How can we convert Watts in DC to Watts in AC? for e.g A device needs 1A and 12V DC input i.e (1A x 12V = 12 Watts) 12 Watts DC. If we use an AC to DC adapter/converter to generate 1A,12V (12Watts) DC then What will be the AC Power/Watts that we have to input into the device's adapter/converter?
Summary: Watts out DC = 75% to 90% of AC Watts in, in most cases.
At 100% efficiency ADC Watts out = AC Watts in.
Energy is 'conserved" and energy = Watts x time. eg we often measure energy in Watt.seconds = Watts x seconds operated = Joules.
The efficiency of conversion depends on the technology. Power level and voltage also give an effect.
Using a conventional iron transformer the AC mains to AV low voltage conversion probably is > 95% efficient. Rectification efficiency depends on voltage and diodes used. As a silicon diode drops 0.6V or more, a single diode can account for (0.6V/(5+0.6)V) ~= 11% efficiency loss. If a bridge rectifier is used there are two diodes in the circuit and this can account for over 20% efficiency loss.
If a switching power supply is used the overall efficiency is liable to be in the 75% to 90% range. More than 90% efficiency is possible with special care.
So Watts out DC = 75% to 90% of AC Watts in in most cases.
Q: "you mean that for 90W or 75W DC out we will need 100W AC input?"
Rearrange these equations:
DC_Watts = 75% AC_Watts so AC_Watts = .....
DC_Watts = 95% AC_Watts so AC_Watts = .....
Watts_Out = Watts_in x Efficiency ( 0 <= Efficiency <= 1.0)
Then Watts_in = Watts_Out / Efficiency. ( 0 <= Efficiency <= 1.0)
So when converting your DC watts being used in AC watts, that would be 100 DC watts equal 75 to 90 AC watts. That is using the inverter and wiring efficiency of between 75% to 90% .
protected by clabacchio♦ Mar 22 '18 at 11:09
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