[help] switch (not the nintendo one) for 5V circuit.

Discussion in 'General Off-Topic Chat' started by nasune, Jan 12, 2017.

  1. nasune
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    nasune GBAtemp Advanced Fan

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    So long story short, I'm in need for an on/off switch (latching push button) for a 5V/7A circuit. I've found some switches that would be ideal, but they are for 250V/1.5A, 125V/3A, or 12V/?A. Would these actually work for my purposes?
     
  2. sarkwalvein

    sarkwalvein More coffee, please!

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    7 ampers?
    That must be wrong.
    That is not your usual switch.

    If you really run 7A through there you will probably end up melting/fusing the lower switch.

    PS: sure any of them will work for a reduced time, but they will end up overheating and falling.
     
    Last edited by sarkwalvein, Jan 12, 2017
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  3. DeoNaught

    DeoNaught ¯\_(ツ)_/¯

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    Over there ;)
  4. nasune
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    nasune GBAtemp Advanced Fan

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    I'm trying to be fancy while consolizing a Neo Geo MV-1FZ, and the manual states that the 5V circuit uses 7A :S .

    All right those look good, thank you.
     
  5. Jack Daniels

    Jack Daniels GBAtemp Fan

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    a switch can handle power, not just amps or voltage... so 5V 7A, means almost any 250v switch would do fine... since if it can handle 250V at 1.5A a quick calculation would mean that 250/5=50, so 1.5A*50=75... this should mean the switch can handle 5V at 75A
     
  6. nasune
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    nasune GBAtemp Advanced Fan

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    Yeah that's kind of what I guessed, but I just wanted to be sure (having bags of useless parts lying around gets old fast :P )
     
  7. sarkwalvein

    sarkwalvein More coffee, please!

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    Actually that is not right.
    A Switch must support a given voltage, for this is given better insulation and contacts that avoid sparks.
    In the other hand a Switch must support current, and for this it is given lower resistence and heat dissipation characteristics.
    A Switch only supports the power given by I^2*R, with R the resistence of the switch.
    It never supports the full power (e.g. 250V*1.5A). The voltage drop in the switch is ideally 0V (and ideally it would dissipate 0W)
    In real life, how much it dissipates depends on its resistance. And you should select a switch that supports the given current (for power dissipation requirements) and voltage (for insulation requirements).
    Never calculating a constant V×I, that is not how it works.
    Prepare for switch melting.
     
  8. Jack Daniels

    Jack Daniels GBAtemp Fan

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    it's not one on one sure... the switch metal distance does doe for the the maximum current as do the thickness of the metal do for voltage... so if the switch devides the metals far enough from each other it's good enough for the amps (though i never seen 5vdc with 7 amps) almost all switches of 250 volts are good for 5v switching with whatever you've got... not all amps might travel over the switch in a circuit, so it's only the amps traveling over the switch that can hurt the switch... for burning in switch there's a solution, use a capasitor parallel to the switch (and recalculate the rest of the circuit for this mod might hurt the rest of the circuit...
     
  9. Mikemk

    Mikemk GBAtemp Advanced Maniac

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    That is not how it works. Max volts depends on insulation as others said, and max amps depends on wire thickness. Reducing voltage won't magically make the wires thicker.

    @OP it may be safer to use a low power switch connected to a power delivery transistor, as if the switch fails, less power goes into the person flipping it.
     
