I think the acquired advantage with the zero
crossing is then there isn't a chance the power
supply will be turned on at the AC cycle peak.
Mark WB8JKR
On Wed, 17 Nov 2004 20:03:55 -0500 jeff millar <wa1hco@adelphia.net>
writes:
> Ed...
>
> I've used zero voltage switched solid state relays twice in 2KW
> amplifiers, one at 432 and one at 144 MHz. The 432 amp included the
>
> normal step start circuit, but once I noticed that the zero voltage
> switching feature, I tried it without a step start in the 144 amp.
> The
> circuit switched on with very little drama, the lights blinked about
> the
> same amount as when transmitting at full power.
>
> One design note on high voltage power supplies suggested that
> extremely
> high surge currents can damage electrolytic capacitors. These surge
>
> current maximizes when the turn on relay or switch happens to make
> contact at the peak of the line cycle. The zero voltage switching
> function reduces the surge currents to approximately the same amount
> as
> what it takes to recharge the caps at the peak of the line cycle.
>
> These amps showed no signs of RF getting into the switches,
> including
> during operation at a big hilltop VHF/UHF multi-multi contest group
>
> with 1.5 KW on all the bands. But for HF amps with a lot more RF
> currents flowing around the shack, it's probably best to run the
> control
> leads through an EMI filter similar to what you find on a AC power
> inlet.
>
> One caution, the off impedance of these switches doesn't look that
> good
> in the spec sheet, leading to the conclusion that an "off" power
> supply
> could have 10 to 100's of volts on the output. I didn't see this,
> the
> voltage didn't rise above a volt or so, but maybe unit to unit
> variation
> or operation at high temperature could cause more leakage.
>
> hope this helps,
>
> jeff, wa1hco
>
> Ed Stallman <n5blz1@houston.rr.com> writes:
>
> >>Wondering if anyone has used a zero crossing circuit on a high
> voltage
> >>supply to reduce inrush current at startup? would this work for
> soft start
> >>or would it just assist?
> >>Ed N5BLZ
> >>
> >>
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