A home-made Capacitor Discharged Ignition unit for an old saw

[Al Smith]

In this ongoing discussion I'm now wondering exactly how does the "Nova"device work .I assumed it triggers on a high peak of the sine wave or if it uses a Darlington,or SCR ..Because for example the coil on a McCulloch only has two stator bars not three .Therefor in comparison to the two mentioned,Stihl and Briggs it has nothing to gate the trigger device to allow for automatic advance .
Now it's got me wondering too if all Stihl coils advance.To tell the truth I never really paid much attention if the coils had two or three stator bars .It either worked or it did not, usually the former .

 

[Al Smith]

Well after nearly going blind from staring at a computer screen I found almost nothing on the net .Some say the Nova and former Atom do advance some swear it doesn't .The conclusion is it works .
Then you get into "hall effect" sensing and open up another can of worms .

 

[chy_farm]

Good evening Al, yep! you seem you are walking on the right way where I am, lol, about this matter. That is what I have been wondering! Not very sure but I think I had a glance at a patent file on this unit submitted by someone in the past, but not sure,,,

 

[wcorey]

Going back aways I was playing around with adapting automotive ignitions like the gmc hei, onto older points triggered motorcycle ignitions.
The hei module can be triggered in a variety of ways (including points) and one of the methods I tried was a simple inductive coil run from the points cam shaft.
I was sort of suprised when I put a timing light on it and found it had the effect of providing an additional advance curve.

I assumed it had to be what Al wrote about the stihl coil were the voltage threshold needed to trigger the module is generated sooner as the rpm increases.
Wouldn't be very straightforward to make it work on a non points saw though...

 

[Al Smith]

Single cylinder saws are relatively easy .You get into modern automobiles it gets rather complicated .I won't delve into it because that's not the subject of this thread but for those who don't know a Ford 3.7 V6 can change the timing around 20 times a second .--and it gets more complicated from there .These are not your great grand dad's model A's .

 

[Al Smith]

The reason I've attempted to delve into this is one of my ongoing projects is to rebuild and restore a Partner P100 super .I'm slowly gathering the parts .There has to be a reason the saw was abandon to sit in some barn for what looked like a long time .My guess of course, it didn't run,why ? If it was a bad trigger I'll need to replace it .They want about 50 bucks for an OEM Rifa brand .If a 15 dollar Nova II would work I'm all for it .Some people are "purists" when it comes to this stuff,I'm not .

 

[chy_farm]

I think I can not say myself to be a purist, but perhaps Revisionist! lol

 

[sixonetonoffun]

I think a lot of us non electrical engineer guys are following along. Hoping to glean some tidbits to help work around nla sems.

Timing curve is an added bonus!

 

[mgr1]

Is the partner p100 coil a 2 or 3 leg one?
The sachs dolmar 112 is a breaker point ignition with flywheel mounted coil. The coil from a ps6800 is a direct replacement so you don't need the breaker point setup any mor, because of the built in electronics in the coil.
What are these electronics? Think it is just like a nova or atom module.
These electronics are also build in stihl and husky coils so big change that the nova and atom can advance the timing.

 

[Al Smith]

I don't remember on the Partner but I have one in pieces in my garage .Regarding to self contain units I'm not so certain you can do anything to them because they are encapsulated .My guess would be the actual coil is okay but the built in trigger unit is faulty .Therefore for all intents theoretically non repairable .
I imagine replacement of self contained units would be possible depending on how it was mounted and if the stater legs aligned with the magnets but I've never attempted it .What might fit what I have no idea .

 

[Al Smith]

The Partner has the strangest ignition system I've ever seen .I'm not sure what to make of it .With the two portions of the coil installed it actually has three stater legs .The two larger laminations ,one on the double( forward ) portion,one on the back single section jumpered together with a wire .I'm thinking the trigger must be the forward section but I'm not sure.It has a large lamination and a smaller which I assume to be the trigger .The rear section has the plug wire .Just when I thought I'd seen everything this pops up .About the only one off the top of my head who might have one would be Scott at Chainsawr .I'll check it out .

 

[mgr1]

Left leg powers the circuit, middle leg triggers, 3 leg gives the spark.

 

[Al Smith]

In trying to research this thing it appears several designs of ignitions were used .With Partner at least in these parts the saws were rare but the concrete saws were considered the best .It seems information for this brand is rather limited unlike Stihl or McCulloch which is plentiful .Then again if were easy anybody could do it .

 

[Al Smith]

Left leg powers the circuit, middle leg triggers, 3 leg gives the spark.

That's about what I concluded .Usually the laminated core is common to all three legs which is what kind of confused me .An ignition coil ,magneto or battery spark is basically like an auto transformer with one side of both the low voltage and the high voltage coil with a common ground .The current flow would be reversed between the coils on ignition trigger,points or solid state because of the collapsing magnetic field (right hand rule for coils )
However after thinking this through it appears the two coils work like this .The low voltage side contains the trigger ,when it fires the voltage is cut off via the jumper connecting the two separate coils and it fires the plug .Makes sense just a different way of doing things .

 

[mgr1]

This circuit makes it a little bit easier.

 

[Al Smith]

Very easy to understand schematic .

 

[Al Smith]

I had to do a little research on SD1 and SD2 .I thought they were xeners but found out they were shottky diodes which I'd never heard of .Then I have to keep in mind this is dealing with pulsating DC not full AC . I haven't delved into this stuff since about 1971 .It's still there but at times I have to search a little deeper in my brain to find it --thank you Google

 

[chy_farm]

Good evening Mgr, nice to know this schematic. Trying to make a simulation for this on the LT spice, a simulation software provided from Liner Technologies. Seems this needs some more values for each element. Will try later again.

 

[mgr1]

Chy_farm: its not a circuit from me. There is a person that reversd engineerd this circuit. The value of C3 is faulty, must be 0.8 microfarad.

When whe know the voltage from the exciter coil whe can build a very simple but effective ignition module with a hall sensor. This can be used for a lot of different types of chainsaws with a 2 pole flywheel.

At this moment i am very busy with family and work. Arround the summer there will be more time for building a hall sensor ignition system to adapt on multiple chainsaws.

 

[chy_farm]

@mgr1 , good evening. I am using one of the hole sensors too, it's small and sensitive to small signals.