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Transformer specification question :)

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adisaat

New Member
I bought a transformer with a specification of

24VA
230V/110V

At one side is 2 pins which is 230V
while the other sided have 2 pins of 110V.

Here is what i think, As the power supply from my household socket is 230 volts, I will connect it to the 230V pins.

And since i wanted 110 Vac, I can just connect wires from the 110V pins to the component im using,

A relay with specification of :
100VDC,
1/6Hp,120V/240VAC
5A,24VDC/240VAC Res.

Can the relay handle the voltage supplied from the transformer? (110VAC)
Also what does the 24VA means on the transformer? :p

Thank you :)
 

MikeMl

Well-Known Member
Most Helpful Member
VA is simply the transformer RMS secondary current multiplied by the RMS secondary voltage, without regard to phase shift. Think of it like Watts.

The maximum RMS secondary current that the transformer will deliver is 24VA/110V=0.218A.

The problem with your relay is that the coil is rated for 100VDC, but your transformer puts out AC. If you just use a single diode as a half-wave rectifier, you will deliver unfiltered half-cycle pulses of DC current to the coil of the relay, and it will buzz loudly. If you put a several uF capacitor (rated at ~150VDC) across the relay coil, it will probably quiet the buzzing, but it is likely to raise the DC voltage across the coil much above 100V.

Measure the DC resistance of the coil with your Ohmmeter, and post the value here. With that information, we can devise a rectifier-filter-resistor network which will operate the relay coil at the correct 100VDC.
 

Hero999

Banned
A relay with specification of :
100VDC,
1/6Hp,120V/240VAC
5A,24VDC/240VAC Res.
That sounds like the contact rating, you need the coil rating if you want to connect it to the mains.

Can the relay handle the voltage supplied from the transformer? (110VAC)
I don't know, you need to check the coil voltage rating.

Also what does the 24VA means on the transformer?
24 Volt Amps which means the voltage times the current, as mike said the maximum current is 24/110 = 0.218A = 218mA.

Note that this isn't always the same thing as power, for example a 24W 110VAC motor will actually draw more current than 218mA because its power factor will be below 1.
 

MikeMl

Well-Known Member
Most Helpful Member

MikeMl

Well-Known Member
Most Helpful Member
Ok, here is what I propose. Note that the filter capacitors delay the turn on and turn off of the relay, but not excessively. The switch depicted is for simulation. If could just as well be in the transformer primary in the real circuit.

V1 models the transformer secondary; the peak voltage is 1.4*110V at 50 Hz.

V2 is for simulation only; it turns the switch on and off.

There should be enough filtering to keep the relay from buzzing.
 

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