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I am working with some small devices and checking input power requirements. Many of the standard labels look like this:

Input Power: 100 - 240 VAC, 50-60Hz, 2.5A

I am trying to determine how much current will be used with 120V or 240V. Because the input voltage is a range of 100 - 240, I am guessing that the device will only pull 2.5A for an input of 100V. Can I assume that for 240V, the maximum current it will draw is 1.0A? There is no documentation on total Watts.

100V * 2.5A = 250W

250W/240V = 1.04A at 240V

UPDATE: Another way to ask this question is how many Watts does this device use? Is it 100V * 2.5A = 250W? Is it 240V * 2.5A = 600W? Does the power vary based on changing the input voltage or will it automatically use less current to maintain the same power? I would like to connect multiple devices to 1 power source

CytotoxicT
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    You'll need to take a look at the efficiency curve of the converter inside the device to find out for sure. Your calculations will be *roughly* correct, but the converter will usually vary a few % efficiency over the whole input voltage range, with usually a steep drop at the low end. – vir Feb 08 '22 at 21:48
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    I think that "Can I assume that for 240V, the maximum current it will draw is 1.0A?" is an interesting question which is not adequately answered by the answers on the supposed duplicate question. – Cassie Swett Feb 08 '22 at 22:17
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    Just a guess, but the 2.5A probably is a promise that it won't draw any more than that amount of current under any non-fault circumstance. – Solomon Slow Feb 09 '22 at 02:16
  • What type of 'small devices' are you looking at? – Bruce Abbott Feb 09 '22 at 04:47
  • @BruceAbbott They are laboratory instruments. Things that heat, shake, vacuum, etc. One specific device is this [centrifuge](https://bionexsolutions.com/hig-centrifuge/). There is also a PC, which is the [Dell optiplex 7490](https://dl.dell.com/topicspdf/optiplex-7490-aio_owners-manual2_en-us.pdf) – CytotoxicT Feb 09 '22 at 15:24
  • Centrifuge specs: 100–127/200-240 V~, 12/6.2A: 50/60 Hz = **different** current ratings for 110 and 230 V. Not a good example. – Bruce Abbott Feb 09 '22 at 20:37
  • @BruceAbbott This [Plate Labeler](https://www.agilent.com/cs/library/usermanuals/Public/G5404-90003_R02_LabelerUG_P_EN.pdf) is another example. The power reqs are on pg. 34 of the manual. – CytotoxicT Feb 10 '22 at 20:29

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