Discussion in 'The Projects Forum' started by harikanaidu, Apr 20, 2016.

1. ### harikanaidu Thread Starter Member

Nov 28, 2014
76
1
Hi, I am working on inverter circuit....i am going use a circuit from google...But my doubt is about the transformer i am going to use...I have 220 v to 12 transformer....can i use it as step-up by connecting in reverse ..?and one of my friend said that,there may be problems ,when any load is connected although it gives 230v output......What is the reason for this...?I i have 100 watts load how to choose the transformer?

2. ### gerty AAC Fanatic!

Aug 30, 2007
1,153
304
If you are going to use the 220/12 volt transformer to step up you must put in 12 volts AC . And at 20:1 ratio you'll need several amps to drive a 100w load.

3. ### KeepItSimpleStupid Well-Known Member

Mar 4, 2014
1,144
203
Your "inverter" may not supply a sine wave. Your measurement system may not employ TRMS (True RMS).

Simple inverters might use a center tapped transformer. But there are "modified sine" and "sine wave inverters". The simplest is a square wave inverter.

Many meters are designed to read RMS only for a sine wave in, They a "Average responding" RMS reading, so the multiply the average by a "fudge factor". e.g. they just precision rectify and multiply by a constant.

There used to be meters that operated on how the waveform heated.

RMS = Root Mean Squared or SQRT (Mean()^2)

For the definition of MEAN, see calculus.

4. ### gerty AAC Fanatic!

Aug 30, 2007
1,153
304
I can't believe I missed the word "inverter" in the original post !! One of the usual problems I've seen is the transformer selected doesn't have large enough (wire diameter) windings on the secondary (12v side). My students have built a few of these, and as KISS stated, used a center tap transformer. The higher current needed on the now primary (12v side) needs a larger diameter wire to work properly.

5. ### harikanaidu Thread Starter Member

Nov 28, 2014
76
1
Can one help me??Is it ok if i use 12/220v -1 amp step down transformer as step up...if so how much current will it produce at the output??

6. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,387
1,605
Usually you can do this, one cannot be sure specifying an unknown part for an unknown circuit.

If you know the output power for step down you can use that same rating for step up. The transformer really has no clue which way the energy is flowing.

Do respect the voltage ratings. For exame, don't drive the 12v side with 24 volts.

7. ### crutschow Expert

Mar 14, 2008
13,006
3,232
Depends upon the type of inverter waveform driving the 12V side as to whether it will work to give you the proper voltage out.
Is the 12V side center-tapped?
A 12V, 1A step-down transformer can deliver 12W maximum at the 220V output or 55mA (power in equals power out) not including any inefficiencies.

Willen likes this.
8. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,797
1,103
In other words, no, that transformer is unsuitable for driving a 100W load.

9. ### KeepItSimpleStupid Well-Known Member

Mar 4, 2014
1,144
203
P1=P2 Power primary = Power secondary
corollary.

V1 * I1 = V2 * I2 = V = voltage, I=current)

You also have V1/V2 = n or the turns ratio

So, the transformer, transforms voltage within it's power limitations. You can't exceed either winding limitation.
The specifications would have to spec both at 100 W in your case. There will be some losses.

10. ### Willen Member

Nov 13, 2015
138
12
So, you need 9 Amp transformer so that you will get 12V x 9 Amp = 100 watts power output and output voltage would be 220V, 450mA.

11. ### ScottWang Moderator

Aug 23, 2012
4,853
767
You could buy one or if you want to DIY then you just google : 12v to 220v converter, then you could get a lot of infos.
as 12V to 220V DC to AC Converter Circuit.

The simple current calculation:
Assuming that Eff = 60%, Eff = Efficiency:
Wo = Wi * Eff
= Wi * 60%

Wi = Wo/60%
= 100 W/60%
= 166.7 Watts

Wi = Vi * Ii
Ii = Wi/Vi
= 166.7 W/12 V
= 13.9 A

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