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Ignition system trouble shooting

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Old 05-24-2012, 07:07 AM
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DL8698
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Default Ignition system trouble shooting

In Sticky: [FAQ] Newbie to Gas General Information, Post #23, it says to check the ignition lead cap by powering the ignition module with the plug not necessarily grounded to the engine. However, I have read somewhere that sending the high voltage discharge to the spark plug which is not grounded to the engine will destroy the ignition module. Is that true?
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Old 05-24-2012, 07:19 AM
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Default RE: Ignition system trouble shooting

The plug is in the boot. With Rcexl ignitions the braided wire shield is earth return, so this ignition can be safely turned on.
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Old 05-24-2012, 07:22 AM
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Default RE: Ignition system trouble shooting

OK, what you do not want to do is try to get a long length spark out of the ignition system. As that quickly causes the windings inside the ignition coil to go bad. But many ignition systems use a metal spark plug cap and it makes contact with the spark plug case and also the shielded braid wire on the spark plug wire. They also may have a small coil spring in the spark plug cap to also grab and hold the spark plug cap onto the spark plug too. Thus the return path or ground is through the spark plug wire.
So you should be able to pull the spark plug and plug it into the spark plug cap and with the ignition system powered up, rotate the propeller to see a spark on the spark plug. It is a small spark so doing it with less light and in the shade is needed. You can also just rotate the crankshaft so the magnet passes by the sensor too.

Now if you have a ignition system that uses a unshielded spark plug wire, then you need to ensure the spark plug body is grounded when you go to check for a spark.


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Old 05-24-2012, 10:55 AM
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Default RE: Ignition system trouble shooting

The old style CH ignitions, with the rubber boot that I have, the wire braid shields are all grounded at the cap. And if they are not grounded, the spark is likely to jump somewhere else and cause trouble. I have one CH with a shielded cap (Bosch-Mercedes Benz) but the shield grounds at the spark plug, not the ignition module.

Even on a RCEXL ignition, if the cap comes loose while the ignition is running (sparking), The spark will jump inside the sensor instead and take it out.
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Old 05-24-2012, 10:59 AM
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Default RE: Ignition system trouble shooting

So the spark return path is the braided shield wire? I'm sure it works but I can't figure out why the high voltage high freq pulses passing through the shield won't emit emf interference, which the braided shield is meant to prevent.
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Old 05-24-2012, 11:12 AM
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Default RE: Ignition system trouble shooting


Quote:
ORIGINAL: DL8698

So the spark return path is the braided shield wire? I'm sure it works but I can't figure out why the high voltage high freq pulses passing through the shield won't emit emf interference, which the braided shield is meant to prevent.
Because its ground. Ground does not emit very well.
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Old 05-24-2012, 01:19 PM
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Default RE: Ignition system trouble shooting

Right...did you ever see lightning travel from earth upwards??? No the high voltage seeks the ground. HA ~ and thats the rest of the story!
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Old 05-24-2012, 02:46 PM
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Default RE: Ignition system trouble shooting


Quote:
ORIGINAL: captinjohn

Right...did you ever see lightning travel from earth upwards??? No the high voltage seeks the ground. HA ~ and thats the rest of the story! [img][/img]

Does lightning strike from the sky down, or the ground up?

The answer is both. Cloud-to-ground lightning comes from the sky down, but the part you see comes from the ground up. A typical cloud-to-ground flash lowers a path of negative electricity (that we cannot see) towards the ground in a series of spurts. Objects on the ground generally have a positive charge. Since opposites attract, an upward streamer is sent out from the object about to be struck. When these two paths meet, a return stroke zips back up to the sky. It is the return stroke that produces the visible flash, but it all happens so fast - in about one-millionth of a second - so the human eye doesn't see the actual formation of the stroke.

From [link]http://www.nssl.noaa.gov/faq/faq_ltg.php[/link]

Now where's the popcorn - It's all your fault John
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Old 05-24-2012, 05:31 PM
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Default RE: Ignition system trouble shooting


Quote:
ORIGINAL: aussiesteve


Does lightning strike from the sky down, or the ground up?

