AVR-Chat

On Tue, Feb 10, 2009 at 08:13:54AM -0800, Steven Hodge wrote:
> I may have posed this question some time ago, but I'm still confused.
> I'm trying to determine if a pcb slide switch will meet my current
> requirements, which in this particular case are 200 mA at 12 VDC.   So
> I'm looking at a page (1646) of the Mouser catalog, for such switches
> all from the same manufacturer (Alcoswitch) and I see one series that
> says:
> 
> "gold, 0.4 VA; silver 300 mA @ 115 VAC"
> 
> So if I divide 0.4 VA by 12 V I get 33 mA.  How come this seems so
> drastically less than 300 mA at 115 VAC (300 mA x 115 V = 34.5 VA)?  I
> know there is an AC/DC thing here but the difference in this "power"
> is almost two orders of magnitude!

Is because "there is an AC/DC thing here." In general a switch can not
handle as much DC power as AC power.

> Another series is similar:
> 
> "gold, 0.4 VA @ 20 VDC; silver 300 mA @ 115 VAC"
> 
> Why was the "@ 20 VDC" added here?  How do I convert the rating to my
> 12 VDC level?

They are saying one should not use more than 20 VDC or nominal 115 VAC
with that switch. That with DC one should stay under 0.4 VA. They don't
say the same thing about AC because one is either going to use 100, 115,
or 220. That rating at 115 is close enough for the oddball places in
Japan running 100 VAC.

> Then another series says only:
> 
> "300 mA @ 125 VAC"
> 
> Does that mean the switch is not usable with DC?

Means it is not rated for DC.

You need stouter switches for your 200 mA.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
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Whom computers would destroy, they must first drive mad.