At 10:15 PM 11/26/96 -0800, you wrote:
>>         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
>
>

        All that I really meant was if you do manage to find an SSR that can
handle the current at startup, it will Drastically reduce the inductive
spike (provided it is the zero crossing type) which is having the
ill-effect of reseting the logic (Pics are especially sensitive to
glitches). For most applications, SSR's are cool!  While I wouldn't try to
run an elevator from a pic, I suppose it could be done with the logic
running on a seperate supply all the way back to the mains, and optically
isolate the power relays (two forms of isolation, why not).  You're right
though,  for every big SSR, there is an equally or bigger motor that draws
even more current on startup as you stated (!)
        Hamilton