Model Engine Ignitions

[74Sprint]

Your almost there. I think I've corrected at least three major errors in your circuits.
For anyone else that has been following along my advice would be Caveat emptor .
I'll stop commenting on your circuits now.

Dave I really don't mind your constructive comments at all. Besides it shows I'm human like everyone else LOL. But yes I do need to slow down and concentrate on what I'm doing. For years I always had someone double checking my work and I double checked theirs. It's only the last 5 years that I'm by myself. But I think we have beaten this 'smart coil' circuit enough and time to give it a rest.
Thanks again Dave
Cheers
Ray

 

[JuanC]

I am looking for help to install a Hall timing on my 10kw Generator so that I can change the timing at will and also get rid of the "back end spark". Any ideas? I am looking into the TIM 6, but this will not remove the "back end spark". I wonder if somebody knows of a system that already does this?

 

[dsage]

What's a "back end spark"

 

[JuanC]

It's also called the "Wasted-Spark-System ". It is the inevitable energizing of the spark plug at the end of the exhaust cycle on a 4 stroke engine using a distributor with a "points" system or a small engine with a magnet in the flywheel system. Most engines do not have this issue anymore becuase they use a "Coil On Plug" system and an electronic triggering mechanism.

The question is: what circuit can I use to that it sends an intermittent signal that I can use to cancel the ignition triggering in every other rotation of the camshaft. In other words: when the magnet passes the first time, the system will be on and remain on, and when it passes the second time, it will be off and remain off. "ON" on odd passes and "OFF" on even passes.

This is just for a regular back up generator from Home Depot that runs with gasoline. These one piston engines have the most basic type of ignition where they put a magnet on the flywheel. The lawnmowers and gokarts also use this type of ignition system. The reasoning behind it is that you do not need an electrical system to run the engine. You start using a pull cord and then the "alternator" is embedded in the engine. The system works like this: at the desired "timing" moment, the magnet embedded in the flywheel passes under a well positioned coil that generates the electrical juice for the spark. The problem is that, being a 4-stroke engine, the crankshafts does two revolutions for to complete the 4 strokes. Hence the spark plug fires twice during the 4 strokes. First at the appropriate time before the compression stroke ends (triggering the explosion and consequent expansion on the "power" stroke), and at the ending of the exhaust stroke, when the exhaust valve is open, and causing a "back end explosion" if there is still fuel remnants on the air mixture.


My idea will be to install an electrical circuit with a regular ignition coil since this generator comes equipped with a 12V starting system, just like a car. So I was thinking to use a hall effect sensor that is triggered by a magnet in the flywheel. I can change the timing by changing the position of the magnet. But the circuit will need to have a design so that on one revolution activates the spark and on the next revolution it cancels it. I am looking at two designs that are on youtube to do the hall effect system, but I need to add the "back spark" removal system to it. My idea is to use two hall effect sensors where the first sensor opens and closes the second sensor, which is the one that triggers the ignition system. The first sensor will have to be connected to a system where, after one pass of the magnet closes the circuit and remains closed until the magnet passes again and then opens and remains open, until it passes again, and so on...

I have attaches some pictures below of the system I have and the circuits I have found in youtube that I'm considering using. Please search and watch these 4 youtube to get a better understanding:


IGBT Transistorised Electronic Ignition using a 3144 Hall magnetic sensor

IGBT Transistorised Electronic Ignition using a 3144 Hall magnetic sensor - YouTube


How To Advance Go Kart Engine Timing WITHOUT a Timing Key

How To Advance Go Kart Engine Timing WITHOUT a Timing Key - YouTube


How to find ignition timing on small engines

How to find ignition timing on small engines - YouTube

Easy Hall Effect Transistor Ignition using a 3144 hall sensor and 2N2907 TIP42C

Easy Hall Effect Transistor Ignition using a 3144 hall sensor and 2N2907 TIP42C Transistors - YouTube


Many Many Thanks for the HELP!!!!

