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From: youngqd@jacobs.CS.ORST.EDU (Dean Youngquist)
Newsgroups: sci.electronics
Subject: Re: solid state relays
Keywords: smoke, sparks, fire, :-)
Message-ID: <1991May11.180531.9108@lynx.CS.ORST.EDU>
Date: 11 May 91 18:05:31 GMT
References: <12500@qisoff.phx.mcd.mot.com>
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In article <12500@qisoff.phx.mcd.mot.com> hbg6@citek.mcdphx.mot.com writes:
>I am building a controller for the evaporative cooler on my house. The
>blower motor has two speeds, selected by providing power to either
>the HIGH terminal, or the LOW terminal.

>text deleted

>Bottom line; if the SSR fails closed and power is applied to
>both terminals am I going to burn up a $200 blower motor?
>
The SSR could fail either open or shorted.  I would suggest some old-
fashioned slow-blow fuses in series with them power source before it splits
into the high/low windings.  If both windings were somehow powered
simultainiously the fuse would blow.  Make sure the fuse is not rated too
high over normal maximam current.

Dean Youngquist
youngqd@jacobs.cs.orst.edu