>         But the "zero crossing" type of SSR will practically
> _eliminate_ the worst inductive spike, which happens when the A.C. is at
> its peaks. I actually designed a zero crossing circuit and used a
> mechanical
> relay and inadvertantly forgot the delay between the time when you
> energize
> the relay and the actual time that the contacts close (doh!).  Needless
> to say there was still a spike but when I switched the relay to an
> immediately
> swithing TRIAC (opticaly isolated) the spike was virtually eliminated,
> as well
> as the reseting problem I was having. P.S. Put a giant 1 ohm resistor in
> series
> with the load and connect a fast digital storage scope across the
> resistor and
> the voltage you see on the scope will convert almost exactly to current
> (minus
> the small loss of power that a 1 ohm resistor has on your particular
> motor).
> Of corse most motors draw more current on startup, but its the Inductive
> kick
> we are worried about here. Another option is to use In-Rush current
> limiters.
>         They make some *Huge* SSR's these days, just use one rated at Twice
> the motor current and it will be fine. (and I wont say "and dandy" 8^)
>         -Hamilton

Last Sunday I was at an olive pressing factory, on starting a
centrifugal filter
380V x3 Phase for the first ten seconds draw 300A per phase at fifteen
secs 200A
at 45 secs about 80A then a timer changed it from star to delta
about 6 mins later it was drawing about 40A
Well pumps are also the same, as are industrial washing machines
spin motors
syncronous motors operating in nonsyncronous mode can easily
draw 10 times the sync current (syncronous motors don't have brushes)
Twice the rated load !! and when they blow closed circuit !!
Try one on your fridge and let me know how you get on
Also try phoning your local lift manufacture and ask them why
they don't use SSR's
ps: I liked the joke about the 0v relay
--
Peter Cousens
email: peter@cousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax