AC and DC related

Discussion in 'General Electronics Chat' started by almraz, Jan 26, 2009.

  1. almraz

    Thread Starter New Member

    Jan 26, 2009
    1
    0
    Hi,

    I am looking for a switch for my boss. He wants an illuminated round rocker switch with 1 amp and 3 to 5 volts with DC. I don't really know a lot about electronics. I've been searching all over the web for a switch that meets these requirements, but no one seems to sell a switch with only 1 amp and 3 to 5 volts.

    My question is: Are AC ad DC related? I mean, if a switch says it has 125VAC, can that be converted to a different amount in DC?

    Can someone please help me.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
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  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    A switch usually has two ratings: AC rating and DC rating.

    It is marked on the body of the switch. For example AC 125V 6A and DC 24V 3A. Use the AC rating if the application is AC and use DC rating otherwise. These are maximum ratings and both voltage and current should not be exceeded when in use.

    A very common mistake for people to make is to take part of the AC rating and part of the DC rating and "combine" them into a "I think it is OK" rating. So in the above case would comment that "DC 24V 6A" is OK but in actual fact it is not.

    There are two ratings because the current switching processes are different for AC and DC. For AC there is a time when the current is automatically zero in the cycle but there is none in case of DC. Therefore a 6A AC rated switch would get damaged when trying to break a 6A DC current.

    Some switch does not indicate a DC rating but has two AC ratings at different voltage and current. In this case, a safe bet is to use 1/10 of the AC rating for the DC use. But it is better to use one with a properly marked rating instead.
     
  4. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    Thanks eblc1388, that is very interesting. I learn something new everyday.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The second most common mistake to make is to assume the switch rating is a "Power rating", expressed in VA by multiplying the given voltage and current together.

    So a switch of 125V 6A has a power rating of 750VA. It means that it can now pass 12A if the voltage is only 60V AC.

    This is wrong. Don't fall into this trap.
     
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