Anybody know much about SSR's?
Have been testing the new electric brewery set-up and had some suspicions about the SSR that is in a PID controlled circuit for a heat exchanger. I have run some tests and have found that if I run the 4 kW heating element via the SSR (switched on full time) it takes twice as long to heat a volume of water to boiling than if I bypass the SSR. So it seem that I am losing half the power of the heating element by running it through the SSR. (I am bypassing the SSR right at the location of the SSR, so it is not anything to do with the rest of the circuitry).
This is a 40A SSR from Jaycar. Is it a case of all SSRs being horribly inefficient, or is it that 'cheap' SSRs are like this, or is it that I have a faulty SSR?
Replies to This Discussion
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Permalink Reply by Nick T on
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Yes that is the one, and it is mounted on the heat sink that is recommended for it. It is being controlled by a Love Controls 16B PID unit. I had the temp probe at about 14 degrees (in a glass of water, not in the water being heated) and set the target temp to 80 degrees, assuming that this would have the SSR 'on' continuously.
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Permalink Reply by Hutch on
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I don't suppose you have an oscilloscope or a multimeter that can tell you duty cycle? I'd find out what the temp pid is demanding of the SSR, even a fairly high duty cycle like 80% might cause the symptoms you're describing.
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I am a bit sparse on those sorts of tools! All I have is a basic multimeter. Perhaps I should run the test again with the PID controller in on/off mode rather than PID mode?
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Permalink Reply by Matt on
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Dont know anything about the 'love controls' pid but i think that would be the key thing to test, since the most likely explanation is that the pid only has the element switched half the time. In other words yer using half the energy as opposed to shedding 2kw through the ssr - though if so you could always mount yer heat sink inside the heat exchanger! ;)
Does the pid have a learn function? It might be it has very conservative auto switching settings outa the box, and it needs to go through a tune protocol with feedback using real data? Either way running in manual mode should help isolate the issue
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I think I have figured it out - doh! I have a small ac transformer in the box to run lights on toggle switches, I routed this through the PID switch, so the SSR is getting an AC signal, not DC that it actually needs, and therefore is 'off' half the time. Next question is how to get a 14V dc power supply - there seem to be plenty of AC transformers on jaycar but the only small DC power supplies seem to be phone adaptors etc - I guess I could just wire one of those up, but surely there is a better solution?
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Permalink Reply by Nic on
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Glad you found your problem.
What's the 14v for? Have a look for something like this- http://www.jaycar.co.nz/productView.asp?ID=KC5446&keywords=regu...
It will take the AC from a transformer, rectify it (turn it into DC) and then regulate the (adjustable) output voltage.
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Ah I see. I will have to learn how to use those electronic component thingys. Presumably not too difficult? When you say 'from a transformer' I presume that this means I won't be able to hook it up to a 240V ac supply direct? THe 14v DC is what the PID output controls (switches on/off), but it needs it as an input of 14vDC to do this.
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Permalink Reply by Vesku on
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If you have an old power adapter for phone or what ever, you could use that if you don't want to play with components. Anything between 3-32VDC should do, if you use the Jaycar SSR-relay.
The price of the relay in Jaycar is crazy (everything is over priced there). You can buy them much cheaper from Ebay or sometimes used on TM.
One thing to remember with SSR's is that they always leak a bit, it's not a 100% switch, good to keep in mind safety wise. If SSR fails, it usually goes in a short circuit, another thing to consider when designing safety features on your system.
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That 40A relay is $Au 17 http://www.futurlec.com.au/RelSS.jsp
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Permalink Reply by Druid on
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I've got all the gear to set up a PID/SSR temp control - I bought the SSR and the PID from the site that TheElectricBrewery recommended.
Now it's just a case of building it and getting the sparky around to wire in a 20A circuit under the house.
Regarding your point about failures resulting in a short circuit - does that mean the SSR fails closed? Or that the control circuit shorts?
And wondering whether you could be more specific regarding how to design for safety if it fails ie. if it's the latter ie. the control circuit shorting out, then a suitably sized fuse would suffice but I'm not sure about the former situation.
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Permalink Reply by mattd2 on
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Yeah, SSR normally fail closed. I have seen others wire a seperate relay/contact in series with the SSR. Relay controls whether the element is on/off & SSR contrlls the duty.
The Auber Instruments gear is pretty much the standard on the Hombretalk.com forums. A few are now using Sestos - function is near identical to Auber (spare only in °C) but the operations manual is crap and useless! I have seen some REXs aswell but they seem to always be labeled wrong on ebay and you are nearly gauranteed to get a relay control instead of voltage pulse!
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