Landing light CB

[Hankal]

Landing light circuit breaker 20 amp. Pops after about one minute.
I have changed the landing light 4552, changed the CB and thought I had the
problem solved.
This morning Taxi at 6 am (still dark) I was pleased to have the landing light
while in close quarters, then the CB popped.
I have checked the wiring and connections and everything looks good.
Will go with my trusty amp meter and see what the bulb draws.
In the meantime can any one give some advise.
The plane is a C 172 with the Avcon conversion.
Thanks
Hank

[Morgans]

"Hankal" > wrote in message
...
> Landing light circuit breaker 20 amp. Pops after about one minute.
>.
> Thanks
> Hank

Check voltage drop across the switch. Could be high resistance in the
switch. Could be corroded slide terminals that go on the bulb. Could be
multi strand wires, with some of the strands broken. Find the culprit, as
one of them could let you down, when most needed. Also, has anyone stole
some power from that circuit, to power some avionics, or such?
--
Jim in NC

[AJW]

> the CB popped.
>I have checked the wiring and connections and everything looks good.
>Will go with my trusty amp meter and see what the bulb draws.
>In the meantime can any one give some advise.
>The plane is a C 172 with the Avcon conversion.
>Thanks
>Hank
>
Any chance something in the landing light fixture is grounding out as it
heats?>
>
>
>
>

[J. Severyn]

"Morgans" > wrote in message
...
>
> "Hankal" > wrote in message
> ...
> > Landing light circuit breaker 20 amp. Pops after about one minute.
> >.
> > Thanks
> > Hank
>
> Check voltage drop across the switch. Could be high resistance in the
> switch. Could be corroded slide terminals that go on the bulb. Could be
> multi strand wires, with some of the strands broken. Find the culprit, as
> one of them could let you down, when most needed. Also, has anyone stole
> some power from that circuit, to power some avionics, or such?
> --
> Jim in NC
>
>
High resistance in the switch will make the current less, with less chance
to pop the breaker.
Likewise for corroded bulb terminals. Likewise for strands broken in the
wires (as long as the strands are not breaking through the insulation and
contacting the airframe.

Now the breaker itself could develop high resistance contacts....heating the
breaker internally and causing it to trip at a lower current than the rated
20 Amps. I suspect the breaker if the insulation on the wiring is in good
shape. Also check the lugs and wires as they attach to the back of the
breaker. If these are loose or corroded, the heated lugs can also warm the
breaker causing premature tripping.

J. Severyn

[Dan Thomas]

(AJW) wrote in message >...
> > the CB popped.
> >I have checked the wiring and connections and everything looks good.
> >Will go with my trusty amp meter and see what the bulb draws.
> >In the meantime can any one give some advise.
> >The plane is a C 172 with the Avcon conversion.
> >Thanks
> >Hank
> >
> Any chance something in the landing light fixture is grounding out as it
> heats?>
> >
> >
> >
> >

The 4522 bulb is a 250 watt bulb at 13 volts. That translates into
19.23 amps. As the charging system comes into play the voltage rises
to 14 volts, and assuming that the resistance of the bulb doesn't
change much, the current flow rises to 20.71 amps. The breaker will
pop after a bit, especially if it's old. It's a Cessna engineering
screwup.
We have a 172 with the same system. We had to increase the breaker
to 25 amps (and go to #10 wire to satisfy AC43.13 requirements for
current flow) to eliminate nuisance tripping.

Dan

[Jim Weir]

(Dan Thomas)
shared these priceless pearls of wisdom:


-> The 4522 bulb is a 250 watt bulb at 13 volts.

Read the original post. The poster said it was a 4552, not a 4522. The 4552 is
a 250 watt bulb at 28 volts.



That translates into
->19.23 amps. As the charging system comes into play the voltage rises
->to 14 volts, and assuming that the resistance of the bulb doesn't
->change much, the current flow rises to 20.71 amps. The breaker will
->pop after a bit, especially if it's old. It's a Cessna engineering
->screwup.

Hardly. The aircraft would never have been certified with a breaker running
that close to limits.


-> We have a 172 with the same system. We had to increase the breaker
->to 25 amps (and go to #10 wire to satisfy AC43.13 requirements for
->current flow) to eliminate nuisance tripping.

Well, ONE of you is wrong. Either the original poster made a typo or you made
an incorrect interpretation. Tell me, though, just for grins, what year and/or
model 172 had this "engineering screwup" so that I can go back through the TCDS
and parts list to see where the screwup really is.

My best guess is that somebody decided they wanted a "flame thrower" landing
light and replaced the normal 100/150 watt bulb with a 250 watt bulb without
doing the recalcs. No logbook entry, of course.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Peter Duniho]

"Dan Thomas" > wrote in message
om...
> The 4522 bulb is a 250 watt bulb at 13 volts.

He wrote 4552, not 4522. The 4552 is a 28v 250W part, putting the current
at below 10A. A 20A breaker ought to be entirely sufficient.