  10. nasune
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    nasune GBAtemp Advanced Fan

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    It's all right, I've grabbed some other switches that should be able to support it. (plus, from what I've found, th neo geo shouldn't be using 7 amps anyway, I just wanted those to be on the safe side)
     
  11. Jack Daniels

    Jack Daniels GBAtemp Fan

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    as far as my middle tech school teached me and my books still teach, the stress a wire (as it is for a switch) can handle is is always in watts... the the same wire (taking it's one single wire of metal like copper) of 10v1a (or take a fuse to check) will handle 5v2a without any risks... then there is one big thing that i indeed didn't calculate: ac->dc is of cource not just the same... ac bring more stress for the wire's or switch as for what it's worth...
    insulating a switch?? you mean protection for your hand i think? cause the old switches for high power didn't even have insulation... air around was all it took... for burning in of the switch, the point is the distance between the contacts and the speed of the internal metal moving to connect/disconnect, it's caused mostly by the current or amps... i'm sorry i used power when i was talking about watts as unit, i don't know what to use for it... but i found out voltage is power... the wire's will not mgiccaly grow thicker i know... just for the 250v you'll need thicker wires anyhow, they'd melt if not thick enough... a 250vac switch will is most likely double built, to switch faster to reduce sparks... and if you are worried a high cappasitor will help reducing the spark , it's common used in vacume cleaners to reduce sparks when turned on... i'm not so good at english when it comes to technicle terms, since my study books were dutch...a swtich is just and open connector with a safety handle... the low switch will not reduce any power traveling through a person, a fuse or automatch switch will help there, but no matter what switch you use, if the current can reach the person it'll hit him just the way it's at the switch, minus minimum resistance from either plastic, air or wood...
    since low voltage switches are normaly not really checked that much for insulation since the danger is thought to be minimal... ac switches are double isolated by dfault, so if safety of your hand is your idea to be better, than i say the 250vac is far better... but as i see it's not gonna be that dangerous anyway... if ever you get the chance go see a really old theatre's main switch for 3 phased 360VAC and you'll be shocked there's almost no insolation except for the handle while it could be handling more than 60A...
     
    Last edited by Jack Daniels, Jan 13, 2017
  12. Mikemk

    Mikemk GBAtemp Advanced Maniac

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    Yes, I meant protection for the hands if the switch fails.
    And by middle school, did you mean when you were 10-13 years old? I've taken college classes. A wire has a maximum ampacity dependent on size. Voltage determines the current amperage. (Pun intended)

    If you force more amps through a wire than the wire can handle, the wire melts. It's the same as trying to force more water through a pipe than it can hold. If there's too much, the pipe bursts.

    — Posts automatically merged - Please don't double post! —

    And air is an insulator

    — Posts automatically merged - Please don't double post! —

    Also, when you post a super long disordered paragraph that randomly changes topic, I only read a few sentences at the beginning
     
  13. Jack Daniels

    Jack Daniels GBAtemp Fan

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    technician 24 when i was finished, low voltage electronics technician... now voltage hing amps (like 1.5 volt, 10 amps will do fine in small wires, it's the total of UxI voltage xcurrent that will turn in to heat... current itself is not heat as is voltage...
     
    Last edited by Jack Daniels, Jan 13, 2017
  14. sarkwalvein

    sarkwalvein More coffee, please!

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    The problem is in your interpretaron of what is that U in UxI.
    That U is not the line voltage, or the insulation voltage. That U is Uwire the voltage drop on the wire that is ideally 0 and in reality very small.
    That Uwire is not specified in the switch characteristics.

    Also: yes, dissipated power turns to heat and P=Uwire x I, that is P=I^2xR.
    R, the resistence, decreases when you increase the wire width, so P is lower and it generates less heat. So making the wire wider makes it support more current.

    Note that in that formula for power I use Uwire = IxR -> P=IxIxR.
    That is Uwire, not Uline, don't mix then up!
     
    Last edited by sarkwalvein, Jan 13, 2017
  15. Jack Daniels

    Jack Daniels GBAtemp Fan

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    forget it, it's allright... it's getting useless anyway... though i'd learner P=UxI, UxR=I, and playing with random numbers we learnned that we could get rid of U by using P=i^2xR, so P=I^2XR was not really to check the heat though it would read that way, it was only to be able to backwards calculate U ideal in my books, not for an accurate P in watts... but you're right that about the detailes of the wire are not specifeid, and guessing is not really a thing to try when playing with power. so it's not necessary to drag the battle further... i take it i missed a few detailles at school.