28V bulb in a 14V Airplane

[MisfitSELF]

1984 M20J -- 14V Electrical System

Since I've had the aircraft (about 6 year now), the landing gear indicator on the floor has been hard to read during the day.  At night the light illuminates the indication adequately.  For a couple of years now, I've been promising myself that I would either clean the transparency or replace the light bulb with a brighter light, perhaps even an LED version.  My bird is an annual right now so it's on jacks with the belly panel off, so now is the time to fix this problem!

So I remove the bulb and it turns out that its a 28V bulb (the GE 327) rather than the 14V GE330 that is specified in the parts book.  That likely explains why I couldn't see it during the day, but would there be a reason for the 28V bulb being installed?  Is the 14V ones too bright at night?  Was some previous owner or A&P just lazy and put in a random bulb that fit?  Could it have been installed that way at the factory?  Is there some advantage such as longevity to using the 28V bulb?  So many questions.

 

Bruce

[PT20J]

You have to check the schematic for your serial number and the electrical parts list at the end of the service and maintenance manual to know for certain what was installed at the factory. But I believe that the 14V airplanes had 28V bulbs installed to make them dimmer at night. There is no reason that you cannot use a 14V bulb. A lot of people also use LED replacements although I found that too bright at night for my taste.

Skip

[Ragsf15e]

19 minutes ago, MisfitSELF said:

1984 M20J -- 14V Electrical System

Since I've had the aircraft (about 6 year now), the landing gear indicator on the floor has been hard to read during the day.  At night the light illuminates the indication adequately.  For a couple of years now, I've been promising myself that I would either clean the transparency or replace the light bulb with a brighter light, perhaps even an LED version.  My bird is an annual right now so it's on jacks with the belly panel off, so now is the time to fix this problem!

So I remove the bulb and it turns out that its a 28V bulb (the GE 327) rather than the 14V GE330 that is specified in the parts book.  That likely explains why I couldn't see it during the day, but would there be a reason for the 28V bulb being installed?  Is the 14V ones too bright at night?  Was some previous owner or A&P just lazy and put in a random bulb that fit?  Could it have been installed that way at the factory?  Is there some advantage such as longevity to using the 28V bulb?  So many questions.

 

Bruce

I recently replaced my bulb with an LED version in my 14v system. It is very bright, and I like it a lot during the day, however, I do not fly very often at night. Be careful removing the light socket, but it sounds like you already did. The wires down there are easily breakable.

[MisfitSELF]

7 minutes ago, Ragsf15e said:

I recently replaced my bulb with an LED version in my 14v system. It is very bright, and I like it a lot during the day, however, I do not fly very often at night. Be careful removing the light socket, but it sounds like you already did. The wires down there are easily breakable.

It wasn't the wire, but the tiny rubber gasket that protects it came apart.  You know the one that protects the wire as it goes threw one of the metal holes up to the socket?  Now I'm considering whether I try to track done the OEM gasket or just fashion my own out of some careful dabs of RTV.
 

[MisfitSELF]

17 minutes ago, PT20J said:

You have to check the schematic for your serial number and the electrical parts list at the end of the service and maintenance manual to know for certain what was installed at the factory. But I believe that the 14V airplanes had 28V bulbs installed to make them dimmer at night. There is no reason that you cannot use a 14V bulb. A lot of people also use LED replacements although I found that too bright at night for my taste.

Skip

The parts manual says it ought to be the 12V bulb  -- the GE330 as referenced in my post.

[LANCECASPER]

40 minutes ago, MisfitSELF said:

The parts manual says it ought to be the 12V bulb  -- the GE330 as referenced in my post.

Most that have the 12v bulb that do night flying have replaced them with 24v to make them easier on the eyes at night. Also remember that when then Nav lights are on they dim as well

[Ragsf15e]

1 hour ago, LANCECASPER said:

Most that have the 12v bulb that do night flying have replaced them with 24v to make them easier on the eyes at night. Also remember that when then Nav lights are on they dim as well

Im not sure the floor light dims.  I could be wrong (and mine is led so doesn’t dim with the stock nav dimmer).  It looks like the vintage airplanes have power for the light wired directly to the down limit switch with nothing connected to a dimming circuit.  Maybe in newer ones?

