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

roadhor 05-21-2003 05:24 AM

Scratch Built Ignition???
tkg : Could you tell us more about how to get the C&H builders kit ? I'm very interested , I've got a 2.4 Sachs I want to build one for. Thanks for all the great advise. Rob

bn120 05-22-2003 03:38 AM

Scratch Built Ignition???
I talked to a enginer buddy of mine and he told me he will make a slope advanced system that will work on any hall effect sw. and you will be able to adjust the amount of advance you want by moving a jumper wire, says it will work on ch ign. also.I will keep you posted when we get it up and running, he says he can sell them for about $20.00.this is just for the programed slope chip and board


captinjohn 05-22-2003 11:47 AM

Isn,t computers neat!!! Sooner or later we will all have a real good but inexpensive ignition system to put on about any single cyl engine!!!!! :) :) :)

jmj 05-23-2003 08:47 PM

Scratch Built Ignition???
There is a good PIC based project at: http://perso.wanadoo.fr/transmic/gb1684.htm

This ignition does have automatic (editable) advance.
This ignition is made for use in a motorbike, and cannot be used in a plane as is, but the PIC code would be the same...

For a scematic of the CDI, have a look at the RCM article mentioned earlyer in this threed. It is based on a free running oscillator, and has a very low part count. It is almost identical to a CH ignition without advance.

I am converting a weedeater 21cc, and will try to put all this toghether..
If it works, i will post something on my web; http://home.online.no/~jon-mj

(Sorry, but it is in norwegian, will try to make some english content soon)

mikenlapaz 05-24-2003 12:40 AM

Scratch Built Ignition???
Good luck and keep this post up-date on your progress, please. I'm sure there is more interest than you may imagine.


av8tor1977 06-01-2003 04:56 PM

More on dwell...
Hi everyone,

I've done some more research on the dwell thing. In a Kettering ignition, which is a non cd type ignition with points or a hall effect/transistor swithing circuit instead of points, dwell is very important. If any of you remember setting the points on the older cars, you remember the setting needed to be correct. This was because that directly affected dwell.

Dwell is the time that the coil is charged with currect. This time must be in the two millisecond range, but don't worry about that at the moment. By the theory of induction, when the current to the coil stops, the magnetic field collapses, and that is when the spark occurs. In the Kettering type ignition, the Hall Effect sensor is "on", and the coil receiving current when the magnet is crossing the sensor. When the magnet leaves the sensor, it turns off, the magnetic field collapses, and the spark occurs. What you want is sufficient time to completely charge the ignition coil, but no more as more time just wastes power, heats things up, etc. This is your "dwell" time.

Now, how to figure out the dwell time in our applications? It can be done completely with math, but there is a simple way. For a two stroke engine the formula is MAX INTENDED RPM X .0075 = DWELL IN DEGREES. Now the trick is to figure out how to have the Hall Effect sensor turned on by having the magnet under it for this amount of "time" or degrees.

You can draw a straight line on a piece of paper, and then with a protractor, draw another line at the dwell degree number away from the first. At the intersection of these two lines, draw a circle of your hub diameter where you are going to mount your magnet, using the intersection as the center point. Now measure where the circle intersects the angle lines. This is how long the magnet must be passing by the sensor to get the correct dwell. You will probably see that it will take more than one magnet to get the correct dwell time. The smaller the hub, the less distance will be needed to create the same dwell. A large hub at high rpms will take a number of magnets to get your dwell time.

If this is confusing, let me know and I will try to come up with a drawing to illustrate.

Thanks, and hope this helps,

av8tor1977 06-01-2003 05:57 PM

1 Attachment(s)
Ah well, went ahead and made a drawing to clarify this anyway. Here you are:



roadhor 06-02-2003 12:29 AM

Scratch Built Ignition???
So what's the difference between a CD ignition & a Kettering ignition ? Thanks for the help , Rob

av8tor1977 06-02-2003 12:53 AM

Scratch Built Ignition???

Well, quite a bit actually. The problem with points was that they had to switch a good bit of current very rapidly and would thus wear out. All 12 volt car systems I'm aware of actually started on 12 volts, then ran through a resistor to cut the power down to 6 volts for running, in an effort to make the points last longer. Eventually, someone figured out that they could design a transistor switching circuit to turn the power off and on like the points, but without the wear and tear. This could be done with a magnetic sensor setup, an optical setup using an LED, or with the Hall Effect sensor, and a simple transistor circuit. This is the Kettering system, how so ever it is switched.

It didn't take them long to figure from there, that this could be taken further to overcome a limitation of points; that is that they didn't like to switch a lot of power without burning up too quickly. More in is more out of the coil, so by using a capacitor circuit along with the aforementioned sensor and transistor switching, they could step up the current through the coil and get a hotter spark. This capacitor is charged, and circuited to discharge through the coil at a higher current and a hotter spark is the end result. The actual benefit of this is generally seen in poor conditions such as a fouled plug, etc. Then the CD ignition definitely out performs the other systems.

As far as I know, the CD systems are not dwell sensitive like the Kettering systems. I will be talking to CH ignitions tomorrow, and I'm going to ask them about this. I'll let you all know if I find out anything new.

