How to find transformers power

[bloody-orc]

Hi

I have a small transformer sitting on my desk right now.
size is 42 x 34 x 30 mm. Takes in 230VAC and gives out 2x 15.7VAC.
Came from an UPS.

Markings on it are 430-0006*6
LEI-4 9352
E154515
Class 130 (B) R1520

Winding resistances:
Primary - 653 ohms
Secondarys- 81 ohms each


Any ideas? How many Amps DC would I expect to get from that?

Thanks
--Rain--

 

[Russlk]

That is very little power for its size, perhaps it is a control tranformer. To answer your question: I=E/R = 15.7/81 = 194mA short circuit output. Maximum power will be with 81 ohm load: I=97mA. The primary current can be calculated from the turns ratio: 230/15.7=14.6, 97/14.6 = 6.6ma. 6.6mA*653 ohms = 4.3 volts drop in input voltage; not a lot.

 

[ericgibbs]

hi rain,

From the physical size it sounds about 2 to 3VA, which means at best 50 to 100mA max on both secondaries, the 81R is a high, so the regulation will be poor.

Connect the mains and load with a 220R 3Watt resistor, check the 17.5Vac

 

[bloody-orc]

So do I understand correctly.
I can get nice 100mA from it at 15.7VAC?
or is it 100mA @ 4.5VAC or what...

I'm kinda new to this AC and transformers world have always relied on battery power you know

 

[Russlk]

If the 17.5 volts is the open circuit voltage, the output to the 81 ohm load will be 17.5/2=8.75 volts. If you connect the two secondaries in series, you can get 17.5 volts to a 162 ohm load.

 

[bloody-orc]

God I feel like a complete idiot right now...
Could you please tell me how many mA will I get when I regulate the voltage to 12V, 5V or 3.3V. One secondary only (I use 2 windings separately to get 2 voltages out of it in one go)

 

[Russlk]

If you use an LDO for 3.3 volts, you will need about 4.5 volts input to the LDO. (17.5-4.5)/81=160mA max.

 

[bloody-orc]

So a nice 100mA at least for logic level electronics (5v) right?

That's enough for me I think
Plus imho i gain 1.7*AC voltage when going to DC (diodes + capacitors)

 

[veronilson]

AC/DC EI Type Power Transformer

Accurate information on the AC/DC EI Type Power Transformermodel 35DOBOP OR LS-A7632-PT, manufactured by leader electronics inc.

veronilson (veronilson@hotmail.com)

 

[mneary]

Plus imho i gain 1.7*AC voltage when going to DC (diodes + capacitors)

You gain 1.414*AC voltage, but then you subtract two diode drops.

 

[Hero999]

Its probably actually rated for 9V, transformers this small have really poor regulation.