On 2/11/2014 8:53 AM, Jim Thomson wrote:
When I had my old drake T4XC transmitter, about every 40th time I turned it
on.... it just went
click and turned on. The other 39 times it made a helluva thump noise inside
the xfmr! There was
NO step start on the outboard AC4 power supply. My conclusion was I hit a
zero V crossing aprx
every 40th time. The zero V cross SSRs caught my eye soon after that.
Sounds like my old 50A Astron. Big transformer and rectifiers. Pass
transistors for a regulator. Once in a while that thing turns on with a
WHummpppp and a low frequency ringing that just trails off.
The SSR is just an on-off switch.......and so is a contactor. On a lot of
contactors, the contacts are field
replaceable and ditto with the solenoid coil. Unlike a relay, a contactor is
essentially two sets of contacts
in series...per pole. Any arc is split into 2 x arcs = zero arcs.
Many have "arc chutes" as well.
73
Roger (K8RI)
They open off fast due to the typ huge spring tension.
Of course you need one helluva lot of magnetism to overcome the spring tension.
Small stuff like P+B 40A relays
have next to nothing for spring tension, and contacts are prone to welding shut.
I find it amusing that all our HVAC stuff at work still uses contactors. Sure
P+B showed an example of a 150 hp electric motor
run on 600V 3 phase..all using a huge mess of SSRs in series parallel.
Problem is.... it would be a trick to trouble shoot
and isolate any int problems...or hard faults.
Jim VE7RF
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