# Help with developing an intermittent circuit.

#### JuanCaste

Joined Dec 8, 2021
16
I am trying to get rid of the back spark in a gas fuel generator. Need to have a circuit that will pass current on one cycle of the wheel and block it on the next cycle. An intermittent solid state circuit that gets triggered by a Hall Effect switch. Help!

#### LowQCab

Joined Nov 6, 2012
2,933
What is a "gas fuel generator" ?
Do You have a Schematic and a description of its operation ?

#### DickCappels

Joined Aug 21, 2008
9,626
Does that mean you you are looking for a spark on every other revolution instead of every revolution?

What kind of signal are you looking for from this new circuit?

#### JuanCaste

Joined Dec 8, 2021
16
What is a "gas fuel generator" ?
Do You have a Schematic and a description of its operation ?
It's just a regular back up generator from Home Depot that runs with gasoline (pictures attached). 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 resoning 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 appropiate 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 remmanants on the air mixture.

My idea will be to install an electrical circuit with a regular ignition coil since this genrator 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 have attached two designs that are on youtube to do the hall effect system, but I need to add the "back spark" removal system to it. One idea could be to use two hall effect sensors where the first senor opens and closes the second sensor, which is the one that triggers the ignition system. The first sensor will have to be conected to a system where, after one pass of the magnet closes the circuit and remains closed until the magnes passes again and then opens and remains open, until it passes again, and so on...

Please search and watch the youtube videos on the screen shots attached to get a better understanding.

Many Many Thanks for the HELP!!!!

#### JuanCaste

Joined Dec 8, 2021
16
Does that mean you you are looking for a spark on every other revolution instead of every revolution?

What kind of signal are you looking for from this new circuit?
Yes, please look at my reply to LowQCab as all the info should be there. Thanks for the help!!

#### shortbus

Joined Sep 30, 2009
9,807
So you want to do away with the lost spark magneto? Don't understand why because those are pretty reliable. But if that is what you after, why not do it like they used to when cars still used points? Use the cam shaft to get the single ignition on the power stroke. The cam turns at 1/2 the crank speed.

#### LowQCab

Joined Nov 6, 2012
2,933
This is properly called a Wasted-Spark-System,
Even many Cars came with a Wasted-Spark-Ignition until
around ~2000 when most manufacturers switched to "Coil-On-Plug" Ignition-Systems.

The ONLY practical way to eliminate the Wasted-Spark is with a "Camshaft-Position-Sensor".

Why do You want to eliminate the extra Spark ?
.
.
.

#### Tonyr1084

Joined Sep 24, 2015
7,248
The ignition on lawnmowers and other gasoline powered equipment is called a "Magneto Ignition". Yes, you do get a superfluous spark between the exhaust and intake phases, but it has never been a problem. The spark occurs before top dead center (TDC) on both the compression stroke and the exhaust stroke. It hurts nothing. Exactly why you want to modify the electronics that - I assume - works doesn't readily make sense to me. However, if it's your goal to remove the magneto ignition coil and replace it with an automotive ignition system you would still use the magneto to generate the fire signal. That signal can be chopped in half using a D style flip flop. However, with such an arrangement you definitely run into the problem of getting the first and third cycle properly clocked. It's the third cycle where you want the spark to occur. But what happens if the system misses a single signal? Now your spark occurs on the first cycle and your engine will stall out.

The RIGHT way to time a small engine like that is via a cam and distributor style setup. No, you don't need a distributor, but you DO need something that rotates once for every two revolutions of the engine. That's the only reliable way to fire the spark plug at the correct time. That or just let it spark twice per four strokes. The only OTHER way to control the ignition would be some kind of electronics package that senses the crank AND cam shaft position so as to know when it's in the proper cycle for firing. I think you're trying to put roller skates on a horse. The horse works better without them.

#### JuanCaste

Joined Dec 8, 2021
16
This is properly called a Wasted-Spark-System,
Even many Cars came with a Wasted-Spark-Ignition until
around ~2000 when most manufacturers switched to "Coil-On-Plug" Ignition-Systems.

The ONLY practical way to eliminate the Wasted-Spark is with a "Camshaft-Position-Sensor".

Why do You want to eliminate the extra Spark ?
.
.
.
I want to run my generator with hydrogen and being so explosive i need to advance the timing closer to TDC, but this might cause an isue withthe Wasted Spark, so I need to eliminate it. A Camshaft-Position-Sensor is somewhat what I am envisioning but I need help designing the circuit.

