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From: <jewen@comporium.net>
Subject: Re: [FlyRotary] Re: Relay Woes
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Date: Fri, 26 Jun 2009 06:28:22 -0400 (EDT)

If you would like to know why it will not turn off ... Inside the SSR are likely SCRs (Silicone Controlled Rectifiers) A SCR is a special diode.  The SCR will not pass current until gated (turned on by a signal) once the SCR is turned on it stays and conducts current in one direction  until it reaches zero volts, at which time it turns off, waiting to be gated again.  These work well in AC applications since the supply voltage on the load side hits or crosses zero 60 times a second. This type of relay will have 2 SCRs, 1 for the positive current and one for the negative current.  Works well in an AC load application, but not with SC, since the supply voltage never drops to zero.  A FET type SSR (such as what Tracy uses as a staging relay on the 20b version of the EC2) would likely do the job for you and should have the same form factoer as your existing realy eliminating the need to rewire.

Joe


---- Original message ----
>Date: Wed, 24 Jun 2009 12:20:00 -0800
>From: "Al Gietzen" <ALVentures@cox.net>  
>Subject: [FlyRotary] Re: Relay Woes  
>To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>
>   Dave;
>
>    
>
>   You'll notice on the data sheet for the relay you
>   bought it says "yes" under the "zero cross function"
>   - Which I'd take to mean for DC it will not turn
>   off.
>
>    
>
>   Al
>
>    
>
>   -----Original Message-----
>   From: Rotary motors in aircraft
>   [mailto:flyrotary@lancaironline.net] On Behalf Of
>   David Leonard
>   Sent: Wednesday, June 24, 2009 7:34 AM
>   To: Rotary motors in aircraft
>   Subject: [FlyRotary] Relay Woes
>
>    
>
>   For you EE types, I have a question.   I am
>   installing a smoke system and wanted to use a relay
>   to control the pump.  I bought this relay from
>   Mouser that I thought would do the trick:
>
>   http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtLEhJ5P%2fNsZ6bnrz6%2f%252b%252bJvA50eSiydqPQ%3d
>
>   The problem is that if there is any load (like the
>   pump or even the 0.02A indicator LED I installed,
>   then the relay will not turn off when I turn off the
>   signal voltage.  So either I do not understand how
>   to use the relay, or I chose the wrong relay.  I
>   have checked my wiring in-so-much as to confirm that
>   the signal voltage does turn on and off with the
>   switch, voltage across the 'LOAD" terminals does
>   disappear when there is no load but not when there
>   is a load (current). 
>
>   Is it possibly because this relay is designed for an
>   AC load?  Other suggestions?
>
>   --
>   David Leonard
>
>   Turbo Rotary RV-6 N4VY
>   http://N4VY.RotaryRoster.net
>   http://RotaryRoster.net