[jdeas]

I am trying to figure out the different readings I am getting from a 'Action Air Parts" Sync box and a Eastern Tech E50 box.
Both mags read very close in resistance values in both the closed and open contact positions.
The AAP box LED's and audio indicators show what is expected for a properly timed pair of mags.
On the E50 what ever lead is connected to my left mag has a constant tone and the LED is partially lit.

There must be a difference in the way the two boxes gauge the impedance of the Mag. Does anyone know the difference between the two timing lights or the implications of the E50's 'half' on lamp when it should be out? Perhaps a shorted condenser?

IO-360 with dual slick mags. Both mags have around 200hrs.

 

[Flying Scotsman]

Just to add to Jim's post...that's my E50 we used, and it operated correctly when timing the mags on my new Lycoming IO-360. That is, no tone or lights until the points opened, then light + tone for each mag as per the manual.

In this case, however, the left mag is showing a "dim" light on the box and a higher-pitched tone until the points open, then the correct "full on" light and correct tone. This is the case regardless of which lead is connected to the left mag, so we don't believe it is the box but something inherent in that left mag.

 

[aerhed]

Could it be as simple as needing a new battery in the Eastern box?

 

[Flying Scotsman]

The E50 is brand new, so it is possible that the battery is weaker. Still, why would only the *left* mag cause the box to exhibit this behavior?

Mags, although simple, are still somewhat of a mystery to me as to how to test, what to look for in cases like this, etc. I've studied all the diagrams and the on-line 3D animated CAD versions and read the Sky Ranch book on mags, etc., to no avail

 

[scsmith]

ideas

I'm not sure what goes on inside that box, but a simple jumper-light works like this: when the points are closed, the current goes through the points, so there is not enough current through the light bulb to light it. When the points open, all the current goes through the light bulb, so it lights.

If you have worn points that are not making very good contact when closed, then you have a higher resistance through the points, and more current will go through the light bulb, perhaps enough to make it glow faintly.

If you had a shorted condenser, then when the points open, you would have a current path through the condenser, so the light bulb would see less current and would not come on full bright with points open. That does not sound like the case here.

 

[Don Jones]

Wiring??

Is there anything connected to the left mag like a tach pickup wire or something like that?

 

[Flying Scotsman]

Is there anything connected to the left mag like a tach pickup wire or something like that?

Nothing connected at all (don't worry...no plugs in the engine and no prop installed yet, so we don't have the danger of a hot mag ).

 

[Walt]

I'm not sure what goes on inside that box, but a simple jumper-light works like this: when the points are closed, the current goes through the points, so there is not enough current through the light bulb to light it. When the points open, all the current goes through the light bulb, so it lights.

If you have worn points that are not making very good contact when closed, then you have a higher resistance through the points, and more current will go through the light bulb, perhaps enough to make it glow faintly.

If you had a shorted condenser, then when the points open, you would have a current path through the condenser, so the light bulb would see less current and would not come on full bright with points open. That does not sound like the case here.

Steve pretty well nailed it but with some minor changes.

The "box" runs an AC voltage through the magneto circuit (that what the buzzing noise is), inside the timing box is a transformer in parallel with that circuit.

With the points closed, all the current goes through the magneto coil and points because the impedance of that circuit is lower than the impedance of the transformer in the timing box.

So with a high impedance in the mag, the timing box is seeing an increase in current flow through its transfomer, and lighting the light.

Bottom line, you need to check the points and coil in the mag, one or the other has high impedance which is not correct.

Diagram of basic timing box:

 

[jdeas]

Steve pretty well nailed it but with some minor changes.

The "box" runs an AC voltage through the magneto circuit (that what the buzzing noise is)

That is the answer I was looking for. I didn't think you could properly check the mag with a ohm meter (DC). The dc resistance is simply too low. Without AC current the impedance of the coil would not come into play.
Looks like it's time to check the points and condenser.

 

[Flying Scotsman]

Steve pretty well nailed it but with some minor changes.

The "box" runs an AC voltage through the magneto circuit (that what the buzzing noise is), inside the timing box is a transformer in parallel with that circuit.

With the points closed, all the current goes through the magneto coil and points because the impedance of that circuit is lower than the impedance of the transformer in the timing box.

So with a high impedance in the mag, the timing box is seeing an increase in current flow through its transfomer, and lighting the light.

Bottom line, you need to check the points and coil in the mag, one or the other has high impedance which is not correct.

So, since the AAP box appeared to show correct timing with no anomalies, but the E50 box showed correct timing but *with* some anomalous behavior, that one of them (the E50) would be preferred?

And how is the AAP box wired differently (I know it works differently than the E50)?

I guess what I'm asking is...is the AAP box missing showing some important data on the health and safety of the mag?