Re: snubber resistor power rating?
From: John Popelish (jpopelish_at_rica.net)
Date: 11/27/04
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Date: Sat, 27 Nov 2004 13:54:47 -0500
legg wrote:
>
> On Sat, 27 Nov 2004 11:52:01 -0500, John Popelish <jpopelish@rica.net>
> wrote:
>
> >At 60 hz, a 1 uf cap has an impedance of about 377 ohms. Put that in
> >series with 170 ohms, and the total impedance has a magnitude of about
> >414 ohms, so the current is .29 amperes. the resistor power is 14.3
> >watts.
> >
> 1 / ( 2 x pi x f x C) gives 2K65 as Z for 1uF.
Thank you. I forgot to hit the reciprocal key on my calculator.
(1/.377=2.65)
> A series 170 ohm resistor has little effect on 60Hz current, which
> will be 90mA @240VAC, producing 1.4W static loss on a non-switching
> circuit.
>
> If this combination snubs a triac, firing at all possible line
> peaks, worst case loss due to the snubbing energy, if the circuit is
> damped effectively by the values used, is
>
> C x Vp^2 x f / 2 = Pd
>
> 1E-6 x 340Vsqred x 120hz /2 = 7W
>
> RL
-- John Popelish
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