Ignition function/repair

[rupedoggy]

The recent thread got me thinking about saw ignition modules. Most of us guys, that work on a lot of saws, see quite a few dead modules. I sure as heck don't know electricity like an engineer but it seems to me that there just should not be as many go out as do. The thing is basically a winding that gets excited as a magnetic field passes by and creates a spark, right? So why does the thing go out? I think it is the little wires becoming shorted or separated. The ones most commonly seen are encased in some epoxy looking stuff. I would guess this is to prevent the wires inside from getting broken from vibration. OK so why do the wires separate? The flow of electrons through a wire should not do it, should it? If that was a problem then there would be wires parting every day, through out the country, on the wires on trillions of poles. Yes I know there are problems but that is normally at a connection, bad transformer or outside interference. They just don't suddenly part in the middle because electricity is flowing through them.
Well the above probably shows how little I know about the problem. I would like to fix some saws that have bad ignitions without buying $80 NLA ignitions that keep going out anyway (like the old Pioneers). And while we are on the subject, does someone know of an interchange chart for ignitions. I know several Stihls are compatible. I think several ignitions coils could be fixed by swapping out the lamentations with a good module. Any electrical engineers out there? Any tinkerers that have swapped a couple different ones around? Mike

 

[casey v]

I have successfully removed the laminated legs from a bad coil and installed a new coil on the legs. Using the same laminated legs insures the timing remains the same.

Mike

 

[RaisedByWolves]

The ones most commonly seen are encased in some epoxy looking stuff. I would guess this is to prevent the wires inside from getting broken from vibration. OK so why do the wires separate? Mike

The most common cause is due to the epoxy and wires expanding and contracting.


On the old style ignitions they used wico magnetos(Im talikng ooold stuff here), these had a coil that was encased in epoxy also. when the coil heats up the windings will sometimes(eventually) crack the epoxy. Once the epoxy cracks the coil is sure to fail due to moisture causing problems or vibration and expansion/contraction having their way with the brittle wiring.


The newer epoxies dont seem to crack as often so moisture is no longer a problem but the wires are still susceptible to expansion and vibration.


Then there is allways the possibility of shorts in the windings.

 

[Fish]

To be honest, coil failure is very rare around here, but the saws around here
are on the smallish side. We have the weekly redneck that comes in wanting
me to order him a new coil, under warranty, of course.

But the ignition is rarely at fault.

just around here........................................................

 

[THALL10326]

The most common cause is due to the epoxy and wires expanding and contracting.


On the old style ignitions they used wico magnetos(Im talikng ooold stuff here), these had a coil that was encased in epoxy also. when the coil heats up the windings will sometimes(eventually) crack the epoxy. Once the epoxy cracks the coil is sure to fail due to moisture causing problems or vibration and expansion/contraction having their way with the brittle wiring.


The newer epoxies dont seem to crack as often so moisture is no longer a problem but the wires are still susceptible to expansion and vibration.


Then there is allways the possibility of shorts in the windings.

Good post RBW. That explains why when coils slowly go dead they always go dead when hot. Its common to see a coil work when cold and taper off to nothing as it heats up. Good post RBW.....

 

[BlueRidgeMark]

Good post RBW.

Yes indeed! Nuthin fer me to do here...

Well, except maybe this:

think several ignitions coils could be fixed by swapping out the lamentations with a good module. Any electrical engineers out there?

Lamentations? You mean like the prophet Jeremiah?

"Laminations" is the word you were looking for.

As for fixing a coil, yes it's theoretically possible. Tedious, but possible. You need the right kind of wire, the right diameter wire, the right insulation, and the proper length of wire and pattern of winding. Even the thickness of the insulation is important. It's usually a type of laquer, and of course, it must have the right heat characteristics.

Sounds easy, right?

There are shops that rewind electrical motors. I'm wondering if one of them could rewind a saw coil for a decent price....

Probably not. You might be better off trying to find a more modern one that will physically fit and still have similar electrical properties.

 

[Lakeside53]

The failures needs to be divided into "Electronic triggered versions" and the points versions...

RBW and others have talked about the non-electronic versions (bascally two winding arranged as an "auto transformer"), but what they say applies to the electronic triggered version equally.

additionally....


Most of the temperature related failure are on the "electronic trigger" versions...

Early electronic triggers were simple (like the atom module or the on-board triggers in coils like the Stihl 0000 400 1300) just detected the rise in primary voltage and triggered their scr (silicon controlled rectifier) appropriately - a simulation of points.

The modern versions clamp the primary (means "short circuit") until the correct RPM is detected, then allow the primary to conduct at the correct timing). This clamping action (basically a diode and scr) requires a lot of energy to be absorbed, causes significant heat to be generated inside the coil, and stresses the internal components. External thermal stressing (engine and environmental heat) adds to this and can cause intermittent or permanent failures of the avalanche diode(s). Ever had a weed eater or concrete saw that starts fine but just won't rev to max and runs like crap? ... No, it's not the carb.. the coil is stuck in one of the first two stages of retardation... the timing cannot advance as the engine speeds up. How about looking at the spark in a MS361 or MS441... No spark? Just pull it over faster... The coils trigger won't allow spark until a certain rpm is reached. It's designed this way to alleviate wrist snapping misfires.

