Homebrew PCBs

>The other two drive the motor at 
>up to 80VDC @ 20A.

Matches a Gecko G320 servo drive. Whatever, switching contacts in 
the range 20A@80VDC would seem to be in order. But if it's the G320 
then you can get by with a lower rating than that. IIRC, 20A is the 
current it trips at so this is a peak rating not a continuous 
rating. Also, will you ever be using 80VDC motors?

Once you've decided on the contact rating, I would recommend 
115/120VAC relays/contactors driven by an appropriate solid state 
relay. The SSR would only need TTL voltage levels for control. Here 
is one being used to control a 3.5A 120VAC drill motor in my CNC 
drill setup;

http://www.pbase.com/eldata/image/46673208

The wires on the left are in the 120VAC circuit and on the right is 
the TTL level circuit. Note the part number and look it up on 
Digikey's web site for zero crossing and snubber features. You 
should be able to get by with one with a lower current rating based 
on the relay/contactor coil current but keep the other features.

You should post this in the Electronics 101 forum if you haven't 
done so already.

--- In Homebrew_PCBs@yahoogroups.com, "bigjamma" <bigjamma@...> 
wrote:
>