By the way; with any of these electronic ignitions systems, a person could rig up two Hall Effect sensors for different timing through a switch. You would not have the smooth transition of the variable timing systems, but it might be the answer for some whom are having a problem with the prop biting them, and would like to just retard the ignition to start the engine.

Hope this all helps,

captinjohn 06-02-2003 01:53 AM

av8tor: You explained that all very good.....keep up the good input.....Thanks Captinjohn :)

av8tor1977 06-02-2003 04:20 AM

Scratch Built Ignition???
Thanks for the compliment. Everyone says I should have been a teacher! All my life I have really loved to dive into things of interest to me and learn all about them. People say I am good at explaining things so that almost anyone can understand. Hope that's true.

Thanks again,


av8tor1977 06-02-2003 04:12 PM

Scratch Built Ignition???
Ok guys, I talked to Ch Ignitions just now, and they said that the dwell time is not critical on their systems. Only the magnet supplied is sufficient to trigger the CD type system, as I thought. All our dwell discussion is relevant to non CD systems only.

I ordered their ignition kit, and he did say that he did not think my stock ignition coil from my little Echo 16cc engine will work with their system. I am a little low on bucks so I'm going to try my coil, and I'll let you know if it works. By the way, he gave me a discount on the ignition circuit board at $31.95 instead of the $39.95 listed on their website.

Thanks and take care,

strato911 07-30-2003 10:14 PM

Update please
AV8TOR - can you provide an update please? How well did the CH ignition circuit work (if at all) using the stock coil from your Echo?

Dr. Crash - how's about an update from you too? You said you would post after you flew using the Tim-6...

av8tor1977 07-31-2003 03:45 PM

CH Ignition with Echo coil...

My setup with the CH Ignition "Kit" used along with the Echo/Kioritz original coil is working great. The kit from CH isn't really a "kit" as it comes with the circuit board assembled.

Now, this Kioritz had a small coil mounted separate from the magneto. It is not an iron core coil like most magneto coils. I have not been able to find any other engines, including other Kioritz's, with this coil. I have heard that some motorcycles came with these small electronic ignition coils, and that you can scrounge them up used at motorcycle shops, but I have not verified this.

Take care,

captinjohn 07-31-2003 07:14 PM

av8tor....can you post a photo of that coil???? Thanks Capt,n

KenLambert 08-02-2003 02:14 PM

Scratch Built Ignition???
here is a pic of my coil that I use and it works well

KenLambert 08-02-2003 02:27 PM

Scratch Built Ignition???
1 Attachment(s)
here is a pic of my coil that I use and it works well

captinjohn 08-02-2003 03:01 PM

Ken....what engine was your coil on?? Thanks Capt,n

KenLambert 08-02-2003 10:50 PM

Scratch Built Ignition???
either a husky or koritz cant remember,I have cut up several of each and this is the only coil like it I have ran across

Antique 08-03-2003 03:39 AM

Scratch Built Ignition???
Husky uses a coil like that, don't know which size..I had one here, worked well, tried to buy another, very $$$$$ from Husky....
C&H sells coils for models, about $20.00, none better :D

captinjohn 08-26-2003 01:51 PM

ignition...home Built
So at this point, if a person used Jerry Harwells cicruit board and a CH coil....would that be a good combination???? Thanks Captinjohn

Don Yarbro 09-01-2003 03:42 AM

Scratch Built Ignition???
The difference between the TIM 6 and the CH unit is that on the Tim 6 only the battery voltage is applied to the coil. In the CH unit there is a circuit that boosts the battery voltage up in the hundreds of volts and that goes to the coil for a much hotter spark. This is called Capacitive Discharge and is the system used on modern cars. Either should work OK but the CH circuitry should be better. Aso CH has a device that will automatically retard the spark for starting with out any mechanical retarding system. In RCM in the 80's there was an article for building a unit like the CH basic unit.

tkg 09-02-2003 02:42 AM

Re: ignition...home Built

Originally posted by captinjohn
So at this point, if a person used Jerry Harwells cicruit board and a CH coil....would that be a good combination???? Thanks Captinjohn
NOT a good idea.
The CH coil is for CDI not Kettering. If you use it with points/TIM-6 it will draw way to much current.
A CDI coil has a different winding ratio between primary and secondary.
Think of it as a transformer instead of a saturation coil.

fokker38cc 09-02-2003 11:02 AM

Scratch Built Ignition???
I am using motorcycle high voltage coil in my CDI.
I am buying new one but also have used from my motorcycle repair shop. When I take one used I check with the CDI and they work.
Check coils from small mopeds, I have mine from Honda 600 off road bike ( I believe the model is XT600, other model is Honda Transalp).
I have coils with cable screwed in the coil and other model with cable melted from factory , this type is bad when you need replace the cable.
Good luck

blue62 09-02-2003 11:53 AM

Scratch Built Ignition???

is that a pic of you in that avatar? just wonderin.......


btw i am following this with gr8 interest as i have a ryobi that i have cut up but i need a better spark system for!

i also want to build a tail strobe for my plane. i have a flash unit out of a camera and it works gr8 for the strobe but you have to touch 2 wires together to get it to trigger!! one is B+ the other is the "ground" side of the tube! so i am in a fix to figure it out! yes i know you can just go buy one but heck where is the fun in that? or the adventure!!


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