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-   -   Scratch Built Ignition??? (https://www.rcuniverse.com/forum/engine-conversions-92/743937-scratch-built-ignition.html)

torquerollin 05-04-2003 06:55 PM

Scratch Built Ignition???
Has anyone ever built a scratch ingnition unit, or know how someone would go about doing it? I was going to build an ignition unit (if anyone knows how) for my 45 cc Homelite chainsaw engine. I know CH-ignitioins has ready built, and a kit that you can do it your-self, but the D.I.Y. kit is almost as much as the one that is already done. So, does anyone know how I would go about doing this, where I would get what I need, and what I would need?

Thanks for the help


h82crash 05-04-2003 08:05 PM

Scratch Built Ignition???
There is a little bit on this subject if you search. Check out this site.

torquerollin 05-04-2003 08:25 PM

Scratch Built Ignition???
Thank You H82Crash!! This should definately get me started. I will post results when I start on this project. (will be a while, have a lot of other things that need to be completed first)


strato911 05-04-2003 08:47 PM

Scratch Built Ignition???
I recently asked the same question (click here). I had found the following sketch at http://www.modelflight.com/ignition.html
The only useful response I got pointed me to http://www.5bears.com . On the Transistorized Ignition Circuits page, I found the TIM 6 circuit below, which closely matches my sketch.

ANeat 05-04-2003 11:10 PM

Scratch Built Ignition???
RC Modeler magazine has an article from 1980 in their archives. You need to be a subscriber to look at it ;)
It is a circuit for a Capacitor Discharge ignition. Its original puprpose was for running the older ignition motors on it. It looks like it might adapt. ??? :confused:
The bad part about most of these setups is the lack of timing advance. One of the things that make the newer elec ignitions seem so nice is the ease of strarting partly because the timing is backed off at low RPM. Of course you could go with some type of throttle coupled advance setup like guys used to run :rolleyes:

I to keep hopeing something comes up because that is something else I like to work on (electronics)


I dont know if it will work for everyone but here is a link,


h82crash 05-05-2003 12:34 AM

Scratch Built Ignition???
Brison still uses throttle coupled spark advance on their line and those are great engines.

torquerollin 05-05-2003 01:25 AM

Scratch Built Ignition???
Thank You for the responses! I will see what I can do.


DUHAWK49 05-06-2003 12:36 AM


foamcutter 05-06-2003 07:03 PM

Scratch Built Ignition???
Count me in, this looks like a great way to occupy some time and energy to learn something new and rewarding! Besides I have a few converted engines I would like to lose the magneto on.

ZAGNUT 05-06-2003 10:45 PM

Scratch Built Ignition???
http://perso.wanadoo.fr/transmic/gbfixe2.htm here you can see a very simple CDI circuit. this does not include the high voltage circuit needed for uor applications but a search of diy electronics sites will find lots of dc-dc converters based on small ferrite E cores.
iv'e made an ignition using the tiny module found in the distributor of a suzuki swift, worked great but with all the coils i tried the lowest current draw i got was a little over 2 amps at 6 volts, not so great. CDI is the only way to go imo.
CDI only uses the coil as a step-up transformer and doesn't rely on the inductance of the coil, so you don't need the big mega-wind coils with the heavy iron core. look at the tiny coils on zenoah engines, these are the same as the trigger-coils used for strobe lights, flashes, stun-guns....and are readily available from electronics suppliers for a fraction of the cost of dedicated model engine coils.
ignition advance/retard:
our engines aren't too picky about timing so a simple solution is to use two ignition sensors, one retarded for idle and start-up and one for high speed, a microswitch operated by a cam an the throttle shaft can switch between the two at about 1/3 throttle. i've been thinking about a simple ignition delay circuit that would vary timing depending on voltage recieved from the pick-up coil (not hall effect sensor) at different engine speeds. i don't know squat about electronics though, so any help would be welcome.


