Main voltage and perfboards

Discussion in 'General Electronics Chat' started by snowbarrr, Dec 7, 2010.

  1. snowbarrr

    Thread Starter New Member

    Dec 3, 2010
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    This is my first project working with main voltage, so I apologize if the questions are kind of dumb!

    I'm planning on using a relay to control power to a lightbulb, and the relay I have would fit nicely on my perboard, along with the control circuitry. This seems dangerous to me -

    Can a perfboard with standard spacing handle 120Vac? Can you solder to a 120Vac wire? Is it safe to place 5V control circuitry on the same perfboard as 120Vac circuitry?

    I'm under-rating the relay I'm using (30A @ 220V), are there any other safety precautions/considerations I should be thinking about?

    Any recommendations or suggestions would be greatly appreciated!
     
  2. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    A circuit diagram of what you want to do would help
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    where did you find a relay that can handle 30 amps at 220volts AC and is triggered by 5 volts?


    Any copper wire can be soldered, even ones that carry 120VAC. Just be sure the voltage is not in the wire when you apply the soldering iron :)
     
  4. snowbarrr

    Thread Starter New Member

    Dec 3, 2010
    13
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    rvh002:
    I haven't drawn anything up. Since my questions were mainly about handling the large AC voltage, I didn't think the control circuitry would be relevant. If your interested, basically, I have an IR receiver that will give me a 1 when certain pattern is received. I'm using that to drive an NPN (because the receiver only drives 20mA, and the relay needs 80mA) that will connect one side of the relay coil to ground when activated. The other side of the relay coil is connected to 5V. I have a diode between the two sides of the coil for protection when the coil deactivates to ensure the current flows back to vcc. I was planning on connecting the contacts of the relay across the 120Vac line in normally closed configuration (the relay is spdt) so the power would be on by default. I'm sorry there is no diagram - I hope you can get an idea from the explaination.

    Kermit2:
    I got the relay for about $2.00 from a company called sparkfun - I hope it's ok to post links: http://www.sparkfun.com/products/100.

    I didn't know if maybe 120Vac gave off a lot of heat (silly?) and could be bad for solder joints (silly again?). So, it sounds like I could safely solder the AC wires to the relay contacts. Great. If I were to solder the relay to the perfboard, do you think there would be an issue with putting that much voltage through the contacts of the perfboard?
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    It's spec'd as a 5 amp relay at 220VAC.

    The voltage will not bother the board. These fiberglass perf boards can safely take up to 600VAC.

    CURRENT flow is what will cause heat build up and let the smoke out of your parts. :) The mere presence of a high voltage doesn't harm anything. Excessive current flow(like a short circuit) will damage the board.

    If you plan on running currents of many amps through the relay(one light bulb doesn't count as high current) then add more copper to the traces on the board to carry the extra current. Solder a wire onto the board from the leg of the relay to the output point. A 16 gauge wire can carry 10-15 amps
     
  6. snowbarrr

    Thread Starter New Member

    Dec 3, 2010
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    That's great! Very reassuring, thank you Kermit!

    I'm mixing up my relays! I have on that is rated 220, 30A, but it's not what I'm using for this project. That little guy can be found at the same company if you were wanting one: http://www.sparkfun.com/products/101
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    Listen to you intuition. As an Electrician, I work everyday with 480/600v systems, and yet, 120v on the test bench requires no less respect. One thing about mains is that you want it to be secure and out of reach. My suggestion would be to mount your relay on a seperate board, securely mounted to a grounded metalic base. Fuse your mains input, and isolate to run the control.
     
  8. snowbarrr

    Thread Starter New Member

    Dec 3, 2010
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    A fuse sounds like a good idea... I'm just not sure how to go about that. If I were to use a 60 watt bulb, in most cases I should never draw more than 1/2 an amp right? But what about when I first turn the bulb on - wouldn't there be a large in-rush current? I would think every time I turned it on, it would blow a fuse and turn back off, unless I used a really large fuse!

    And another issue is - I want the bulb to be on my default. If my control circuitry gets fried somehow, I want the bulb to just operate like a normal bulb. A fuse worries me, because if anything went wrong, the power would be shut off to the bulb.

    It seems like carefully seperating the circuitry, and ensuring the mains circuitry is secure would be the best bet. Do you think the fuse really necessary for safety?
     
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    it's either the bulb or the branch circuit. A fuse is more for equipment/wiring protection than safety. For safety, isolation is the way to go.

    If your device is wired according to code requirements, branch circuit protection is adequate. But while your on the breadboard, take extra precautions.
     
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