Re: gEDA-user: SSRs vs. discrete triacs

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

On Sat, Mar 03, 2007 at 09:06:26PM -0500, DJ Delorie wrote:
> 
> > I need to switch <1A @ 24VAC loads,
> 
> Been there.  http://www.delorie.com/house/furnace/
> 
> I use an opto-triac and an alternistor.  Alternistors handle the two
> polarities with different silicon, which helps with inductive loads,
> which is what I've got.  No additional discretes are required, except
> for a 38 ohm current limiting resistor between the opto and the
> alternistor.

Nice design.  Your MCU-controlled zero-cross scheme is very nice, but
not applicable in my case because I am not guaranteed that all the
loads I'm switching will be in phase, so I'd need several phase
detectors, and I'd rather just get zero-cross triacs (and I will pay
attention to turn-on voltage -- thanks for pointing that out).

On an unrelated note, how do you like the Weidmuller spring-clamp
terminal blocks on that board?  I had given up on terminal blocks for
field connections myself -- these days I solder 3-6" of 22ga discrete
wire, and then use wirenuts to make the connection in the field (and
by "in the field" I mean not in the lab/workshop -- i.e., while lying
on your back in a gravel crawlspace at 95F/98%RH with poor lighting
and dirt getting into all of your bodily orifices).  But those
connectors look nice and are reasonably priced.  The one thing they
don't have that my wirenut system does is the ability to gang several
wires together (e.g., shared common).  Still I can always just stick a
5" length of wire in one of those connectors and fall back on my
wirenut system when necessary.

Randall


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