[Amps] Solid state relays and step start

[Mike Saculla]

Roger, your last line tells the story. If it fails shorted, it should be obvious by the fact that the equipment won't shut off. But a failure at some resistance would certainly set up a potential dangerous situation. I've only seen the shorted situation, but you have a lot more experience than I with SSRs. This is important info for those that use or want to use SSRs in their amps. Thanks!

Mike K6MDS


> Date: Fri, 5 Mar 2010 02:29:04 -0500
> From: sub1 at rogerhalstead.com
> To: fqm at msn.com
> CC: amps at contesting.com
> Subject: Re: [Amps] Solid state relays and step start
> 
> Many years of working with the things I agree ... mostly.  Although they 
> normally fail shorted, they do occasionally fail "leaky" in a mode from 
> low to high resistance, but rarely open. Not never, but rarely.
> So, it's bad enough to have them fail shorted, but then a small 
> percentage will leave you guessing.
> If they fail other than shorted and under load it can get real smelly in 
> there.  OTOH they can fail with enough resistance that the circuit won't 
> work, but is quite capable of electrocuting you.
> 
> 73
> 
> Roger (K8RI)
> 
> Mike Saculla wrote:
> > When solid state relays fail, they fail in the shorted condition. One of their downfalls.
> >
> > Mike K6MDS
> >
> >
> > From: garyschafer at comcast.net
> > To: Amps at contesting.com
> > Date: Thu, 4 Mar 2010 15:53:17 -0500
> > Subject: [Amps] Solid state relays and step start
> >
> > Has anyone had problems using a solid state relay to short out the step
> > start resistor in a power supply?
> >  
> > I have heard of problems of not enough current thru the SS relays (when amp
> > is in standby) when used as the primary on/off relay. Sometimes a resistor
> > has to be placed in parallel with the transformer primary so the relay works
> > properly.
> >  
> > When used in a step start circuit the current could be quite low as well as
> > the voltage at the relay due to the resistor across the relay.  Any issues
> > here?
> >  
> > 73
> > Gary  K4FMX 		 	   		  
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