Timing and those little aftermarket electronic ignition modules

[harrygrey382]

Can someone explain to me how the little aftermarket electronic ignition modules are timed? I can't work it out - they are only connected to the coil, how does it know where the piston is and when to let the spark plug spark? I'm talking about the one you use to convert ay an 070 to electronic

 

[67L36Driver]

opcorn:

Very good question.

When I find one in a saw, I remove it and clean/adjust the points.

 

[Cantdog]

opcorn:

Very good question.

When I find one in a saw, I remove it and clean/adjust the points.

Damn......and I thought I was alone all this time.......and yes it is a good question...someone here may even be able to explain it to us....

 

[zogger]

Those are trigger modules that replace the points, and can operate at much higher rpms than a conventional mechanical point system. Timing is the same because you haven't done anything to the flywheel setup, that is unchanged. Magnets go by the coil, you get some juice, it happens when it is supposed to happen, flywheel to coil pickup is the "timing" with single cylinders, so there ya go.

Capacitor discharge ignition - Wikipedia, the free encyclopedia

I know there is all kinds of nostalgia for points, and I own points driven stuff...but no manufacturer today, small engine or vehicle, uses points, none that I am aware of. If points were better-in ALL aspects***- from an engineering standpoint, they would still use them.

This is just like the carbs versus fuel injection....no car companies ship with carbs anymore. If it was better, one might think at least one major company would do this. *Eventually* saws will have fuel injection, autotune and mtronic, with stratocharging, are a stop gap before that time.

***yes, I know, easy to use your old book of matches to clean and set some points on your desoto. Been there, done that a lot. Times moves this away, forward >. That was then, this is now. From the same displacement, vehicles now get loads more horse and torque, and double the fuel economy. Solid state ignitions and fuel injection did this, primarily. Saws got higher rpms from solid state ignitions.

 

[67L36Driver]

it happens when it is supposed to happen

Call me old fashioned but, I prefer it happens 25-30 deg. BTDC. Besides, XL-800s arn't high winders.

 

[3000 FPS]

Those are trigger modules that replace the points, and can operate at much higher rpms than a conventional mechanical point system. Timing is the same because you haven't done anything to the flywheel setup, that is unchanged. Magnets go by the coil, you get some juice, it happens when it is supposed to happen, flywheel to coil pickup is the "timing" with single cylinders, so there ya go.

Capacitor discharge ignition - Wikipedia, the free encyclopedia

I know there is all kinds of nostalgia for points, and I own points driven stuff...but no manufacturer today, small engine or vehicle, uses points, none that I am aware of. If points were better-in ALL aspects***- from an engineering standpoint, they would still use them.

This is just like the carbs versus fuel injection....no car companies ship with carbs anymore. If it was better, one might think at least one major company would do this. *Eventually* saws will have fuel injection, autotune and mtronic, with stratocharging, are a stop gap before that time.

***yes, I know, easy to use your old book of matches to clean and set some points on your desoto. Been there, done that a lot. Times moves this away, forward >. That was then, this is now. From the same displacement, vehicles now get loads more horse and torque, and double the fuel economy. Solid state ignitions and fuel injection did this, primarily. Saws got higher rpms from solid state ignitions.

Ok so usually on a points set up there is a cam to open and close them at the correct time. So with this solid state trigger module what is used to trigger it at the correct time. Is it some how connected to the coil and uses that or does use the magnet off the flywheel or What?

 

[bob15]

I guess I'm the odd one. I like the Atom and newer Nova ignition modules.

When i built my SP-125 from scratch, I didn't think about using points, put in an electronic ignition and be done with it. No different than a car. When I rebuilt my '67 Camaro twenty years ago, I put in a Mallory unilite, no points, no hassels. And that was in a time when you could go to KMart and buy AC Delco points, condenser, rotor and distributor cap for a tune-up.....not any more. The only things I still deal with points are my Deere 2020 & B tractors. Definitely not saws.


bob

 

[zogger]

Ok so usually on a points set up there is a cam to open and close them at the correct time. So with this solid state trigger module what is used to trigger it at the correct time. Is it some how connected to the coil and uses that or does use the magnet off the flywheel or What?

