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How to convert minimum contact load for a relay (300 mA 12VDC) to mA @ 240VAC 50/60Hz? Answered



5 years ago

There is no minimum current requirement on the contacts above
90 VAC or 90 VDC because there is enough voltage to overcome the
contact metallic isolation boundary even at the miniscule current to
read voltage with a high impedance voltmeter.

This is a very good reason why superior connectors use gold plating
on contact pins to help reduce the minimum signal voltage between
the mating pins  for electronic devices.

The reason contacts can handle more AC voltage then DC is arcing
is self interrupting on AC reversals.  While DC arcing is only quenched 
by the distance from contact to contact in our atmosphere.

...unless its specifically designed for DC, in which case magnets are used to throw the arc

Right !
Arcs are current that magnets can easily bully :)

Did U know that we may be allowed to drive at 85 mph soon.

No AC value, because it doesn't need on on AC. DC on contacts can cause issues with oxidation, and corrosion phenomenon, On AC, there is no unilateral corrosion, half a cycle there may be, in the next there is an opposing reaction


5 years ago

Listen to Steve !

A relay coil is the motor that activates the mechanical action ONLY.
And you cannot change the voltage of IT !
Some large relays " Contactors " allow you to exchange coils with different voltages.

The mechanical contacts are a different matter, they are the switches that
close or open electric circuits and the voltage and current ratings are determined
by how far they  separate = voltage and
the size of the contact buttons = current..

The concept of relay is a small energy can control a LARGER Energy  :)


I know how relays work. I don't know how to convert from a "Minimum recommended contact load=130mA@12VDC" [NO AC VALUE GIVEN!] to an equivalent amperage at 240VAC. (P&B KUP-11AT5-240V Relay)

Relay has an AC-coil; the contacts have both AC & DC max. switching specs. Is there a rule-of-thumb conversion to obtain the MINIMUM number for AC switching current?

I know how to convert DC volts/amps to AC volts/amps; but the physics of the CONTACT characteristics in AC & DC are different. The MINIMUM reliable AC current at 240V is what I am looking for.

Thanks for your inputs.

You can't. If the relay doesn't have a 240V AC contact rating IT ISN'T DESIGNED FOR, OR SAFE ON, 240V.

The relay in question DOES HAVE A 240VAC contact rating of 10A@240VAC. The SPEC-SHEET only gives a "Minimum Recommended Load" in VDC; need to convert to VAC.

Load isn't expressed in VDC, it would be in W or A.