A new ignition circuit

[dsage]

BTW.
Perhaps it wasn't clear, but you can connect your points to the input instead of the hall sensor. The hall sensor and magnet works like points i.e. normally high input going to ground when active.
Eliminate the capacitor / condenser that it typically across the points on your engine. It is not necessary and will cause issues.

 

[Oldiron]

I have bult 3 of these but this is the first one I've used with points. No condenser used. The led comes on and it fired when the points close for sure and went out but didn't fire when the points openied when I was trying to set the timing last night. You have to barely turn it to set the timing so the lock out may be the problem but how do you get around that. The parts are as specified and built on the same PCB board as the others so I dought wiring is the problem but I will build another today just in case. BTW thanks to everyone involved in designing this. Bob

 

[dsage]

When you turn the engine over by hand it may "appear" that the spark is occurring when the points close (the LED lights). In fact when it is operated so slowly the timeout is triggering every time. The timeout is only about 15 mill-seconds (I think) after the points close (the LED turns on).
So what you see is the LED go on, the timeout happens and the timeout will issue one spark before you can turn it enough for the LED to go out. Once triggered (by timeout or otherwise) it will not generate another spark until the cycle repeats.

You can set your initial timing using the LED. The led follows your points operation.
Use a degree wheel or degrees marked on the flywheel with a TDC mark reference. A timing light will be of no use turning by hand because of the timeout spark triggering it
Turn the engine over by hand and watch the LED go ON. Ignore the spark and keep turning until the LED goes OFF. Set your timing according to the marks.
Just set it roughly. You can use a timing light once the engine is running.
The 15ms timeout is a non-issue when the engine is running.
Unless like I said, you have a very slow running single cylinder engine. Typically a full sized hit-miss.
You should also check and adjust the dwell degrees of the points. Most hit-miss engines have excessively large dwell time (points closed time). This is just a waste of power and overheats the coil keeping the coil charged for more than the 6ms or so it takes to fully charge it.

 

[dsage]

I never envisioned the timeout being an issue. And it hasn't been. The circuit could have been designed for a several second (or longer) timeout. Something more in line with times that might actually damage a coil should it stay energized.
But that would require more circuitry than the driver itself. The point was to keep the circuit as simple as possible. Tradeoffs are always in play with circuitry.
As mentioned C2 can be increased a bit if you get kick-back from a large single cylinder engine when pulling it over by hand. But the LED starts to act funny if it gets to be more than a few microfarads.
Decreasing the dwell is an all round better solution.
You can do the math for your engine minimum rpm / dwell time etc.

 

[Oldiron]

Ahh, so the spark occurs when the LED goes off if running at speed. Time to fire when the led goes off and disregard the false spark. Thanks. Bob

 

[Oldiron]

It worked out great. The engine runs. Thanks. Bob

 

[dsage]

Great. Another happy customer.

 

[dsage]

TonyM:
Back in post 237 you posted a perf board layout for the ignition circuit. Did that work out?
If you made any changes that resulted in a finished product would be willing to post them?
Your solution would be easier for folks to build than the pcb's I posted and would help get more made.
Perhaps a picture of the finished product too - Thanks

 

[TonyM]

TonyM:
Back in post 237 you posted a perf board layout for the ignition circuit. Did that work out?
If you made any changes that resulted in a finished product would be willing to post them?
Your solution would be easier for folks to build than the pcb's I posted and would help get more made.
Perhaps a picture of the finished product too - Thanks

Hi Dave.
I didn't make it yet. Hobbies have been on a back burner because I have been rebuilding part of the house.(out of necessity)
What little time I have had is trying to make a 1/4 scale 'electronic' magneto. The printed body containing the circuit, coil, battery and reed switch trigger using the parts from the 'Ridders' type ignition.
I was hoping to discuss alternative circuits with you when I restart. Probably in a month or two.

 

[dsage]

Ok. Let me know.
Thanks

 

[peterl95124]

DSage, hope you're still reading this thread,

question, why not a "free wheeling diode" in the primary LC circuit ?

Peter.

 

[dsage]

Sorry a poor explanation but in short you really don't want a free wheeling diode per se. It will dampen the coil output.
If you use a regular transistor it actually breaks down when the reverse energy from the coil is created. Sort of like what a free wheeling diode would do.
It doesn't really hurt the transistor but it can be as low as say 100v which limits the coil energy output.
When you use an IGBT the reverse breakdown is several hundred volts because of the zener etc inside the as shown below. So you can get a higher energy output from the coil.
Maybe I've misinterpreted your question.

