nuckolls.bob(at)aeroelect
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 Posted: Fri Oct 18, 2013 3:57 pm Post subject: Switch question !!!OOPS!!!! |
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At 04:12 PM 10/18/2013, you wrote:
| Quote: | I purchased some very nice DC-rated Mil-spec Honeywell switches (#MS24523-23) to use as ignition switches with my Rotax powered Kitfox. In checking the spec sheet after the fact, I see that they have “silver cadmium oxide” contacts. Then there is a statement that “non-arcing loads (generally less than 12v & 0.5 amps) are not recommended” with silver cadmium oxide contacts. Can anyone tell me if using these style switches with the silver cadmium oxide points, for ignition (or master switches with the DPDT version), would be acceptable & prudent?
John Evens |
Yes, I don't understand that admonition in
in the spec sheet. Did you find that on the
'net? Very few applications for toggle switches
are free of arcing. The degree by which arcing
is generated can be all over the map but in your
airplane, the worst case loads that might exist . . .
paired with the exceedingly low duty cycle for
switches in light aircraft do not pose any
threat of premature failure due to overloading.
Can you sent me a copy of the spec sheet or
a link for downloading it?
Had a momentary case of keyboard-in-mouth disease.
Meeting design life with switches/relays with
silver-cad ASSUMES some degree of arcing to help
burn away corrosion. Non-Arcing is sometimes
referred to as 'dry contact' switching too. Switches/
and relays working in these tiny loads generally
have gold plated contacts . . . no corrosion . . .
but don't hit them with an arcing load or you
burn away the gold and convert the thing to a
really bad, dry-circuit switch.
Short answer is yes, those switches are entirely
suitable for use on your airplane. There is a
very SMALL possibility that they'll 'go open'
because they're not used enough . . . I.e.
a special application switch that is not routinely
used.
Found this in a Beechjet once. It was in some kind
of seldom used press to test function. The tech was
headed off the stockroom to get a new switch.
I told him to hold off. Got a bench supply that
I set up for 28v at 3A constant current and used
the open swicth to 'short out' the power supply.
I wiggled the switch a couple dozen times and rechecked
it with a micro-ohmmeter. Contacts were restore to like
new.
Bob . . . [quote][b]
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