va for transformer

[[email protected]]

hi.

i required a transformer of 24v for 2A load. i saw a transformer with 24v and 2va. so i don't understand that what is va? can i use 2va for 2A load?

 

[tronitech]

Transformers are rated in VA (Volts x Amps) so you'll need a 48VA (24V x 2A) transformer. It's better to go higher unless it rarely needs to supply 2A but if it's a steady 2A load I'd be looking at getting a 100VA transformer. Hope that helps.

 

[[email protected]]

thanks friend...

i have 1 another question..

if i want to convert 230v ac to 24 v dc than any direct ic available or not.

 

[tronitech]

The 78S24 is rated at 2 Amps but you'll need the input voltage close to it's minimum and good heat sinking. I'd go with something like the 7824 and a bypass transistor. Do you plan on using a bridge rectifier because a 24VAC transformer would give you 24 x 1.414 = 34V which is a little high.

 

[KeepItSimpleStupid]

You can read this article on VA or reactive power: https://en.wikipedia.org/wiki/AC_power#Reactive_power

Basically for resistive loads, it's the same as Watts or Volts * Amps but VA and Watts are different units. AC generators have to be sized in VA and must be large enough to handle the motor starting current.

 

[dr pepper]

You gan get single chip power supplys that convert mains directly to dc, these are common in standby power supplys in tv's, but you need 2 amps, for this much power you'll need a transformer or smps.

 

[ronsimpson]

Look at a data sheet on a transformer. At the max power, the temperature will be very hot. Way too hot to hold.

 

[[email protected]]

ok..

can i use two 12v transformer in series and use 24v ?

 

[KeepItSimpleStupid]

Yes,, in series you will get 0 or 24 V (was a typo) depending on the phase (0 or 180 degrees). Windings will add or subtract depending on phase (polarity)

You can also put similar transformer secondaries in parallel to increase the current. The transformers must be phased properly.

 

[[email protected]]

ok...thanks..

 

[ericgibbs]

ok...thanks..

hi
I think KISS has a typo Yes,, in series you will get 0 or 12 V, I am sure he meant 0 or 24V.

E.

 

[KeepItSimpleStupid]

Thanks Eric. Noted and fixed in post.