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relays

Discussion in 'Beginner Electronics' started by asdf, Dec 13, 2003.

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  1. asdf

    asdf Guest

    Hi all

    I'd like to control home appliances (120v, 1-2 amps, even more would be
    better) using relays powered by my PC (either serial port or parallel
    port... I've seen circuits that used 12v to drive the relays and the data
    lines to switch it, but it was relay vague and I didn't understand it - but
    since I could simply use one of the PC power connectors to power it for more
    amps that'd be just fine). I've also red about dozens of relay types,
    mechanical, reed, magnetic reed, solid state, micro electronic, sensistive
    reed, etc. Which ones should I use? Suggestions for safe circuitry so that I
    don't fry my serial/parallel port? Any links would be appreciated.

    Also, on the same subject, I'm looking in a catalog (digikey.com) for relays
    and there's all kinds of information... I'll use an example to see if I'm
    getting this right:

    Ex:
    Coil VDC = 5
    Coil Res. = 50 ohm
    Contact Rtg's Resistive (A) 24 VDC = 2
    Contact Rtg's Resistive (A) 115 VAC = 0.5
    Oper. Volt. (% of Rated) Pull/Drop/Max. On/Out/Cont. = 75/5/120

    This reed would need 5VDC to switch with 0.1A (5V / 50 ohm = 0.1) (obviously
    too much power for serial/parallel port, I know, but this is just an
    example). And the relay would be able to switch a 115VAC circuit of 0.5A
    (average?). At 5% of 0.5A, the circuit would close, 75% of 0.5A would be the
    nominal? rating, and 120% of 0.5A would be the max. rating. Is this all
    correct?

    Thanks
     
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