Need Relay advice please

Discussion in 'General Electronics Chat' started by Hurdy, Mar 10, 2006.

  1. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Hi everyone,

    I was wondering if someone could help me please. I am from the UK and order my electronic parts from a site called www.rswww.com

    Now, I need a relay that when a 5VDC input is applied from a PIC it will turn on a mains supply device (230VAC). Can anyone aid me please?

    Thank you,

    Rob
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,794
    Like many posters here your question lacks important detail, and I don't know if it will work for your application bu a solid state relay might be just the ticket. Like this one

    Solid State Relay

    Good Luck
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    How much current can your PIC supply? You'll need a relay coil drawing no more current than that. How much current will your mains-powered device draw? The relay contacts must be rated to handle such current.
     
  4. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Ok I have made a timer using a PIC. During count down I have made one of the PICs output pins go HIGH. I need this HIGH output to be connected to a relay so I can turn a pump on during the down count. When the countdown finishes the output pin of the PIC will fall low, therefore turning off the pump.

    The pump is rated at 240V, 50Hz 5 amps.
    The outout of the PIC is 5V output. not sure about the current. I have attached the datasheet for the PIC used if anyone can find the max current output please be my guest. These datasheets or huge!!!
     
  5. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3
    Table 10 page 73 of the data sheet shows the maximum output currents for I/O pins. For Port A the maximum source current is 50mA, and for Port B it is 100ma.

    The coil of a relay is inductive and voltage spikes can occur when the relay turns off. For that reason it is advisable to use a transistor to drive the relay to give buffering from your PIC. You could use any general purpose NPN transistor and feed its base via a 1K resistor from your port. Connect your relay between collector and +5V and connect a diode across the coil (anode to collector).

    You need a relay with a 5V coil but you will be more likely to find one for 6V (these will operate at voltages of 4.5V – 9V). Your choice of relay depends on how you want to mount it and how you make your connections to it. Pick one with contacts rated in excess of 5A – there are a lot to choose from.
     
  6. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    I don't know about anyone else but I personally don't like using solidstate relays to switch 230VAC mains. I know some are rated for it but something inside tells me it is not as safe a a good old mechanical relay.
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Hurdy: At first glance, it looks like Part No.: DK1A-5V will work. Use the diode Pebe suggests at the very least. Pretty much any of the 5v relays will work if driven by a transistor, as long as their contacts are rated at 5A or better.

    Windoze Killa: I would critisize you for being a luddite if I were not in 100% agreeement with you.
     
  8. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
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    Hey thingmaker3, I have been a technician/engineer for nearly 30 years and I was weened on 10KW HF transmitters and 2MW surveilence RADARs. So you can imagine that the power requirements of these beasties preclude the use of such miniscule things like solidstate relays. Or I should say at least in the power stages and supply areas.

    Having said that, I am all for solidstate relays. They are great for applications that require small foot prints for parts. They are fast and bounce free. They don't suffer for back EMF problems.

    But seeing 230VAC across the O/P of these little black chips is still scary.
     
  9. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Thank you for your help guys. Really appreciate it alot!

    I have ordered a DK1A-5V. One more question concerning the relay is what type of relay socket do I order?
    I have a link below for my search results, but they talk PT2, PT3, PT4, PT5. Do you know which one I need for my relay?

    http://rswww.com/cgi-bin/bv/rswww/searchAction.do

    I have put on my order list a NPN power darlington transistor,TIP110. Is this a correct transistor to you use?

    What dioide would you suggest to use?
     
  10. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Ok I have ordered a 1N4001.
     
  11. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
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    The relay you ordered is a PCB mount relay. Unless you plan on blowing it up on a regular basis I would solder it straight to the board.

    You don't need a power darlington. Although it will work fine it is a little bit of over kill. Nearly any NPN transistor that can handle a collector current of 100mA would do it. The relay coil is rated at 200mW which is 40mA at 5V.

    Also, the diode your ordered is fine but again overkill. A boring old 1N914 would have been ample at these power levels.
     
  12. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    For the purpose of my applications use I would much rather use a relay socket. But suppose I do decide to PCB mount the relay, what track size would you recommend to use on the board? Because the device is to be mains supplied pulling up to around 5amps, I would guess thats a hell of alot of current to send down a small track that you would use for say a transistor or logic chip where they pull a few mA.

    Off the top of your head what type of NPN transistor would you suggest that would fit the requirement of my circuit rather than the darlington?

    Thank you for your time and help, it is very much appreciated.

    Rob
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Handy online utility for calculating trace widths based on current expected:
    http://www.geocities.com/capecanaveral/lab.../TraceWidth.htm

    You'll need to convert from mils to millimeters. Divide mils by 39.37 to get millimeters.

    For NPN transistors either a 2n2222 or a 2n3904 will work. Supplier cited in first post carries both in several different package styles. Many others would work as well - these two just happened to pop into my head.
     
  14. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Thank you very much. I will look into the TraceWidth when I get a couple of minutes free today.

    Thanks again,

    Rob
     
  15. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    On the PCB calculator it says 'Enter Temperature Rise'. What does that mean?

    Also whats the usual conductor thickness of a copper board in oz. per sq. ft.?
     
  16. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
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    The average PCB copper thickness is 1oz. As far as temperature rise I am not sure. Pick a few different figures and see how it affests the track width. I would guess 50thou would be suitable. Make sure you keep your clearance between tracks because of the 230V. Don't want it arcing.
     
  17. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
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    Temperature rise means the maximum tolerable increase of track temperature at designed current.
     
  18. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    pebe you said 'For that reason it is advisable to use a transistor to drive the relay to give buffering from your PIC. You could use any general purpose NPN transistor and feed its base via a 1K resistor from your port. Connect your relay between collector and +5V and connect a diode across the coil (anode to collector).'

    Could someone draw me a diagram of this please.
     
  19. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,794
    One relay driver
    [attachmentid=1278]
     
  20. wigginzhang

    New Member

    Mar 15, 2006
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    Edited.

    No advertising of any kind is accepted.
     
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