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Question about voltage vs current
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gkmaia:
I have an equipment that takes 25W of power to run.

If I run it with AC 220 it is expected to drive 0.11Amps
If I run it with DC 12v it is expected to drive 2.08Amps

I based the current consumption on I = P/V

Is that correct? Higher the voltage less current it will need to run?
rstofer:
Yes, your solution is correct.
MrAl:

--- Quote from: gkmaia on January 22, 2019, 11:05:58 pm ---I have an equipment that takes 25W of power to run.

If I run it with AC 220 it is expected to drive 0.11Amps
If I run it with DC 12v it is expected to drive 2.08Amps

I based the current consumption on I = P/V

Is that correct? Higher the voltage less current it will need to run?

--- End quote ---

Hi,

As long as the load is a pure resistance.  If it is reactive or partly reactive then you have to take into account the angle between the current and the voltage or know the power factor:
P=V*I*cos(TH)
where TH is theta the angle between current and voltage.
The apparent power is:
P=V*I

and that may be of concern also.
helius:
There is no equipment that simply uses less current when supplied with higher voltage. The usual result is that it burns out when supply voltage is too high (https://www.eevblog.com/forum/blog/eevblog-1160-weller-responds/), or cannot function if it is too low.
Note that Ohm's Law (V = IR) has V and I proportional. That's the opposite relationship to the definition of power (I = P/V) where V and I are reciprocal. Among these two equations, the defined quantities are usually V (by the supply wiring) and R (by the equipment), and I and P are the unknowns. As V increases, I increases proportionally, and P increases quadratically.

There do exist pieces of equipment that automatically sense the supply voltage and adjust themselves within a limited range. So-called "universal switching power supplies" have a label indicating compatibility with 90 to 260 VAC at 48 to 62 Hz. Other machines are capable of running from either AC or DC as long as the RMS voltage is roughly the same (universal motors, where the meaning of "universal" is quite different). But this adaptability is not the norm and should not be assumed.
Doctorandus_P:
There are plenty of cheap small SMPS circuits on Ali / Ebay / Etc, based on for example LM2596.
If you use them to generate an output of 5V, and you adjust the input voltage between 7V and 30V then you will see that the input current gets lower for higher input voltages. Input power stays about the same. You can expect efficiencies betwen about 80% and 90%, so input power is only a bit more than output power.

Just buy a few of these and experiment with them.

These are usefull to have in a lot of projects.
I find the versions with the adjustable current limit most usefull.
You can even use these as a simple adjustable lab power supply if you change the trim pots for regular pots and add some panel meters for voltage and current.

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