#### JuanCaste

Joined Dec 8, 2021
16
The ignition on lawnmowers and other gasoline powered equipment is called a "Magneto Ignition". Yes, you do get a superfluous spark between the exhaust and intake phases, but it has never been a problem. The spark occurs before top dead center (TDC) on both the compression stroke and the exhaust stroke. It hurts nothing. Exactly why you want to modify the electronics that - I assume - works doesn't readily make sense to me. However, if it's your goal to remove the magneto ignition coil and replace it with an automotive ignition system you would still use the magneto to generate the fire signal. That signal can be chopped in half using a D style flip flop. However, with such an arrangement you definitely run into the problem of getting the first and third cycle properly clocked. It's the third cycle where you want the spark to occur. But what happens if the system misses a single signal? Now your spark occurs on the first cycle and your engine will stall out.

The RIGHT way to time a small engine like that is via a cam and distributor style setup. No, you don't need a distributor, but you DO need something that rotates once for every two revolutions of the engine. That's the only reliable way to fire the spark plug at the correct time. That or just let it spark twice per four strokes. The only OTHER way to control the ignition would be some kind of electronics package that senses the crank AND cam shaft position so as to know when it's in the proper cycle for firing. I think you're trying to put roller skates on a horse. The horse works better without them.
I want to run my generator with hydrogen and being so explosive i need to advance the timing closer to TDC, but this might cause an isue withthe Wasted Spark, so I need to eliminate it. A Camshaft-Position-Sensor is somewhat what I am envisioning but I need help designing the circuit. Many systems will work and some even better than what I am envisioning, but at the moment I just want a simple method that I can easily retrofit to the engine without major modificaitons. Putting extra gears and systems on the camshaft is out of the question. The youtube videos that I have put on the description provide and elegant simple system. The Model Engines on Radio Controlled planes and cars use them all the time. Take a look at this website: https://www.model-engine-ignition.com/

#### JuanCaste

Joined Dec 8, 2021
16
So you want to do away with the lost spark magneto? Don't understand why because those are pretty reliable. But if that is what you after, why not do it like they used to when cars still used points? Use the cam shaft to get the single ignition on the power stroke. The cam turns at 1/2 the crank speed.

#### geekoftheweek

Joined Oct 6, 2013
928
I want to run my generator with hydrogen and being so explosive i need to advance the timing closer to TDC, but this might cause an isue withthe Wasted Spark, so I need to eliminate it. A Camshaft-Position-Sensor is somewhat what I am envisioning but I need help designing the circuit. Many systems will work and some even better than what I am envisioning, but at the moment I just want a simple method that I can easily retrofit to the engine without major modificaitons. Putting extra gears and systems on the camshaft is out of the question. The youtube videos that I have put on the description provide and elegant simple system. The Model Engines on Radio Controlled planes and cars use them all the time. Take a look at this website: https://www.model-engine-ignition.com/
Radio Controlled engines are two stroke engines. They spark every revolution.

If you're lucky enough to have metal cam lobes a proximity sensor could be used to sense when the cam ls in the right position. The only problem with that is now you have something inside the engine that could come loose, fall, and get thrown out the hole in the block it creates when the crank finds it.

Edit... it just hit me. The two stroke radio controlled engines I've seen don't even have spark. It's more along the lines of a two stroke diesel.

Last edited:

#### geekoftheweek

Joined Oct 6, 2013
928
You could also measure the vacuum on the intake port to figure out when you are on the intake stroke and use that as a reference and make it spark the next trigger, and then skip the next.

Edit... there may not be enough vacuum when starting depending on how the carb is set up so maybe it won't work.

#### JuanCaste

Joined Dec 8, 2021
16
Radio Controlled engines are two stroke engines. They spark every revolution.

If you're lucky enough to have metal cam lobes a proximity sensor could be used to sense when the cam ls in the right position. The only problem with that is now you have something inside the engine that could come loose, fall, and get thrown out the hole in the block it creates when the crank finds it.
Yes, RC's are mostly 2 stroke, but mostly they are using the system that I am trying to implement. There is plenty of small model engines that are 4 stroke and also employ this system becuase of the size constraints. In the picture attached you will see that the flywheel will be the place to glue the magnet to, just like it is in the original system.

#### geekoftheweek

Joined Oct 6, 2013
928
Actually being an overhead valve (I always forget about that) a sensor of some variety could be mounted in the cover to sense when the intake valve is opened. Instead of gluing another magnet to the flywheel why not use the ones already in it? Other than that I don't have a clue. I know how I would go about it, but I am not an expert and I do not want to blow up your neighborhood. Good luck

#### shortbus

Joined Sep 30, 2009
9,807
I want to run my generator with hydrogen
You have done some research into this, right? It's not as simple as you think it might be. An IC running on hydrogen needs a much higher compression ratio, not diesel high but higher than one on gasoline. then comes where are you going to get a large enough amount of hydrogen? You see people online, or used to, say they will make it with electrolysis but that's not a practical thing. A hydrogen generator to supply the volume of hydrogen will be large, larger than you may think. You don't show or say what cubic inch the motor is but you need to figure that times the RPM. Read some of this - https://en.wikipedia.org/wiki/Hydrogen_internal_combustion_engine_vehicle

