distortion in ac output from transformer

[Prototype21]

Hi guys,
I want to know, why I am getting a distorted output from a step-down transformer? Why is it not a proper sine wave? Is it normal?
What may be the problems? Does adding a 100uF capacitor solve this problem?

 

[chemelec]

Saturation of the Core.
Try to Reduce the input Voltage.

 

[Tony Stewart]

Why do you have no specs for your transformer , application or test method?

 

[JimB]

Saturation of the Core.
Try to Reduce the input Voltage.

I agree with chemelec.

Does adding a 100uF capacitor solve this problem?

No.

JimB

 

[audioguru]

If this is the output from a loaded mains transformer then its core is saturating because this transformer is overloaded.
At first I thought it is a vacuum tubes audio output transformer that is overloaded. But if the vacuum tubes are clipping then the upper and lower horizontal clipped parts would be slanted due to the phase shift of the transformer.

 

[Prototype21]

I pulled the transformer from a circuit board which is used to charge a 6V sealed rechargeable battery. The above output is from the secondary coil when a 220V is applied to the primary.

Try to Reduce the input Voltage.

The transformer works on 220v AC, as its primary coils were directly connected main supply wires before it's pulled out from the circuit board. That means it designed to work on 220v mains.

Is it normal to have this kind of output in transformers?

 

[crutschow]

Is it normal to have this kind of output in transformers?

No, the output should look like the input sinewave.
Are you sure the transformer was connected directly to 220Vac?

 

[Prototype21]

Are you sure the transformer was connected directly to 220Vac?

yes, the transformer is directly connected to mains.

 

[audioguru]

A charger does not care if the transformer core is saturating. Then it can be very cheeeep.

 

[fourtytwo]

Many small transformers do this, the size found in small wall warts, as chemelec said its core saturation, a design feature!! Thats why such transformers have a surprisingly high offload power (often a watt or so). Somewhat annoying if you want a reference sine for example, that can be solved by incorporating a primary series resistance to lower the voltage enough to stop the saturation or you can by an EXPENSIVE transformer for such purposes.

 

[Prototype21]

A charger does not care if the transformer core is saturating. Then it can be very cheeeep.

That makes sense.

solved by incorporating a primary series resistance to lower the voltage enough to stop the saturation

How to calculate the required resistor?

 

[audioguru]

I have a Chinese +9V, 100mA wall wart that produces +17V with no load and +9V with 100mA load. It gets hot with and without a load.
I think its transformer core is made of rice or poop.

 

[JimB]

How to calculate the required resistor?

I am not sure that there is a quick and easy calculation that can be done without knowing a lot more about the transformer.

If you really want to use that transformer to to give a sinewave, the easiest way would be to experiment with a few different resistors and see which works best.
To start with, try something between 10 and 100 Ohms and see what happens.
If the resistor gets hot and smokes, you need one with a higher power rating.

Of course, putting a resistor in series with the primary of the transformer will reduce the voltage regulation. So if you try to draw any power from the secondary, the secondary voltage will fall. Just like AGs rice cored transformer.

JimB


PS, Anybody know the magnetic permeability of rice?

 

[Ylli]

Your initial post indicates 50 Hz. Is this transformer rated for 50 Hz, or is it designed for 60 Hz?