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Need easy source for relay 3v/110v — Parallax Forums

Need easy source for relay 3v/110v

Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
edited 2009-02-24 01:12 in General Discussion
Has anyone got an easy source for a relay that can be trigged at 3.3v to control a 110v circuit? (lamp)

Radio Shack used to carry one 275-310, which would have been easy to grab but it looks like
they've dropped the item. I only see the 5v unit now. (275-232 IIRC)

Thanks!
OBC

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Post Edited (Oldbitcollector) : 2/19/2009 4:49:19 PM GMT

Comments

  • rjo_rjo_ Posts: 1,825
    edited 2009-02-19 18:17
    the 5V(275-0232) triggers from 3.3V just fine...I use it all the time.

    Rich
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-02-19 18:52
    Thanks Rich! I have one, but I thought I had tested that and had it fail.

    Will test again. Thanks for hope!

    OBC

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    New to the Propeller?

    Check out: Protoboard Introduction , Propeller Cookbook 1.4 & Software Index
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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-02-19 19:08
    OBC,

    If you have 5V available, you can drive the relay through a transistor. This is probably safer anyway, since it isolates the micro from inductive transients that would otherwise get shunted to Vdd through the protection diode.

    -Phil
  • Carl HayesCarl Hayes Posts: 841
    edited 2009-02-19 23:56
    Well, Phil, you can use a kick diode even when driving a load directly from a micro.· And if you look closely, the kick diode does shunt the transient, but not to Vdd or anywhere else.· It causes the stored inductive energy to be dissipated in the resistance of the inductor it's placed across, so it won't get pumped back to Vdd or to the switching device.

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    · -- Carl, nn5i@arrl.net
  • Carl HayesCarl Hayes Posts: 841
    edited 2009-02-20 00:05
    Have a look at Mouser stock number 769-TX2-3V and others on the same or nearby pages.·

    www.mouser.com

    I've edited this post.· The first time, I got the part number wrong!· My apology.

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    · -- Carl, nn5i@arrl.net

    Post Edited (Carl Hayes) : 2/20/2009 12:13:59 AM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-02-20 00:51
    Carl,

    Yes, I understand all that. The purpose of the diode is to protect the pin driving the inductor from a voltage spike when the drive voltage is removed and while the inductor continues to pass current. The diode will shunt that current from the inductor to Vdd if the other end of the inductor is connected there. Where it goes from there is dependent upon all the connections to Vdd and not just the inductor. You're right insofar as the current being returned to Vdd by the diode will equal the current the inductor is pulling from Vdd. If the diode is connected directly to the inductor and not some other point on Vdd further removed, the localized effect on Vdd will be nil.

    It's a minor point.

    Nonetheless, I would still recommend using a transistor to drive the relay from its rated 5V instead of relying on 3.3V. The lower voltage not only cuts the steady-state coil power by 56% but slows its pull-in response.

    -Phil
  • Mike2545Mike2545 Posts: 433
    edited 2009-02-20 01:45
    Oldbitcollector,

    I have some 3vdc relays with 2amp 120vac/ 2amp 24vdc contacts from all electronics.
    Here is a link www.allelectronics.com/make-a-store/item/RLY-623/3-VDC-DPDT-DIP-RELAY/-/1.html

    They are a steal at $1.50 each or $1.25 for 10 or more.

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    Mike2545

    This message sent to you on 100% recycled electrons.
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-02-20 14:49
    Mike,

    Bingo! Thank you!


    OBC

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    New to the Propeller?

    Check out: Protoboard Introduction , Propeller Cookbook 1.4 & Software Index
    Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
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  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-02-20 19:26
    OBC - I'd use an SSR for that.
    www.crydom.com/en/Products/Catalog/AdvancedWebPage.aspx?CategoryText1=PCB%20Mount&CategoryText2=CX%20Series%20SIP%20SSR%20-%20Ratings%20to%205A%20@%20280%20VAC%20-%20AC%20or%20DC%20control&SBCatPage=

    e.g. CX240D5.

    Zero Cross over switching .. no moving parts ... no contact arcing can be controlled directly from prop.. no reverse biased diode ...good·Isolation

    Regards,
    John

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    'Necessity is the mother of invention'

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  • Mike2545Mike2545 Posts: 433
    edited 2009-02-20 19:32
    I have the data sheet here for those relays.

    The mechanical life is 10^7...that's a big number.

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    Mike2545

    This message sent to you on 100% recycled electrons.
    pdf
    pdf
    Kest relay.pdf
    291K
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-02-21 04:02
    John,

    Excellent suggestion! -- I may have to pick up both!

    Thanks!!

    OBC

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    New to the Propeller?

    Check out: Protoboard Introduction , Propeller Cookbook 1.4 & Software Index
    Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
    Got an SD card connected? - PropDOS
  • rjo_rjo_ Posts: 1,825
    edited 2009-02-23 03:21
    Oldbit...

    I wasn't talking about AC... of course.

    It sounds like you now have everything under control.

    What I use for a diode is from RadioShack. I have build a remote controlled, camera switcher and a stepper motor controller, without any problems. I didn't have a good enough theoretical understanding to select a diode ... I just thought I should throw something in there. I have one diode connected in series with each pin. I have looked for the packaging, which would have the part number[noparse]:)[/noparse], no luck. I also tried measuring one ... but the only thing I know how to do is measure the voltage drop... .6V... but that doesn't help much.

    Next time I'm at RadioShack, I'll see if I can find it.

    As usual, thanks to the real guys for an excellent thread. For every response there is a huge number of interested readers...140 to this date[noparse]:)[/noparse]

    Rich
  • rjo_rjo_ Posts: 1,825
    edited 2009-02-23 16:01
    I found it!!!

    The diode is a switching diode... part number 276-1122. The guy at RadioShack... who is rarely wrong thinks... you can get away with this so long as your current is fairly low... how low that is? I don't know.

    Rich
  • rjo_rjo_ Posts: 1,825
    edited 2009-02-24 01:12
    http://www.fairchildsemi.com/ds/1N/1N914.pdf

    Looks like it would work.
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