mag ground wire 0470 R engine

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stapler101

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stapler101
0470R engine, 1974 Cessna 182
I just found that both mag ground wires are connected to one mag (the right side) rather than one wire to each mag.
I assume it has been this way for "years" because the hot wire and the 2 ground wires were zip tied together.
Is this correct?
 
stapler101 said:
0470R engine, 1974 Cessna 182
I just found that both mag ground wires are connected to one mag (the right side) rather than one wire to each mag.
I assume it has been this way for "years" because the hot wire and the 2 ground wires were zip tied together.
Is this correct?
Click to expand...

No, it's incorrect, each should have its own P-lead. If you had ever done a 'mags cold' check by briefly turning the switch to off before shutting down, you would have noticed it would have kept running as you have a 'hot mag'. Not safe in the slightest.
 
Henning said:
No, it's incorrect, each should have its own P-lead. If you had ever done a 'mags cold' check by briefly turning the switch to off before shutting down, you would have noticed it would have kept running as you have a 'hot mag'. Not safe in the slightest.
Click to expand...

Further, the normal pre-flight mag check will give him ERRONEOUS idea of whether his redundant ignition system was working. He never tested the grounded mag in isolation.
 
I always do the normal mag check, both, left, and then right.
The wiring was just noticed by an ap yesterday when he was replacing some cowling.
 
Are you talking about the p-leads or the bonding wire on the case?
 
stapler101 said:
I always do the normal mag check, both, left, and then right.
The wiring was just noticed by an ap yesterday when he was replacing some cowling.
Click to expand...
Like Ron said, you only thing you were checking both mags but in reality the left mag was operating when you thought you were checking the right one as well as when you were checking the left. While unlikely, it's quite possible that running only on your right mag would result in a rough running engine.
 
Skylane81E said:
If the mechanic is the one who called them grounds I imaging that they are NOT the P leads
Click to expand...

Also if it were the p-leads I'm certain the mechanic would have corrected the situation prior to re-installing the cowling. The OP stated that they ARE both connected to one mag indicating it's still that way.

[EDIT] Although the ground wire should connect to the magneto case the mag itself will ground through it's mounting to the engine, even with the gasket. The bonding wire should however be connected to the case of the mag for positive circuit integrity.

In other words, the mags have been operating properly despite this condition (which should be corrected)
 
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Silvaire said:
Also if it were the p-leads I'm certain the mechanic would have corrected the situation prior to re-installing the cowling. The OP stated that they ARE both connected to one mag indicating it's still that way.
Click to expand...

Yeah, I don't allow planes in my hangar with hot mags
 
I guess my wording was incorrect.
It is not the p-lead.
I can't say for sure that the ap said "ground" wire, that is probably my word.
The wire is the shielded wire that is attached to the screw on the mag.
As I stated, both shielded wires are connected to one mag.
It will be changed and one wire placed on each mag.
 
It really doesn't make any difference which ground wire is attached to what, as long as it is a good ground, because all the outer diameter coaxial wire is providing is a radio shield ground.

The ground for the mag is done inside the ignition switch.
 
stapler101 said:
I guess my wording was incorrect.
It is not the p-lead.
I can't say for sure that the ap said "ground" wire, that is probably my word.
The wire is the shielded wire that is attached to the screw on the mag.
As I stated, both shielded wires are connected to one mag.
It will be changed and one wire placed on each mag.
Click to expand...

The shielded wire attached to the screw on the mag, IME, is indeed the p-lead.
 
Tom-D said:
It really doesn't make any difference which ground wire is attached to what, as long as it is a good ground, because all the outer diameter coaxial wire is providing is a radio shield ground.

The ground for the mag is done inside the ignition switch.
Click to expand...

The ground for the P lead to shut the mag down is in the mag switch. The ground that lets the mags fire spark plugs happens through the engine itself.

I assume the ground wire in question is likely to be the shield for the P lead so it wouldn't make a really huge difference, but it woud make sense to have each shield to to the appropriate mag. But I ain't even a real pilot any more, much less an A&P.
 
jesse said:
The shielded wire attached to the screw on the mag, IME, is indeed the p-lead.
Click to expand...
I hope that you are referring to a slick mag.

the inner wire or center of the coaxial is attached to the condenser pole of the mag. and will make ground in the ignition switch for the left mag when the right is selected, and visa versa.
 
