It’s been a rainy day here so I couldn’t get out and fly. My idle mind has come up with a few questions about how an electronic advance/retard system works on our modern day ignition systems.

The instructions on a CH Electronics Syncro Spark (CTC) equipped system say to set the ignition to spark at 28-32 degrees before top dead center while slowly rotating the prop. I did this using a degree wheel and the engine runs just fine. My assumption is that while the engine is running at idle, the CTC senses the crankshaft at 28 degrees (my timing) and delays producing the spark until around 4 degrees BTDC (retarded condition). As the engine is advanced in RPM the delay is reduced until at about 4000 RPM where the advance is back to 28 degrees BTDC. With the ignition initially timed for 28 degrees BTDC, what keeps the engine from trying to knock my hand off the first time that it fires? At this point the CTC doesn’t know anything about RPM or rotational rate since it has only sensed one pulse.

On my ZDZ80RV engine equipped with the Falkon ignition the timing instructions say to mechanically set the sensor at a specific distance (6 mm) from the center of the magnet with the engine at TDC. The engine runs fine with this setting. I put a degree wheel on the engine just to see where the spark occurred. It was at 4 degrees BTDC. This makes sense to me from a starting standpoint. The only reference that the ignition has for timing is the relationship of the sensor to the magnet. This means that to advance the timing the only thing that the electronics can do is to delay the spark a certain number of degrees, based on engine RPM, after the initial pulse from the sensor. As far as I know there isn’t an anticipator circuit to know when to fire. If the engine starts out at idle at 4 degrees BTDC then, as the engine increases in RPM, the delay before spark occurs will decrease from as an example: 356 degrees, 350 degrees, 345 degrees, etc. This is absolute degrees of delay.

It seems that these two systems are operating on a different principals. I very well may be all wet in my suppositions and that is where I would like for you ignition wizards to straighten me out.

Ken

You got the basics dowm pat. The CH Syncro Spark is lot smarter than any 3 fliers put togather
It measures RPM not by counting pulses but by dwell time, so RPM is known on first flip.

Followup question. If I turn the prop on a CH ignition equipped engine very slowly, then it fires at 28 degrees advance, and could really make your hand smart???

IF you are turning an engine so slow that the Syncro stays advanced you aren't turn fast to draw fuel.
The magic number is 200 rpm. The average flier can hand prop a G-62 sized engine in the 600rpm range.

OK Terry, I see exactly what you mean and I understand dwell. If the engine is already choked properly and you are dumbly pulling it through very slowly (just goofing around) then you very well may get whacked because the timing is still fully advanced. Just as you indicated Diablo.

Does the Falkon ignition, since the initial spark occurs at about 4 degrees BTDC, actually delay from about 330 to 360 degrees before it fires the second time?

Thanks,
Ken

If you keep your hand around the prop you won't get whacked, you'll just feel a bump when it fires...Been there....[8D]

Goofing around with a 70cc engine with a 24" prop is a very bad habit, and it will get you a new nickname

does this mean that using different size magnets would screw things up??


dave

Yep it sure does. The Syncro spark is "calabrated" for a 3/16" dia magnet and will work OK with 1/8"-1/4" magnets.
Magneto sized magnets will get your hand wacked.

DUMB question..the ignition fires when the trailing edge of the magnet passes under the edge of the sensor..Why would a wide magnet fire at a different point than a narrow one ? Unless some person substituted a wider magnet in a fixed system made for a narrow magnet ?
Would a modeler do this ? Not follow instructions ?
Who just inherently KNOWS how such things work ?

The ignition will fire at the trailing edge of the magnet with or with out a Syncro Spark.
BUT if you look at the signal line from a hall switch it is a square wave, the signal goes high at the leading dege of the magnet and low at the trailing edga. It is the duration of the square wave that the Syncro Spark calculates the RPM from. A wide magnet gives a longer signal
and the Syncro Spark says long square wave = slow rpm and it will stay advanced
THIS IS ROCKET SCIENCE

Never knew about square waves, my circuit was designed by someone else who has since died..Good thing Ed came along so we ALL could have electronic spark advance

Newbie here,
I have been reading about the differences in the electronic ignitions, mainly the one by Jerry Howell and the one manufactured by CH. I knkow that the Howell one is a basic Kettering design and the CH is a CDI unit. My question is: Will the Syncro Spark module for the CH work with the Howell ignition? From what I understand, it plugs in between the Hall effect sensor and the rest of the circuit. I plan on using the Howell system on a 100cc Tecumseh snowblower engine. It is a 2 cycle piston port engine and stripped down (minus flywheel and mag) it weighs in at about 7 Lbs. Thanks for all the info.

A comment on the ignition system from Jerry Howell. I spoke with Jerry on the phone last week and his hobby is the stationary gas engines. The reason for his disclaimer on using his ignition on RC weed eater type engines is one of possible radio interference, not that they wont work with that ignition system. Jerry told me to make sure the entire ignition system is grounded to the engine and to keep the radio reciever and antenna as far away from the ignition as possible. I hope this helps answer some of the questions concerning this ignition system.

The Syncro Spark will NOT work with the Howell system. The Howell system requires several magnets in a row to get enough dwell for the coil to fire. See above posts about the Syncro Spark and long dwell magnets.