To step down ac voltage

[Electro Builder]

hi frnds i was new to this forum...i want to construct a basic ac stepdown voltage circuit with out using transformers...is any body aware of this pls reply me along with the circuit

 

[goldsmith]

Dear Electro Builder
Hi
Is that means that isolation isn't important for you ? do you know about hazards of a non isolated AC voltage ?
Anywhere , how much current and voltage do you need and how much is frequency of operation ?
Best Wishes
Goldsmith

 

[Electro Builder]

here i have 50hz freq and i want to step down 240-120v

 

[rfredel]

Hello Electro Builder,

you don't write, how much power or current you load takes.

There are a three ways to step down the voltage.

1) You take a autotransformer. That the easiest way and you must not calculate a resistance. See picture1 in the attached drawing.

2) You must calculate a resistor. The formulars are R = (Uin - Uout) / I or R = (Uin - Uout)² / P. The power of the resistor Pres = (Uin - Uout) * I. Carefully the resistor will get very hot.. (Picture 2)

3) You must calculate a capacitor. This will only function with resistive loads or lamps, not for inductiv loads. Xc = (Uin -Uout) / I or Xc =(Uin - Uout)² /P ==> C = 1 / (2*3.14*50*Xc)

Regards

Rainer

Attached picture:

 

[tpetar]

Few examples :

 

[rfredel]

Hello tpetar,

I am not Electro Builder, but he wrote, that he need a step down converter from 240V AC to 120V AC.

Your attached files and your circuits are for low voltage - and DC - output.

Regards

Rainer

 

[tpetar]

Uh sorry I didnt pay attention on his post #3.


Voltage stepdown from 220V to 120V is done with transformator. There is many trafos which regulate US Europe voltage device conflict.

But without trafo this is also possible but should pay attention on needed current.

You can look some solution with usage of Triacs in design for light dimmer control and such things.

 

[Electro Builder]

cn u pls explain the first circuit

 

[tpetar]

cn u pls explain the first circuit

If you read attached PDF from post #5, you will get answer.

It uses capacitive reactance instead of resistance, and it doesn't generate very much heat. The circuit was designed to provide a cheap compact power supply for Cmos logic circuits that require only a few milliamps.
C1 is the X rated AC capacitor that reduces high volt AC. Gretz rectifies AC to DC and 470uF removes ripples. R1 is the bleeder to remove stored current in AC when power is off. R2 limits inrush current. A Zener can be used in the output to get regulated DC.

- - - Updated - - -

http://dmohankumar.wordpress.com/2010/05/10/transformerless-power-supply/

 

[rfredel]

Hello Electro Builder,

an autotransformer is a simple and cheap form of a transformer to make a step up or step down voltage. It has only a single winding for input and output. To get the wanted voltages the input - winding is tapped. One connector is common to the output. So you have no isolation between input and output.

The most use of this transformers are to connect home appliances of other countries with different voltages to your own country.

For example:
My wife use some specialy home appliances from her country with 120V here in my country with 230V.
In the other way, when I am going to my holydays to the country of my wife, I use one of this transformers to connect my shaver there.
Also I have some messuring instruments from USA with 115V in my workshop, so I use autotransformers to connect it here. This is cheaper then to change the maintransformers in the instruments.

I think, you can buy this transformers at every good electronic supplier or in EBAY.

I hope I explain it good, else look at this additional Link.

Regards

Rainer

 

[tpetar]

Hello Electro Builder,

an autotransformer is a simple and cheap form of a transformer to make a step up or step down voltage. It has only a single winding for input and output. To get the wanted voltages the input - winding is tapped. One connector is common to the output. So you have no isolation between input and output.

The most use of this transformers are to connect home appliances of other countries with different voltages to your own country.

For example:
My wife use some specialy home appliances from her country with 120V here in my country with 230V.
In the other way, when I am going to my holydays to the country of my wife, I use one of this transformers to connect my shaver there.
Also I have some messuring instruments from USA with 115V in my workshop, so I use autotransformers to connect it here. This is cheaper then to change the maintransformers in the instruments.

I think, you can buy this transformers at every good electronic supplier or in EBAY.

I hope I explain it good, else look at this additional Link.

Regards

Rainer

This is transformeless power supply without transformer. Autotransformer is transformer. :wink:

 

[rfredel]

Hello tpetar,

I know, that Electro Builder has ask for a transformerless circuit. In my first post (#4) I give 3 ways to step down the voltage.

In my answer now, I've discribe my first diagram, becaus Electro Builder has not ask, who has to answer. :-?

I know your circuits well and it will function, but the output is DC. It can be calculate for higher voltages. That is not the problem, but it is DC-Output. Electro Builder has not write, what he want. DC or AC output. I Think he will connect an equipment with 120V. So he need AC-output.

Reards

Rainer

 

[AMSA84]

Hello there guys.

a variable auto-transformer is cheap? I must disagree. At least in my country a variable auto-transformer is very expensive.

 

[AMSA84]

Hello there guys.

A variable auto-transformer is cheap? I must disagree. At least in my country a variable auto-transformer is very expensive.

 

[rfredel]

Hello AMSA84,

it's a question what is expensive and what is cheap. I know, if you don't have so much money, a little amount looks very expensive

I'm in Germany and here I can get a variable autotransformer with 1kW power for € 150,00. and a one with fix voltage for € 50,00. Both are brandnew and from a electronic supplier. In EBAY.com the prices will start at US$ 10,00. I think that will be cheap.

I know, that there are supplier, which sell them for a few hundred € or $. That will be expensive. Here it is your business to look for cheap offers.

Regards

Rainer

 

[Electro Builder]

yeah hero i want ac output

- - - Updated - - -

i want to make this without using step down or autotransformer.....so cost will reduced significantly.....help me guys

 

[tpetar]

I agree with rfredel autotransformer usually is cheaper then real transformer, and price is relative thing.

Electro Builder what current you need on 120V AC ?

You can use first section from circuit what I post (capacitor with resistor in parallel, and one resistor in serie with them).

 

[AMSA84]

You say that in ebay.com there are auto-transformers starting from $10.00? Can you show me the link please?

About the comparison that you did, I consider it a very expensive for the application. Stepping down 220VAC to 120VAC, by far, is more reliable and cost effective using a fixed voltage transformer.

Imagine now a 10kW auto-transformer. How much is the cost? If we begin to increase the power you'll see the huge difference that it is.

Best regards.

 

[Electro Builder]

less than 1A is enough for me

 

[tpetar]

less than 1A is enough for me

Transformeless way is for up to 100-150mA all over that need big capacitor and its very expensive.

Why you try to avoid conventional and right way with trafo ?

Small trafo up to 300mA-500mA are very cheap, always you can extract them from some chinese adapter.
But in your way you should get some small nice real trafo 220V to 110-120V.

Tell me one more thing, what device you need to supply with 110V, maybe this is necessary, maybe that device use 5V or 12V on input, and you can use 220V to 12V or some adequate needed voltage.