I guess with transformers the relay should switch in on the peak voltage.
As current peaks 90 degree behind that should be the best moment with least
surge current.
73
Peter
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of TexasRF@aol.com
Sent: Montag, 10. Februar 2014 18:50
To: donroden@hiwaay.net; amps@contesting.com
Subject: Re: [Amps] Solid State Relays Again
But, unlike a mechanical relay, the SSR typically fails with a short
circuit. The power supply could be energized when expected to be off. There
is a
bit of residual current leakage in the off state that can leave a few
hundred volts present on a hv power supply.
Of course the relay can fail with welded contacts and have the same danger.
A capacitor input type filter will cause much higher current peaks (5X not
unusual) than the average current. This makes over sizing the SSR current
rating very important. In addition, there are small losses that are subject
to peak current squared heating. At 100A and only .01 ohms, this amounts
to 100 watt peak power loss and the SSR does get warm. This makes attention
to adequate heat sinking important as well.
After loosing a couple of 70A rated SSR's in a 70cm kw amplifier I went
back to the original mechanical relays.
Can someone please explain why turning on/off at a zero crossing is a
problem? Seems that could still happen at times even with the random
on/off.
73,
Gerald K5GW
In a message dated 2/10/2014 8:58:26 A.M. Pacific Standard Time,
donroden@hiwaay.net writes:
Quoting KA4INM <ka4inm@gmail.com>:
> and an instant disconnect if the protection circuit detects too much
> screen current or a sharp increase in (negative) power supply current
> (an arc) surely make them well worth bothering with.
> --
> Ron KA4INM
If for no other reason.
Don W4DNR
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