Tom-D said:
I hope that you are referring to a slick mag.

the inner wire or center of the coaxial is attached to the condenser pole of the mag. and will make ground in the ignition switch for the left mag when the right is selected, and visa versa.
Click to expand...

All I have experience with are the Bendix mags on my Flybaby, referring to the wire attached here (pic from my plane):

QSsk69s.jpg
 
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Capt. Geoffrey Thorpe said:
The ground for the P lead to shut the mag down is in the mag switch. The ground that lets the mags fire spark plugs happens through the engine itself.

Isn't the engine grounded to the airframe? if not why does the starter work?
But let us confine you conversation to the primary circuit in the mag, the ground for the spark plug is the engine on one end and the negative of the mag coil on the other end.

I assume the ground wire in question is likely to be the shield for the P lead so it wouldn't make a really huge difference, but it woud make sense to have each shield to to the appropriate mag. But I ain't even a real pilot any more, much less an A&P.
Click to expand...

the normal attachment of the "P" lead harness is to attach the outer coaxial to the mag as close as possible to give maximum radio shielding. It can be attached to any good ground. and it should be attached to the mag ground at the ignition switch as well.
 
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jesse said:
All I have experience with are the Bendix mags on my Flybaby, referring to the wire attached here (pic from my plane):
Click to expand...
That mag is older than me, :) it's an old Eisman patten made by Bendix it a whole different animal.

Yes the connection you show is the "P" lead wire, the outer coaxial can be attached anywhere as long as it has a common ground with the mag/engine.
 
The shield is often times used as the ground for the mag. Yes, the p-lead goes to the switch in the cockpit then back out to ground to the magneto case. This way you have a complete grounding circuit directly to the case of the magneto and you do not rely on grounding through the engine and the engine to airframe bonding strap. On Slicks there is normally a bonding wire that connects the magneto case to airframe ground (same reason)

I believe it is this bonding wire that the OP is talking about.
 
Tom-D said:
That mag is older than me
Click to expand...
It seems to mag along quite nicely. My only issue is that I have a ton of ignition noise in my radio that overpowers the squelch. I've yet to figure out how to fix it since all the wires going to the plugs are shielded...Drives me crazy though (I just turn the radio off when I leave the pattern).
 
stapler101 said:
I always do the normal mag check, both, left, and then right.
The wiring was just noticed by an ap yesterday when he was replacing some cowling.
Click to expand...

Yes. But in this case it would be BOTH, RIGHT, and RIGHT.
 
jesse said:
It seems to mag along quite nicely. My only issue is that I have a ton of ignition noise in my radio that overpowers the squelch. I've yet to figure out how to fix it since all the wires going to the plugs are shielded...Drives me crazy though (I just turn the radio off when I leave the pattern).
Click to expand...

I do not see a condenser (noise filter) on that installation, and I don't remember if that mag has one internal in the "P" lead circuit. I'd order one from Spruce and place it in parallel to the "P" lead connection and see if the noise goes away.

http://www.aircraftspruce.com/catalog/eppages/magnetoFliter.php?clickkey=291290
 
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jesse said:
And how exactly is it installed? In-line with the p-lead or?
Click to expand...

Tab on the side of the filter is mounted to a known good ground, the wire goes to the same pole as the "P" lead from the ignition switch.
 
Tom-D said:
Tab on the side of the filter is mounted to a known good ground, the wire goes to the same pole as the "P" lead from the ignition switch.
Click to expand...

And the p-lead then goes to the filter?
 
jesse said:
And the p-lead then goes to the filter?
Click to expand...

no,,, you will attach the filter to the same pole as the "P" lead, IOWs two wires on the same point on the mag.
 
jesse said:
This seems to imply that it goes in-line...
http://www.aircraftspruce.com/catalog/pdf/magfilternstall.pdf

Just ordered it. Sorry for the thread drift OP.
Click to expand...
The capacitor is electrically connected in parallel with the breaker points. It's purpose is NOT to reduce ignition noise but rather to store energy from the coil when the points open. This not only reduces the arcing at the points but also increases the energy delivered to the spark plugs.

It's size (capacitance) needs to be matched to the coil and I don't think it's a good idea to be adding one externally to the magneto, at least not without some analysis. Too much capacitance and the points will suffer.

It is possible that the capacitor in your magneto has failed (open or high impedance) but that's fairly unusual in "modern" capacitors (old ones tended to "dry up" and lose much of their capacitance over time). If the capacitor (aka condenser) was defunct you might see increased ignition noise but more importantly your points would quickly deteriorate.

