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5 vdc to control 24 vac device — Parallax Forums

5 vdc to control 24 vac device

MJMJ Posts: 2
edited 2007-11-06 15:34 in BASIC Stamp
Can anyone recommend a specific transistor and relay to control a 24 vac device with a micro controller. Looking for the best way to switch on and off a 24 Vac 5 amp device.·

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-11-04 22:40
    Any relay rated at least for 5A contact current should do. Jameco has one with a 5V coil rated at 5A here: www.jameco.com/Jameco/Products/ProdDS/761336.pdf.

    Any switching transistor will work with this. A 2N2222 or equivalent general purpose NPN switching transistor will work.
    Don't forget the reverse connected diode across the coil (1N4001 or equivalent).
  • MJMJ Posts: 2
    edited 2007-11-05 14:56
    Thanks, thats exactly what I was looking for, part# ect. so I know what to buy. But since the post I learned a little about Thyristor and Triacs.· Is it possible that one of these can do the same Job. I have a jameco catalog.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-11-05 20:15
    If you're looking for a Solid-State device, consider an SSR (Solid State Relay). The ease of lighting an LED and the handle the switching for you. Many switch during zero-crossing to reduce electrical noise. Take care.

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    Chris Savage
    Parallax Tech Support
  • steve_bsteve_b Posts: 1,563
    edited 2007-11-06 15:06
    Chris, wasn't there a post somewhere about IGBT's and such and referencing zero-crossing switching devices!?

    I'm working on an AC switching project and am using regular old crydoms....less than 5A on the load side, but am concerned that I'll reduce the life of the relays for not using zero=crossing detectors....thoughts?

    (sorry for the hijacking!)

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    <FONT>Steve



    What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
    Lee Travino after the second time being hit by lightning!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-11-06 15:34
    Steve,

    Could benefit everyone…As far as I know the lifetime of the SSR wasn’t the issue with older non-zero-crossing-detecting systems. It was just higher noise on the line due to the abrupt changes on the line at arbitrary points in the sine-wave. On some systems this can be a headache. Some wouldn’t matter. On the other hand I don’t consider myself to be an expert on SSR technology, and there are probably a dozen people on these forums who have used them in commercial applications and know a little more and may have more updated information than me. I read an article before I started using the Crydoms back in 2000 and sometime later I remember a mention of the zero-crossing detectors and how they prevented noise. Certainly that type of noise could contribute to premature wear on the solid-state components as well. Take care.

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    Chris Savage
    Parallax Tech Support
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