Just wondering if any one is using a shielded spark wire (automotive plugs) with PMAG and any experience/feed back as well as the level of noise reduction. I have been using the PMAG provided spark plug wires and suspect some RF noise though I have taken extra steps to separate them and not touching any metal part to the extend possible.
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shielded spark wire for PMAG
- Thread starter Bavafa
- Start date
In automotive applications (like the Pmag setup), interference is reduced by using 5K resistors in the plugs (the "R" suffix means resistor on most plug brands) and therefore do not need shielded leads/wires, like non-resistor aviation plugs.
If you are getting interference from your Pmag ignition, it is likely caused by using non-resistor plugs or some other problem with your installation. Did you check the gap on your plugs when you installed them?
Larry
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I have been using the NGK 3961 BR8ES with the recommended gap of .31-.35. But all the instructions warns of some possible RF noise if the wires are not all separate or touching metal parts.
Separating wires is a good practice in general. You can find separators at any autoparts store. However, I use EI (not Pmag) and my wires make contact with each other in many areas. I have never had interference issues. I use a standard inductive coil that I believe is the same design as the pmag. Good quality wires have more than enough dielectric resistance to avoid jumping spark energy when the plug gaps are kept in a reasonable range. The plug gap sets the overall resistance. Large gaps produce greater energy, but their larger resistance also encourages the energy to find an easier path to ground.
Avoiding ground contact is also a good idea. However, a properly setup installation with good wires should not jump a spark to ground. However, over time you can eventually burn through the insulation, as the energy tries to jump that point to ground over time (millions of cycles can eventually do this). However, there are MANY auto installations (non OEM) that are problem free with the wires laying on the intake manifold. I don't believe this inherently creates RF, though it can over an extended period of time as the wire breaks down in that area.
Just some thoughts here. I would extend your search for the RF source beyond just ignition leads.
Larry
Delta Bravo
Active Member
My ignition noise from my single EMAG turned out to be the screw on tips on my auto spark plugs. They loosened up with time. As per Emagair I used a small amount of red thread lock when I tightened them back up and the problem was solved. Next plug change I will ensure that I use solid tip plugs.
This creates additional resistance and therefore problems. I have also heard folks have problems with the ignition leads loosening up at the Pmag itself (this can also create additional resistance and problems.
Larry
petehowell
Well Known Member
"Jimmy" the thread
You can also slightly deform the threads of the screw tips with a pliers to lock them on. This works well if you only have this type plug available (or you get a killer on-line deal on them).
You can also slightly deform the threads of the screw tips with a pliers to lock them on. This works well if you only have this type plug available (or you get a killer on-line deal on them).
In my case, I am using the NGK spark plugs with the solid tip and have ensured firm and good connections on both sides. I have also used dielectric grease on the inside of the boots as recommended. I do hear a faint tic tic spark noise in my headset on low RPM. This goes away with a higher RPM (1300-1400+) as the interval gets shorter and becomes undetectable. But also have had a couple of times that my EGT spikes for a tenth of second for nearly 200 degree which seems to be as a result of some RF noise. The issue of jump on EGT did not exist till recently that I have tidy up the spark plug wires. This could be a pure coincidence but if I can get a different set of wires the eliminate all of this, it would make me happier. Again, I have taken care to the extend possible to make sure all spark plug wires are separated and not crossing over each other.
Toobuilder
Well Known Member
Some wires are very finicky when it comes to fabrication technique. I've found the 8mm stuff from Emagair to be pretty forgiving - Just bend the core over and crimp the connector - but I have nicked (or broken) the wrap on the core on other wires and it has shown up as RF noise.
Given your response, I would be looking for a wire with a defect (cracked insulation, broken internal core, etc.) or possibly your movement placed an ignition wire in direct contact with another, sensitive wire that is feeding the noise into your avionics. The ignition wires do get a magnetic field around them that builds and collapses. The collapsing magnetic field is energy and can be absorbed by another wire that it too close. Not sure this is technically RF, but it will appear and disappear with each spark event (i.e. tied to the RPM).
The EGT is a VERY low current signal and could be influence by this type of magnetic field. Look for areas where you have long, parallel contact between an ignition lead and EGT wire
In summary, you should be less worried about the wires touching each other and more worried about them touching other sensitive wires. I have EI ignition wires that are tie wrapped together for 2-3' and have no interference.
Larry
The EGT is a VERY low current signal and could be influence by this type of magnetic field. Look for areas where you have long, parallel contact between an ignition lead and EGT wire
In summary, you should be less worried about the wires touching each other and more worried about them touching other sensitive wires. I have EI ignition wires that are tie wrapped together for 2-3' and have no interference.
Larry
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Shielded wires are used for reasons other than shielding, the capacitance between the coaxial wires is part of system the ignition is designed around. The wires store energy until the plug resistance is overcome, then the field collapses dumping energy into the plug, or something along those lines. Even if you managed to do it, it might have unintended consequences.
Not saying I understand it, I just read about in John Swarner's Magneto book.
Tim Andres
Not saying I understand it, I just read about in John Swarner's Magneto book.
Tim Andres
I saw this also and switched to the #3961 NGK P/N with the solid tops.
I found the problem not from a noise issue, but I noticed the dielectric grease had turned black on one plug and went looking for the problem, which was a loose top.
Tim Andres
This is good to know as I have taken a lot of care not to have them touch each other. I will be looking at it this weekend since this is a rather new issue I know I did a bit of re-routing. The issue you described with the magnetic field is precisely what I am hoping to avoid if I can use a different type wire.
I am not an Electrical engineer, but I believe that the shielding will only contain RF, not magnetic fields. I would heed the advice of the previous poster and look to resolve your problems in another way. I have never seen shielded wiring on a traditional coil setup other than on a magneto (a somewhat unique ignition device) and would be concerned that you could be introducing new problems (remember, the shield is part of ground path and your ignition was not designed for that). 100's of millions of cars have been produced with coils just like yours and use non-shielded ignition wires very successfully. I think you'll find a resolution to your problem without the need for shielded wiring.
Larry
