Scratch Built Ignition???
 

My understanding was that the Hall affect transistor was on all the time,charging up the capacitor, and when the magnet goes by it, it switches off, discharging the capacitor and firing the plug. when it goes off the magnet,it switches back on again,charging up the capacitor again. Correct me if I'm wrong.

Scratch Built Ignition???
 

Flypaper ; That sounds better to me , If it relied on the dwell time to charge , then at 7000 RPM that would be very little time to charge a coil sufficiently. Any experts out there care to comment. Later ,Rob

Scratch Built Ignition???
 

I don't know about the Howell circuit, but the CH units I have fire when the magnet leaves the hall switch.

Scratch Built Ignition???
 

I agree with Flypaper, that's how I think it works, I just don't know enough about the system to debate it.

what if....
 

question

couldnt you program a PIC chip to advance and retard the timing for high and low RPM's? maybe based on a pulse timing from the hall effect sensor. seems like that would be a great way to vary the timing.

it looks to me, and im not an electrical engineer YET, but all this is a cap gets charged and discharged via a transistor with a hall sensor that does the triggering. if you are using it on engines like the ryobi even CH says you dont need to change the timing at different RPM's.

Sparks
 

The TIM-6 is not a CDI it is a Kettering type ignition with a transister trigger instead of points. Dwell time is important for this type of ignition. Yes the sparks run down at high speeds.
The CH unit is a true CDI unit, however even it will run out of sparks at a very high rpm. Recharge time of the capicator ya know.

IGNITION
 

TKG: What are the pros and cons of each system .... kettering vs CDI ...... Thanks Capt,n

Scratch Built Ignition???
 

Output vs input.
CDI gives you more output for the same input curent.
As long as your plug is clean, one system has very little advantage over the other.
CDI's advantage starts to show up when the plug is fouled

Scratch Built Ignition???
 

Another member was looking into the pic chip idea. Looks like a great thing to try. The ignition curve could be tailored to suit the engine and flying style.

tkg, could something like this be added to a non-synchrspark C&H unit (kind of like the add on synchrospark)?

Scratch Built Ignition???
 

Thank You all for the GREAT responses. I never knew there was this much information on this subject. I think I am going to be looking at the Jerry Howell ignition for my gasser bipe and ryobi project. Thanks again!

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

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

Darin

ignitions
 

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!!!!! :) :) :)

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)

Scratch Built Ignition???
 

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

motorbike.....Hummm!!!!

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,
AV8TOR

A DWELL DRAWING FOR YOU
 

Ah well, went ahead and made a drawing to clarify this anyway. Here you are:





Thanks,

AV8TOR

Scratch Built Ignition???
 

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

Scratch Built Ignition???
 

Hi,

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,
Thanks,
AV8TOR

ignitions
 

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

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,

AV8TOR

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,
AV8TOR

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...

CH Ignition with Echo coil...
 

Hi,

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,
AV8TOR

coil
 

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

Scratch Built Ignition???
 

here is a pic of my coil that I use and it works well

Scratch Built Ignition???
 

here is a pic of my coil that I use and it works well

COIL
 

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

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

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

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

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.

Re: ignition...home Built
 

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.

Scratch Built Ignition???
 

Hi
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
Jose

Scratch Built Ignition???
 

av8tor1977

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


john

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!!

john

Scratch Built Ignition???
 

Browsing through the RC Modeler archive index, I found that they published an article on building a CD ignition system in the 12/80 issue. Anyone have that issue?

RE: Scratch Built Ignition???
 

I have built the TIM-6 ignition and installed it on a 18cc weedeater engine. The ignition works great. Wish I could say the same for this engine. (really weak!) I calculated the dwell angle using the formula from (av8tor1977)'s post in this thread. I had to mount the magnet as close to the shaft as I could to come close to the dwell angle. I calculated at 7500 RPM's I did notice that with a smaller prop that as I approched 8000 RPMS the engine started missing like it had a rev limiter. (Not enough dwell?) I have ran the engine over an hour on a 1200mha battery, don't really know how long it will run on a single charge? I think I will install the ignition on a ryobi or Mac32 and see how it does. May also try two magnets to increase the dwell angle, but don't think I will really want to exceed 7500 RPM's anyway.

RE: Scratch Built Ignition???
 

Congrats on the ignition system. Sounds like you are running out of dwell near 8000 rpms as you suspected. It will start missing like you said when it doesn't have enough dwell for the rpms occurring. More dwell will increase your battery drain, but that doesn't sound like a problem if you're getting an hour or more out of a battery.

You won't believe the difference in power if you go to the Mac 32!!

Oh, and someone asked if that's me in my avatar... Nope, that's my beautiful wife and I'm a lucky dog!

Take care,
av8tor

RE: Scratch Built Ignition???
 

Hi Sukhoi_One,

AFAIK, the Jerry Howell (JH) ignition has fixed ignition timing unlike the CH ignition that has automatic advance/retard. It sounds like you have found an advance angle that allows the engine to start easily, but the angle may be too retarded at the top end to produce good power. This could be one reason for the "really weak" performance. Of course, the engine itself is a factor, as mentioned by av8tor1977.

You may want to check the advance angle on the JH ignition. As I recall, the CH ignition, when properly set, changes the advance angle from around 4 degrees when starting, to 28 degrees at top end. If your advance angle is significantly less than 28 degrees, then the top end power could be suffering.

Also, what coil did you use?

Thanks,

Bruce

RE: Scratch Built Ignition???
 

The 18cc Featherlite is a pretty lame engine no matter whos ignition is used. The engine is small enough to be run at full advance with out any timing control. So just crank up the timing to a full 30 deg BTDC and go for it. The engine may idle a little faster, but thats what the throttle is for.
I think the best we ever got one to run was 7600 on a 14x8. The lower end is the same as the 21 or 24cc, so the easiest hopup is more cubic inches.