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

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.


Flypaper 2 05-18-2003 01:22 AM

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.

roadhor 05-18-2003 01:43 AM

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

wvarn1957 05-18-2003 02:23 AM

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.

h82crash 05-18-2003 02:45 AM

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.

buckeyes1997 05-20-2003 04:08 AM

what if....

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.

tkg 05-20-2003 01:27 PM

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.

captinjohn 05-20-2003 01:37 PM

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

tkg 05-20-2003 11:33 PM

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

bdtsr 05-21-2003 12:25 AM

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)?

torquerollin 05-21-2003 02:39 AM

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!

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