DougT 05-06-2003 10:46 PM

Scratch Built Ignition???
I just sent off the money order today for a TIM-6 ignition setup with coil. $41 total including shipping. I hope to have it running on my Ryobi 26cc by the end of the month. I'll let everyone know how it turns out. I don't think it has variable timing. Might have to rig a mechanical throttle-spark advance.

DUHAWK49 05-06-2003 11:05 PM

tim 6
is that setup all that is need to make an ignition? ive got a couple friends that are electrical engineers.. i think ive got them talked into trying something out for me as well. if thats all you need i may have them look at that and see how to improve it if possible.. :cool:

captinjohn 05-07-2003 01:49 PM

home-built ignitions
More on ignitions in the GIANT ENGINE FORUM

Dr. Crash 05-08-2003 06:29 PM

Scratch Built Ignition???
I just put together one of Jerry Howell's kits, the one mentioned in this thread, It is working fine, You just have to obtain the spark plug wire and the plugs and wiring for the sensor and battery. The timing is fixed.


foamcutter 05-08-2003 06:31 PM

ignition kit
I also have ordered the TIM-6 ignition parts. Looks like to me we will need to turn a small hub to go on the crankshaft to hold the magnet to pass by the pickup. From his information I read on the site I will need to do some calculations to get the right diameter hub for the correct dwell time. I also ordered the back issues of the IC magazine he talks about to see if there is any good info in them. Will post when I know something new.

DUHAWK49 05-08-2003 06:33 PM

tim 6
ya i will be curious to see how yours works.. keep us posted :cool:

h82crash 05-08-2003 10:03 PM

Scratch Built Ignition???
Hub diameter won't affect dwell time. At a given rpm the linear speed at the perimeter will increase as diameter gets larger. Time remains the same.

roadhor 05-09-2003 04:00 AM

Scratch Built Ignition???
Dr. Crash ; Could you show us some pics of your setup. I'm converting a 2.4 saw engine & am thinking of building one of these. Thanks, Rob

Dr. Crash 05-09-2003 10:35 AM

Scratch Built Ignition???
I will post pics this afternoon, probably around 4:00 PM

Dr. Crash 05-09-2003 11:08 AM

Scratch Built Ignition???
I agree the number of times the ignition fires per minute is the same no matter what the diameter. However, if you're talking about dwell time, the time the coil stays charged, is dependant on the size of the magnet and the diameter of the hub. The bigger the diameter the faster the pick-up crosses the magnet, hence the dwell time is shorter.


ZAGNUT 05-09-2003 12:54 PM

Scratch Built Ignition???
on the tim-6 with hall effect sensor the dwell time is determined by how long the magnet stays under the sensor. this is the major drawback to this ignition. i've seen a similar system adapted to a motorcycle useing 2 sensors, one opened the current to coil and the other one closed the current, this gave an adjustable dwell angle. the only advantage to the single sensor that i can see might be low current draw. these systems were originally designed to be used with points where dwell angle would not be a problem.


foamcutter 05-09-2003 01:21 PM

Scratch Built Ignition???
Ok, I understand how this works. With the dwell time being determined by the time the magnet is under the sensor, my question now is what problems does this create for us using it on our conversions? Is there a better way that doesn't cost signifigantly more. I ask because I don't know much about this stuff yet and want to know all I can. Thanks

strato911 05-09-2003 01:44 PM

Scratch Built Ignition???
In another thread I'm following, someone associated with CH Ignitions has indicated they have just released an ignition circuit for those of us who want to build our own (click here):

Originally posted by tkg
OK calling all tinkerers. For those of you who can't wait to shock yourselfs silly, Ch has put togather a built and tested CDI circut and a coil for $45.
You will also need a magnet, hall sensor and a high voltage lead and plug cap.


Dr. Crash 05-09-2003 08:33 PM

Scratch Built Ignition???
1 Attachment(s)
Here are pictures of Jerry Howell ignition and Homelite 45 conversion.

Dr. Crash 05-09-2003 08:38 PM

Scratch Built Ignition???
1 Attachment(s)
Can't seem to get but one attachment at a time.

