Antique

My Feedback: (4)

I KNOW it's a resistor plug, no arguement there..And yes, using a non resistor plug will cause radio interference..
BUT..It takes a stronger spark to go through the resistor, so why put one in a shielded circuit ?
My UNshielded ignitions take less than 200 MA at ANY rpm...A small 500 MA battery will run the engine for over 2 hours...You don't NEED a big heavy battery for the ignition...
There are thousands of these out there after 18 years...
I have been converting G26s since they first appeared...They use Champion resistor spark plug and a rubber plug boot..NO one has needed a resistor cap or shielded wire...
good thing, no one makes a shielded cap for the RZ7C spark plug....C&H has a spacer that works with that spark plug and a Bosch cap.....
I put a CM6 spark plug and a 3W cap on one to make the engine shorter...Lost some rpm, the shorter thread on the CM6 made the compression less...Spot faced the cylinder to put the plug flush on the inside of the coumbusiton chamber, got the rpm back....
I like the K.I.S.S approach...Or
If it ain't broke, don't fix it

Howie-RCU

You are confusing two separate issues. The screening doesn't negate the need for a resistor. In some form or another, every ignition system we use in RC has some resistance in the HT circuit.

"BUT..It takes a stronger spark to go through the resistor, so why put one in a shielded circuit ? "

This is simply not correct. The resistor takes very little energy from the spark. Typically it is less than 10%. Its primary purpose is to reduce the dV/dT of the arc voltage. Lower dV/dT means lower harmonic content. (Less radiation and lowers the frequency of the radiation.)

The screen is not some magic wall that stops all EMI escaping the ignition system. You can't make a noisy system perfect by enclosing it in a screen. Take one of your ignitions and put a non-resistive spark plug in the engine. No amount of screening you add is going to make it usable for RC.

The primary purpose of the braid is to make the voltage potential (at RF frequencies) of the ignition box and the engine as close to the same as possible. This is why the earthing is in the form of a braid. A braid has lots of surface area so its RF impedance is low.

There are many other factors involved in EMI. Some of the ignition systems I have tested have more radiated noise from the flyback converter than the HT circuit.

“I put a CM6 spark plug and a 3W cap on one to make the engine shorter...Lost some rpm, the shorter thread on the CM6 made the compression less...Spot faced the cylinder to put the plug flush on the inside of the coumbusiton chamber, got the rpm back....�

I too have done similar conversions. The loss in RPM is not related to compression. Having the CM6 stuck up the threaded hole gives you a very retarded flame front. I fixed it the same way you did and put the CM6 electrode down into the combustion chamber. Life would be easier if someone made a spark plug with the same thread length of an RCJ7Y and a top the same as a CM6.[8D]

dirtybird

My Feedback: (5)

Although I had calculas it was 50 years ago. I don't remember what dv/dt means exactly. I think what it means is the frequency of the harmonic content of the radiated energy is limited to below the frequency of the control system. That would mean we should only need a resistor plug as works with most magneto systems (Zonoah).
I have found this is not the case. I have a C&H system that was designed to use a shielded lead and a non resistor plug (1/4x32). I replaced the shielded lead with a non shielded solid core wire and a cap with built in resistor and a resistor spark plug(14 mm). It ran the engine fine but wiped out the radio.
I then obtained a shielded lead with a bosche cap from C&H and installed it. I now don't have enough spark to run the engine.
Apparently the electronics need to be designed to fit the shielding system to be used.

rc_cdi

bcchi

The CH ignition uses a carbon resister spark plug wire with the full shielded metal cap for the 10MM-cm6 spark plug.This is the reason for no resistor. The CH system with the Bosch cap which has a built in resister uses a stranded wire core. Always use a Resister plug if one is available.NGK does make a 10 MM resister plug a CMR6A . This is a 5/8 hex plug the top the same as the BPMR6F The thread is 10MM long compared to the CM 6 8MM. I have used them in 3/W engines with one added copper gasket. The CMR6A is a gasket type plug.

bcchi

bcchi

The CH ignition module for the Bosch cap has a higher currant drain then for the 1/4 x 32 spark . If you install a Bosch cap and lead on a CH with out the Bosch you would need to up the currant drain by changing the bias resister. You are correct the Ign module must be taylored for the shielding and spark plug cap used. Also CH uses a stranded copper wire core lead for the Bosch not the resister lead used on most of other systems

BCCHI

dirtybird

My Feedback: (5)

Interesting.
It would be helpful if you mention this when you sell the Bosch cap.
You would also need to point out which resistor is the bias resistor that needs to be changed and what to change it to.

bcchi

We try and tell every one that we sell a Bosch not install on a system with the carbon core resister wire. This is also some where in our instructions but I cannot say for sure right now where it is. Will take a picture of circuit on what ressiter to change and what to change to.


bcchi

dammud

D= Delta=change
V=voltage
T=Time

DV/DT (change in voltage divided by change in time) or the steepness of the voltage rise which is the factor that influences harmonics

Actualy braid is not as good of an RF barrier as a solid shield, but is more flexible.

Ken

captinjohn

bcchi: Is the letters for Bill Carpenter at CH Ignition....right? Would it be correct to say...If you use a cap with built in resistor in combination with a braided resistor wire...the total resistance would be to much? or not correct for that ignition? Thanks, Capt,n