Hello! I need help with optocouplers and relays!

Discussion in 'The Projects Forum' started by Kim_Kusanagi, Jun 3, 2010.

  1. Kim_Kusanagi

    Thread Starter New Member

    Jun 3, 2010
    Hello, partners. I'm a newb here, so if you have ever seen me at other unrelated message boards, you can tell me where and who were you freely.

    Regarding this thread, I have problems with this:

    I have an energy meter, ES210. This device has two digital outputs that feed two optocouplers (one each, I'd only use one). You can connect a +40VDC MAX power source to the common collector and can have a maximum current of 150mA. However, I need also to connect either a 12VDC or a 24VDC relay to it in order to connect a 110VAC strobe light to the relay's power contacts.

    What should I do? Use a 12VDC power source connected straight to the collector and connect the relay as a resistor at the emissor? I fear of damaging the output. And using a 24VDC or 40VDC at the emissor creates the need of having a voltage divider with two resistors at the emissor, but since I don't know which relay should I use, I don't know what would the resistive value be and therefore any resistor I connect it in parallel with would be unreliable.

    What do you suggest?

    Any ideas will be more clever than mine. Thanks and see you.
  2. John P

    AAC Fanatic!

    Oct 14, 2008
    I'm not totally clear on what kind of optocouplers you're talking about, but I'd be inclined to make the output drive a transistor, and run the relay with that. Even if the optocoupler has the capacity to control the relay, I'd do it just because I'm not confident that optocouplers can pass any significant amount of current. A 2N3904 transistor ought to be able to drive a small relay, and you'd also want a freewheeling diode across the relay coil. Plus a base resistor (1K?) for the transistor and a pulldown resistor (47K?) fron the opto output to Gnd, in case the optocoupler is little leaky.
  3. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    Using a relay would be the way to switch 120VAC. Just make sure you do not exceed the listed specifications (40 VDC and 150 mA).

    What is the load on the relay ...(the 120 VAC device)? That will determine the contact rating on the relay. You'll need to decide on the relay before proceeding.
  4. Kim_Kusanagi

    Thread Starter New Member

    Jun 3, 2010
    I, in the end, managed to solve it, using a regular relay, a TIP31C and a couple resistors. Using the transistor as a switch, I controlled the relay, and the relay switches the strobe light. Of course, the diode was a must.

    So, your advice was successful. Thank all of you.

    P.S: the bad part is that a couple of days ago, my boss told me that wasn't what he asked for, even though everyone heard when he requested it. *facepalm* I think I should start voice recording as a counter measure.