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Z-12 contactor failure
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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 24, 2018 9:55 am    Post subject: Z-12 contactor failure Reply with quote

At 11:15 AM 4/24/2018, you wrote:
Quote:

. . . . Not wanting to venture into the dark side of some of these "conversations", I just want to relay what I have personally viewed on this subject of old switches and WD40.....

Some legacy Cessna switches were simple pull-push, like a Master.

Geesh! That goes back aways. I think some of those
switches (automotive devices from the likes of
Cole-Hersee) were sill in production airframes
when I joined Cessna in '64. C-H still makes those
venerable devices.

[img]cid:.0[/img]

Quote:
I have repaired 2 of them. If one is (very) careful bending the retaining tabs the switch can be worked apart and resealed. What I found in both was severely hardened original lubricate. Hardened to the point that if a piece gets into the contacts, it can cause a faults.
Cleaning with the usual sprays and re-lubing with modern electrical grease has fixed both and they are still working today.... but, it was the old lube that caused random failure. These were master switches.

Yeah, fortunately the enclosure alloy would allow
opening and re-closing the tabs without fracture.
But I would have been hard pressed to 'sell off' the
procedure in a Service Parts Manual!

I do recall an 'approved' disassembly, refurbishment
and re-assembly of the OFF-L-R-BOTH-START switches
from Aircraft Spruce when the electrically destructive
nature of modern starter engagement solenoids was
discovered. And that was, as Barry intimated, an AD . . .

https://goo.gl/QV3gTF

Quote:

About WD40, . . .I have used it on a lot to things, but this comment is about use on guns. I have pulled rifles from several years of storage and not been able to operate the bolt action. The one flaw I see with WD40 is that once the lighter carry fluids evaporate, it leaves a strong, thick film that can almost seize close fitting parts. Other than that issue, it does great duty as a penetrate and shield from water and rust. . . .

Absolutely fine stuff . . . there are probably a half
dozen cans scattered around my shops and the truck-box.
Yes, I've seen the results of WD40 used to lubricate
Oilite bearings. They became clogged and totally
un-recoverable. Had to cut new ones from raw stock
on the lathe.


Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 24, 2018 10:08 am    Post subject: Z-12 contactor failure Reply with quote

Quote:
Most devices give us advance clues as to their
distress before they fail outright. I suggest that
the FIRST time a switch, relay or contactor demonstrates
an electrical infirmity, it is time to replace it.

Stubbed my toe here a bit. I do recall the electrical
failure of a mil-spec switch in the overhead panel
on a Beechjet. It was a spring-loaded, press-to-test
switch that was seldom used . . . and carried a tiny
fraction of rated current.

Yet, the switch had gone totally open . . .

The tech I was working with started the procurement
process for a new switch . . . which would have taken
several hours and exercised a lot of people. Pondering
the range of possible cause/effect I hypothesized that
the switch's failure may be the result of DISUSE.

The 10A rated, silver-cad contacts DEPEND on some degree
of electrical arc to burn away a thin film of corrosion.
So before he put the requisition into the slot, I
got a 5A, 30v constant current power supply from the lab
and connected it right across the switch such that
the 'failed' contacts provided a dead short on the
supply.

After a few dozen transitions of the switch, it became
conductive and demonstrated a very low on-resistance
(less than 10mv of drop at 5a). We were able to declare
the switch 'refurbished' and put the panel back together.

That particular application would have benefited from
gold-plated contacts on the switch. Such contacts are
designed for conductive longevity while working very low
or zero-current switching conditions.



Bob . . .


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skywagon



Joined: 11 Feb 2006
Posts: 184

PostPosted: Tue Apr 24, 2018 10:35 am    Post subject: Z-12 contactor failure Reply with quote

Hi Bob,

Yes, you picked up on exactly the switches I was referring with my comments.
If you come across replacements, please put a P in your memory bank to let me know where to obtain.
Much appreciated. .
Dave


 [quote] ---


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 24, 2018 11:22 am    Post subject: Z-12 contactor failure Reply with quote

At 01:34 PM 4/24/2018, you wrote:
Quote:

Hi Bob,

Yes, you picked up on exactly the switches I was referring with my comments.
If you come across replacements, please put a P in your memory bank to let me know where to obtain.
Much appreciated. .
Dave

check through the offerings here

https://goo.gl/4r9M3x

you may find a suitable substitute if
not exact replacment. the switch
I illustrated is a Cole-Hersee 50047
which is probably available through a
Coll-Hersee dealer.



Bob . . .


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alec(at)alecmyers.com
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PostPosted: Tue Apr 24, 2018 4:13 pm    Post subject: Z-12 contactor failure Reply with quote

I lost track of which Bob was recommending annual WD-40 as a switch failure preventive prophylactic, and which Bob wasn’t.
Can someone advise?

On Apr 24, 2018, at 3:21 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

At 01:34 PM 4/24/2018, you wrote:
Quote:

Hi Bob,

Yes, you picked up on exactly the switches I was referring with my comments.
If you come across replacements, please put a P in your memory bank to let me know where to obtain.
Much appreciated. .
Dave

check through the offerings here

https://goo.gl/4r9M3x

you may find a suitable substitute if
not exact replacment. the switch
I illustrated is a Cole-Hersee 50047
which is probably available through a
Coll-Hersee dealer.
Bob . . .


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