The timing right off the flywheel, same as the points, the timing point is set by where the magnets are in location to the stroke and when they cross the coil legs. Nothing has changed with the timing, just how the spark gets to the plug.

You still have the coil, just that solid state circuitry in place of the points can handle everything faster and doesn't wear out or go out of time, the same as pitted points or point flutter or bounce at higher rpms, etc will change the timing enough to be discernible.

That link I provided above there explains it WAY better than I can. Just remember capacitor=condenser at that link.

 

[3000 FPS]

The timing right off the flywheel, same as the points, the timing point is set by where the magnets are in location to the stroke and when they cross the coil legs. Nothing has changed with the timing, just how the spark gets to the plug.

You still have the coil, just that solid state circuitry in place of the points can handle everything faster and doesn't wear out or go out of time, the same as pitted points or point flutter or bounce at higher rpms, etc will change the timing enough to be discernible.

That link I provided above there explains it WAY better than I can. Just remember capacitor=condenser at that link.

Ok I got it. I read the explanation on Capacitor discharge Ignitions and see that the coil is used for the timing and charges the cap for a spark. That is simplified but that is the basics.

 

[eyolf]

The wiki article is next to worthless as afr as explaining how the module works. Most small engines work like this, factory or aftermarket CDI ign:

The magnets in the flywheel run up near the windings in the coil and the moving field starts a current flowing in the primary winding of the coil. Nothing can really get going in the secondary winding yet because the spark gap won't let current pass until voltage rises high enough to ionize the spark gap.

At the point where the magnet is just passing under the first leg of the coil, you will usually find the highest amount of voltage (potential). As the magnets move past, voltage will begin to drop (actually current flow would reverse, dropping to zero) Generally, point-style ignition systems were times so that the points opened at this spot...when the points opened, current could no longer flow, causing a collapse in the filed within the coil: the wires in the secondary winding went by the rapidly collapsing field and a voltage high enough to jump the spark plug gap was created. The condenser help out by actually discharging itself backwards as the points open, causing an even faster collapse.

With a CDI, the solid-state circuitry inside the "brain" senses the changing polarity on the primary circuit and shuts off the circuit in the same way. Timing will be dependant upon the
design parameters and quality control and value tolerances of both the module and the other ignition components; when current directions changes exceed certain values the unit "fires". The short answer is that most makers designed their engines the same way, with the same internal values, and the will fire close to right with a module. These small engines aren't usually that picky that a few degrees at 10k rpm means much.

also see this thread: http://www.arboristsite.com/chainsaw/186437.htm#post3295413

 

[XPLRN]

The wiki article is next to worthless as afr as explaining how the module works. Most small engines work like this, factory or aftermarket CDI ign:

The magnets in the flywheel run up near the windings in the coil and the moving field starts a current flowing in the primary winding of the coil. Nothing can really get going in the secondary winding yet because the spark gap won't let current pass until voltage rises high enough to ionize the spark gap.

At the point where the magnet is just passing under the first leg of the coil, you will usually find the highest amount of voltage (potential). As the magnets move past, voltage will begin to drop (actually current flow would reverse, dropping to zero) Generally, point-style ignition systems were times so that the points opened at this spot...when the points opened, current could no longer flow, causing a collapse in the filed within the coil: the wires in the secondary winding went by the rapidly collapsing field and a voltage high enough to jump the spark plug gap was created. The condenser help out by actually discharging itself backwards as the points open, causing an even faster collapse.