The answer is both. Cloud-to-ground lightning comes from the sky down, but the part you see comes from the ground up. A typical cloud-to-ground flash lowers a path of negative electricity (that we cannot see) towards the ground in a series of spurts. Objects on the ground generally have a positive charge. Since opposites attract, an upward streamer is sent out from the object about to be struck. When these two paths meet, a return stroke zips back up to the sky. It is the return stroke that produces the visible flash, but it all happens so fast - in about one-millionth of a second - so the human eye doesn't see the actual formation of the stroke.

From [link]http://www.nssl.noaa.gov/faq/faq_ltg.php[/link]

Now where's the popcorn - It's all your fault John
an upward streamer is sent out from the object about to be struck

I have read advice that if you happen to be in an open area where there is lightning activity nearby, and, you feel a tingling sensation in your body and your hair rises up (like what you may have seen with people who demonstrate effect of static electricity on the human body), this upward (I think it's downward) streamer is what you are feeling, and means YOU are the object about to be struck. You are advised to ASAP throw yourself to the ground as flat as possible or roll your body into a ball on the ground. The hope is that you now make yourself a less "attractive" target and the lightning strikes something else.

Read more: www.comportone.com/cpo/weather/lightng.htm

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Old 05-24-2012, 07:31 PM
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Default RE: Ignition system trouble shooting

Typically, when lightning strikes something on the ground, the object that is struck sends a faint channel upward that joins the downward developing flash and creates the connection to the ground. Taller objects are more likely than shorter objects to produce the upward channel. But it is also possible that something that locally affects the ability of the ground to conduct electricity (such as the salt or moisture content of the ground at the time, the presence or absence of rock, standing water, pipes or other metal objects in the ground), the terrain shape, the shape of leaves or twigs, or something else might make a particular location more likely than another nearby location to be struck.

Like Antique says...do not asume anything. I did and was wrong! Lightning did hit a tree in my back yard...a tall white pine...it got split down the center and crashed to the ground. Now more work too do. This is not a good RC season so far...... Capt,n

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Old 05-25-2012, 10:45 PM
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Default RE: Ignition system trouble shooting

I've had 2 close calls with lightning.

1.
Long, long,....long ago, when technology was still quite low tech, I was changing an engine on a (full size) B707, with the help of a mobile crane, in the open tarmac. It was not really raining heavily, just drizzling, with a very dark overcast sky. A few of us were standing on the engine stand, with the crane cable attached to the engine stand, and pointed straight into the sky. This steel engine stand supports the engine with the crane once the engine mount bolts are disconnected.

Suddenly all of us felt an electric shock, and we all jumped off the engine stand, actually we fell off. Apparently, a small bolt of lightning had hit the top of the crane, and fortunately I think most of the electric current went thru the aircraft instead of us, since we did not really have a direct connection with any earth. We did not suffer any after effects from the jolt. Then it was "down tools" till the storm blew over.

2.
I used to live in a 25 storey flat (apartment block) on the top floor. Whenever there was a thunderstorm I just loved to stand at my window and watch the rain and lightning flashing all over.

Just above my head, a bit to one side, at the extreme top corner of the flat was a lightning conductor rod. Suddenly, there was a loud noise, similar to the sound that electric arc welding makes, and a whole shower of sparks fell in front of me. It appeared that lightning had struck the lightning conductor rod. Needless to say, I hurriedly closed the window and went deep into the safety of my room.

Strange thing is, on both occasions, I did not remember hearing the thunder itself. Just a sound similar to that made by a big spark.

It has been said that Singapore is one of the most lightning struck places in the world. Not sure how true that is.

Be careful when there is lightning activity around. Lightning can strike up to 5 or more KM away from where the thundercloud is. I always stop flying the moment I spot a lightning bolt anywhere in the sky, no matter how far away it looks or how clear my part of the sky is.
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