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I have just bought a HY-M285 SSR that I want to allow a 12V DC signal to control a 240V AC mains signal. I'm using this to let the 12V output from my amplifier switch my active sub-woofer on and off.

The AC side of the relay is trivial - it's just two screw terminals. Unfortunately, the DC side has three terminals, labelled DC+, DC- and CH1. So, my question is: how do I connect the 12V control signal? I've tried across DC+ & DC- with no effect.

Do I need to construct a voltage divider, to push (say) 5V through the CH1 connector, as well as the DC+/- inputs? Or can I get away with something much simpler - e.g. +12V direct to CH1?

Apologies for the lack of detail but the module doesn't include any documentation whatsoever, so I'm hoping that someone here may have prior experience.

Thanks.

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  • \$\begingroup\$ Buying components without data sheets is a pretty bad idea. You should accept this as a learning experience and buy a relay that comes with proper documentation. \$\endgroup\$ May 7, 2021 at 18:18
  • \$\begingroup\$ Agreed, but surely somebody out there has the info I need? \$\endgroup\$
    – Andy
    May 7, 2021 at 18:33
  • \$\begingroup\$ It says right on the storefront: "SSR module power supply: DC[,] and the voltage must match the voltage of the relay." If I were to guess, and that's all that this is, one would connect the voltage printed on the relay to pins "DC+" and "DC-". When one desires to turn in "On", apply a Vpulse (of the DC relay voltage) to "CH1" to trigger it. Does it latch on/off? Who knows... until you try. I would throw this thing out, and get a proper unit before someone's house burns down.. \$\endgroup\$ May 7, 2021 at 18:52
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    \$\begingroup\$ @Andy Consider it tough love. Hang around here awhile and you will see many questions like yours, where something was purchased at a price "too low to be true" but without documentation. The story usually does not end well. \$\endgroup\$ May 7, 2021 at 19:24
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    \$\begingroup\$ My comments are not meant to be mean. They are meant to be serious. My apologies if it translates as being curt. What you are doing (switching mains) is serious business. Remember, the toaster that cooks up your toast for tea also runs from a fused plug. It would have no problem catching the drapes on fire... Though unlikely, you could make a toaster of this thing. \$\endgroup\$ May 7, 2021 at 20:03

3 Answers 3

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Using the voltage rating marked on the part for dc, apply this to V+ and V-. The tolerance of that voltage “may be 15%” like 5V on a 6V part, (edit: OMRON says 5V +/-1 = 20% ok) but 6V might be more reliable when hot or might not make any difference. But 12V on a 6V part will damage it. The trigger current is small like < 15 mA.

Using an only collector NPN switch to trigger and V- or test with dry contact switch or wire shorting Trigger to V-, will activate the Triac.

PNP trigger means negative voltage trigger relative to V+ or in this case 0V= V-.

  • since it says near 0V for activating, I can assume the current limiting IR resistor is included to drive the isolated Triac output.
  • Since it is encapsulated, no heatsink and low power dissipation e.g. a couple watts max loss at a low current rating of 2A.

But the woofer amp will have large energy storage caps to supply power measured in mJ or J. Thus your surge current could be 10A your rated current for the 1st cycle. They might be able to handle this. But check the temperature rise when doing this. If it is a zero-crossing type switch, the surge is reduced greatly by the rise time during switching. If not it is possible to synchronize your power on pulse with line frequency somehow if it does appear too hot when turning on, since it is only rated by heat rise for 2A into a non capacitive load. They have carefully removed the OMRON logo so you buy their part instead, so good luck ;)

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enter image description here

Figure 1. According to the photo on that dodgy website the SSR is 5 V triggered.

The G3MB-202P is an Omron part number but there is no Omron logo on the device so, most likely, it is a cheap clone (and specification including electrical isolation) is suspect.

Assuming you have the 12 V version, then to see if you can get it to work connect:

  • DC- to GND or 12V-.
  • DC+ to 12V+.
  • Trigger: most likely connecting it to DC+ will turn it on. If not then try connecting to DC-. You can then permanently connect it to the one that works.

If you have purchased the 5 V version then some further modifications may be required.

You will, of course, have added an inline fuse on the 240 V AC line.

See the SSR datasheet for other voltage options.


Please learn a lesson from this. You have saved money but have no data, no support and no idea how safe this product is. "No datasheet? No sale!"

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  • \$\begingroup\$ Thanks Transistor - your reply has the benefit of adding both light and heat :-) I'll take your advice. I've been looking at Farnell and RS-WWW sites and they do sell SSR chips. Unfortunately, their modules come in at £100's and their chips are frequently minimum order 100's - I'm only an 'umble 'lobbyist :-( Not only that, if I built my own PCB/VERO circuit, it's likely that - from a professional perspective - I'd probably be no better than these cheap clones. Oh, I did at least order the 12V version. And, being in the UK, all 240V supplies are fused, plus RCBO. \$\endgroup\$
    – Andy
    May 7, 2021 at 19:24
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I've finally decided to go for one of these. The wiring is much simpler and it's rated at 90A. It looks like a Chinese product but it has CE approval. I'll probably bolt it to the metal back panel of the speaker, which will act as a heatsink.

Thanks for all the advice - it was certainly a fun ride while it lasted...

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    \$\begingroup\$ Hmmm. Another Amazon purchase of a device with no branding or datasheet. Oh well, I tried. Don't forget to accept one of the answers - even your own - to indicate that your question has been answered. \$\endgroup\$
    – Transistor
    May 8, 2021 at 10:01
  • \$\begingroup\$ Yup, I know and I admit I am ashamed. Would you recommend this: uk.rs-online.com/web/p/solid-state-relays/9032970? It's around twice the price but it has a brand (i-Autoc) \$\endgroup\$
    – Andy
    May 8, 2021 at 10:08
  • \$\begingroup\$ Yes, RS are a long established company and will have vetted all their suppliers. They'll have traceability back to the original suppliers, etc., warranty and tech support. Good man! \$\endgroup\$
    – Transistor
    May 8, 2021 at 10:10
  • \$\begingroup\$ You don't need to tell me about RS :-) I was using them around 45 years ago when they were Radio Spares - I used to love browsing through their (paper) catalogue. Size of a telephone directory (tho these don't exist any more, do they!) \$\endgroup\$
    – Andy
    May 8, 2021 at 10:14
  • \$\begingroup\$ I am of that era too! \$\endgroup\$
    – Transistor
    May 8, 2021 at 10:18

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