> From: daveb <daveb@buffnet.net>
Hi Dave,
> an anode transformer primary (2.5Kw level) ? I've noticed that
> 25 Amp versions are available that switch on at zero crossing.
> Sounds like a nice way to eliminate the mechanical relay with current
> limit resistor for surge protection.
That's a total misconception Dave, and you are not alone. One
amplifier manufacturer I know of also sells an amp with a zero
crossing turn on "thinking" and claiming it limits inrush.
What is forgotten is this. Inrush occurs over several AC
cycles, not just a fraction of one cycle.
Starting at zero almost guaranties maximum inrush damage to
components, because the entire first quarter cycle of ramp up is
available every time for surge, as well as the start of the next
half cycle, and so on.
What you really want to do is slowly start the supplies, and remove
limiting after all the components have had a change to charge (or
filaments to reach higher temperatures.
Inrush is a duration problem over a few seconds, it is absolutely not
a 1/240th of a second spike problem cured by zero crossing turn on.
Zero crossing is like using a fuse to protect a grid...
73, Tom W8JI
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