What size fuse for Cessna Clock?

[Mark Martindale]

Does anyone know what size fuse is used in the clock circuit in a 172H.
This fuse is located in a holder by the battery box. POH only shows fuse
and no ampere rating. I would guess 1 or 2 amp??

Thanks,
Mark

[George Patterson]

Mark Martindale wrote:
> Does anyone know what size fuse is used in the clock circuit in a 172H.
> This fuse is located in a holder by the battery box. POH only shows fuse
> and no ampere rating. I would guess 1 or 2 amp??

The last time I had to replace one, it was something ridiculous like a tenth of
an amp.

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

[nobody]

My service manual for the C172, 1969 through 1976 models,
indicates in the electrical load anaylsis tables that the clock is
negligible. The smallest load listed in the table is 0.33 amps
so the clock is smaller than that. The manual does not provide
the fuse size as far as I can tell.

My guess would be 1/4 amp for the fuse.


"Mark Martindale" > wrote in message
...
> Does anyone know what size fuse is used in the clock circuit in a 172H.
> This fuse is located in a holder by the battery box. POH only shows fuse
> and no ampere rating. I would guess 1 or 2 amp??
>
> Thanks,
> Mark

[nrp]

I suggest 1 Amp as the OEM clock is an occasional very short but sharp
current pulse type of load. Certainly the wiring to the clock can take
1 amp without smoking anything but the fuse. If you put in a smaller
fuse, they may fail after a while.

[RST Engineering]

Will you all please put this person in your "watch" before "kill" file.

This is absolutely bogus information.

Jim



"nrp" > wrote in message
oups.com...
>I suggest 1 Amp as the OEM clock is an occasional very short but sharp
> current pulse type of load. Certainly the wiring to the clock can take
> 1 amp without smoking anything but the fuse. If you put in a smaller
> fuse, they may fail after a while.
>

[George Patterson]

nrp wrote:
> I suggest 1 Amp as the OEM clock is an occasional very short but sharp
> current pulse type of load.

Say what? It's got a little motor in it. Current draw is constant.

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

[nrp]

You must have a different clock than I have. Mine is the OEM (still
running after 30 years!) that has the rewinding clunk every 5 minutes
or so. Like they once used in cars 40 years ago.

[jls]

"George Patterson" > wrote in message
news:zxNee.56$Dn.52@trndny02...
> nrp wrote:
> > I suggest 1 Amp as the OEM clock is an occasional very short but sharp
> > current pulse type of load.
>
> Say what? It's got a little motor in it. Current draw is constant.
>
> George Patterson
> There's plenty of room for all of God's creatures. Right next to the
> mashed potatoes.

I just replaced one of those fuses on a 172 from the sixties. It was under
the cowl, near the battery, something like 1 or 2 amps, and the POH stated
the fuse was for the clock. A new fuse never helped the clock to work,
though. It's still deader'n 4 o'clock.

Those old clocks are cute but don't last.

[Mark Martindale]

nrp wrote:
> You must have a different clock than I have. Mine is the OEM (still
> running after 30 years!) that has the rewinding clunk every 5 minutes
> or so. Like they once used in cars 40 years ago.
>
Thanks for the replies. My clock is like nrp's and has the rewinding
solenoid that clunks about every 2 minutes. There is only a load on it
for a fraction of a second and is too fast to measure with my dmm. I am
going to put a 1 amp fuse in and see what happens.

Thanks,
Mark

[Scott Skylane]

Mark Martindale wrote:


> Thanks for the replies. My clock is like nrp's and has the rewinding
> solenoid that clunks about every 2 minutes. There is only a load on it
> for a fraction of a second and is too fast to measure with my dmm. I am
> going to put a 1 amp fuse in and see what happens.

Mark,

The Cessna part # for the fuse is an S1091-1. This is a 1 amp *rated*
fuse. The physical *size*, however, is a little different than your
standard automotive "AGC" glass fuse. The length is the same, but the
diameter is slightly larger. These are called "AGS", and if your local
NAPA doesn't have them, your local Cessna dealer will (they are pretty
inexpensive".

Happy Flying!
Scott Skylane
N92054

[Clyde Woempner]

On my clock, Cessna p/n C-664-08-0101 It has a contact points and a solenoid
inside. The points come together and the solenoid will the ratchet a spring
loaded gear and open the points at the same time. The spring pulls the gear
around, which drives the clock till the points make contact again. This
process is repeated each minute. There is no motor and current draw is only
while the points are closed and the solenoid is energized. My .02 cents
worth. Hope this helps. A story concerning fuse replacement, I suggest you
not guess at the fuse. The circuit is hot at all times (master off) in
order for the clock to work. In 1964 my friend and I was using his Dad' new
Chevy pickup. One night the dash lights failed (it had nothing to do with
the girls we had with us) and the tail lights and dash lights are on the
same fuse. We had taken the vehicle to our local garage, and they replaced
the fuse. The next morning the inside of the pickup was on fire, the
vehicle was a total lost. The insurance company, stated that this was a
common fault with the wiring on this model vehicle and just bought a new
one. I had noted that the replacement fuse was .25 amps larger than the
original. The mechanic stated, if you have a short it will blow. The fuse
had not blown, the red wire from the battery + post going into the wiring
harness and through the firewall had melted. The fire had started under the
dash. Lesson well learned.
Clyde

"George Patterson" > wrote in message
news:zxNee.56$Dn.52@trndny02...
> nrp wrote:
> > I suggest 1 Amp as the OEM clock is an occasional very short but sharp
> > current pulse type of load.
>
> Say what? It's got a little motor in it. Current draw is constant.
>
> George Patterson
> There's plenty of room for all of God's creatures. Right next to the
> mashed potatoes.

[nrp]

That's that's the OEM clock I have. Just between us girls, mine only
ran about 10 years before it hung. I opened it up, washed it out in
solvent, and reoiled with 15W50 Mobil 1 oil. It's been keeping good
time for about 15 years now.

They have a really clever mechanism in them that adjusts the speed very
slightly as you adjust the hands of the clock. If you have to keep
advancing them, it speeds up etc.

Are you sure it (the replacement fuse) wasn't 25 amps bigger? It is
hard to imagine a fire being started from a measley (sp?) 250
milliamps..........

[RST Engineering]

If you take a look at the current pulse during the solenoid pop, you will
find that it is just a little bit over 250 mA (0.25 amp) during the tug, but
the current only flows for a quarter of a second or so.

I recommend a "slow-blow" type fuse for the application where the current
has to exceed the rated current for some period of time before it blows.
The amount of time is dicatated by the amount of current. A short circuit
of ten amps or so will pop it in a few milliseconds, yet it will hold half
an amp for a couple of minutes.

The slow-blow gives you the best of all possible worlds with pulsed current
like this.

See also the Kitplanes article on making your own LCD clock with a Rat Shack
module. Current draw is something on the order of half a milliampere.

Jim



"nrp" > wrote in message
ups.com...
>

[Greg Farris]

Jim -
No apologies to the guy you torpedoed out of the water a few posts ago, but
who came out being pretty close to the mark????

[RST Engineering]

Huh?

Jim


"Greg Farris" > wrote in message
...
> Jim -
> No apologies to the guy you torpedoed out of the water a few posts ago,
> but
> who came out being pretty close to the mark????
>