Landing light CB

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

"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

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?

"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

emove (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

(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

"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

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.

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

No everything is tight and nothing shorted.
Hank

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