With a CDI, the solid-state circuitry inside the "brain" senses the changing polarity on the primary circuit and shuts off the circuit in the same way. Timing will be dependant upon the
design parameters and quality control and value tolerances of both the module and the other ignition components; when current directions changes exceed certain values the unit "fires". The short answer is that most makers designed their engines the same way, with the same internal values, and the will fire close to right with a module. These small engines aren't usually that picky that a few degrees at 10k rpm means much.

also see this thread: http://www.arboristsite.com/chainsaw/186437.htm#post3295413

Thanks for a great ignition explanation.....been wondering about the solid state upgrade on older stuff also!! :msp_thumbsup:

 

[harrygrey382]

Big thanks to eyolf and logger, I now understand. So really it was my lack of thorough understanding of ignitions in general. It's funny, I really though it was the points opening that triggered the spark - but really it is just coincidental...

 

[67L36Driver]

Interesting footnote.

I have a Lombard AP-42 type (68cc) on my bench right now. The coil/points bracket is slotted to adjust the spark for some 10 deg. (estimated).

We will be looking for (or making our own) timing marks and setting the lead like we used to do our old Yamaha Enduro. Using a tattle-tale light.

 

[Cantdog]

The wiki article is next to worthless as afr as explaining how the module works. Most small engines work like this, factory or aftermarket CDI ign:

The magnets in the flywheel run up near the windings in the coil and the moving field starts a current flowing in the primary winding of the coil. Nothing can really get going in the secondary winding yet because the spark gap won't let current pass until voltage rises high enough to ionize the spark gap.

At the point where the magnet is just passing under the first leg of the coil, you will usually find the highest amount of voltage (potential). As the magnets move past, voltage will begin to drop (actually current flow would reverse, dropping to zero) Generally, point-style ignition systems were times so that the points opened at this spot...when the points opened, current could no longer flow, causing a collapse in the filed within the coil: the wires in the secondary winding went by the rapidly collapsing field and a voltage high enough to jump the spark plug gap was created. The condenser help out by actually discharging itself backwards as the points open, causing an even faster collapse.

With a CDI, the solid-state circuitry inside the "brain" senses the changing polarity on the primary circuit and shuts off the circuit in the same way. Timing will be dependant upon the
design parameters and quality control and value tolerances of both the module and the other ignition components; when current directions changes exceed certain values the unit "fires". The short answer is that most makers designed their engines the same way, with the same internal values, and the will fire close to right with a module. These small engines aren't usually that picky that a few degrees at 10k rpm means much.

also see this thread: http://www.arboristsite.com/chainsaw/186437.htm#post3295413

Exxcellent explanation eyewolf!! The "How" and "Why" were addressed perfectly, with the "when" being a tad sloppy by the design nature of a "one size fits all" unit. This answered some questions I have always had. Also confirmed my long held suspicion that though these units work well enough and are cheap they are not the most accurate method of timing a spark. I knew someone could explain these to us in terms that are easily understood...Thanks!!

BTW I like electronic igns...but have no problems with points and timing. One of my 49sp Jonsereds has a module that I thought I would try as it came to me on a parts saw. It starts and runs well enough but I have noticed that it has a slightly different exhaust note/tone than all the other points driven 49SPs I have.

 

[madhatte]

Let me add a bit to this excellent discussion.

By definition, Capacitance is "that property of a material which opposes a change in voltage", and Inductance (coil) is "that property of a material which opposes a change in current". That said, the magnet in the flywheel passes the coil and builds a field, which collapses when the magnet is gone, in a vain attempt at maintaining a current. This collapsing field has to go somewhere. With points, the cam opens the points and tells the field when to collapse, and the capacitor/condenser serves to set a delay which places the spark at the plug in the right moment to ignite the fuel in the combustion chamber. With a CDI module, the function of the cam and points are replaced by solid-state logic, but the capacitor serves the same purpose. In both systems, the coil builds and collapses the field relative to the position of the magnet in the flywheel, and the capacitor holds that potential energy until the exact moment when a spark is needed for ignition. Only the decision-making mechanism is different between the two systems.

 

[Cantdog]

Are the points not merely just a timed switch, that while closed shunts the current to ground (and the condenser) and while open (no ground) allows the current in the coil to jump the spark plug gap and back to ground, simply in a different place?

