Nav Light Wiring Question

[markejackson02]

I was looking at the wiring diagram for my early model M20J (24-00048).  Need a replacement nav light bulb.  What was weird was that in tracing the wiring, there are four wires on the nav light switch.  Three nav lights (l, r, & rear) and the gear unsafe light.  I'm not an electrical whiz but how is it possible that the gear lights are wired through the nav light switch?  I typically leave them off during the day but the gear lights seem to work anyway.

Mark

[RLCarter]

There is voltage (power) on one side of the switch all the time (if the master and CB is on) Maithili out seeing a diagram, my guess is they are getting power for the gear light from the hot side of the switch

Edited October 16, 2016 by RLCarter

[markejackson02]

Doh, of course, that makes sense.

[RLCarter]

1 hour ago, RLCarter said:

Maithili

Not sure what this is but it should have been "with out"

[M20S Driver]

On my Eagle, the Nav light "On" sends a voltage to the "Gear Down"  light to dim it.  The idea is to dim the gear down light at night or whenever  you turn on the Nav light.

[Guitarmaster]

What you are seeing is a ground wire.  Your gear down light grounds through the nav light bulbs when the nav lights are off.  When you turn the nav lights on, it lifts that ground and and re-grounds through a resistor to create the dimming of the gear down light.

This is why, if you replace the nav lights with LED, your gear down light will always be dim unless you have a shunt resistor installed.

It's a pretty ingenious system for it's time... 

 

Edited October 16, 2016 by Guitarmaster

[Guitarmaster]

Nav lights off



Nav lights on




Sent from my iPad using Tapatalk

[carusoam]

Matt's ingenious!

The same system being used in the 90's, not so ingenious.  I like to have my nav lights on during daylight hours and be able to see my gear down light at the same time...

Now I'm thinking of the shunt resistor... ( pretty far down the maintenance List)

I still have to get over The bulb for the KAP150 button...

Best regards,

-a-

[ArtVandelay]

When I installed my LED lights, I didn't have this problem, I also don't have the green gear down annunciator, mine is white which makes me think my annunciator was modified at some point.

[markejackson02]

19 hours ago, Guitarmaster said:

What you are seeing is a ground wire.  Your gear down light grounds through the nav light bulbs when the nav lights are off.  When you turn the nav lights on, it lifts that ground and and re-grounds through a resistor to create the dimming of the gear down light.

This is why, if you replace the nav lights with LED, your gear down light will always be dim unless you have a shunt resistor installed.

It's a pretty ingenious system for it's time... 

 

Wow, thanks, learn something new every day....

[Guitarmaster]

22 hours ago, carusoam said:

I like to have my nav lights on during daylight hours and be able to see my gear down light at the same time...

 

I do too.  I would much rather see a "dim" setting for all the annunciators on a separate switch.

[bradp]

19 hours ago, Guitarmaster said:

I do too.  I would much rather see a "dim" setting for all the annunciators on a separate switch.

It may be considered a minor modification by your IA to rewire the gear indicator to  its own  rheostat so long as you have your floor indicator as a lit backup. Never hurts to ask.  

[markejackson02]

Wouldn't it make sense for a manufacturer of LED nav light replacements to incorporate a resistor into the circuit so that you could use existing rheostats?  Otherwise it would seem at some point we'd have to do a lot of re-wiring to accommodate LED lights.

[ArtVandelay]

Wouldn't it make sense for a manufacturer of LED nav light replacements to incorporate a resistor into the circuit so that you could use existing rheostats?  Otherwise it would seem at some point we'd have to do a lot of re-wiring to accommodate LED lights.

The resister is on the Mooney, not in the lights, if above is correct then it's grounding the gear down light through the 3 bulbs, which means current is passing through the bulbs but not enough to cause them to light. So between the circuitry (diode, gear down light) the voltage is too low to drive the LEDs, so no current passes.
When my avionics guys mistakenly set the power supply to 24v, my LED lights turned on, but weaker than normal, now I know why.

[Guitarmaster]

5 hours ago, markejackson02 said:

Wouldn't it make sense for a manufacturer of LED nav light replacements to incorporate a resistor into the circuit so that you could use existing rheostats?  Otherwise it would seem at some point we'd have to do a lot of re-wiring to accommodate LED lights.

Yes.  that is exactly what I worked with Bob at PSA on.  The light now has an incorporated resistor in the base.  Problem solved.

[Guitarmaster]

4 hours ago, teejayevans said:

The resister is on the Mooney, not in the lights, if above is correct then it's grounding the gear down light through the 3 bulbs, which means current is passing through the bulbs but not enough to cause them to light. So between the circuitry (diode, gear down light) the voltage is too low to drive the LEDs, so no current passes.
When my avionics guys mistakenly set the power supply to 24v, my LED lights turned on, but weaker than normal, now I know why.

Two different things.  The dimming resistor is on the back of the annunciator and has it's own ground.  Since the path of least resistance it through the incandescent bulbs, no current flows through the dimming circuit.  With no path to ground because of the nature of LED bulbs, the current chooses to go through the dimming circuit.  I am referring to using a shunt resistor to supply the ground that was lifted by the infinite resistance caused by the LEDs.  

Edited October 19, 2016 by Guitarmaster