#### Tonyr1084

Joined Sep 24, 2015
7,248
I want to run my generator with hydrogen
You have done some research into this, right? It's not as simple as you think it might be. An IC running on hydrogen needs a much higher compression ratio, not diesel high but higher than one on gasoline. then comes where are you going to get a large enough amount of hydrogen? You see people online, or used to, say they will make it with electrolysis but that's not a practical thing. A hydrogen generator to supply the volume of hydrogen will be large, larger than you may think. You don't show or say what cubic inch the motor is but you need to figure that times the RPM. Read some of this - https://en.wikipedia.org/wiki/Hydrogen_internal_combustion_engine_vehicle
Geez @shortbus - I was going to say the same thing. From where are you going to get hydrogen? If you're thinking HHO - yeah people have managed it, but it's not very practical. And at best they've just barely managed to achieve the results. But now your HHO generator is going to draw a lot of current. What are you going to have left over to run the electrical generator? And a lot of those HHO video's where they show you how they make liters per minute are questionable. I have messed with HHO and I can tell you - it's not so easy to produce those kinds of quantities. And many of those video's are faked.

Joined Jan 15, 2015
7,148
The generator you have is a perfectly good generator and it was designed to run and give you years of service using gasoline.
" Use regular unleaded gasoline with a minimum octane rating of 87 and an ethanol content of 10% or less by volume".

While I can appreciate your desire to run on a different fuel like hydrogen this engine was not designed or intended to run on a fuel other than gasoline, not even natural gas or propane fuel. The engine was designed around a specific compression ratio in addition to the timing. I do not see taking a new unit like this and trying to modify it for hydrogen. The amount of energy produced by hydrogen, per unit weight of fuel, is about three times the energy contained in an equal weight of gasoline. I suggest you note what Shortbus has pointed out and Tony was about to point out. This project is far from simple. If something goes terribly wrong you will have a hard time with the warranty on what looks to be a new unit. Even if you try to make things look like they were never modified. Additionally hydrogen at a low level will cost more to make than the return on the investment.

With 9.2 KW of continuous power you can likely run whole house with power to spare unless you are running whole house air conditioning and electric heat in which case you would not be running both at the same time. I run whole house with automatic transfer on a 16 KW unit running on natural gas which I can easily switch to propane. Far be it from me to discourage but if you want to try hydrogen start with a simple cheap expendable engine. Your generator depending on retailer runs between $1,350 and$1,550 which can result in an expensive lesson.

Ron

#### JuanCaste

Joined Dec 8, 2021
16
You have done some research into this, right? It's not as simple as you think it might be. An IC running on hydrogen needs a much higher compression ratio, not diesel high but higher than one on gasoline. then comes where are you going to get a large enough amount of hydrogen? You see people online, or used to, say they will make it with electrolysis but that's not a practical thing. A hydrogen generator to supply the volume of hydrogen will be large, larger than you may think. You don't show or say what cubic inch the motor is but you need to figure that times the RPM. Read some of this - https://en.wikipedia.org/wiki/Hydrogen_internal_combustion_engine_vehicle
Thanks for the help! But I mostly need advice on the circuit I need to develop to cancel the "back end spark". Can you help me with that?

#### JuanCaste

Joined Dec 8, 2021
16
The generator you have is a perfectly good generator and it was designed to run and give you years of service using gasoline.
" Use regular unleaded gasoline with a minimum octane rating of 87 and an ethanol content of 10% or less by volume".

While I can appreciate your desire to run on a different fuel like hydrogen this engine was not designed or intended to run on a fuel other than gasoline, not even natural gas or propane fuel. The engine was designed around a specific compression ratio in addition to the timing. I do not see taking a new unit like this and trying to modify it for hydrogen. The amount of energy produced by hydrogen, per unit weight of fuel, is about three times the energy contained in an equal weight of gasoline. I suggest you note what Shortbus has pointed out and Tony was about to point out. This project is far from simple. If something goes terribly wrong you will have a hard time with the warranty on what looks to be a new unit. Even if you try to make things look like they were never modified. Additionally hydrogen at a low level will cost more to make than the return on the investment.

With 9.2 KW of continuous power you can likely run whole house with power to spare unless you are running whole house air conditioning and electric heat in which case you would not be running both at the same time. I run whole house with automatic transfer on a 16 KW unit running on natural gas which I can easily switch to propane. Far be it from me to discourage but if you want to try hydrogen start with a simple cheap expendable engine. Your generator depending on retailer runs between $1,350 and$1,550 which can result in an expensive lesson.

Ron
Thanks for the help! But I mostly need advice on the circuit I need to develop to cancel the "back end spark". Can you help me with that?