Which way is a switch oriented in a schematic?

Discussion in 'General Electronics Chat' started by TehYoyo, Apr 20, 2013.

  1. TehYoyo

    Thread Starter New Member

    Apr 20, 2013
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    How do you know which way to orient a switch in a schematic?

    i.e:

    [​IMG]

    Thanks,
    TehYoyo

    Note: I'm using a SPST, 2 lug switch.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    A SPST switch has no orientation, so you can plug in those two wires either way.
    Or do you have a preferred orientation when you simply join two wires together?
     
    TehYoyo likes this.
  3. ScottWang

    Moderator

    Aug 23, 2012
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    Although the circuit is drawing a SPST switch, but usually we using a SPDT switch.
     
  4. TehYoyo

    Thread Starter New Member

    Apr 20, 2013
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    Why would you "normally" use a SPDT switch for the circuit I posted? Every switch has its place. I'm not using a light-up switch or anything that requires power.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    There are two reasons.
    The first is that the price is similar or equal, and the second is that the 2 pins switch is not easy to buy.

    When I using the 3 pins switch, if only two pins is needed then just left the other unused pin and don't care about it, maybe just soldering some solder on the unused pin.
     
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  6. TehYoyo

    Thread Starter New Member

    Apr 20, 2013
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    That's a good point. Although I didn't find buying my switches very hard. Maybe it's different in Taiwan.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    There is another reason that I don't need too much classification of parts, as that I bought 1N4007 to replace all of 1N4001~1N4006.

    Sometimes you using the parts that you can buy, it's up to you.

    When our electronics manufacturers moved to China, there are many parts that we can't easy to get, now many parts and kits are came from there, the price is cheap then Taiwan. but the quality is bad, some products that we call "The products of black heart", as a 4GB USB Flash drive using the software to cheated user as a 32GB Flash drive.
     
    Last edited: Apr 21, 2013
  8. TehYoyo

    Thread Starter New Member

    Apr 20, 2013
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    I see.

    One more question:
    Can you recommend switches that are especially durable? I'm making a light for my photography studio. It uses 8x 55watt bulbs at 12 VDC and I want to use a switch to turn it on... can any switch do that? Do I need a 440 watt (8*55)-rated switch? Do I need a 37amp-rated switch?

    Thanks,
    TehYoyo
     
  9. #12

    Expert

    Nov 30, 2010
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    I don't think you can buy a 37 amp toggle switch.
    In my industry, we use a box called a, "disconnect" and buy the kind that can hold a 45 or 50 amp circuit breaker. However, it isn't considered nice to use a circuit breaker for a switch, so you will probably end up using a relay.

    Here. I have a drawing left over with a battery where you connect the 12 volts.

    Don't forget to install a fuse. This is the kind of energy that starts fires.
     
    Last edited: Apr 21, 2013
  10. ScottWang

    Moderator

    Aug 23, 2012
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    440 watts is not so high, but 37A is a high current, although it just only 12V.
    Maybe you can build a small circuit and using MOSFET IRF3205, it has little internal impedance, 37A * 8mΩ = 0.296 Watts, and adding the heatsink that I think the IRF3205 mosfet can affords it.

    IRF3205,Nch,55V/110A,8mΩ.

    Circuit breaker, 250Vac/100A, about 70Adc, or you can searching some other types.
     
  11. panic mode

    Senior Member

    Oct 10, 2011
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    circuit posted by #12 is not meant to drive single LED like that. the LED in that circuit is a load which could be your lamp(s).

    btw. always be aware of dissipated power:
    37A * 8mΩ = 0.296 Volts
    (37A)^2 * 8mΩ = 10.952 Watts which is quite a lot (some of my soldering irons are 7-8Watt) and using this transistor, you would definitely need a nice heatsink for it too.

    transistors like STH260N6F6-2 have Rds less than 2.4mΩ (2mΩ up to 90A) so dissipated heat would be <2.8W. If anything "heatsink" could be just some copper on the PCB.

    but using automotive relays will also get you there but there will be an audible click and dissipated power is likely to be higher. always check the datasheet. for example 40A rated relays can be capable of 60A if using only NO contact which is your case:
    http://datasheet.octopart.com/R51-1D40-12F-NTE-Electronics-datasheet-26498.pdf

    either way, transistor or relay, will handle the large current, your switch will only see very small current so switch can be smaller and with softer spring if you prefer... switches handling large current are requiring quite a bit of muscle ;-)


    the other option is to not switch DC but AC. your 12V power must come from some power supply so you could use standard switch (like the ones used in home/office for lights) if you switch the AC side.
     
    Last edited: Apr 22, 2013
    killivolt and #12 like this.
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Well, it's complicated.

    There actually are breakers rated as switches. It will be stamped right on the device.

    But in lieu of such a marking don't use a breaker as a switch.
     
  13. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Especially not an AC rated breaker instead of a DC switch, they are just not meant to do that.
     
  14. TehYoyo

    Thread Starter New Member

    Apr 20, 2013
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    Thanks for the help guys. Can you take a look at this post? I'm asking questions about the same project, so I figured I'd condense it into one thread.

    Thanks,
    TehYoyo
     
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