Re: relay thanks

--- In CAD_CAM_EDM_DRO@egroups.com, "Terry Ackland" <hexagon@o...>
wrote:

> guys,
> I would like to thank you all for the imput regarding ssr. I

connected

> up my so called "3hp peak power", 7amp Shopvac and the 16 amp ssr
> operated ok. I then added my 3.3 amp router and the ssr handled

both

> together.

Terry: You did what most engineers would finally do...hook it up and
see if it blows! Seriously, the issue from the start was not just
one of horsepower. Solid State relays are built with semiconductors
that are much more sensitive to voltage and/or current spikes than to
load over time (Horsepower, BTU's, etc). Those type of loads
translate into heat which if not controlled in semi's causes failure,
however a voltage spike of only a millisecond (in some cases
nanoseconds) that is above the rated value can mean instant
destruction. Most of that is factored into the the relay design.
Almost all semiconductor ratings are at some low room temp and you
have to derate the max numbers for each degree above that value. The
trick is to try and keep the temp as close to that level as possible
by using heatsinks and airflow. Driving motors with solid state
devices has always been interesting to say the least. Most SS relays
are built on Triac designs that are hearty little devices that don't
have a lot of loss and are built to take abuse. I would have been
comfortable taking the 16A rating and the amp ratings of the motors
and doing what you did and hooking it up and going with it. The only
potential problem is if either motor stalls for any reason you could
see currents of several times the rated value.

Your question sure did stir a debate about horses and such.