If his post has a typo, and he actually means a 4522 bulb, then of course
your post offers very useful information.

Pete

[Hankal]

>Now the breaker itself could develop high resistance contacts....heating the
>breaker internally and causing it to trip at a lower current than the rated
>20 Amps. I suspect the breaker if the insulation on the wiring is in good
>shape. Also check the lugs and wires as they attach to the back of the
>breaker. If these are loose or corroded, the heated lugs can also warm the
>breaker causing premature tripping.

I thought it was the breaker, but the new one does alo trip.

[Hankal]

>Any chance something in the landing light fixture is grounding out as it
>heats?

No everything is tight and nothing shorted.
Hank

[Dan Thomas]

Jim Weir > wrote in message >...
> (Dan Thomas)
> shared these priceless pearls of wisdom:
>
>
> -> The 4522 bulb is a 250 watt bulb at 13 volts.
>
> Read the original post. The poster said it was a 4552, not a 4522. The 4552 is
> a 250 watt bulb at 28 volts.
>
>
>
> That translates into
> ->19.23 amps. As the charging system comes into play the voltage rises
> ->to 14 volts, and assuming that the resistance of the bulb doesn't
> ->change much, the current flow rises to 20.71 amps. The breaker will
> ->pop after a bit, especially if it's old. It's a Cessna engineering
> ->screwup.
>
> Hardly. The aircraft would never have been certified with a breaker running
> that close to limits.
>
>
> -> We have a 172 with the same system. We had to increase the breaker
> ->to 25 amps (and go to #10 wire to satisfy AC43.13 requirements for
> ->current flow) to eliminate nuisance tripping.
>
> Well, ONE of you is wrong. Either the original poster made a typo or you made
> an incorrect interpretation. Tell me, though, just for grins, what year and/or
> model 172 had this "engineering screwup" so that I can go back through the TCDS
> and parts list to see where the screwup really is.

1972 172L. All breakers and bulbs were as per parts manual.

Dan

[Hankal]

>Well, ONE of you is wrong. Either the original poster made a typo or you
>made
>> an incorrect interpretation. Tell me, though, just for grins, what year
>and/or
>> model 172 had this "engineering screwup" so that I can go back through the
>TCDS

Ok here are the facts.
The plane is a 1973 Cessna 172 M.
The landing light is a 4522. 250 watt at 14 volts. By ohms law is draws 17.86
amps.
The Circuit Breaker Part number is S-1360-20---20 amp
This is from the equipment table on page 20-35
Either the Cessna book is wrong or the light should be of lower wattage or the
circuit breaker should be of a higher amperage.
Hank

[Dan Thomas]

"Peter Duniho" > wrote in message >...
> "Dan Thomas" > wrote in message
> om...
> > The 4522 bulb is a 250 watt bulb at 13 volts.
>
> He wrote 4552, not 4522. The 4552 is a 28v 250W part, putting the current
> at below 10A. A 20A breaker ought to be entirely sufficient.
>
> If his post has a typo, and he actually means a 4522 bulb, then of course
> your post offers very useful information.
>
> Pete

Here's what the original poster said in a subsequent post in
rec.aviation.owning:

>Nobody looks it up. The 4522 lamp is usually used in a swing-down
lamp.

>The landing lamp is a GE 4522.

>If I posted different, then it is my error and I appologize.
>Hank

I assumed a typo right off, since I knew of no 4552 in any 172s.

And after Jim Weir razzed me, I doublechecked the Cessna parts
manual again, and for a whole serial number range they call for a 4522
bulb on a 20 amp breaker. They DO make mistakes sometimes.

Dan

[Jim Weir]

(Dan Thomas)
shared these priceless pearls of wisdom:


-> I assumed a typo right off, since I knew of no 4552 in any 172s.

Neither did I, but there are some really goosey things done in the name of STC,
and when he said that he had a non-stock STCd engine, I figured that perhaps
they wanted a heavier filament for vibration, or that there was some subchapter
footnote that said that engines of such and such a horsepower needed a brighter
lamp... I didn't question the bulb, since the 4552 DOES cross to an aircraft
landing light bulb.

->
-> And after Jim Weir razzed me, I doublechecked the Cessna parts
->manual again, and for a whole serial number range they call for a 4522
->bulb on a 20 amp breaker. They DO make mistakes sometimes.

To which I abjectly apologize. However, "they" was all the way up the chain of
command, from the design engineer to the chief engineer to the certifying FAA
office to...with no subsequent AD to replace the breaker AND the wire or replace
the bulb with a 100-watter.

The person with the original question is now in somewhat of a dilemma. Replace
the wire and breaker on a 337 (yes, I *do* consider this a major change) or
replace the bulb on a 337 (again...) or do either one and just shutta uppa da
mout'.

Yer choice. I know mine.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[[email protected]]

That's all funny. I'm sure the bulbs for our two cowl mounted lights
in our 172M are a 4509s. Maybe our two bulb system is different?
But, we were going thru bulbs at an incredible rate when I happened to
try two fixes to the problem - unfortunately at the same time so I
don't know which one worked.

