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I have a 12v 300 watt power supply. I replaced 13 20watt halogen bulbs with 13 3watt LED bulbs. Questions:

  1. should I downgrade power supply since I'm now drawing 39 watts as opposed to the 260watts I was pulling with the old halogen bulbs?

  2. Am I correct in assuming that power usage is based on the total wattage of the lights and not the rated wattage of the power supply? If true, then my power consumption has dropped from a rough equivalent of 3 100watt light bulbs to approximately a single 40watt bulb, correct?

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1) You could if you wanted to, but it's probably not necessary. Drawing less than the rated power should not hurt it.

2) yes and yes.

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  • $\begingroup$ Simple, but correct - it's nice to not over complicate answers sometimes :) $\endgroup$ – Jonathan R Swift Jul 31 '18 at 14:52
  • $\begingroup$ Doesn't actually address the question - should I replace it with a smaller one. He knows he could if he wanted to. He wants to know if he wants to. $\endgroup$ – Phil Sweet Aug 1 '18 at 0:16
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What Daniel said is the best, correct answer. To add my two cents, keep in mind that a device will only ever pull as much current as it needs. Most devices have a constant, non-changing impedance -- just a simple case of V=IR.

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