[SOLVED] is there any different type of transformer needed square and sinwave ?

[thannara123]

is there any different type of transformer needed in square and sin wave inverter ?.

Can i use same transformer for both sin wave inverter and square wave inverter ?

 

[Warpspeed]

Can i use same transformer for both sin wave inverter and square wave inverter ?

Yes if the average voltages and frequencies are the same.

 

[jiripolivka]

Yes if the average voltages and frequencies are the same.

There are types of transformers which differ by application:

1. Power transformers, with iron cores, mostly made of strips to reduce loss. Their "signals" are generally sinusoidal and usually core magnetization does not cause much distortion. Used for AC 50, 60 or 400 Hz.

2. Audio transformers with iron or ferrite cores, designed for undistorted signal transmission. Core design is important and magnetization by DC current reduced, so sinusoidal signals can be transmitted without distortion for audio range, 20 Hz to 20 kHz, sometimes even wider.

3. Pulse transformers, usually with ferrite cores, designed for various applications. Some types use core saturation to form pulse shapes. Special ferrites are used for RF transformers for up to 1 GHz.

 

[schmitt trigger]

The key is to prevent core saturation, which means not exceeding the maximum flux density Bm.

For a given core geometry, material and number of primary turns, a square wave yields 11% more flux density, with the same peak voltage and frequency.
Which means that a transformer designed to operate 230V, 50Hz sinewave, will only withstand a 207V, 50Hz squarewave.

By squarewave I am talking about a full squarewave, not modified squarewaves.

 

[FlapJack]

Not enough information given. Many times square wave out inverter's are big iron transformers switched at 50 Hz.

Sine wave inverter's almost have to be high frequency switching transformers in order to have reasonable sized component's to produce a sine wave. Such as a LC filter.

The switching frequency is typically from 20 KHz to 70 KHz and are made of ferrite.

 

[Warpspeed]

All very true.

But the original poster is asking if you change nothing else but the wave shape will the same transformer work ? Same voltage, same frequency.

The answer has to be yes, provide you use the average vale of the sine wave not the rms value when measuring the ac voltage.
Its only a small difference (11%) but needs to be mentioned for correctness.

 

[Audioguru]

The original poster is asking about the transformer in an inverter. A sinewave inverter does not use a huge 50Hz or 60Hz transformer because it does not have a very hot linear amplifier. Instead it uses a high switching frequency and a small ferrite transformer and Pulse Width Modulation to make up the low frequency sinewave.

 

[Warpspeed]

More than a few sine wave inverters DO use a huge 50Hz/60Hz transformer, and drive the primary with PWM at low voltage.

 

[thannara123]

Thanks for reply . I am asking that can I use the same transformer in sinwave inverter and square wave inverter ?
For example
A) a sinwave inverter having 500 watt with 50 Hz .
B) a square wave inverter having 500 watt 50 Hz.

Can I use the same transformer for the above conditions A and B .

Transformer 12 volt primary . 230 volt secondary .

 

[Warpspeed]

Yes the same transformer will work.

With sine waves the primary will need to be driven with a PWM sine wave signal.
With square waves the primary is just switched on and off.

 

[KlausST]

Hi,

Yes if the average voltages and frequencies are the same.

The average input voltage to a transformer should be zero.

For sure you meant: RMS voltage.

Klaus

 

[Warpspeed]

Klaus,
Average of sinewave = 0.637 x peak
RMS of sinewave = 0.7071 x peak

When calculating with volt microseconds of a sinewave its the average value that is important.
So for a transformer, the operating conditions, particularly the flux swing when comparing a square wave to a sine wave, its the average of the sine wave voltage that you always use.

 

[FvM]

Clear what you mean. For clarity, we should say average of a half wave or average of rectified value.

 

[thannara123]

finally concluded that both can be use thanks

 

[FlapJack]

Yes the same transformer will work.

With sine waves the primary will need to be driven with a PWM sine wave signal.
With square waves the primary is just switched on and off.

Have you seen successful sine wave PWM of the primary of a 50 Hz transformer? Very cleaver if it works.

- - - Updated - - -

It looks like there is commercial PWM 50 Hz transformer inverters.

http://solar4living.com/pureSineInvPWM.htm

"Pure Sine Wave (Low frequency transformer)

These are the 'traditional' pure sine wave inverters. Similar in design to the 'traditional' square wave inverters, the primary of the large iron core transformer is fed by a 12v PWM push-pull stage, which generates a sine wave. This is stepped up to 230v AC, and the secondary is fed into the load.

The resulting sine wave usually has up to 4% distortion. The output RMS voltage is on par with the mains. Like its predecessor, these inverters need good cooling, otherwise they will overheat rapidly. This is expecially important when operating near, or at their rated continous capacity."

 

[Warpspeed]

It looks like there is commercial PWM 50 Hz transformer inverters.

It may seem like an ugly solution using a huge iron transformer driven by high frequency sine wave pwm, but it does have one very big advantage.

Something like that in practice will be far more robust, able to survive short term inrush and extreme power factor overloads reasonably well that typically go with real world mains type inverters.

Compare that to a high voltage 1Kw dc/dc switching power supply generating 340v dc that is then PWM'd into ac.
Try drawing 3Kw from it for a couple of seconds and see what happens.

A 1Kw iron lump would much more easily handle a x3 overload for a few seconds, the output voltage may sag a bit, but it will survive.
Provided there are enough switching transistors on the primary not to pull out of saturation, the whole thing can be built to be pretty bullet proof.

When you start looking at starting up some really nasty loads like induction motors (refrigerators/air conditioners) and fluorescent lights, many of the fly weight high tech inverters simply cannot cope with that type of abuse.

 

[thannara123]

How to calculate a transformer .with 12 volt primary (sinwave ) 230 volt output to draw 500 watt ?

 

[Audioguru]

A transformer has an efficiency of maybe 90% then for 500W output you need 555W input from the 12V. The 12V will have maximum RMS current of 555W/12V= 46.25A which has repeating peaks of 65.4A.
If the output is 230V RMS at 500W then with a low load current it might be 253V RMS or more unless there is negative feedback from the output.