[GreenKeys] Solid State relays

[John Nagle]

> From: "Larry Tighe" <larryradio at att.net>
> Subject: [GreenKeys] Solid State relays
>

> I have a solid state relay, rated at 240 VAC, 20 amps.  It can be keyed with
> 6 VDC.  I put the ohm meter (analog) across the AC terminals and it opens
> and closes the "switch" with 6 VDC.
>
> I tried to key a tty loop with it and it won't close the circuit.

    AC "solid state relays" are usually coupled to a control circuit
so that they switch when the AC line crosses zero.  This minimizes
heating.

    DC solid state relays are available.

> Message: 10
> Date: Wed, 25 Aug 2010 16:09:11 -0500 (CDT)
> From: Jim Haynes<jhhaynes at earthlink.net>
> Subject: Re: [GreenKeys] Solid State relays
> To: Paul Kasley<kasley at fnal.gov>
> Cc: Larry Tighe<larryradio at att.net>,greenkeys at mailman.qth.net
>
> On Wed, 25 Aug 2010, Paul Kasley wrote:
>
>> >    use MOSFETs instead of SCRs. I'm not sure if you can
>> >  find an optocoupler with a 300V VCEO transistor output that can pound 60mA
>> >  directly. Also, you need to snub the coils to manage the inductive kick when
>> >  the transistor turns off - a simple 1N4004/5/6 diode may do the trick
>> >  without excessively lengthening the current pulses thru the coils.
>> >
> Look at the Fairchild HSR312 and related products.  I haven't got around
> to trying this yet, but it looked good - until someone pointed out that
> the turnoff time is in milliseconds.

    The HSR312L will run a Model 15 at 45.45 baud quite well, provided
you snub the inductive spike coming back from the selector
magnet.  I use those parts.  See

	http://www.aetherltd.com/connecting.html

for circuits and board layouts.

The data sheet says worst case turn-on time is 3ms; turn-off time
is 0.5ms.  That's good enough for 45.45 baud.  Actually, the
device is somewhat faster than its worst case spec.  The parts cost
about $3 each.

					John Nagle