 

[dsage]

I understand the typical waste spark system.
I guess my question now would be who cares if it has a wasted spark?
Wasted spark is in fact used on many engines these days. All those with say six cylinders and only three coils are waste spark engines. They don't have any issues with back firing. I would say if the mixture is still at a concentration to fire again when it has already been burned you have an issue with the mixture, ignition timing or valve timing (or other).
And why go to all that complexity to eliminate it. The wasted spark should do no harm and complexity just breeds problems. The simpler the better. Which, I imagine is why they built it like it is.
KISS.
BTW. The last circuit you show above is one I designed and was later improved through a collaboration with John Gedde and I.
It was well documented on this forum. It will work. But you should implement any differences from your drawn circuit. The improved circuit is better.
https://www.homemodelenginemachinist.com/threads/a-new-ignition-circuit.20415/page-8Post 144
The one drawn on squared paper I would not recommend for a lot of reasons.
Have fun.

 

[Steamchick]

Hi Juan C: The simple (Ha Ha!) solution to eliminating the redundant spark that causes back-fires on this engine would be to affix the hall effect trigger on the CAM-shaft, not the Crankshaft. - It runs at the half crank speed that you require. Of course, you will have to work out "How" - and "When?" to trigger the spark. Sometimes, the gear on the end of the camshaft is the largest radius for affixing whatever you need for the Hall effect sensor. (a button or a hole?).
K2

 

[Harglo]

Hi Juan C: The simple (Ha Ha!) solution to eliminating the redundant spark that causes back-fires on this engine would be to affix the hall effect trigger on the CAM-shaft, not the Crankshaft. - It runs at the half crank speed that you require. Of course, you will have to work out "How" - and "When?" to trigger the spark. Sometimes, the gear on the end of the camshaft is the largest radius for affixing whatever you need for the Hall effect sensor. (a button or a hole?).
K2

I use a small micro switch that stays open till the Hall is ready to close. I fab it up its trip on the exhaust valve to open just as the valve closes there are other places for a switch to be mounted with an adjustable trip arm over the switch lever arm.
Harvey

 

[Steamchick]

I guess the micro-switch could be arranged mechanically to open when exhaust valve is closed while electrically being across the contact breaker points: (so the electric circuit sees the points opening and sparks) yet when the Cam or rocker opens the exhaust valve the contacts close in the micro-switch (so the electric circuit does not see the contacts open = no spark).
Seems easy to arrange electrically and mechanically. = clever!
K2

 

[bluejets]

Seems easy to arrange electrically and mechanically. = clever!

Ever heard of switch bounce.......(= not so clever)

 

[willray]

Ever heard of switch bounce.......(= not so clever)

I think Steamchick is thinking of having a switch that opens and closes only when the hall effect sensor is already closed - so any bounce on the mechanical switch would be invisible as the hall effect sensor is already conducting.

 

[bluejets]

I think Steamchick is thinking of having a switch that opens and closes only when the hall effect sensor is already closed - so any bounce on the mechanical switch would be invisible as the hall effect sensor is already conducting.

How quick can you open and close a micro compared to a hall effect...?

 

[willray]

How quick can you open and close a micro compared to a hall effect...?

Hardly matters. The OP would like to invent a hall-triggered system that only fires once per 2 revolutions of the flywheel. A hall sensor on the flywheel can give good resolution for spark timing, but opens (briefly) on every revolution, and OP would like to cancel one of those.

The cam provides a way to identify which spark should fire and which should be cancelled, but lacks the resolution for good spark timing.

So long as the microswitch is fast enough to close after the hall closes on the correct firing, and it's finished bouncing before the hall opens for the (desired to be eliminated) wasted spark, any bouncing on closing doesn't matter. So long as it opens just after the hall closes from the wasted spark, and it's finished bouncing before the hall opens for the correct spark, any bouncing on opening doesn't matter.

In this design, the microswitch would open and close while the hall is conducting, and it has almost an entire revolution of the flywheel to accomplish reaching a stable state upon opening or closing. It really shouldn't have a hard time accomplishing that.

Now, I'm with dsage - I don't think it's a tremendously necessary modification - but conceptually, using a low-resolution signal from the cam to short across the hall sensor during the unwanted spark should solve the "problem".

 

[dsage]

Or conversely (I think). The microswitch could be used in series with the signal line from the hall sensor. As long as the microswitch closes (and passes the signal to the ignition system) some time in advance of when it's needed and opens some time after when the signal is not wanted - Job done. No critical timing required. And no bounce to worry about. The switch will be stable for many degrees before it's a problem.
Way too much complexity for me. As I mentioned if you have the conditions necessary for the mixture to fire in the exhaust system there is something not right with the engine.

