[GreenKeys] Motor start relay sizing

[John Nagle]

> Anyone have an opinion if a single ST6's motor control power outlet could
> handle powering _all_ of the following (on a power strip):
> 
> 28 KSR + LPW Paper Winder
> 28 ASR + LPW Paper Winder + Tape Winder?
> 
> Can the contacts on the relay and the wire used throughout handle the
> current of all of these (say at all once when a signal comes in and turns on
> the relay)?

    First, do you mean the "ST-6" RTTY demodulator from 1965, or an
ST6 8-bit microcontroller board?

    The original ST-6 ("http://www.jptronics.org/radios/Teletype/st6/st6.html")
was an article, not a product.  Choosing the relay was up to the builder.
So one can't tell what the contact ratings are.  If the relay is 40 years old,
the contacts probably need some burnishing.

    Personally, I use a Continental 25A SV series industrial solid-state
relay for Teletype motor control.  Those little encapsulated bricks
are routinely used to start motors much bigger than anything in a Teletype.
This is more solid state relay than is really needed here; a smaller Opto 22
unit would work just fine.

    With all the stuff you're starting, you need at least a 15A relay.
Figure 7A per Teletype.  Since this is an inductive load, some snubbing
at the contacts is indicated, or in time, the contacts will burn out.
Solid-state industrial relays have that protection built in.

				John Nagle