small engine electronic ignition

Okay, I understand. Typically, though, a set of points (properly set) and a *good* condenser should last *years and years* without any problems. If the points are burning prematurely, changing the condenser should cure the problem. Oil getting on the points is also a "no-no" and can cause problems. Considering the "old" points and condenser used in cars would go 12K miles, the intermittent use of a lawnmower would seem to indicate almost "lifetime" duration - although I realize that's not the case. I am familiar with the little unit that replaces the points and condenser that is available retail - somewhere around $16 and the only requirement for it is that the coil is good - (no battery needed). I understand, from the paperwork included with the unit, that it "fires" the plug dozens of times - providing reliable ignition - just how it does this, I don't know. I will "look around" a little for you to see if I find a schematic for the setup you are looking for. Maybe I'll stumble onto something. Ken.

There are two approaches to electronic ignition. One is to connect the coil across a power source, let the current build up then interupt it. V = L di/dt so voltage rises and in both primary and secondary until plug fires. That's how pointed ignition systems worked. Early "transistorized" ignitions simply replaced the points with a transistor triggered by points or optical or magnetic sensor.

The second is capacitor discharge. Here a cap is charged up from an appropriate power supply and discharged through the coil primary. These are generally better.

The power source can be a vehicle electrical system or a coil and magnet.

Pretty quick and dirty explanation but there is just no way you're going to do it with just a Zenner diode.

(I've designed and built a few of both kinds.)

Ted

Replace the condenser. A bad condenser will either stop the engine dead or just get it to eat points.

See my post elsewhere in this thread. That doesn't work.

Ted

Ted-I've always seen these types of diodes called zener, just one "n", not two. Are they really called zenner? ERS

A zen(n)er alone obviously won't work. That plus an SCR to switch the current sounds almost plausible....

Jim

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Yes, I should have said points and condenser. The end of the condenser is the lower contact of the points set.

Ron Thompson On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

The ultimate result of shielding men from the effects of folly is to fill the world with fools.

--Herbert Spencer, English Philosopher (1820-1903)

In all my years of mowing with junk mowers, I have never replaced points; touched them up on the grinder a couple times, freed up the plunger occasionally and replaced the plug once or twice. Most I ever paid for a mower was $15.00 but that one lasted 22 years mowing a minimum of three lawns full time. Gerry :-)} London, Canada

I will keep an eye out for a junked engine with an electronic module in it. i have been curious about that too.

Dan

Only if you can depend on the ringing to turn the SCR off again. Not sure whether I would bet on that.

Enjoy, DoN.

That would be a Diac.

Gary

Or SBS, SUS, or SIDAC. The first two are pretty much obsolete. The latter are used in ignition systems. Diacs are typically spec'd for triggering larger thyristors.

Best regards, Spehro Pefhany

You are right and I am wrong. I just looked it up. It's Zener.

BTW, NEVER trust my spelling, especially when it comes to ddoouubbllee leters. :-)

Ted

Maybe you were thinking of Gunnnn diodes....

Jim

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Actually, I new Dr. Gunn. He was a prof in the Solid State Physics group at University of British Columbia. It was told around the Physics department that on a trip to San Fransisco in his Jag, a piston colapsed. He pulled over to the side of the road, got out the tool kit and removed the piston and rod from that cylinder. He then carried on on seven to 'Frisco where he could get a replacement piston.

Ted

Ian Gunn worked at IBM research for some time. Apparently he had quite an attraction to earth moving equipment (backhoes) as well.

Jim

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On 14 Jun 2004 13:30:41 -0700, jim rozen calmly ranted:

Uh, Ted. How did he get the oil pressure to stay up without a rod in place (to stop the gaping oil holes in the crank)?

That sounds like an old story, back when you could see the engine as a separate entity from the underbonnet.

Who doesn't?

I have no idea. Hose clamp on the crank covering the oil hole?

Early '50s.

Not many! It was summer. The walls were poured, damp-proofed and insulated. Time to backfill. We could have someone come in and do it in a day for around Cdn$400. For the same money, we could rent a Bobcat for a week. This was just before the July long weekend and we had a bunch of visitors comming.

We decided to go the rental route. Well, our guests were unanimous that that Bobcat was more fun than a trip to Disney Land. There was a constant line up of eager drivers of all ages.

The back filling got done along with some other earth moving projects.

Ted

I actually saw a guy do it in our lot back in 1969. A 235 Chevy 6 in a '55 Bel_Air from Newfoundland pulled into the station, knocking like a son-of-a-gun. The young fellow bought a pan gasket and a rad hose clamp and borrowed a couple of wrenches. He crawled under the car with one set of wheels on the curb, dropped the pan, unbolted the offending con-rod, and jammed the piston up in the cyl with a block of wood. He then took off his belt, cut off the end, and wrapped it around the crankpin, clamping it with the rad hose clamp. He bolted the pan back on, filled it up with oil, and left Elmira Ontario for Come-By Chance or Joe Bat's Arm on the Granite Planet.

So it CAN be done.

On Tue, 15 Jun 2004 02:28:04 GMT, Ted Edwards calmly ranted:

Sounds like a blast. I've never driven a tractor or bobcat. I'll have to ask that steam roller owner if I can stand on for the parade if his little boy isn't with him next week at the Pottsville, OR steam/tractor shindig. I can't believe the prices they get for those old hit 'n miss engines.