variable solid state relay
- Thread starter gr3
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RufusBrewer
Well-Known Member
I do not know what solid state relay pot rate is. A google search brings me to this post.
Generally speaking........ Solid state relays are on or they are off. Nothing in between. A pot (potentiometer) will not change that.
What you can do with an SSR, is turn it off and on real fast. You do not want to try this with a conventional coil and contact relay.
If you turned on an SSR for 2 seconds and turned it off for 2 seconds, you would get half the power. If you turned it on for 3 seconds and off 1 second, you would be at 75% power. On 1 second, off 3 seconds 25% power.
Instead of pot you are looking for a variable on/off device. Variable on/off devices are called Pulse Width Modulators, PWM.
Research PWM for SSR in connection to electric breweries and should get a much information. Also see if there is any Solid State Relay 101 tutorials on the web.
Generally speaking........ Solid state relays are on or they are off. Nothing in between. A pot (potentiometer) will not change that.
What you can do with an SSR, is turn it off and on real fast. You do not want to try this with a conventional coil and contact relay.
If you turned on an SSR for 2 seconds and turned it off for 2 seconds, you would get half the power. If you turned it on for 3 seconds and off 1 second, you would be at 75% power. On 1 second, off 3 seconds 25% power.
Instead of pot you are looking for a variable on/off device. Variable on/off devices are called Pulse Width Modulators, PWM.
Research PWM for SSR in connection to electric breweries and should get a much information. Also see if there is any Solid State Relay 101 tutorials on the web.
RufusBrewer
Well-Known Member
I learn something new every day. Thanks passedpawn.
What gr3 has is an SSR with a PWM inside it. Or at least it has the nominally equivelent circuity inside the puck. You control the On to Off ratio with an external potentiometer. The trigger voltage comes from the puck.
Back to the OP. Assuming you are running 120 VAC with Hot, Neutral and Ground. Yes, put one SSVR on the Hot leg of your circuit. Do not put a second SSVR on the Neutral leg, leave that as a direct connection from the device's Neutral point to AC socket.
If you are running 240 VAC, balanced power, that is an especially trick question. I could guess and assume, but I do not do that with 240 VAC. I would defer to somebody with specific knowlege.
I switch both legs of the 240VAC. Can't do that with this gizmo since you'd want the single PWM control signal connected to two SSRs. It's not technically necessary to switch both legs, but it makes me feel better knowing they are all off.
RufusBrewer
Well-Known Member
You could put one leg of 240 VAC, but that would get you down to 50% power. After you got leg A to off, you could turn leg B down to get from 50% to zero power. I would not run both legs on an SSVR and expect consistant results. No way to control the phase between the two SSVR.
One PWM split to two conventional SSRs should work nicely. How ever, if I wanted to make sure my relay was off, I would have a switch that pulls the input to ground. I do not know how much faith I could put into a PWM.
One PWM split to two conventional SSRs should work nicely. How ever, if I wanted to make sure my relay was off, I would have a switch that pulls the input to ground. I do not know how much faith I could put into a PWM.
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I have an SSVR on one leg of 240v and it works beautifully. The attached voltmeter (and cold element) confirm that it works as expected.
Yes, my voltmeter readings vary from zero to 240 as I rotate the pot. You want to solder to the center lug and one of the other legs. Resistance will increase or decrease depending on which side you use.