 

[Chris-PA]

In an automotive points ignition system, when the points are closed current begins to flow through the primary coil winding, building up a magnetic field around the core. You cannot change the current though an inductor instantaneously, so current ramps up from zero, until the points open. Now there's a problem - the points opened, and the current can't flow there anymore, but the current can't change instantaneously though an inductor! There's energy stored in the magnetic fields and it cannot stay there without a current flow, so the voltage increases until it finds a way out. Because there is a secondary winding with a lot more turns, the voltage increases over there more quickly, until it arcs across the spark plug gap.

The need for the condenser is to prevent the arc from happening at the points. The points open slowly, so it would be easy to arc across them at first, and once the arc was established it would just grow as the points opened. With a small capacitor across the points, it gives the coil current somewhere to go to maintain the current flow for a moment. By the time the capacitor is full and current stops flowing into it, the points are fully open - too far to arc across.

The points opening controls the timing.

For saws there is no battery, so the moving magnet provides the current to charge the fields.

CDI kits for cars still used the points, but only as a trigger. I don't know what the CDI systems in saws use - probably the field collapsing as the magnet moves away. Clearly new saws don't use points as a trigger, so it is not required.

The question in my mind is relative timing - while you don't need points to trigger it, you do need to locate the module at the correct angle so that whatever the time delays of the trigger circuit are, the spark comes out at the right time. Is that location the same as where you would locate the coil (angle/position wise) if points are timing your spark? I have no idea.

 

[Termite]

Your right on Warrior.

 

[Cantdog]

In an automotive points ignition system, when the points are closed current begins to flow through the primary coil winding, building up a magnetic field around the core. You cannot change the current though an inductor instantaneously, so current ramps up from zero, until the points open. Now there's a problem - the points opened, and the current can't flow there anymore, but the current can't change instantaneously though an inductor! There's energy stored in the magnetic fields and it cannot stay there without a current flow, so the voltage increases until it finds a way out. Because there is a secondary winding with a lot more turns, the voltage increases over there more quickly, until it arcs across the spark plug gap.

The need for the condenser is to prevent the arc from happening at the points. The points open slowly, so it would be easy to arc across them at first, and once the arc was established it would just grow as the points opened. With a small capacitor across the points, it gives the coil current somewhere to go to maintain the current flow for a moment. By the time the capacitor is full and current stops flowing into it, the points are fully open - too far to arc across.

The points opening controls the timing.

For saws there is no battery, so the moving magnet provides the current to charge the fields.

CDI kits for cars still used the points, but only as a trigger. I don't know what the CDI systems in saws use - probably the field collapsing as the magnet moves away. Clearly new saws don't use points as a trigger, so it is not required.

The question in my mind is relative timing - while you don't need points to trigger it, you do need to locate the module at the correct angle so that whatever the time delays of the trigger circuit are, the spark comes out at the right time. Is that location the same as where you would locate the coil (angle/position wise) if points are timing your spark? I have no idea.

That is about how I understood a points ign to work too. As far as the position of these modules, I believe they can be placed almost anywhere and do not need to be in a certain position in order to time more or less correctly. I believe they use a microprocesser to evaluate the changes in current from the magnets passing the two coil legs and use that info to trigger with. I have heard that they like to be located in the airflow from the fan for cooling purposes. Again I believe that they are less than optimum timing wise but close enough to work decent on a large varity of single cyl engines..As I said earlier I have only one saw running a module and though it runs fine...I have noticed it has a slightly different exhaust sound/note than the other 8 exact same model saws with points igns that I have/run.

 

[galde]

Right on, Woodheatwarrior! The condensor's capacitance (the microfarad rating) was set to minimize the acring at the points. Too much capacitance and one of the points would loose metal at the point of contact, too little and the other point would lose metal. I forget which way it went, but the erosion could be minimized by fine tuning the capacitance by moving the lead wires to add or detract from the capacitance. On older saws with no spark I always preferred to find points and condensor rather than an electronic ignition module. Cleaning and gapping the points almost always restored spark, but a dead electronic module could mean up to $100 for a new module because a 50-cent chip died in the old one.