Inverter Calculation

Your calculation is almost correct, except the consideration of output power factor. If you know the power factor, the formula is:

Idc = (Vac x Iac x p.f) /(efficiency x Vdc)

Keep in mind, the efficiency may vary with the load. If you use the correct efficiency for the load, the calculated DC current will be correct, otherwise, it will be close approximate.

- MS

Hi msamad,

are you sure the pf should be integrally multiplied?

IMHO I can see the reactive current component will increase losses in the inverter ckt, but guess the DC [link] current does not depend on load phase.

But I certainly lack practical experience with large inverters.

brgds

Snel

Hi Msamad,

my comment was not correct. Your formula is.

brgds

Snel

Also, the AC values should be RMS values.

You can indeed calculate theoretically the approximate DC consumption using formulaes however in practice I have always come to rely on an actual measurement. I use a Fluke i1010 ac/dc clamp connected to a Fluke Digital Multimeter using the DC millivolts scale. I have often been surprised at the difference between theoretical and actual real values.

Happy New Year

John

An inverter is simply a type of power supply, and a power supply's efficiency is highly dependent on its load. Most power supplies reach their peak efficiency at around two thirds of their rated load current (assuming the manufacturer is honest about the rating). So above and below that point, all bets are off, so to speak.A power supply with a 92% efficiency rating may have only 30% efficiency at a 10% load, or 75% efficiency at a 95% load. Typically the worst efficiency is going to be seen at 10% or less load.

I just found this free resource at ezigbt.com. Too bad the recommend section does not work. I could use help on that right now.