Here is the Ignition.


strato911 05-09-2003 11:28 PM

Kit questions

Originally posted by Dr. Crash
Here are pictures of Jerry Howell ignition and Homelite 45 conversion.
Looks like a pretty simple setup. How does it run?
Will it hand flip?
Have you had a chance to measure the current load on the battery?
What is the input voltage range?
Does the kit come as a bunch of loose parts or are they already soldered to the circuit board?
Does the kit include the Hall effect sensor?

Sorry to ask so many ???'s... ;)

Dr. Crash 05-09-2003 11:45 PM

Scratch Built Ignition???
So far it is doing just fine. Haven't measured the current load, but it should be pretty small. Hand flips just fine on the homelite 45 witht he timing set at 28 degrees. Coil is running cool, which is good. The kit comes with the hall sensor and the magnet. All the components for the circuit board have to be soldered, but the instructions are pretty good.


roadhor 05-10-2003 02:39 AM

Scratch Built Ignition???
Dr. Crash : It looks like you're not running a shielded plug wire & boot. Is this true & if so have you had any trouble with interference ? How did you figure out how much dwell time you needed on your pickup ? By the way that looks like a first class job on the conversion , what size prop does it spin ? Sorry for all the questions , thanks a ton for the pictures. That really helps alot. Thanks, Rob

Dr. Crash 05-11-2003 12:10 AM

Scratch Built Ignition???
You are correct, I'm not running a shielded wire, but I am running a carbon core wire and a resistor plug. The Bolly prop, 20X8 is turning 7200 RPM.

As far as the dwell time, I think anything around a 1" diameter will do fine. If the dwell time is too short you want get a spark, if it's too long you will use more current and warm up the coil.


captinjohn 05-11-2003 03:00 AM

homebuilt ignition
Dr. Crash: Nice job. Is that a model "S" ignition coil? Also...how did you attach the carbon core spark plug wire to coil. Is there a solid wire part way up into the cabon core??? Thanks Captinjohn

h82crash 05-11-2003 04:49 AM

Scratch Built Ignition???
I understand the whole dwell time with the magnet now, and I agree, the difference is nil.

Dr. Crash 05-11-2003 10:18 AM

Scratch Built Ignition???

Yes to both questions. The wire was tinned with solder to make insertion easier.


captinjohn 05-16-2003 11:56 PM

power consumption
Dr Crash: How many minutes will this system run on say a 500 MAH battery?? Is plug gap critical? Thanks John

Dr. Crash 05-17-2003 01:19 AM

Scratch Built Ignition???
The plug gap doesn't seem to be critical at all. That coil throws a pretty good spark. This outfit is supposed to be pretty efficient, I can only tell you that I'm using a 1400 MAH battery pack and don't really know how long it would last.

mikenlapaz 05-17-2003 04:48 AM

Spark plug modifcation
An idea to maximize the current at the plug. Have not tried yet but seems reasonable.


captinjohn 05-17-2003 12:53 PM

spark plug mod
I remember when Dario printed the article on spark plug mods. He also was the guy who had a over-balance job he done on engines. My cousin at the time sent his Quadra to him. When he got it back it really run a lot smoother. Thanks Capt,n

captinjohn 05-17-2003 01:02 PM

DR. Crash: In post #25 you have a photo of your ignition. Do you plan to place coil and circut board in some kind of box? If so is metal (like aluminum) better than plastic too keep radio glitches to a minimum? By the way....have you flew a plane with this system....with no glitches? Thanks Capt,n

Dr. Crash 05-17-2003 03:02 PM

Scratch Built Ignition???
I do plan to put the ignition in an aluminum box to help cut down on interference. No, I haven't flown with the ignition yet, but plan to do so soon. I will post the results.


cu. in. 05-17-2003 05:04 PM

Scratch Built Ignition???
Dr. Crash,

Is your aluminum box an "ounce-of-prevention" move, or have you actually experienced interference while running the engine?

It would save time if the box could be eliminated.



Dr. Crash 05-17-2003 07:26 PM

Scratch Built Ignition???
I may try it without the "box". It may not need it.


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