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I am making a DIY Raspberry Pi laptop. So far I have found a suitable board that will drive my display (M.NT68676.2A). From research I have found out that it will run off of anything from 12 V to 5 V, and that it uses around 3 A (I am not sure if that's at 12 V or at 5 V). I've also found a 14.8 V 6600 mAH Li-ion battery from Tenergy that I'm thinking of using (5 A output max).

What's the best way of converting the 14.8 V output from the battery to a suitable 5 V for both the board (5 V 3 A?) and the Raspberry Pi (5 V 2 A) without wasting too much energy or spending too much?

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    \$\begingroup\$ Buck converter. \$\endgroup\$ – Eugene Sh. Aug 8 '16 at 17:49
  • \$\begingroup\$ Synchronous buck converter. \$\endgroup\$ – Andy aka Aug 8 '16 at 17:56
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There are dozens of small, inexpensive DC-DC converters available on Ebay, Amazon, etc. They are based on industry-standard converter chips and are quite convenient to use. You can find versions with fixed output voltages, as well as those with user-adjustable output voltages.

I would probably use TWO of these converters. One for the display (at 12V) and one for the RasPi (at 5V). The very first hit I found on Ebay shows that you can buy 10 of them for less than US$12 with free shipping. They are good for 2A, but will do 3A if you add a heat-sink to the regulator.

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You can buy one through Digikey, or ebay, or Seeed Studios for a reasonable price, or you can make one using a buck converter such as the TPS54331DR if you have a PCB that you are making.

Are you planning to draw a current in the range of Amperes from a 6600mAh battery? If you're looking at 3A for display and 2A for the Pi: 6600 mAh / 5000mA = 1.3h. For some of that time the voltage may fall below what is required for the regulator to maintain a regulated 5V output, as well -- so you might only get an hour out of a fully charged battery.

What are you connecting to the Pi to be able to draw 2A - a lot of the bare board configurations are under 500mA?

You can also get a 10" Touch screen (Waveshare 10") for the Pi that looks to have substantially lower power requirements (<1A). If you can get the whole thing working in 1.5A, then you have 6600/1500=4.4h, which is more reasonable, but still fairly short in terms of laptop performance.

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