Mains rated solid state relay test box

building-a-mains-solid-state-relay-test-box

We like our nice, safe, 5V prototyping projects where the only thing that might get fried is a chip. But there are times when you want to switch appliances for one reason or another and then you’re going to want a mains rated relay. [Viktor] got tired of having exposed high voltage on the bench during the prototyping stage of these projects so he recently built a solid state relay test box.

The only thing he bought for the project was the SSR itself. To act as an enclosure he used the brick from an old laptop power supply. This is perfect for a couple of reasons. First off, it’s designed to contain high voltage if there is ever a short or other problem. Second, it’s already setup for incoming and outgoing power. He just needed to remove the guts and mount the relay. Notice that it comes with a clear plastic shield that physically separates the high voltage side from the low voltage control end. This, along with the cable routing, keeps the dangerous stuff on one side to ensure you won’t get an arc to the low voltage portion of the project.

Comments

  1. Nick says:

    Built something similar with an SSR, but built it into a nice hefty metal power strip. Hooked it up to my serial port, wrote a program, and hey, I can turn things on and off!

    • cutandpaste says:

      Metal is good.

      The HaD descriptions mentions that a plastic laptop power supply brick is ideal because it is made to withstand high voltages.

      I saw this and scratched my head, especially since so many folks here get all wonky when ever it comes to a project involving mains voltage.

      It seems so much more durable and safer to just get a $1.39 handy box at the hardware store and assemble it all into that, and ground it using a #10-32 screw into the tapped hole already supplied in the box…

      Ugly? Perhaps. Safe? Very. Cheap? It’s not always “I had it laying around already” cheap, but it’s pretty darn close. And being a metal box, the relay will be cooled better (which is important).

      Or, as you say: A metal power strip would also work nicely, and safely. (This is actually on my shorter list of useful things to build someday.)

  2. Big-J says:

    ER….. some clarification needed… please tell me there is a Mix up with the cable colours and that [Viktor] is not just switching the Neutral side of the circuit. Because if he is that box could be lethal I.E. Risk of death etc.

    • some old bollocks says:

      From the pics it looks like he’s indeed switching the neutral instead of the live, and also connecting them to the wrong terminals on the output connector?

      • JimHung says:

        Yeah – I’m not too experienced with Mains hacks but if my memory of basic plug wiring serves, he really is switching the neutral, not live. That seems like a lot of faith to put into the isolation of the enclosure.

      • drrickdaglessmd says:

        Yeah – I’m not too experienced with Mains hacks but if my memory of basic plug wiring serves, he really is switching the neutral, not live. That seems like a lot of faith to put into the isolation of the enclosure. I think the output wiring is correct, though.

    • Kevin says:

      However, he lives in Greece and in most part of europe we don’t have polarized wall outlets so there’s no easy way to know which wire is hot or neutral. I would prefer to switch both wires on/off instead of just one of them.

    • SBF says:

      OK, you need to switch the “hot” line instead of neutral, but since an SSR doesn’t isolate galvanic like a “real” relay, you will still be shocked when you touch the output. Even when it’s switched off.

  3. Allan Stirling says:

    I would suggest not switching anything heavier than a light with that SSR in that configuration. There’s a reason it has an exposed metal pad on the back.

    • Velli says:

      Lickability?

    • josh says:

      I agree. Most people I know don’t understand the difference between maximum recommended ratings and normal operating specs. My company went through this with a couple of customers who kept complaining that the relays were burning up within a week of installation. Even though they were the same model they’ve bought for the past 25 years, they figured there was a design change and kept sending them back for warranty exchange. I finally got into their plant and found that they were not only ignoring the heat sink integrated into the machine, they were letting the relay dangle in free air with red electrical tape (the kind with really gooey adhesive) around it to “insulate” it from the chassis.

    • J says:

      Just to help other people, that metal is for attaching a heatsink which is required for switching higher amperage loads.

  4. luckybot says:

    Chill out, it’s only 120v. Don’t work on your project after taking a swim and I think you will be just fine.

  5. Velli says:

    I do think it’s kind of silly, people getting worked up about wiring like this when they use something as outright insane as the standard NEMA 1-15 (Type A).

    It does look like he’s switching the ground, though.

  6. Okian Warrior says:

    Don’t purchase your SSR from eBay.

    Some Chinese engineer actually designed and produced a board with *fake* SSR guts and put a whole bunch of them inside authentic FOTEK enclosures.

    These things look real, will test real on the bench, and burn out when used to switch a heavy load.

