a NPN transistor you can still use it as long as you hook up the battery in a positive ground configuration.

I'm still not seeing any advantages to this setup. It's one way to make your mag work if your magnets are bad, but so is just hooking a battery up to the points.
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Old 01-29-2009, 08:41:27 PM
Ed Stoller Ed Stoller is offline
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Default Re: Do-it-yourself transistorized ignition?

Check out the point saver on http://overnight-solutions.com/index_files/Page457.htm or kirkengines.com.
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Old 01-29-2009, 09:38:32 PM
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Elden DuRand Elden DuRand is offline
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Default Re: Do-it-yourself transistorized ignition?

Quote:
Originally Posted by K D Redd View Post
Elden,

Those little modules WILL NOT work with battery igniton. MAGNETO ONLY

Kent
Kent:

I goofed. I made the ass-u-mption that your engine had a magneto.

A bit farther down, someone shows a schematic using a PNP transistor to drive the ignition coil, thereby taking the load off the points.

It also has the advantage of eliminating the condenser. If I were doing it, I think I'd add a relatively high value resistor from the base of the transistor to 12 volts to ensure the transistor turns off quickly.

Also, unless the transistor has a voltage rating of over 500 volts, I think I'd put a diode across the emitter and collector (cathode at the emitter) to protect it from the inductive spike generated by the coil when the transistor turns off.

BTW, the condenser can be left out because the transistor will turn off faster than the coil can discharge. With points, they open relatively slowly and, without the condenser, the coil's collapsing field causes the points to arc which quenches the damped oscillation of the coil. The arcing eats up the points and the quenching causes the coil's output to be very weak.

Take care - Elden
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Old 01-30-2009, 07:38:22 PM
Fred M. Fred M. is offline
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Default Re: Do-it-yourself transistorized ignition?

Grey-

Your circuit is very close to one I used back in the 70s on my Buick Skylark. I used a "doorknob" Tungsol PNP power transistor mounted on a heat sink. It may have been a 2N173 or 2N174. I believe mine also had a zener diode between collector and base to protect the transistor from the spike, but my memory is vague on the details. It may still be in my junk collection, but I haven't seen it in years.

No doubt such a transistor will stop points from sparking. However I didn't notice much difference on how the car ran.

Fred
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Old 01-30-2009, 11:47:17 PM
pegasuspinto pegasuspinto is offline
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Default Re: Do-it-yourself transistorized ignition?

Doing this is more or less a waste of time, IMHO. You still are going to suffer from the other problems distributors get, like point block wear, worn lobes, floppy shafts, sticky advance, burned out caps and rotors. Points switched transistor ignition was only a very brief and pointless(or not pointless enough?!? lol) phase in ignition development.

Robert
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Old 01-31-2009, 02:29:30 AM
JohnCarter JohnCarter is offline
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Default Re: Do-it-yourself transistorized ignition?

There are several decent circuits for battery powered transistor ignition available. They require more components than just a transistor to function properly and over the long term. Here are links to two:
www.gavner.se/html/ignition.htm
http://www.cs.berkeley.edu/~wkahan/TransIgn.pdf

A better replacement is a capcitive discharge ignition (CDI) system. I installed one of these on a 1970's 4 cylinder engine and saw an immediate idle speed increase of 200 RPM.

There are also some magnet + Hall effect sensor units that eliminate the points entirely, thus eliminating problems with distributor lobe and point rubbing block wear.

John
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Old 01-31-2009, 07:35:29 AM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Do-it-yourself transistorized ignition?

Quote:
Originally Posted by JohnCarter View Post

A better replacement is a capcitive discharge ignition (CDI) system. I installed one of these on a 1970's 4 cylinder engine and saw an immediate idle speed increase of 200 RPM.


John
I think if you gained 200 rpm at idle you either changed the timing or you had a very poor ignition system before this installation, my bet is on the timing.
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Old 01-31-2009, 10:44:25 AM
K D Redd K D Redd is offline
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Default Re: Do-it-yourself transistorized ignition?

You all know that later K-series Kohlers had a CDI but the parts are so expensive for them, most people convert them back to points. The point life on a K-series Kohler is not that bad unless you have a bad point burning problem. Them you may need to look at the coil. BE SURE it is a 12 volt INTERNAL RESISTOR coil. IT DOES NOT need to be one from a Kohler dealer as some around the web have claimed. They claim you need a KOHLER coil because the point stay closed so long on a K-series engine. The point on a K-series are closed for one crankshaft revolution and open for one crankshaft revolution. The point open when the cylinder fires and remain open until they close at the start of the intake stroke. The points then open for the next spark event and the cycle repeats.

Kent
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Old 01-31-2009, 11:41:36 AM
JohnCarter JohnCarter is offline
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Default Re: Do-it-yourself transistorized ignition?

I make no claims for the quality of the original ignition - GM cut a lot of corners to sell the Vega cheaply (including valve adjusters that changed in increments of 0.003").

The engine spec was around 800RPM idle (in neutral) which dropped when the automatic transmission was put in gear.

John
I've lost count of the number of engnes I'd rather not have worked on.
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