 

[GailInNM]

One possible problem with microswitchs is the number of operations before failure rating. Typical rating for high quality name brrand switches is 1 million operations. The best high rel switches are about 10 million operations and consumer grade import switches is often only a few hundred thousand if they are rated at all.

Taking the 1 million operations, at 1000 rpm the switch will be operated 500 times/minute and that translates into about 30 hours of operation before the switch will need to be changed. If you are only going to run your engine occasionally for only short periods of time this may be acceptable. As I sometimes put 20 hours on an engine at a long weekend of running it would not be for me.

I would use two Hall effect switches. The Hall switches can be in parallel so both have to be actuated, or de-actuated depending on your circuit, for spark to occur.
Gail in NM

 

[Kenif]

I recently came up on this with a 1940's B31 motorcycle I'm rebuilding.
Try:
https://www.aliexpress.com/item/32234642130.html?spm=a2g0s.9042311.0.0.27424c4dJ0M7nEThey also do coils and triggers. The unit has adjustable advance mapping using a laptop or a mobile phone with optional blue tooth adapter. When you purchase the box the supplier will give you a link to the software. I got the software before I bought it to see how good / easy it was / is.
For about AUD$120 delivered, coil was AUD$6 and trigger AUD$2.00 needless to say I bought a couple of spares. It was a good option for me.
My use is a bit different as old bikes use manual spark control and too much advance at low revs will kill them... So it's now fixed so anyone can ride it!

 

[Steamchick]

Or conversely (I think). The microswitch could be used in series with the signal line from the hall sensor. As long as the microswitch closes (and passes the signal to the ignition system) some time in advance of when it's needed and opens some time after when the signal is not wanted - Job done. No critical timing required. And no bounce to worry about. The switch will be stable for many degrees before it's a problem.
Way too much complexity for me. As I mentioned if you have the conditions necessary for the mixture to fire in the exhaust system there is something not right with the engine.

I agree that this ignition problem is just as likely to be a carburation problem = to rich.
I have experienced odd problems on over-run pop-backs on motorcycle engines where the idle was "too much and too rich"...
K2

 

[gilbycoath]

I don't about model engines but I run race cars and they all run with crankshaft triggers ( wasted Spark ) no problems.
Ron

 

[Steamchick]

I recently came up on this with a 1940's B31 motorcycle I'm rebuilding.
My use is a bit different as old bikes use manual spark control and too much advance at low revs will kill them... So it's now fixed so anyone can ride it!

Hi Kenif: Last B31 I had (1951 model, with a 250 Norton swinging arm fitted instead of the plunger rear end!) was fine with the magneto and manual advance.... I never had any problems, but that was mid-1970s and "old codgers" like me had used so many different bikes at various times, we just got on with it and learned to use whatever controls existed... But Magneto re-builds cost more than your house now...
K2

 

[CFLBob]

"The OP would like to invent a hall-triggered system that only fires once per 2 revolutions of the flywheel. A hall sensor on the flywheel can give good resolution for spark timing, but opens (briefly) on every revolution, and OP would like to cancel one of those. "

I've been kind of watching this discussion and wondering if anyone has tried the approach that seems like the obvious answer to me. A circuit trick to divide a frequency by two requires just one component: a D-type flip flop. The "generic" part number in logic parts is a 7474. If you were running this on 12V, you could use a higher voltage logic family, like CMOS, making it a 74C74.

If the "every other" pulse is a problem, this will effectively make it go away. The only gotcha I see is that this assumes the first one is the one you want.

Several of you have played with electronic ignitions far more than I have, so I wonder if this is ever used.

 

[Kenif]

Popping exhausts on the over-run can also be a burnt exhaust valve or by an exhaust leak - sucking air into the exhaust and igniting unburnt fuel. On a motor bike I would use a lambda sensor - to test for correct fuel air ratio OR do a "plug chop" - run the engine 'till its hot with a used spark plug with correct gap.... Run at full power for say 15-20seconds shut throttle and stop straight away - do not let it idle. Plug should be clean and light brown - if its sooty and black - to rich, if its oily black - bad rings or guides. If its white to lean. There are good articles by "Gordon Jennings" on "How to read spark plugs". The spark plug will tell all....