Two the fellow's earlier comment on not using the 5V line, when
reworking my 32A, that was the first thing I did - move to SS
specifically to idle the 5V line and avoid the risk of the well reported
short involving the 5V line.? Toward the end of the process, I was
getting ready to finish up alignment and had let the transmitter run
overnight to ensure it had reached stable temp across the chassis.? When
I came down the next morning, the rig was dead.? Painfully confirmed
later that some amount of windings on the primary or secondary had
shorted (there were no detectable winding-to-winding shorts at idle -
and I did not have a spare HVPS available at that time to test higher).?
However, as the variac was ramped up, the current draw of the
disconnected transformer soared.? So the 5V to HV short is apparently
not the only transformer failure mode with this model, unfortunately.
I solved the problem by cannibalizing another HT32.? But assuming Murphy
may like to come see me soon, I bought one of those shiny Dahl
transformers and it's here on the bench ready to run to the rescue when
the current transformer eventually dies.? Of course, with my luck,
simply having bought the Dahl transformer may keep Muphy away allowing
the current transformer to run the rest of my days.? ha ha.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
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On 7/1/2024 4:15 PM, Paul Christensen wrote:
"In addition, if you choose the "right" SSR, it will turn-on at
"Zero-Crossing" meaning it will activate when the sine-wave passes zero
volts (they're designed that way)."
Be careful when using zero-crossing (ZC) SSRs to switch extra-large power
transformers. I recently tried ZC type in my Collins 516F-2 and Drake PS-7
power supplies. In each case, it resulted in pulsing high current surges.
In one instance, the 4A fuse blew open in my Collins power supply during a
high-surge event.
The attached Tyco Application Note warns against using ZC type SSRs with
highly inductive loads.
The problem was fixed by changing to a random-switching type SSR from
Crydom. The AC load is switched from antiparallel SCRs. Datasheet
attached. I know others have used ZC type SSRs to switch large transformers
without any problems. I'm only offering this advice out of caution from my
own experience.
Paul, W9AC
