Mac Mini and Firewire drive power consumption

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Hawaii Cruiser's picture
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Joined: Jan 20 2005
Posts: 1434

Since one of the nice things about owning a Mini over a tower is the lower electricity bill, I am wondering, does the power block for a Mini actually sleep? The power supply in a modern tower under deep sleep draws nothing but the trickle needed for sensing a hardware stimulus for waking (keystroke, mouse movement, power button, etc.), correct? But what about the Mini block during deep sleep? And likewise, if you've got a permanent setup booting a Mini off of an external Firewire drive, does the Firewire drive's power block go to sleep during deep sleep? Power blocks and wallwarts continue to draw significant current just by being plugged in, whether or not the appliance is turned on. Is that still the case with the Mini and Firewire drive PSU's?

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Dr. Webster's picture
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Most modern AC power adapters

Most modern AC power adapters -- whether they're for a peripheral, laptop, or Mac mini -- have a variable amperage output, meaning they'll supply as much juice as the device they're powering demands (up to the design limitation of the power adapter). That means, if your mini only needs 1 amp of power for what it's doing right now, it'll only draw 1 amp and the power adapter will only 1 amp's worth of AC power into DC. If, later, the mini wants 3 amps because it's really cranking away on something, the power adapter will ramp up to match. A simple experiment to confirm this for yourself is to measure the temperature of the mini's AC adapter when the mini has been asleep for a while, then fire up a processor-intensive task for a while and measure the temperature again -- it'll have risen. There's no logic built into the adapter that lets it "know" when the mini is asleep, and likewise there's no "sleep" function in the adapter itself, because there's nothing to put to sleep; power adapters are pretty simple in design and have already been minimized component-wise as much as possible (the AC adapter that ships with the iPhone still boggles my mind for how tiny it is).

That said, AC power adapters still have some loss when converting AC to DC -- it's not a 100% efficient operation -- and will still draw a small amount of power even when nothing is connected to the DC output side. The most energy-efficient thing to do with an AC adapter when you have nothing connected to it is to unplug it from the wall.

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TheUltimateMacUser's picture
Joined: Jan 28 2004
Posts: 615
...

You could get a Kill-A-Watt (URL) and use it to measure power usage while churning away / idle / asleep.

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Hawaii Cruiser's picture
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Joined: Jan 20 2005
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Thanks Doc

Thanks Doc. You always come through with the answers.