I don't see where zero-crossing voltage is a problem since it only happens during application of AC power. There is no collapsing flux since it hasn't been established.
The SSR's during turn off, don't "disconnect" (if that's the right word) until at "zero" current.
From the Opto22 spec sheet:
And actually, there is a "chance" every time one turns any piece of gear off, of having the contacts open at the "right" (or wrong) time(or somewhere in between) . I have "pulled the plug" on many devices while they were powered and sometimes there's a spark and a "snap" and/or see a spark and sometimes there is not.
Turning the radio off then right back on is of course another issue regardless of how the circuit is interrupted either by a switch, relay contact or Triac.
I cannot think of any reason why one would do that intentionally.
And in the case of the original question I am afraid I have diverged from it by even mentioning the use of SSR's to reduce switch failures (as is the mention of step-start systems etc)
REF: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Can someone please indicate the page in the HT-37 manual where it says NOT to this?
While I still cannot think of a reason why anyone
would do this, I only found the "CAUTION" text I excerpted and posted earlier. (that is, to pause in STBY before turning it off)
After printing out a pretty good copy of the HT37 schematic and taping it all together so as to see what's going on, (OPERATION SW is in the OFF position) .... It appears that the transformer remains powered and all voltages are present until selecting OFF.
There are 3 wafers that control bias switching, and other low level "stuff"
The only thing I can see that could be a problem is if one was doing RTTY , transmitting at full power, and then went from MOX directly to OFF, there might a problem with MAX AC current in.
But that's just a guess . Again, I don't see how it would be a problem if the transmitter wasn't transmitting (or keyed)
Again, the original "question" concerned OFF-ON-OFF rapidly.
No reason to do it, so don't!
Sorry for the long answer!
73/Rick
On Sat, Jul 13, 2024 at 11:37 PM, Jim Whartenby wrote:
As more zero voltage crossing SSRs are installed to power ON these radios, it will be interesting to see if there is an increase in power transformer failures due to corona discharge (aka wire insulation failure) in the? high voltage winding of these hallicrafters radios.??
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Zero voltage crossover is at the instant where current in the transformer winding is at a maximum.? Inductive circuits want to maintain a constant current flow through a winding so the collapsing magnet flux at turn OFF will generate as high a voltage as is possible so as to maintain this current flow.? This is the nature of inductive circuits.??
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I do not know what the exact failure mechanism is when switching from ON to STANDBY to OFF to STANDBY to ON in rapid succession.? But evidently it is the worst possible condition which generates a voltage high enough to cause the wire insulation to fail.? Not understanding this failure mechanism means to me that any proposed solution is just a shot in the dark.? Perhaps this point was understood by the HT-37 design team and that a workable solution was either just too costly or perhaps not even available?
Regards,
Jim
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73/Rick
W4XA
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73/Rick
W4XA
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All posts are created using OpenSuSE Leap 15.5 x64 Linux
Rick W7IMM