Small, 3v Buzz Coil Ignition

[jschoenly]

I needed a buzz coil for a little Stove Pipe Domestic I just got from a friend (the Herder engine casting set, with about 4" flywheels). One of the things I always loved about my good friend George Luhr's models what how he hid the coils in a relatively small base and used 2 AA batteries for ignition so you could walk around with his tiny models.



Well, I wanted to hide the ignition in the small coil box on this engine, so I was looking at how others used the standard auto relay's and a regular coil for a buzz coil. The complaint occasionally is that the 12v relay needs 12v for the ignition. Enter George's use of the Modelectric 3v model aircraft coils. I thought why not get a cheap 3v coil relay and try the same setup. Well, I must say so far it looks great! I need to hook it up to the engine and test longevity, but it seems to throw a wonderful healthy spark!

 

[Vietti]

Like your idea!! What 3 volt relay do you use and who still sells Modelelectric coils??

Thanks

 

[jschoenly]

The relay was one of the first that showed up on amazon searching "3v relay". They are a pretty small 5 pin pcb relay and reasonable in a 10 pack. It also uses a 0.1 mfd cap (the current one is only 50v ceramic, not sure if that will last?).

The coil is from a small stash George had that I ended up with. Unforunately I'm not sure they are being made, but there is a place in Spring Valley PA that lists ignition engine coils as a product but I email and I haven't heard yet if they are still making them. So as for a coil source - I don't know unfortunately! It should work for a variety of coils but I'm not sure what other coils might go that low on primary voltage. I have seen vintage coils on ebay but mileage may vary there....

 

[bluejets]

We've used Ford OTP coils for ages which look to be around the same size.......no worries if you shove 'em in a box underneath.
The Spark plug wire we use is Belden HV rubber around 3mm dia so looks scale.
The coils will run fine on one LiPo cell (18650) 3.7v.
I put details in here ages ago but no one was interested.
I run them on points or hall effect whereas others work them as a buzz coil.

 

[rweber]

We've used Ford OTP coils for ages which look to be around the same size.......no worries if you shove 'em in a box underneath.
The Spark plug wire we use is Belden HV rubber around 3mm dia so looks scale.
The coils will run fine on one LiPo cell (18650) 3.7v.
I put details in here ages ago but no one was interested.
I run them on points or hall effect whereas others work them as a buzz coil.

I am curious, which Ford coils do you use? They run with just 3.7v?

 

[bluejets]

I am curious, which Ford coils do you use? They run with just 3.7v?

That's what I said yes.
I'll see if I can find where I posted the details.

Found a couple of photos....these are OTP coils (on the plug) from BA Ford Falcon down here in Aus.
I stripped all the unnecessary gear off the coils.

Originals are shown with all bits attached.
I picked mine up at local wreckers for a couple of bucks each.
Connection is exactly the same as a Kettering system....i.e.battery + to the coil ( terminal shown +) and other side goes to a set of points to ground with a capacitor across the points......(maybe 0.1uF 400v ...X2 type)
HT is then taken from centre post and return HV is ground.

There is also the other CDI system I devised from the small pocket rocket motorcycles....... played with it for a while and one other bloke here suggested an improvement with a small reed coil attached to the input to simulate the original P/U ....I used a small relay coil and did away with some of his unnecessary add-ons and it works extremely well.
Runs off 12v and uses off-the-shelf 4 wire black box, a small CDI coil and either points. or hall effect as the switching sensor.
I have a small add on pcb which holds the relay etc and it is normally hot glued to the top of the black box.
Cost of all the parts is less than AUD$40, places like Ebay etc.

Cannot find the video I had for the Ford Coil but I'll keep looking......... the CDI system I mentioned is covered in a video here......