# ignition system



## raym 11 (Feb 3, 2008)

Anybody know where I might look for .3 or .4 mfd capacitor? Looks like Radio Shack has everything but.

raym


----------



## Lew Hartswick (Feb 3, 2008)

What are you using it for? 0.25 and 0.5 are standard values of cap. Voltage rating is another important
factor. If this is simply a spark suppressor it isn't at all critical. 
  ...lew...


----------



## raym 11 (Feb 4, 2008)

I am using it on ignition system for my model hit & miss and small engines. 6v batt, 12 volt auto coil . suggestions? Would a 6v coil be ok? Existing is working ok,(with a .5 cap . [I think]) too much spark if any thing. Also looking to downsize physically.  

Where can I look for a .25 cap.?

raym


----------



## Brass_Machine (Feb 4, 2008)

Check these places. I am sure you can find them here

Mouser

Digikey

Eric


----------



## raym 11 (Feb 4, 2008)

Thank you Lew.


Choices......... ;D

raym


----------



## miker (Feb 4, 2008)

Ray, are you refering to the capacitor that goes across the points? If so, that cap is there to reduce Arcing across the points and has no effect on the actual spark produced at the plug. It is to reduce the cratering of the points due to Arcing.
I don't know how the system works on that type of engine though.


----------



## raym 11 (Feb 4, 2008)

Yes Miker I'm getting too much arcing across the points. 
I'm assuming a lower capacitance will help ???

ray M


----------



## cfellows (Feb 4, 2008)

It seems like it ought to be the other way around. You need more capacitance to absorb the spark, right?

Chuck


----------



## Lyn S. (Feb 4, 2008)

All breaker points arc somewhat, if they are burning blue or piting then you have a problem. If you are using a round can type auto coil , then use a auto condenser.
Any older auto shop should have alot of cond. laying around. Don`t worry about 
capacity. Find real old auto shop as breaker ignition went out of style 20 years ago. 
 Lyn S.


----------



## Sprocket (Feb 4, 2008)

I've made a couple of hit and miss types with points, but never had a problem with arcing. 12 volt auto coil, 12 volt battery, auto condenser. Most recently, I used an electronic ignition system from MJN fabrication.
http://www.mjnfabrication.com/pages/948292/index.htm
The CDI unit would replace the everything but the battery. It runs on six volts, or there is a voltage regulator so you can use a twelve volt battery.
It struck me as a strange mix of technologies to use a CDI ignition on a hit and miss model, but it works well. It also can allow you to adjust the ignition timing.
No connection, but I have liked his products.
Doug


----------



## raym 11 (Feb 4, 2008)

Lew;

If I changed from a 12v coil to a 6v coil  ???

Ray M


----------



## raym 11 (Feb 4, 2008)

Doug,
I have a Mjn CDI module . Tried it on my twin and it didn't work well (weak). I talked to MJN and he said they have found they don't work well with points. I guess I could convert to magnet & pickup,......... Hybrid hit & miss 

I tested a 'Buzzcoil' and it works well on the singles. 

The spark was not strong enough for the Upshure twin. I think it has to do with my distributor. This is where I want to use my existing ignition system. It runs well but eats points and likes to arc all over the dist. cap, (finally getting back to my original pondering).

Ray M


----------



## zeusrekning (Feb 5, 2008)

This is what i was wanting to build. It is a 12volt CDI unit. Finally tracked down all the parts but debating on building one or buying a similar kit from austrailia.
http://www.molla.org/DIY-CDI/index.htm


----------



## Lew Hartswick (Feb 5, 2008)

Way too many unknowns here to comment. I'd need to see the circuit and components to even 
hazard a guess. I played with Capacitor discharge systems a bit back a bunch of years ago. 
Built up from components, switching supply to generate the high (as I remember 200V ) voltage and 
a high voltage fast switching transistor to pulse the coil. The points only had a very low current 
through them and one of the problems was they didn't "arc" enough to keep them clean in the engine
environment. For a model that may be a good system. Especially with the relatively slow RPM of a
hit and miss engine the dwell time is in you favor. For a car engine with a red line of 4 or 5 K and 
8 cyl there isn't a lot of time to charge up either a cap or the mag field of a coil. :-(
  ...lew...


----------



## zeusrekning (Feb 5, 2008)

I found the PDF file with more info if anyone is interested in the CDI. 

View attachment SC-DIY-CDI-article-hires.pdf


----------



## Sprocket (Feb 5, 2008)

RayM:

I used the Hall Effect pickup and magnet, so no points on that one. I believe that they work with multi cylinder engines, just use more magnets. I think the "Open Six" in
Model Engine Builder used that type of ignition and three magnets.

Also, I didn't understand that the arcing was in the distributor, that makes more sense.

Doug


----------



## raym 11 (Feb 6, 2008)

Doug 

The reason I mentioned using CDI with points is because MJN bundled a schematic with the CDI designed to work with points. When I talked to Mike Neal he said sure 'nough they found the system didn't' work well with points.

Lew 
The 'Buzcoil ' system from Cliff Ward supposedly runs only .0035 amps across the points.

raym


----------

