I got one question, my input is 24V DC, 21A, and I going to make a 240V, 500W inverter, I need to power a load about 300W.

I want to know how to calculate the size of the transformer needed for this project? What else precaution I should take since I am a newbie in electronics.

 

Since the DC source cannot give you more than 504W then a 500VA transformer will be fine.

Is it going to be a true sinewave inverter?

What kind of load is it?

 

I was trying to make a modified sine wave inverter, the output is used to drive a small water pump which is 300W

 

you best check your data for an FLA, and it's starting method. Me thinks you'll be looking at around 1500VA, which has some implications on the input.

 

hmm.. what is FLA?

 

I got one question, my input is 24V DC, 21A, and I going to make a 240V, 500W inverter, I need to power a load about 300W.

I want to know how to calculate the size of the transformer needed for this project? What else precaution I should take since I am a newbie in electronics.

You will need to know both efficiency and power factor.

 

Google volt ampere. you will find the answer?

 

if your powering a resistive load (pf = unity) then wattage is your indicator. With a motor however, you have several other factors to consider. As indicated, you'll need to know your motors FLA (full load amps). This rating considers the motors power factor and efficiency. Then you need to make some assessments as to it's starting requirements, which depend on the starting method. Suppliers' data sheets typically contain this information.

Tack onto that the effeciencies of your converter/inverter.

 

For a single phase transformer, figure about 90% efficiency, for 3 phase transformers, about 95% efficiency, for AC motors, about 86% efficiency. Don't overload your transformers as the voltage will sag when they go out of regulation; current goes up and they over-heat.

Cheers, DPW [ Spent years making heaters out of op-amps.]