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Newbie Question - Small Voltage Devices to Control Large Current Devices

Discussion in 'Electronic Basics' started by John, Jan 21, 2005.

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  1. John

    John Guest

    I am brand new to electronics and have just started taking a beginning
    electronics class at the local college. My long-term interest is in
    controlling devices such as 120V/240V lights, motors, and/or solenoids.

    In general, is it correct that large current devices are controlled by
    smaller low-voltage electronic components? In other words, a small
    transistor might be used to switch on/off a larger coil-based relay,
    which would, in-turn, switch on/off a light or motor.

    TIA
    John
     
  2. Andrew Holme

    Andrew Holme Guest

    Yes, that's often the case.
     
  3. Miles Harris

    Miles Harris Guest

    You're John Fields and I claim the $5!
     
  4. Chris

    Chris Guest

    A relay is a good way for a beginner to get introduced to controlling
    "real world" electrical loads such as lamps or solenoids.

    Let's say you have an HCMOS logic chip or a PIC operating with a 5V
    supply. The output pin can be programmed to be logic low (0VDC) or
    logic high (5VDC). The pin itself can only source or sink a few mA.
    Here's one way to use that logic output and those 10 milliwatts of
    power (5V * 2mA) to drive a relay which can switch a 100 watt, 120 VAC
    lamp (view in fixed font or M$ Notepad):

    Fuse
    VCC VCC .-. ____ Line
    + + .-----( X )-----|_--_|----o
    1N4002| | RY1 | '-'
    - C| | 60 Watt 3AG 1A
    ^ C| o
    | C| - - '\ CRY1
    | | \ 120 VAC
    | | o \
    '---o |
    Logic Level | |
    Output | |
    ___ |/ '-------------------------o
    o-|___|-o-| 2N4401 Neutral
    2.2K | |>
    ..-. |
    | | |
    2.2K | | |
    '-' |
    | |
    === ===
    GND GND
    created by Andy?s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    This will get you there, and you can buy all the components from Radio
    Shack. Their 275-240 relay has a 5VDC coil, and will switch up to 1
    amp at 120VAC.

    If you're going to be using hazardous voltages like 120 VAC, make sure
    you have your teacher or someone who knows what they're doing check
    your work before you plug anything in. Safety first.

    Good luck
    Chris
     
  5. Harold

    Harold Guest

    Hi John:

    Buy some triacs and diacs from the store. This part is used to control
    dimmer switches and drill motors. Its simple to hook up and uses 4
    parts.
    Harold
     
  6. JeffM

    JeffM Guest

    controlling devices such as 120V/240V lights, motors, and/or
    solenoids
    1 part:
    http://www.google.com/search?&q=solid-state-relays+teledyne+crydom+omron+nec
    http://www.digikey.com/DigiKeySearch.html

    BTW, did the leading whitespace on Chris's print
    get deleted for anybody else
    (who's not looking at this at Google Groups)?

    View with Courier font.
    .. Fuse
    .. VCC VCC .-. ____ Line
    .. + + .-----( X )-----|_--_|----o
    .. 1N4002| | RY1 | '-'
    .. - C| | 60 Watt 3AG 1A
    .. ^ C| o
    .. | C| - - \ CRY1
    .. | | \ 120 VAC
    .. | | o \
    .. '---o |
    ..Logic Level | '-------------------------o
    ..Output | Neutral
    .. ___ |/
    .. o-|___|-o-| 2N4401
    .. 2.2K | |>
    .. .-. |
    .. | | |
    .. 2.2K | | |
    .. '-' |
    .. | |
    .. === ===
    .. GND GND
     
  7. CFoley1064

    CFoley1064 Guest

    I guess Google Groups Beta munged the whitespace here. Try this (view in fixed
    font or M$ Notepad):


    VCC VCC .-. ____ Line
    + + .----( X )-----|_--_|----o
    | |RY1 | '-'
    1N4002| C| |
    - C| \ o
    ^ C| - - - \ CRY1
    | | \. 120VAC
    | | o
    | | |
    '---o |
    | |
    Logic ___ |/ '------------------------o
    o-|___|-o-|2N4401 Neutral
    Signal 2.2K | |>
    .-. |
    2.2K| | |
    | | |
    '-' |
    | |
    === ===
    GND GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    Thanks to all for the "heads up", sorry for the confusion..

    Chris
     
  8. Bill Bowden

    Bill Bowden Guest

    Yes, large current or large wattage devices can be controlled by
    smaller device. An example of controlling 120VAC lamps from
    a low voltage circuit is here:

    http://ourworld.compuserve.com/homepages/Bill_Bowden/page7.htm#aclamps.gif

    It's a chaser circuit where 4 120VAC lamps light in sequence.

    -Bill
     
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