First thing I'd do is confirm that the plugs have internal resistors. Without some series resistance in the high voltage path considerably more RF noise is generated and radiated. Next I'd confirm that the shields on the spark plug wires are well grounded on both ends and make certain that the P-lead shields are continuous from the magneto back to the switch. There shouldn't be any more than an inch or so of unshielded wire on either end of those leads.

One way to determine if your ignition noise is from the primary side (P-lead) or secondary (spark plug wires) is to temporarily disconnect both P-leads from the magnetos and see if the noise abates.

BTW it might just be that your antenna isn't well grounded at it's mounting. On a fabric covered airplane you may have to fabricate a ground plane under the antenna.
 
jesse said:
And the p-lead then goes to the filter?
Click to expand...

The condenser is a parallel circuit with the switch on the P-lead. Put both the condenser pigtail and p-lead on the same screw and ground the case of the condenser. Think of the condenser as a shock absorber/knock stopper for electricity.
 
gismo said:
The capacitor is electrically connected in parallel with the breaker points. It's purpose is NOT to reduce ignition noise but rather to store energy from the coil when the points open. This not only reduces the arcing at the points but also increases the energy delivered to the spark plugs.

That one is internal to the mag, its only purpose is to stop arcing of the points, when it fails he will see very high mag drops. he has no symptoms of that.

It's size (capacitance) needs to be matched to the coil and I don't think it's a good idea to be adding one externally to the magneto, at least not without some analysis. Too much capacitance and the points will suffer.

It is possible that the capacitor in your magneto has failed (open or high impedance) but that's fairly unusual in "modern" capacitors (old ones tended to "dry up" and lose much of their capacitance over time). If the capacitor (aka condenser) was defunct you might see increased ignition noise but more importantly your points would quickly deteriorate.

First thing I'd do is confirm that the plugs have internal resistors. Without some series resistance in the high voltage path considerably more RF noise is generated and radiated. Next I'd confirm that the shields on the spark plug wires are well grounded on both ends and make certain that the P-lead shields are continuous from the magneto back to the switch. There shouldn't be any more than an inch or so of unshielded wire on either end of those leads.

One way to determine if your ignition noise is from the primary side (P-lead) or secondary (spark plug wires) is to temporarily disconnect both P-leads from the magnetos and see if the noise abates.

BTW it might just be that your antenna isn't well grounded at it's mounting. On a fabric covered airplane you may have to fabricate a ground plane under the antenna.
Click to expand...
if that were the problem he would have noises from the generator, both mags and any other noise emitter
 
gismo said:
The capacitor is electrically connected in parallel with the breaker points. It's purpose is NOT to reduce ignition noise but rather to store energy from the coil when the points open. This not only reduces the arcing at the points but also increases the energy delivered to the spark plugs.

It's size (capacitance) needs to be matched to the coil and I don't think it's a good idea to be adding one externally to the magneto, at least not without some analysis. Too much capacitance and the points will suffer.

It is possible that the capacitor in your magneto has failed (open or high impedance) but that's fairly unusual in "modern" capacitors (old ones tended to "dry up" and lose much of their capacitance over time). If the capacitor (aka condenser) was defunct you might see increased ignition noise but more importantly your points would quickly deteriorate.

First thing I'd do is confirm that the plugs have internal resistors. Without some series resistance in the high voltage path considerably more RF noise is generated and radiated. Next I'd confirm that the shields on the spark plug wires are well grounded on both ends and make certain that the P-lead shields are continuous from the magneto back to the switch. There shouldn't be any more than an inch or so of unshielded wire on either end of those leads.

One way to determine if your ignition noise is from the primary side (P-lead) or secondary (spark plug wires) is to temporarily disconnect both P-leads from the magnetos and see if the noise abates.

BTW it might just be that your antenna isn't well grounded at it's mounting. On a fabric covered airplane you may have to fabricate a ground plane under the antenna.
Click to expand...

Not sure if my plugs have the resistor. I plan on looking into that tonight... I did some looking at the antenna today via an inspection cover and it appears to be a home made whip antenna with a ground plane about like this:
Antenne_gp_vhf_3.jpg

Not sure what the lengths of the groundplane poles are..or if any of it's wired up right..need to look some more.

At this point I'm not going to open the filters until I investigate the antenna more, check the spark plugs, and triple check the p-leads.
 
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