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Can I use a 10 amp 120 volt relay for more then 10 amps if the voltage is lower? Answered

I am currently working on a mini A/C with a TEC that draws 12V and 12 amps and the relays I want to control it with have a rating of 10 amps 120v. not sure if it is as simple as this but 10A*120V=1200 watts. While 12A*12V=144 watts so in my eyes this would work because there is much less power flowing through the relay but I would like to request advice from someone who is a bit more knowledgeable then I. Help would be greatly appreciated thanks a bunch.



Best Answer 4 years ago

Sure you can ............... NOT

But don't really expect the relay contacts to open more then thrice !!!

The first few times they will arc and pit the button contact metal setting up the ultimate resistance weld of contact to contact on the next few relay cycles.

Not for SSRs.

You see ... When a relay closes there is a high speed multiple mechanical contact bounce for about 200 ms during which time there is an arcing plasma that can melt micro fissures into the button contact metal with dirt as any welding will cause.

Doesn't this happen to all contacts ?

Not really, the relay designer select the contact mass and amount of silver to avoid this pitting when the arc occurs to prevent overheating the metal and causing the contacts from becoming a single welded connection.

... Yes, a good designer will have an added safety factor for extra current,

BUT the company directors only care about profit, so you take care.


BTW when Steve says a relay DC contact current rating is lower then AC now makes sense because the alternating reversal of current helps limit the Arc intensity by interrupting the current 120 times a second in the USA.


4 years ago

Yes you can. You go by total power.


Answer 4 years ago


Both limits have to be respected - separately.

Over current (almost regardless of voltage) will kill and weld and/or fry the contacts.

Over voltage may break down the isolation barrier.

It's not guaranteed to fail, but you are surely not on the safe side any more.


4 years ago

No, a relay can only handle so much CURRENT, not total power. Current is what will destroy the contacts. The DC rating of a relay is lower than the AC as well.