how to calculate resistor watts,

[vembaiyan]

resistor watt

Dear all

i have to get the output voltage of 20v from 230v Ac. without using the step down transformer. i Have a idea of connecting the higer watt resistor to get the required output. But i m not aware of how much watts should be connected to get the required output. Is there any calculation to get the accurate watts resistor to get the required output.

thanks in advance
Vembs

 

[cameo_2007]

calculate resistor wattage

simple law...
P = I*V or
P = I*I*R
where P, is the power going to be disspated across the R and I,the current you r drawing through the resistor(from 230VAC) and R,of course the resistor value and V,210V(for ur application)


regards,

 

[IanP]

resistor watts

Maybe you can do this:
Instead of a watt-rated resistor use a high-voltage capacitor ..
Zc=1/ωC
The main adventage is - no heat !!!

Regards,
IanP

 

[cameo_2007]

calculating resistor wattage

IanP,

I didnt get that logic.How would you able drop the voltage with a cap.
could you pls clarify it.

regards,

 

[xunzhaoziwo]

how to calculate resistor wattage

IanP,

I didnt get that logic.How would you able drop the voltage with a cap.
could you pls clarify it.

regards,

Same question with Cameo.

 

[wisepie]

how to calculate resistor

First, you must make sure what is your output load. Then from there you can calculte the value of current flows. Resistor watt required: (Output voltage of transformer - desired output voltege)x current.

 

[fguihot]

resistor wattage calculation

IanP,

I didnt get that logic.How would you able drop the voltage with a cap.
could you pls clarify it.

regards,

Same question with Cameo.

It's a capacitive divider, like a resistive divider. You could built a divider with any component. Z1/(Z1+Z2)
It divide only the AC signal, and it works great only if the load is constant ( the voltage depend on the load...)

 

[ender84567]

how to calculate resistors

any other requirements? 20V ac or DC?? use an AC/AC or AD/DC converter.

 

[johnyaya]

calculate resistor watts

Without a transformer you cannot isolate from the mains, so be VERY careful. Don't count on the outlet being wired properly either. Tranformers are an important safety issue.