From: Fred Bloggs
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Subject: Re: V regulator input cap size?
References: <firstname.lastname@example.org> <0001HW.B9D9CD54001A5D15163F7590@news.covad.net> <0001HW.B9DAE8B7003F6E14163F7590@news.covad.net> <3DC1A954.email@example.com> <1%hw9.136243$Q3S.firstname.lastname@example.org> <3DC1AF48.email@example.com> <3DC1C89E.firstname.lastname@example.org> <email@example.com> <3DC1DBEA.firstname.lastname@example.org> <email@example.com>
Date: Sat, 02 Nov 2002 17:16:00 GMT
NNTP-Posting-Date: Sat, 02 Nov 2002 09:16:00 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Spehro Pefhany wrote:
> Not an oversight, John. I recommend changing the relay for a 24VDC one by
> using a very small filter cap for the relay coil eg. 22uF/50V (NONE will
> actually work with virtually all DC relay designs). A resistor was
> mentioned in the text, but I don't think it will be required. A 24V coil
> relay will cost about $0.005 more, in 10K quantity, than a 12V coil relay,
> but I think it is worth it to keep all the power in the coil. ;-)
> Fred: Sorry about changing the "rules" in order to get an elegant and
> reliable design that can be produced cheaply.
Using simple arithmetic, the DC component of Vrms is 0.9x. You can't get
a 24VDC stock coil to operate reliably over any standard temperature
range, environment, or manufacturing spread, using FW 60Hz. Give me a
specific part number so that I can show you how it fails.
The OC LED drives off the unregulated do not turn out to be all they're
cracked up to be. My calculations show the requirement for a 1W resistor