The problem - I think the filaments vibrate due to cowl vibration.
Hold a good bulb to your ear and rap it sharply with a finger tip.
Hear the lightly damped ringing iside. We thought maybe we needed
some vibration isolation even though the cowl is floating.

Fixes?

1) I sprayed silicon on the cowl baffling strips to minimize the
friction between the engine vibration and the cowl surfaces. We later
added teflon tape to the interface surfaces on the cowl interior.

2) I added four 8-32 rubber shock mounts between the landing lite
brackets and the cowl as a secondary vibration isolator. This spaced
the lites back maybe 3/8 inch, but there seemed to be room for
everything.

We have not replaced a cowl light in about 10 years.

I don't know which scheme worked but it sure did.

[Dan Thomas]

) wrote in message >...
> That's all funny. I'm sure the bulbs for our two cowl mounted lights
> in our 172M are a 4509s. Maybe our two bulb system is different?

172M's used both the single 4522 and the twin 4509s. We have two
M models, both with the twin lights, but the parts manual shows that
the single bulb was installed in some serial numbers.


> But, we were going thru bulbs at an incredible rate when I happened to
> try two fixes to the problem - unfortunately at the same time so I
> don't know which one worked.
>
> The problem - I think the filaments vibrate due to cowl vibration.
> Hold a good bulb to your ear and rap it sharply with a finger tip.
> Hear the lightly damped ringing iside. We thought maybe we needed
> some vibration isolation even though the cowl is floating.
>
> Fixes?
>
> 1) I sprayed silicon on the cowl baffling strips to minimize the
> friction between the engine vibration and the cowl surfaces. We later
> added teflon tape to the interface surfaces on the cowl interior.
>
> 2) I added four 8-32 rubber shock mounts between the landing lite
> brackets and the cowl as a secondary vibration isolator. This spaced
> the lites back maybe 3/8 inch, but there seemed to be room for
> everything.
>
> We have not replaced a cowl light in about 10 years.
>
> I don't know which scheme worked but it sure did.

There's a cowl shock mount used as a bumber in the cowling,
and it rides against a small plate bolted to the alternator mounting
bracket on the engine. It's supposed to keep the cowl roughly in line
with the prop hub, but as the engine mount rubbers sag, the engine
contacts the bumber rather firmly and shakes the daylights out of the
cowl and anything attached to it, like landing lights. That bumber
rubber gets hot enough from being pounded and rubbed that it can melt.
Some folks turn the landing lights 90 degrees in their mounts to
get the filaments vertical rather than horizontal, and they claim
better bulb life. Others use the Q4509 or H7604, which are the same as
4509s but with a separate quartz/halogen bulb within the main
envelope. These have a life expectancy of 100 hours rather than 25.
I wish Cessna had left the lights in the wing leading edges, or
had not gone to the rubber-mounted cowlings. We have a couple of
Citabrias with 4509s in the cowls, and they get good life because the
cowls are rigidly mounted to the firewall and the engine has no
contact other than through baffle seals. The cowl doesn't get shaken
up.

Dan

[[email protected]]

>
> There's a cowl shock mount used as a bumber in the cowling,
> and it rides against a small plate bolted to the alternator mounting
> bracket on the engine. It's supposed to keep the cowl roughly in line
> with the prop hub, but as the engine mount rubbers sag, the engine
> contacts the bumber rather firmly and shakes the daylights out of the
> cowl and anything attached to it, like landing lights. That bumber
> rubber gets hot enough from being pounded and rubbed that it can melt.
> Some folks turn the landing lights 90 degrees in their mounts to
> get the filaments vertical rather than horizontal, and they claim
> better bulb life. Others use the Q4509 or H7604, which are the same as
> 4509s but with a separate quartz/halogen bulb within the main
> envelope. These have a life expectancy of 100 hours rather than 25.
> I wish Cessna had left the lights in the wing leading edges, or
> had not gone to the rubber-mounted cowlings. We have a couple of
> Citabrias with 4509s in the cowls, and they get good life because the
> cowls are rigidly mounted to the firewall and the engine has no
> contact other than through baffle seals. The cowl doesn't get shaken
> up.
>
> Dan


The resonant frequency of the filament system of a 4509 bulb has to be
in the several KHz range, and the damping is incredibly low, since it
takes place in a vacuum. Exciting that combination with an 80 Hz
complex waveshape thru a rubber bumper would normally seem hard to me
(based on my experience with vibration) in that we'd be dealing with
maybe a 40th harmonic. The front cowl mount is still soft after all
these years in our 172M.

At any rate that's why I tried to isolate the bulb mounts from the
cowl, and also minimize the stick-slip of the baffling-cowl interface.
From experience in unrelated applications, stick-slip effects can
create a lot of very high freq harmonic content.

I had heard of rotating the lites, but didn't try that.