 

[Lakeside53]

I have successfully removed the laminated legs from a bad coil and installed a new coil on the legs. Using the same laminated legs insures the timing remains the same.

Mike

Yep... And I've done it on OLD coils that are quite different... so long as the internal core size is the same, and the coils physically fit, they usually work.

 

[BlueRidgeMark]

I've made hand wound inductors for low pass loudspeaker crossovers. It's not too difficult. With loudspeakers space is not at such a premium.

Yeah, I'm sure there have been thousands made that way. Space is the issue. Also, while precision isn't really required, you do want your coil to have at least similar characteristics to the stock one. It can be done, but you do have to know a bit about what you're doing.

When I was in college we had a bomb scare one day and there was a fellow caught in the electronics lab with some hand would inductors. Good thing the professor knew what he was doing and stood up for me........I mean him.

State police do not react real well to hand wound coils!

I would think a breakdown in the insulation would be a major failure point in chainsaw coils. Once windings start shorting or arcing to one another the heat generated is going to break down more insulation and lead to more arcing or an open.

Yes, insulation breakdown is the big killer of windings, whether in a coil or a motor.

 

[ozflea]

Fitting Electronic ignitions to the older Mac's is easy.

http://users.bigpond.net.au/ozflea/phelon.html

McBob

 

[scottr]

Old Pioneers

Mike , are the old pioneer ignitions electronic or points type ignitions ?

 

[rupedoggy]

Well the ones I am most interested in, and working on, are the P39, P40, P41, P42, P50, P51, P52, P60, P61 and P62. Some of the Poulan BPs were also of this type. The ignitions are all electronic and do not have points. Some are two piece however. It is hard to imagine but they all seem to mount different or have different flywheels. Some are real close to being the same but just a little different. Some have .018 gap and some take .035. The one thing they all seem to have in common is they go bad! Mike

 

[donnyman]

blue modules

Hi guys.Im givin up a secret here,but if you remove the coil and heat it up with a propane torch a reinstall it and set the air gap this will bring them back to life 50% of the time and never fail again.Pioneers and homey with the blue module Im talking about here.Works for me and what you got to lose .Nothing.Donnyman.

 

[rupedoggy]

OK "THAT'S WHAT I'M TALKIN' ABOUT!". That boys and girls, is stuff you will not find in any repair guide. Can any of you "electrical guys" explain why this may work? How hot should we get these units to try to rejuvenate them? Any special place to apply the heat? Should we take out the laminations first? I have a bunch of 056 ignitions that are shot and would like to try it on them too. How about the Betty Crocker repair "bake in an oven preheated to 450 degrees for one hour"? Actually 250 may be better. I read somewhere that epoxy loosens its grip at about 300.
I actually helped several people back in the 1970s get their electronic ignitions, in their automobiles, going again. The trick then was to pour ice cold water onto the "box". The engine would start and you could drive it to the repair shop. Don't know why it worked but it saved several people a tow bill. Mike

 

[Lakeside53]

OK "THAT'S WHAT I'M TALKIN' ABOUT!". That boys and girls, is stuff you will not find in any repair guide. Can any of you "electrical guys" explain why this may work? How hot should we get these units to try to rejuvenate them? Any special place to apply the heat? Should we take out the laminations first? I have a bunch of 056 ignitions that are shot and would like to try it on them too. How about the Betty Crocker repair "bake in an oven preheated to 450 degrees for one hour"? Actually 250 may be better. I read somewhere that epoxy loosens its grip at about 300.
I actually helped several people back in the 1970s get their electronic ignitions, in their automobiles, going again. The trick then was to pour ice cold water onto the "box". The engine would start and you could drive it to the repair shop. Don't know why it worked but it saved several people a tow bill. Mike

I wouldn't try the bake method on the 056 ignitions... Different failure mode... unless you want cook them completely. I'm getting the genuine bosch repair info for the 045/ 056 system togther for scanning... will post in a week or so..

 

[BlueRidgeMark]

OK "THAT'S WHAT I'M TALKIN' ABOUT!". That boys and girls, is stuff you will not find in any repair guide. Can any of you "electrical guys" explain why this may work?

Hmmmm. Might melt the expoxy enough for it to flow and fill in some cracks, thus sealing off a short.

It would be very interesting to research that...

 

[scottr]

Heat

You might heat the module or coil in a oven to drive out the moisture at 150 dgf for an hour or two then seal the unit with a thin coat of lacquer . The torch method might over heat a component and cause total failure .

 

[Lakeside53]

You might heat the module or coil in a oven to drive out the moisture at 150 dgf for an hour or two then seal the unit with a thin coat of lacquer . The torch method might over heat a component and cause total failure .

Laquer won't last... and absorbs moisture.. use "Conformal coating" or a very thin epoxy.

 

[pioneerman]

Picked up a Pioneer P39 today with a dead blue prestolite module. Tried Donnyman's advice and applied some heat to the module. First module didn't work, but the second one I tried did. Saw fired up and runs good. Will have to try some wood cutting to see if it stands up. Amazing what you can learn on this site.