240v switch in a 12v circuit

Daz2009

I'm looking for a couple of on off on rocker switches for use in a 12v environment.
I've come across some on ebay that are rated the following
15a 250v ac
20a 125v ac

What current would they be capable of taking in a 12 volt circuit ?

esuhl

I'm not an electrical expert, but... isn't the current rating the limiting factor...?

i.e. the 15A switch would still only be suitable for a maximum of 15A no matter what voltage you use.

P=IV, so at 12V, the switch would be suitable for a load of 180W

But that's really just a guess -- don't take my word for it!

Daz2009

esuhl wrote: »

I'm not an electrical expert, but... isn't the current rating the limiting factor...?

i.e. the 15A switch would still only be suitable for a maximum of 15A no matter what voltage you use.

P=IV, so at 12V, the switch would be suitable for a load of 180W

But that's really just a guess -- don't take my word for it!

Haha I was thinking along similar lines but the 20amp at 125v was confusing me if that was the case

[Deleted User]

Switching AC and DC is very different because AC reduces to zero and snubs out the arc every 10ms, and DC doesn't. This makes a lot of difference if the contacts of the switch break slowly or if you have inductive loads. DC ratings can be as little as a tenth of the AC rating.

Daz2009

jack_pott wrote: »

Switching AC and DC is very different because AC reduces to zero and snubs out the arc every 10ms, and DC doesn't. This makes a lot of difference if the contacts of the switch break slowly or if you have inductive loads. DC ratings can be as little as a tenth of the AC rating.

So unless the rating for 12v is shown there's no actual way of knowing ?

Heedtheadvice

Unfortunately there is not a direct correlation.
AC switches often have to cope with arcing at high voltages and need to ensure disconnection when there is the potential for those arcs. Being accepted the voltage passes through zero so that isvfactored into the design.

DC switches often have to switch capacitive loads and can be designed for much higher (short duration) current carrying capacity. Also the voltage does not periodically pass through zero so the design and ratings take that into account as well.

However as a rule of thumb if you are only looking at low levels of DC current (say 1amp or less) then a much higher AC rated switch such as you give examples of, if there is no dc capacitive load, should be more than adequate. If you are looking for say a 10amp switch then maybe look again.

Need it be a rocker switch? If you search for 12v SPDT switch you should get better results to meet your need and in different styles. (SPDT ; single pole double throw such as in one input two outputs)
Edit: apologies to those already making the same points: I blame my slow typing!!

[Deleted User]

Daz2009 wrote: »

So unless the rating for 12v is shown there's no actual way of knowing ?

Not for sure, no. This is not 12V, but you get the idea:
https://www.youtube.com/watch?v=Zez2r1RPpWY

Gloomendoom

Daz2009 wrote: »

So unless the rating for 12v is shown there's no actual way of knowing ?

What kind of current are you talking about? I use 240v switches for switching 12v LED lighting circuits with no issues.

[Deleted User]

Heedtheadvice wrote: »

AC switches often have to cope with arcing at high voltages and need to ensure disconnection when there is the potential for those arcs.

No, it's the DC switches that have to cope with arcing, AC current reduces to zero every 10ms.

Daz2009

Needs to be a rocker,load is approx 180w so 15amp.
1 throw runs a fan,the other a fan plus a heating element

[Deleted User]

Daz2009 wrote: »

1 throw runs a fan

That makes matters even worse, the back-emf could be 100V+.