[Amps] Solid state relays..again

[Roger (K8RI)]

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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