 

[BabaG]

I am a new member, so please excuse me if I should be asking my question somewhere else. I just breadboarded this Sage/Gedde ignition coil driver and it is working great with a Ford DG-508 COP and RCEXL 1/4-32 sparkplug. Many thanks to Sage and Gedde for making their design available.

Eventually I will be using this type of coil driver for the ignition system in a five cylinder radial that I have just started building. My plan is to use an Arduino Uno to control the ignition timing, so I have connected two US5881 hall effect sensors to the microcontroller. One tells the Arduino when cylinder 1 is at top dead center and the other generates a pulse when any of the 5 cylinders is at TDC. The Arduino keeps track of which cylinder needs to fire and calculates the engine RPM (not an essential feature, just something I wanted to do). I have verified that my Arduino sketch is working and I can get it to trigger a spark using my breadboard circuit (just verifying that I can get one plug to fire at this point, but verifying the other four cylinders by lighting LED's in the appropriate sequence).

So the question is what to do for the other four cylinders? The path of least resistance seems to be just duplicating the Sage/Gedde circuit four more times and have each one attached to its own coil, spark-plug, and GPIO pin on the Arduino. Does this seem like a reasonable way to go or is there something I am overlooking? Any advice is welcomed. Thanks - JG

 

[peterl95124]

I am a new member, so please excuse me if I should be asking my question somewhere else. I just breadboarded this Sage/Gedde ignition coil driver and it is working great with a Ford DG-508 COP and RCEXL 1/4-32 sparkplug. Many thanks to Sage and Gedde for making their design available.

Any advice is welcomed. Thanks - JG

if you like tinkering with arduinos go for it, but this forum is mostly about machining, I suggest machining a distributor like all the rest of us do !!!

 

[stevehuckss396]

Nooo. This forum is about model engines and all that goes along with it. Years ago Dave Sage's partner had an engine running on electronic valve timing circuitry. Loved it tho I had no idea how it worked. If you want 5 circuits with 5 coils then that's what you do. Don't let anybody tell you home to be a model engineer!

 

[minh-thanh]

Nooo. This forum is about model engines and all that goes along with it.

I totally agree .
Moreover with the homemade engine we can do everything according to our preferences

 

[dsage]

I'm glad the ignition circuit is working out for you.
IMHO if you are building a multi-cyinder model engine it will be dwarfed by the circuitry and coils.
That said I know of someone using 8 coils and 8 ignition circuits all hiding in the base box of the engine.
A distributor would probably be cheaper and easier but can be troublesome in a small scale.
Good luck with whichever path you choose and keep us posted.

 

[BabaG]

I agree with your opinion that the engine will be dwarfed by all the coils, but I was thinking of putting them in the base box as you have seen others do. I guess it might offend the sensibilities of some, but I do enjoy tinkering with microcontrollers AND metalworking so I am going with the Arduino sequencing five coils approach. Thanks for the feedback.

 

[stevehuckss396]

I agree with your opinion that the engine will be dwarfed by all the coils, but I was thinking of putting them in the base box as you have seen others do. I guess it might offend the sensibilities of some, but I do enjoy tinkering with microcontrollers AND metalworking so I am going with the Arduino sequencing five coils approach. Thanks for the feedback.

Who cares who it offends! If thats what you want to do then thats what you do. I would love to see it completed. Better idea! Go with dual plugs and 10 coils! Hahahaha!!!!

 

[Eccentric]

I am going with the Arduino sequencing five coils approach.

I attempted to use an Arduiuo to control the timing advance of my model engine and could never get it working. the Electromagnetic Interference from the ingition system always (eventually) killed the micro controller. I went from a CDI to a TCI (transistor controlled ignition) which was supposed to be quiter from an EMI standpoint. I used resistor spark plugs, I used a ballast resistor, I isolated the microcontroller, I used lots of local decoupling caps and an inductor isolation circuit with an encolsed metal case, I used a seperate battery and opto isolators.... I spent way too much time trying to get it to work until I finally abandoned the project. If you can get the arduino working, you need to let me know what you did. I wrote some really neat code to control the spark advance, but to no avail. Good Luck.