# Transformer Efficiency

Discussion in 'General Electronics Discussion' started by imperium2335, Oct 3, 2012.

1. ### imperium2335

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Sep 15, 2011
Hi,

I have just bought a transformer.

Its 230 or 240v in, and 55v @ 2.27 amps out.

My question is how do I work out the efficiency of it? I do not know the input current so I am confused as to how to figure it out.

Also, the transformer has three connections on the secondary as 55 - 0 - 55.

Does this mean I have two 55v outputs so totally it's really 110v out if I combine them somehow?

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,501
2,841
Jan 21, 2010
55-0-55 is 110V centre tapped.

The input current will be a little more than the output current times the output voltage divided by the input voltage. The efficiency is likely to be in the high(ish) 90's

3. ### imperium2335

10
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Sep 15, 2011
Hi Steve,

Does that mean I can only use one of the 55v outputs at a time, with the negative lead going to the 0v connection?

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,501
2,841
Jan 21, 2010
no, you can use both at once. There is no -ve lead as such because the transformer outputs AC.

5. ### imperium2335

10
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Sep 15, 2011
So I have a potential difference of 110v between the two 55v outputs? One being "high" and the other being "low", when combined they form the full wavelength?

I guess I will need to rectify this too? As I need it to power an LED circuit.

How would I wire it to use it properly?

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,501
2,841
Jan 21, 2010
What "LED circuit" are you wanting to power?

These sort of voltages are unusual for that sort of application.

7. ### imperium2335

10
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Sep 15, 2011
Hi,

The total voltage needed is about 32v which will be regulated from the transformer.

It's an LED matrix with 12 rows of mixed voltage LEDS, about 11 or 12 per string.

8. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,501
2,841
Jan 21, 2010
55VAC will give you approx 78VDC after rectification and filtering.

You'll need to regulate that (preferably via a constant current source)

9. ### imperium2335

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Sep 15, 2011
Thanks,

I just wired up my transformer and it works!

I didn't realize I can get 110v out of it by using the two 55v terminals.

Is this pretty dangerous even though it is an isolated transformer?

10. ### Harald KappModeratorModerator

11,996
2,810
Nov 17, 2011
Not especially, Connecting transformer windings in series is pretty common. Think of it as a transformer with twice as many windings.

11. ### BobK

7,682
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Jan 5, 2010
Yes, 110V AC is dangerous enough to kill you, even if it is isolated.

Bob

12. ### imperium2335

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Sep 15, 2011
I had a feeling it was. Thanks Bob, I will take care.