nuckollsr(at)cox.net
Guest
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 Posted: Sun Sep 10, 2006 10:06 am Post subject: Switch Ratings |
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| Quote: | >
<jskiba(at)icosa.net>
>
> Okay,
>
> I Have gone and confused myself, I am looking at ordering some
switches for
> my OBAM aircraft and can't rember which would be better Higher current
> switch
>
> The catalog states two options:
>
> 1: Silver Rated 3A (at) 125V AC
>
>
> 2: Gold Rated 0.4 VA max (at) 28V AC/DC max
>
>
> My application will be used in a 12-14 Volt system I want the switch with
> the higher switch capability which is it?
>
> THANKS in advance
>
>
> P.s. my guess is option one the silver contacts but for some reason I
don't
> think that is correct....
===================================
OK, here is the break down:
Silver is the better conductor - But - Oxidized much more.
Gold is obviously slightly less in conductivity (but, you will never know
that) than Silver - But - for the practical, does not oxidize.
Without getting ridiculous in explaining a switch ... If you Double the
Voltage you Half the current. So a Switch that is rated at 0.4 Amps (at) 28
VDC will
be able to handle 0.8Amps (at) 14 VDC.
As for your amperage rating of the switch:
1 - Find out what the circuit draw at MAX will be.
2 - Use a switch that is about 50% over rated than the MAX draw.
3 - If a switch is rated in AC DE-RATE the amperage by 36 to 40%
[This is a rule of thumb. It has NEVER FAILED for me. Some pencil pusher
may have worked out a more accurate number but definitely not a better one.]
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Don't make it any more complicated than it needs to be. Check
out the article at:
http://www.aeroelectric.com/articles/swtchrat.pdf
I've never seen a failure of a switch in a TC or OBAM aircraft
that can be attributed to failure to observe ratings. The ratings
assume many thousands of operations that you're NEVER going to
achieve in your airplane. On the other hand, if you keep your airplane
10 years or longer, it's almost a given that you'll have to replace
some switch, some time . . . but not because you 'overloaded' it. See:
http://www.aeroelectric.com/articles/Anatomy_of_a_Switch_Failure/Anatomy_of_a_Switch_Failure.html
http://www.aeroelectric.com/Pictures/Switches/miniswitches.jpg
Here's and airplane flown often and had over 5 years service on MINATURE
toggles in the landing light, nav light, and strobe circuits. All of
these switches could be said to be 'overloaded' when the catalog
ratings are treated as limits.
Gold contacts are for very small signal switching, what Microswitch
calls "non-arcing" in . . .
http://www.aeroelectric.com/Mfgr_Data/Switches/tl_series.pdf#search=%22switch%20ratings%22
We often purchase 5A relays with silver-cad contacts plated with
a thin layer of gold. If NEVER subjected to higher currents, the
gold plating allows the relay to function well in very small signal
switching . . . but if ever used in a higher current application,
the gold layer is damaged and it officially reverts to a silver-cad
contact relay.
Someone at Beech decided years ago that it would be a good thing
to do 100% receiving inspection of all incoming super whippy mil spec
relays.
They set up a test bench and dutifully subjected every incoming relay
to 5A switching loads and pronounced them 'fit for duty'. Months later
we were having a rash of field failures in some circuits due to the
fact that inspection blew off the gold on relays used in both
"power" and "signal" switching applications. An EXPENSIVE way
to learn difference.
Bob . . .
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