# Measuring current consumption from DC power supply

Suppose you have DC power supply and a consumer connected to it (i.e. computer PSU and a hard drive).

Suppose PSU which was supplied with the consumer has output 5V 1A. So I assume that the consumer should not consume more than 1A.

Suppose the original PSU is broken now and I want to replace it with the one I have which is 5V 10A.

My guess is that current is something which depends on the consumer. So if the consumer consumes normally 1A then it will not consume more than that even if it is connected to 10A PSU.

In other word - am I right assuming that the consumer will not burn out being connected to a power supply with higher current output?

P.S. my understanding is that voltage is something independent from the consumer. If you give it higher voltage it will burn (voltage is from PSU to the consumer). However current must be in opposite - consumer sucks as much current as it need not as much as PSU can provide (of course given that max PSU current is greater than the consumer needs)

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Just as others have said, standard PSUs behave as voltage sources, meaning that they try to keep constant voltage, while current is a function of load's impedance, so you're right. – AndrejaKo Jan 9 '11 at 22:08

## 2 Answers

The amps that a device draws remain constant as long as the amps supplied to the device are greater than or equal to the amps drawn. If the amps supplied to the device are less than the amps the device draws the power supply will be overloaded and either blow a fuse (if you are lucky) or burn up internally.

So just make sure your new power supply provides AT LEAST as many amps as your device needs.

Voltage on the other hand should always be matched. If a device requires a certain amount of voltage make sure your power supply DOES NOT give it more than that required voltage. Giving excess voltage will most certainly destroy your device, and giving to little will cause (at the least) erratic operation.

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Just one one caveat that a PSU that is rated a lot higher than needed may use more electricty, as the efficiency bell curve usually peaks at around 60%-80% of maximum load. Higher rated PSUs tend to be more efficient in general though. – paradroid Jan 9 '11 at 22:47

Provided that the source voltage is the same, the current consumption should not be any different.

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