Another thing to remember is that it’s only on when gear are down.  I still wouldn’t want it to be blinding at night though…

[LANCECASPER]

Just now, Ragsf15e said:

Im not sure the floor light dims.  I could be wrong (and mine is led so doesn’t dim with the stock nav dimmer).  It looks like the vintage airplanes have power for the light wired directly to the down limit switch with nothing connected to a dimming circuit.  Maybe in newer ones?

Another thing to remember is that it’s only on when gear are down.  I still wouldn’t want it to be blinding at night though…

Now you have me wondering. I'm sure others will chime in.

[Ragsf15e]

2 hours ago, MisfitSELF said:

The parts manual says it ought to be the 12V bulb  -- the GE330 as referenced in my post.

Some are moded with different light receptacles too, mine took a very slightly different bulb.  I think a GE327 but I’ll have to find the old thread.

[LANCECASPER]

1 minute ago, Ragsf15e said:

Some are moded with different light receptacles too, mine took a very slightly different bulb.  I think a GE327 but I’ll have to find the old thread.

The 327 is just the 28v version of the 330 (14v)

[PT20J]

1 hour ago, MisfitSELF said:

The parts manual says it ought to be the 12V bulb  -- the GE330 as referenced in my post.

The IPC is not always accurate for electrical components. The IPC only shows a GE330 which is a 14V bulb for all serial numbers, but clearly that is not correct for 28V airplanes.

The schematic reference for the bulb is 21WE06A. The service manual for 91-20-01 ELECTRICAL HARDWARE CHART for S/N 24-0001 through 24-1685 lists 21WE06A as a GE 327.

 

Skip

[Ragsf15e]

Just now, LANCECASPER said:

The 327 is just the 28v version of the 330 (14v)

Yep, just realized that.  Mine took a 336.  Here’s the thread with pictures if it helps anyone.

 

[PT20J]

4 minutes ago, Ragsf15e said:

Im not sure the floor light dims.  I could be wrong (and mine is led so doesn’t dim with the stock nav dimmer).  It looks like the vintage airplanes have power for the light wired directly to the down limit switch with nothing connected to a dimming circuit.  Maybe in newer ones?

Another thing to remember is that it’s only on when gear are down.  I still wouldn’t want it to be blinding at night though…

The floor light doesn't dim -- only the annunciator panel light dims when the nav lights are on.

[Ragsf15e]

1 hour ago, PT20J said:

The floor light doesn't dim -- only the annunciator panel light dims when the nav lights are on.

And even that is only on newer models.  Mine has the “cat eye” manual closure to “dim” the gear lights on the panel.

[Hank]

1 hour ago, PT20J said:

The floor light doesn't dim -- only the annunciator panel light dims when the nav lights are on.

 

11 minutes ago, Ragsf15e said:

And even that is only on newer models.  Mine has the “cat eye” manual closure to “dim” the gear lights on the panel.

Wow, I didn't realize that my 1970 C is a "newer" model. She's 53 years old now, and has a factory dimming rheostat at the top of the panel beside the Push to Test button for the instrument lights.

[Ragsf15e]

Yours was probably built with electric gear from the start so maybe better coordinated.  Mine is a 1968, built with a jbar but modified at the factory (before delivery) with electric gear. 

the interesting thing would be to know if your floor gear indicator dims, but I don’t think it will.  It may already be dim with a 24v light in it?

[PT20J]

Well, this is a Modern Mooney thread and the OP apparently has a M20J 

[1980Mooney]

The other reason that some used to put a 28v bulb in the floor landing gear indicator light socket in place of a 14v bulb is because it will last forever. You are derating a bulb.
 

The 28v filament was sized to provide a certain level of light with a 28 v drop while maintaining a filament surface temperature that doesn’t burn up the filament. Halve the voltage and you have less light, but importantly, much lower temperature. Incandescent filaments usually fail when cycled during the power up phase. Cooler filament temperature makes it last longer.  

[EricJ]

I have a 12V M20J and replaced the floor gear indicator lamp with an LED from Amazon.   It was too dim to see even though the lamp was "working", but now it's about perfect and easily readable during the day.   I rarely fly at night, so can't really comment on that part, but it's so far out of view that I wouldn't think it would be an issue.

One of these (it says 28V, but works fine in my 12V system):

https://www.amazon.com/gp/product/B08GKY8S7L

 

[MisfitSELF]

My LEDs came in today.

 

[flyboy0681]

13 hours ago, MisfitSELF said:

My LEDs came in today.

 

My LED.