I have a relay whse contact rating is specified as follows
Power : 460VA / 48Watts Current : 2A @ 24V DC or 230V AC
If I am not wrong, 460VA is from 230V AC * 2A. If my applications is required to switch 16V AC max with 5A max current (i.e 80VA), Can I use this relay? or max current is 2A only irrespective of voltage and AC or DC.
Load is inductive (4 ohm loud speaker) if this matters.
required to switch 16V AC max with 5A max current (i.e 80VA), Can I use this relay? or max current is 2A only irrespective of voltage and AC or DC.
In my opinion, it'll be fine as long as there's no safety hazard in the event of the relay contacts not opening, but I wouldn't do it commercially. It's outside the specification of the relay so there's no comeback if someone dies in a raging inferno.
The 2A figure is the relay's rated switching capacity under at max conditions with a stated number of cycles.
When closed, the contacts can handle far more.
** The arc has to quench itself as the gap between contacts increases so 2A and 24VDC are the max conditions where this happens reliably over a large number of operations.
Relays and small toggle switches are lousy at switching DC of any size.
The use of speaker relays in audio amps is a non trivial subject with which I am very familiar.
Such materials have those characteristics, but nobody uses such materials these days, and therefore sees no such resistive media build-ups.
Common MODERN contact media is typically Platinum. You probably read your spec sheet 50 years ago. That was how long ago it applied. Hell, the PINBALL industry cleared all that hash up. Where the f*ck were you? Contacts on reed type switching assemblies, which nearly all are some form of, have been low or NO oxide materials for decades. Even an enclosed switch has little short 'reeds' with contact heads on the ends.
Platinum exhibits exactly ZERO oxidation, even after 100 YEARS of exposure. The only way to coat it with anything is to have super moist, particle laden air.
Both it AND Gold are the best metals at NOT EVER getting ANY 'tarnish' on them. Especially Platinum. Look at the valence shell!
Imbalances can cause contacts with momentary HV pulses involved to migrate surface molecules from one contact and meld them onto the other, thereby causing degradation.
It's also sometimes called thermal contact rating, which may also be expressed as a duty cycle. There is also the I^2t rating which is used for fuse selection.
Ratings such as this are usually shown for power contactors and motor starter relays. They are rated for a certain HP and locked rotor current. We use contactors for switching transformer taps and setting series and parallel connection, under "dry" conditions with essentially zero current and voltage (other than leakage through an SCR snubber).
Here is a rather extensive glossary and explanation of relay terms:
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Don't see platinum in any of the contact materials. Gold (mostly flashed and plated for low level signals), of course, and silver alloys with palladium and ruthenium.
Here is an extensive study of relay contacts, and platinum is only mentioned once regarding plating them with gold.
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