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Discussion in 'MacBook Air' started by vega07, Dec 13, 2013.
Does leaving a SD card attached (for extended storage) drain any power?
If yes, how much?
:O I never even thought of this... I'd like to know that too.
Though my best bet is if it does drain power, it would be minimal. I think...
The only time an SD card is going to draw any significant amount of current is when it's actively reading/writing data. If your MBA is asleep or powered down, it's not going to be reading or writing.
Current draw when an SD is in "sleep" mode is around 250 microamps. When reading/writing it bumps up to 100-200 milliamps. They operate at approx. 3 vdc, so in watts that, what, 0.00075 watts? The battery in a 2013 11" MBA delivers 38 watt-hours. If my math's right, it would take about 50,000 hours (5.7 years) for an SD card to fully discharge that battery.
I love you! Thanks for the doing the math and research.
5.7 years? Whoa, that drains quickly... :/ might not go for an SD after all.
Very good job someones willing to do the maths couldn't be bothered doing that!
Sort of... when you sleep a new Macbook Air it goes into regular sleep for three hours, then enters a "deep sleep" or hibernate mode that uses far less battery power than regular sleep mode does. If you have a SD card inserted it will prevent the Air from entering hibernate mode and the battery will run down faster when the machine is asleep.
Regular sleep mode uses about 1% battery per hour of sleep, while hibernate mode can last up to 30 days on battery power. So you can see how having the SD card in would make a big difference.
Interesting. Is there a source for this? Doesn't make sense for Apple to design the power draw like this.
Please feel free to correct my simple and naive maths :
1) my 13 rMBP states it will last 11 hours (ish) at full charge when awake : 100% battery power = 11 hours
2) if I'm using 1% of that power per hour of sleep I should theoretically get 11 * 100 hours : 1100 hours = 45 days (ish) and that's basing it on the power being calculated on the awake mode duration
Yep... straight from Apple right here.
You misunderstood. What I was saying is it will use about 1% of the battery capacity per hour of sleep. So if it is in sleep mode (not deep sleep) for 24 hours, the battery would lose about 24% of the charge.
Thanks. What do you think about ejecting the SD card? Will this solve the problem of having ANY power draw?
I don't think just ejecting it will do it, it needs to not be inserted at all is my understanding or it won't enter that deep sleep battery saving mode. See this thread where a forum member verified it does not enter deep sleep with the card inserted.
Thanks. I knew there had to be a flaw in my thinking