    “BuyInCoins” is one eBay seller to avoid, probably many others as well.

    http://www.ebay.com/itm/SSR-solid-state-relay-pid-thermocoupler-controller-fotek-knockoffs-/261125660922?pt=LH_DefaultDomain_0&hash=item3ccc4d60fa

    • Some guy says:

      Wow that’s shady. I bought a couple from a proper retailer and it was pretty expensive, but I’d been looking at getting a few more from listings like these: http://www.ebay.com/itm/New-Solid-State-Relay-SSR-25DA-25A-250V-3-32VDC-/260945364922?

      Any recommendations on testing, other than ripping them open to take a look?

      • I’m in the same boat… I’ve got one like that on the way already.

        The ebay “warning” item states that “I have bought from several different sellers in china and have yet to find a real fotek ssr”

      • cutandpaste says:

        I have such an Ebay solid state relay installed as a remote turn-on for an amplifier. Says Fotek, 25A, etc — just like the one you show.

        I don’t know what constitutes switching a “heavy load,” but it’s been switching the good-sized linear power supply of that amp without episode, several times a day, for a year or so.

        Big transformer, big diode bridge, big 120,000uF Sprague caps at 75V. The lights in the house dim for a moment when it turns on.

        I have it nut-and-bolted to the steel chassis with heatsink goo, and the chassis is itself fan-cooled and normally cool to the touch at that point.

        Perhaps cooling is an issue for some applications. I note that some Ebay sellers have a matching heatsink…

        But based on my experience, I wouldn’t hesitate to use another one just like it for any manner of normal plug-in 120V device, at least in the realm of hacking. (I try to stay away from unusually-cheap Ebay goods when I’m selling a project for a profit, just on principle.)

        • cutandpaste says:

          Er. Off by a factor of 10 on the caps — 12,000uF, not 120,000uF (which would be a mighty capacitor indeed). But, anyway, it’s still working fine, and I don’t notice any difference between the cheap SSR and the front-panel switch that bypasses it.

  7. Dax says:

    You are NOT supposed to solder on wires to the tabs. You’re supposed to use crimped connectors such as abiko because if a fault occurs and there’s a short, the solder on the ground/zero wire may melt and the wire can slip off, leaving you with a lethal device.

    • josh says:

      Barring some really expensive electronics, I have yet to see connections NOT soldered. The connections have an eye so you can hook the wire through and solder.

      • dan says:

        nope, they have an eye so that the dimple on a matching connector sits in it and helps keep it in place.

        same reason that decent spade connectors have a hole, to that the mating female spade connector is attached more securely.

        that said, I’d have soldered it too.

  8. Ray says:

    I personally like using remote controlled power sockets:

    http://rayshobby.net/?p=3381

    Safer and pretty easy to work with.

    • Hitek146 says:

      Right on! My local hardware store has them on sale for $8.99, and I bought the last three they had. Yea, this is the little town I live in, and my hardware store is the most awesome I have found no matter where I have been in the country. They stock almost everything one can imagine, in a town of 2500 people(nearest large town 20 miles away), even stuff that Home Depot and Lowes don’t carry(even some electronic components!), at prices usually lower:

      http://www.westhardware.com/Sale/BargainsoftheMonth.aspx

      XLR to 1/4″ phono adapter – $1.99
      HDMI to Mini-HDMI adapter – $3.99
      BNC – F adapter – $0.99
      25′ HDMI cable – $14.99
      RJ-45 crimp connector – $0.29

      Tons of extruded aluminum and steel, threaded rod, smallish gears, and a small spring selection upwards of 200 different items…

    • Hitek146 says:

      Also, about these wireless switches, the channel they operate on is selected by a set of pins on the controller that are connected by copper traces to ground. In production, apparently a worker cuts one of the traces(appears to be with a rotary tool and cut-off disk) to set the channel that the transmitter transmits on, so that the transmit channel could be selected by cutting all of the traces on the transmitter and connecting them to output pins on the controlling device in order to select between multiple receivers. I’m working on this right now using opto-isolators, but this is standard procedure, and hardly worth documenting and posting…

  9. Bogdan says:

    I really like his text: ” I remembered how much pain it was to test the solid state relay (SSR) with naked mains cables running around” ……

    ….. he must have touched some live wires if pain was involved….

  10. Sven says:

    I have a whole bunch of old CAD machine screen savers for this purpose.

    They attach between computer and keyboard+”mouse” and shut off the screen’s 230V power if the computer has not been used in a while. They contain an RC clock, a 10, 11 or 12 (selectable) bit divider and an optically isolated triac so it’s basically a solid state relay with computer power passthrough.

    I just cut out the timer and attached a resistor and leads directly to the optocoupler and got a neat filtered 3A SSR

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