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Jul 14, 2015 9:42 PM in response to stevelavvby stevelavv,And ideally I would like to hear from someone who has actually tried this and so knows for certain.
In some places I have read that you need to reach a certain wattage before it will charge, but in other places I have seen people talking about charging MacBooks from portable batteries through usb-a to usb-c, so this is at 5V and with only a couple of amps.
Thanks
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Jul 15, 2015 7:25 AM in response to stevelavvby Lanny,If you look at the math, you're substituting a 29 watt power supply with a 10 watt power supply. So, if you don't mind waiting 3 times longer for the charge, it would probably work.
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Jul 15, 2015 8:16 AM in response to Lannyby stevelavv,Thanks for your reply.
So far thats the best I can get - "Probably" !
Its just I have read in places that the macbook does not accept this low charge.
I have now found my cable which was tucked in some bubble wrap, but still it could be useful to know if you can trickle charge your macbook with a phone charger overnight in emergencies.
Anyway I have ordered a usb c to usb a cable and will post my findings.
Thanks
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Jul 15, 2015 11:54 AM in response to stevelavvby Lanny,So far thats the best I can get - "Probably" !
Just try it and see, then you can report back.
Note: the USB-C cable that ships with the MacBook is for power only, not data.
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Jul 17, 2015 6:58 PM in response to Lannyby stevelavv,Hi, and just to clarify for those interested -
The phone charger does charge it slowly when sleeping, maybe 10% per hour. But when awake I am can not tell if it charges as the battery seems to drain at the usual rate and in the power menu it says "power source - mains", "Battery is Not Charging".
So useful to know, you can charge it slowly from any usb power supply, in your car or where ever..
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Nov 28, 2015 4:07 AM in response to stevelavvby Treval,Hello:
For anyone interested in the details of Macbook 12" charging via 5V USB, here some data points.
Using an Orico charger with 2.4A (nominal) "Supercharger" port, and IOGEAR USB-A to USB-C charge cable (3.3ft), I record a power draw of 2.60A with a voltage of 4.72V (voltage drops from nominal 5.00 due to the strong draw).
Meanwhile, the Macbook (Coconut Battery) reports a discharge of <10mAh (less than 0.2% of battery capacity) per minute at this current and voltage, thus essentially keeping the battery level charged, while the Macbook is in operation.
With the Macbook being folded shut (i.e., sleep mode), the Macbook reports a charge of 50mAh for 3 minutes of charge. Thus, a total charge would take approximately 300 minutes or 5 hours.
In summary, a 5V/2.4A (12W) charger can keep a Macbook 12" operating almost continuously, but without charging it. Once the Macbook is in sleep mode, the 12W charger is able to charge the notebook in about 5hrs.
What about lower current chargers or portable batteries? It appears the Macbook attempts to draw at least 1.5A from its power supply. When it negotiates the power draw with the supply unit, and the power supply unit cannot provide the 1.5A at minimum 4.4-4.5V voltage, The Macbook discontinues its power draw. I found none of my 3 (cheap) portable batteries able to supply the Macbook, whereas a portable charger was able to charge the Macbook at 4.55V with 1.5A current.
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Nov 28, 2015 9:06 AM in response to stevelavvby Treval,★HelpfulHello:
For anyone interested in the details of Macbook 12" charging via 5V USB, here some data points (revised). Please ignore my earlier post, as I re-measured many of my earlier data points.
1. Charge with an Orioco 5V/2.4A Charger
Using an Orico charger with 2.4A (nominal) "Supercharger" port, and IOGEAR USB-A to USB-C charge cable (3.3ft), I record a power draw of 2.60A with a voltage of 4.72V (voltage drops from nominal 5.00 due to the strong draw). Meanwhile, the Macbook (Coconut Battery) reports a slight charge while in operation (playing a B&W movie) amounting to 0.077mAh per second, equivalent to a full charge in 19+ hours. With the Macbook being folded shut (i.e., sleep mode) and at 70-80% battery capacity, the Macbook reports a charge of 0.36mAh per second. Thus, a total charge would take approximately 4 hours (likely a bit more, due to the current drop-off when the battery is almost full).
In summary, a 5V/2.4A (12W) charger can keep a Macbook 12" operating continuously, charging it at the same time in slightly less than one day. In sleep mode, the 12W charger is able to charge the notebook in about 4-5hrs.
2. Charge with an Apple 5V/2A Charger
When charged with a 10W Apple charger, the Macbook draws 1.8A at 4.61V in my set-up, and reports a charge of 0.23mAh per second of charge in sleep mode. Thus a total charge would take about 6.5 hours (likely more due to the current drop-off near full charge). When watching a B&W movie in full screen mode, the 10W charger still provides enough power to charge the Macbook at a rate of 0.054 mAh per second, equivalent to a full charge in 27 hours.
3. Other Charging Methods
What about lower current chargers or portable batteries? It appears the Macbook typically attempts to draw at least 1.5A from its power supply. When it negotiates the power draw with the supply unit, and the power supply unit cannot provide the 1.5A at minimum 4.4-4.5V voltage, The Macbook discontinues its power draw. I found none of my 3 (cheap) portable batteries able to supply the Macbook, whereas a portable charger was able to charge the Macbook at 4.55V with 1.5A current. To note, from an old iPod charger (5V/1A) the Macbook will draw 0.5A at 4.86V (my set up). Also to note, a small wall charger (Apple style) at close to max capacity will produce considerable heat.
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The attached photos show power draw from my Orico charger.

