Trembler Coils--(Constant spark)

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Today I'm learning all about trembler coils. Perhaps more than I ever wanted to know!! I have everything hooked up, electric starter, engine, and trembler coil. The trembler coil fires the sparkplug like crazy ---but only when the engine first begins to rotate, or when the engine is coasting to a stop. However, it doesn't want to fire the sparkplug while the engine is turning at a higher rpm. Okay, that's weird!!! My best guess is that this failure to perform at higher rpm has something to do with the amount of flat that I have on the cam. Damn!! I thought this was going to be easy. This coil fires when the points first MAKE contact, opposite to a conventional points and coil system which fires the coil when the points BREAK contact. Right now, the cam has a flat on one side only, as shown in the attached model. MAYBE I have to make the flat area on the cam extend part way around the 360 degree body of the cam so the system has a longer "dwell" with the points in contact with each other.
3qXzKJ.jpg
 
Maybe the cam should look like this, so that the points stay in contact a much longer time. This would agree with what George Britnel is saying, that the ignition cam should almost look like a valve cam. I'm kinda lost in the woods here.---Brian
EVcnrc.jpg
 
That profile will likely give far too long a spark and you will run the battery down and get a hot coil, If you want a bit more spark duration then you need a profile more like this which would give a spark for 45deg of cam rotation therefore 22.5deg of crank rotation which should be more than enough

45cam.JPG


You don't need much of a change between base dia and the reduced diameter, you can just about see the change on this cam from the "Lightweight" that I built some time ago.

DSC01073.JPG
 
How high of an rpm does it cut out at? I assume drill cranking speed because you never said you got it to run. So maybe 3000 rpm crank??
In any case:
Do a bit of measurement to determine how many degrees of cam rotation the trembler is active.
At the rpm in question how long (in time) is the trembler activated? Simple math involved equating - revolutions per second - degrees per second which leads to time the cam activates the trembler.
From experience there is a defined time for the relay to start oscillating. It might be that the cam is activating the relay for such a short time it can't even begin to oscillate.
Conclusion - you might need a wider cam lobe.
 
I will modify my cam to match what Jason has suggested. I have tried turning the engine over by hand with the sparkplug out, and the spark duration is very short.
 
Today I'm learning all about trembler coils. Perhaps more than I ever wanted to know!! I have everything hooked up, electric starter, engine, and trembler coil. The trembler coil fires the sparkplug like crazy ---but only when the engine first begins to rotate, or when the engine is coasting to a stop. However, it doesn't want to fire the sparkplug while the engine is turning at a higher rpm. Okay, that's weird!!! My best guess is that this failure to perform at higher rpm has something to do with the amount of flat that I have on the cam. Damn!! I thought this was going to be easy. This coil fires when the points first MAKE contact, opposite to a conventional points and coil system which fires the coil when the points BREAK contact. Right now, the cam has a flat on one side only, as shown in the attached model. MAYBE I have to make the flat area on the cam extend part way around the 360 degree body of the cam so the system has a longer "dwell" with the points in contact with each other.
3qXzKJ.jpg

I have used a similar lobe with a 2 stroke engine and the engine runs quite well., With this ignition system, the force F as shown in the picture needs to be strong enough for the parts are always in contact at high speed.
A.jpg
 
Wouldn't it be simpler to replace the auto ignition points (normally closed switch) with a simple normally-open reed switch for the cam to close for each firing of the plug? That's how it works on all the engines I have worked with. I've had a few full-size hit and miss engines that use buzz coils and they all had a very conventionally shaped positive cam to close the firing circuit. I think mechanically it would be a lot easier to rapidly push a switch closed momentarily than to try to let one close rapidly in a negative cam.
 
Flats or a lobed cam both work fine at lower revs that Brian wants his engihe to run at I've built engines with both. You don't even need to have a cam something as simple as a stud sticking out of the cam gear (or wasted spark if on the crank somewhere) and an insulated brass wiper contact is all it needs

DSC03876.JPG




20231130_153908[1].jpg



 
You don't even need to have a cam something as simple as a stud sticking out of the cam gear (or wasted spark if on the crank somewhere) and an insulated brass wiper contact is all it needs
I agree .
 
I agree .
As do I. However, Brian is doing the opposite, using a cam to hold the automobile style ignition points open until the firing part of the cycle. I'm not sure the points will close rapidly enough to make a spark even at modest RPMs regardless of the cam geometry. Seems far easier to do it the way you guys do, where even a stud poking out at the right place closes the firing circuit. Because it is a buzz coil, the timing really isn't that critical because all the "magic" of generating the hot spark is built into the coil. It generates a hot spark every time the buzzer cycles while the circuit is closed - many times per second!
 
I am interested in trembler coils, similar to that used in Model T fords. In a conventional points style ignition, you get one spark at the plug when the points open. With a trembler coil system, you get a series of sparks whenever the points are closed. There are a ton of "How to" articles on building your own trembler coil on Youtube, and it seems that I already have most of the components (a 12 volt coil and a condenser.) It seems that all I need to buy is a special relay, which is commercially available. Does anyone have more information pro or con about these trembler coil systems?---Brian
I built one and Wow it can bight! Burned right through the insulation of ordinary wire.
 
Hi, I built a free running multivibrator running at 200Hz which is switched by a reed switch and magnet. Output of the multivibrator switches a transistor which switches current to the coil. Used it on several of my IC engines both 2 stroke and 4 stroke. No problems at all.
The multi spark created is much hotter and stronger then a conventional single spark.
 
As do I. However, Brian is doing the opposite, using a cam to hold the automobile style ignition points open until the firing part of the cycle. I'm not sure the points will close rapidly enough to make a spark even at modest RPMs regardless of the cam geometry.

It would be fine, but the problem with flat lobes is that the switches need enough force so they stay in contact with the lobes
With a slight force, the engine will run at low speed - But the problem is how many rpm will that speed be? and also depends on many other factors, most importantly the flywheel. At a speed of a few hundred or thousand rpm, they will pass each other due to inertial force
I usually test them with a drill, at slow speed (100 rpm!?? not sure) and fast speed (about a few thousand rpm) if there is always a spark then it will be fine with the engine.
 
Last edited:
Time now to put this thread to bed. I did build a trembler coil using a standard 12 volt coil, a condenser, and a 5 pin relay. It worked like a charm, with a marvelous series of sparks. I ended up not using it, but it worked, and worked very well. Not everything I build works out successfully, but this did work as advertised, and I was very pleased with the end result.---Brian
 

Latest posts

Back
Top