ign woes

An open forum to ask members questions about old time spark ignition engines.

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ign woes

Postby collie » Tue Jun 28, 2005 11:29 pm

Can anyone tell me just what causes radio interefence in ign systems?
Is it the plug firing,the elec current in the plug lead,the metal points banging together,the elect field in the coil?How do I stop the interefence?Tried Fm,PPM,PCM,resistors every where,still get the ocasional radio hit,high speed duration models wont survive this glitch. HELP
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Postby loucrane » Wed Jun 29, 2005 12:33 am

collie,

I'm no expert, but the coil field collapse, the hi-voltage lead to the plug, and the plug spark are all pretty intense EM spectrum emitters.

Resistor plug leads help in some cases, according to instructions I've seen. (I prefer control-line - it is directly tactile. No RX glitches.) Possibly orienting the coil differently, or finding a way to shield the 'hot' spark pieces from the antenna, RX and servo wiring.

There must be a way, as there are a lot of spark R/C models flying...
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Postby Frank Klenk » Wed Jun 29, 2005 6:22 pm

Lou is right, these all cause problems. I put all my ignition stuff (coil etc) as far forward as possible. Then I mount the receiver as far rearward as possible. You must keep these components isolated. I also use the transistorized switching system for the points, they work well. Also check your spark plug wire, make sure the insulation is intact, if not replace it. Hope this helps.

Frank :)
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Ign Woes

Postby Ken McClenahan » Thu Jun 30, 2005 8:27 pm

From an electrical engineer (I are one): the problem is cuased by the spark that is created every time the points are opened. The solution is to use a capacitor (the old fashioned word was condensor) wired across the points. The capacitor short circuits the high frequency components of the arc between the contacts.

All of the automotive point sets used to include a capacitor. When you bought a set of points, you got a capacitor.

Make sure that you have a capacitor wired across the points.

Problem: capacitors can fail. Check by connecting the capacitor to an ohmmeter. If the capacitor is good, the meter will surge to low resistance and then the resistance will rapidly increase to infinity.

Using resistor type spark plugs and resistor spark plug leads also help by limiting the spark current and damping the spark oscillations.
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Postby Frank Klenk » Fri Jul 01, 2005 7:44 am

Ken
You're right, point arc causes interference. With the transistor setup I use the points just open and close the circuit and the transistor now handles the load, hence no more arc at the points. Another plus with this setup is points last a lot longer.

Frank
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