Relay ratings

[kr15_uk]

Ladies and gents,

I've bought couple of relays from the eBay and they are rated DC 30V/10A but I'm planning to use it with 12V. Is there a way to figure out how much it can handle AMP on 12V?!

Probably I'm wrong (that's why I'm asking) but my only logical conclusion was to figure out the hardware resistance - 30V/10A = 3ohm, 3ohm/12V = 4A
Am I on the right track or just talking rubbish?!

Thanks.


Regards,
Kris M

[Brumby]

Ohms law does not apply to the contact rating.

At 12V DC, you can run that relay up to the stated limit of 10A.

[StuUK]

Ohms law does not apply to the contact rating.

At 12V DC, you can run that relay up to the stated limit of 10A.

Should be able to! depends whether they are cheap rubbish that don't meet their specification....

[dmills]

Not the way it works, the two numbers (30V, 10A) are maximums, there may also sometimes be a power or VA product limit.

You can run the thing at up to 30V and up to 10A, so maximum current at 12V is 10A, just the same as the 30V case.

You might sometimes see (30V, 10A, 100w) in which case all three limits apply, at less then 10V, the limit is 10A, at less then 3.33A the limit is 30V, and between the two you have a straight line that respects the power limit

Interestingly you will often find relays rated for far more voltage in AC service then DC, this is because an AC arc will tend to quench when the current goes thru zero due to the AC supply, where a DC arc can last.

AC relays also have different ratings depending on the load, usually highest for resistive loads, and very much lower for inductive,  tungsten lamps, florescent lighting or motor loads.

Regards, Dan.

[Brumby]

Ohms law does not apply to the contact rating.

At 12V DC, you can run that relay up to the stated limit of 10A.

Should be able to!

Absolutely not.

depends whether they are cheap rubbish that don't meet their specification....

That's only applicable if the ratings given were bullshit in the first place and/or construction was inadequate.


Read what dmills posted.