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nuckolls.bob(at)aeroelect
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 Posted: Sun Feb 12, 2012 9:39 am Post subject: Switch Ratings Conversion (AC to DC) for ST23N Toggle Swit |
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At 12:31 AM 2/12/2012, you wrote:
--> AeroElectric-List message posted by: Dan Jones <warbirds(at)shaw.ca>
Hi Bob,
I just finished reading your article "Switch Ratings, What's it all Mean?" and Chapter 11 of THE BOOK but I can't quite decipher the data for some switches I would like to use. I have some old (but mint condition) ST23N switches salvaged from a DC-3 audio box that was almost certainly a 28 volt airplane. I want to use them in a 14 volt Stearman restoration. I like them because they have a nice heavy feel, they're made in the USA, and they're from an era when people made stuff to work and to last. They also look nice and "period". Gleaned off the internet I have the switche's max rating of 250 VAC, and the contact load current rating at max rated voltage of 2.0 amps inductive AC, and 5.0 amps resistive. My running of the numbers and adding a fudge factor into it makes me think that 30 amps inductive and 75 amps resistive at 14 volts isn't out of line. Or am I talking out of my butt?
Study the data chart more closely and keep in mind that
a switch has THREE ratings: The ability to BREAK a circuit
(which is where the high voltage ratings come from) and
the ability to MAKE a circuit (which is the largest
influence on the high current ratings. Finally, there is
the ability to CARRY a current . . . which is generally
not a published rating because it is so heavily
influenced by ambient conditions and to some extent,
installation techniques. But in any case, the CARRY
current is not less than the max MAKE current.
[img]cid:.0[/img]
I could not find detailed data on the switch number you
quoted . . . but the data I did find gives me the impression
that these are pretty much plain vanilla, two pole toggle
switches. If you got them out of an audio box, the likelihood
that they were tasked with handling a lot of current seems
unlikely.
You would be on safe ground stressing these switches to
the lightest of the categories in the data chart
(Electrical Code Rating of 2). There are few instances
where the switch needs to be much more robust.
How would you LIKE to use them? In any case, your
assumption that the current ratings are inversely
proportional to operating voltage is flawed. There
are numerous, interleaved influences on the SERVICE
LIFE of contacts be they in switches, relays or
contactors.
Bob . . .
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stearman456
Joined: 14 Aug 2010
Posts: 49
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| Posted: Sun Feb 19, 2012 11:19 pm Post subject: Re: Switch Ratings Conversion (AC to DC) for ST23N Toggle |
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Thanks, Bob. After rereading your article I see where my math went awry. It looks like those switches will work out fine.
Dan
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