Opening a 12v valve on a 5v signal

Discussion in 'The Projects Forum' started by Transition, Jun 9, 2011.

  1. Transition

    Thread Starter New Member

    Jun 8, 2011
    8
    1
    So i've got a project. We're adding a centralized air system here in our shop and we need to be able to electronically turn on/off the air at each workstation. Each workstation has an industrial laser which sends a 5v signal over a cat3 cable (rj11 head) when it wants air. I figured i'd just use a 5v triggered relay to turn on power to the solenoid valve. Except that's where my electronic expertise ends :D

    Here's what i have so far..


    I still need to find that relay (help?), and from what i understand i might need to put a diode between the solenoid and relay?
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    The valve you linked to is a 24VAC valve.

    Here's the one I think you meant to link to:
    http://cgi.ebay.com/1-4-SS-12V-DC-S...009?pt=LH_DefaultDomain_0&hash=item43a4f18711

    This valve coil draws 600mA. Did you intend to have a seperate supply for each work station? If so, that should work.

    In order to assist you further, we will need some more info about the laser (output current of the 5V 'signal', most importantly). will it drive enough current to operate a relay coil?

    You shouldn't need a diode between the solenoid & relay. I think you are referring to a surge suppression diode, which you would put in parallel with the solenoid, and also one in parallel with the relay coil.
     
  3. Transition

    Thread Starter New Member

    Jun 8, 2011
    8
    1
    Whoops - you're correct about the valve voltage.

    The laser is outputting a 5v signal when it needs air. I was hoping to connect the power supply to the relay (750ma) to provide the power for the solenoid.

    I took apart one of our compressors here which is triggered by the 5v. The relay being used inside of that compressor housing is a Magnecraft 70S2-04-C-12-N. Although that is triggering a compressor - not just a solenoid valve.
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Is this your laser? ULR-75
    If not, please post a link to the manual

    Something doesn't add up about the relay; the one you linked to has a 30V coil, not 5V.
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    correction: the relay is 3-30VDC.

    I won't be here all day. from the manual in the link I posted, I don't see an output for cooling. So, I must have the wrong manual.
     
  6. Transition

    Thread Starter New Member

    Jun 8, 2011
    8
    1
    There is no manual that explains what i'm doing. What i'm doing was never intended to be modified by the end consumer. What i know from the tech's is the laser sends out a 5v signal to the compressor when it wants it to turn on. I am not using a compressor anymore as I have a centralized air system. I instead intend on using that 5v to trigger a solenoid valve.

    The mention of the relay above is what they are presented using to turn on the compressor. I just supplied that so you'd know what's presently being used with the 5v signal.

    And for reference the laser is: http://www.ulsinc.com/products/ils1275/

    And here's the manual (i don't have the automation board): http://www.engraversnetwork.com/support/pdf/ILS_User_Guide.pdf
     
    Last edited: Jun 9, 2011
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Ok, your relay for the compressor is a SSR; you can't use that same relay for DC. The input mA (coil) of that relay is 7-16mA; that's a good place to start, since we already know that your laser will supply that much. They probably picked that one for the low coil current

    ...


    Here's a list of relays with 5V coils. The relay with the lowest coil current in the list is 24mA, 3 times what you have now.

    Not knowing where your 5V is coming from, I don't know what's safe. 24mA draw on that 5V might be just fine, or it might wreck your laser.

    We should stick to the ~7mA number, so you are going to need to drive that relay with a transistor.

    no, scratch that, since your solenoid is DC, we'll just drive the solenoid with the transistor and eliminate the relay.

    ok, try this:
    [​IMG]

    This will only draw ~2.2mA from your laser and maybe safer and prolong the life of it.
    The TIP120 is a darlington pair NPN transistor; you can get it and the 1N4004 diode at radioshack. if you are going to Frys or somewhere else, look for NTE2343, and you can sub the 1N4004 for a NTE116.
    these should only cost you a few cents, maybe a couple of dollars.
     
    Transition likes this.
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    In case you haven't already thought of it, (if this is shop air, and not labratory quality air) you will probably want to install at least 1 air seperator/dryer in your air line, especially if this is going to be cooling the electronics.
     
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    so, what's the news? did you try it? did it work?
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    +1, except I'd suggest a logic level MOSFET instead of the transistor. That'll have a much lower "on" resistance than the transistor and therefore make less heat, higher "off" resistance, and will need essentially zero current to drive its gate. In the provided schematic, gate = base, source = emitter = ground, and drain = collector. I'd also add a pulldown resistor, say 20k, from the gate to ground, so that the solenoid is definitely pulled "off" when the control signal from laser isn't "on". Maybe optional, but good form.
     
    Transition and strantor like this.
  11. Transition

    Thread Starter New Member

    Jun 8, 2011
    8
    1
    Awesome suggestions guys. Sorry for the slow response - i'll be doing a test build soon and i'll be back with results. :)
     
  12. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I understand - when it's for work, you don't always have time to come back right away. It is nice to hear back if things work, when you get around to it.
     
    Transition likes this.
  13. Transition

    Thread Starter New Member

    Jun 8, 2011
    8
    1
    The schematic you provided works great! Radioshack had all the parts so i just put it together for around $10.00. The 5v power supply i was using to simulate the laser wasn't registering any draw (5v @ 0.00a) - so things were looking good there.

    I'd like to try it with the MOSFET transistor as well but I'm not sure what the correct one to use is.

    Thanks again for your help - much appreciated.

    http://www.youtube.com/watch?v=UbABeep4cRI
     
    Last edited: Jun 15, 2011
    strantor likes this.
  14. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Thanks for the feedback, complete with video! Glad I could help. As for the MOSFET, I don't know either. Maybe someone else could help? That would be good info for me also.
     
  15. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Take a look at, for instance, IRF7484
     
Loading...