Portable Laptop Charger (Cheap and Easy)




Introduction: Portable Laptop Charger (Cheap and Easy)

About: I want computers to be wilder. https://www.instagram.com/hikinghack/ https://twitter.com/HikingHack https://www.youtube.com/user/blorgggggg https://github.com/quitmeyer

Charge your LAPTOP with inexpensive 5-volt cellphone battery packs! Get crazy long lasting power anywhere, planes, trains, jungles! It's also only about $5 more than a regular cellphone charger. The total cost is only about $10-$30!

You don't even need to solder, you just need to screw some wires together!

You can actually purchase battery packs that are meant to charge laptops already. For instance these battery packs that I have used before, have 19V modes for charging laptops. The problem is that because they are in such smaller demand than regular 5V charger packs, their prices are CRAZY HIGH. These batteries usually cost between $150-$300. E.g. http://www.amazon.com/gp/product/B00BB5VQCE?psc=1&...

Also i suspect that they are little more than just a regular Li-Po battery pack with an integrated voltage booster (which is exactly what we are building here for 1/10th of the price!).

Step 1: Background

This project was developed during a Hiking-Hack Art, Tech, and Science project. (See the video and we explain more). We create mobile physical computing "maker" laboratories in the middle of the forests around the world. A key problem is being able to keep our laptops powered for the many days we are out there. We need dense, portable power; and since these expeditions usually have a shoestring budget (if any), we also need this power to be cheap.

As mentioned before, you can buy existing battery packs for charging something like a laptop, but BOY they are expensive! For much less money, you can get the same energy capacity and charge your devicesfor 1/5th to 1/10th of the price!

So we tried it out on a hack and had great results! This big fat battery packs that I could find deals for $12 each, would give us 26 amp-hours each! Several of these were enough to keep our laptops running for 9 days! (We also augmented with a bit of solar, but not much). You can tap into many 5V power-outlets also, and various sizes of 5V battery chargers (though a couple mysteriously won't work, might have lame current-draw protection).

It's also just super handy to have such devices when traveling anywhere! USB DC power will fast become the universal power-source, and if you can tap directly into it, you are golden! This project will open up lots of possibilities for you hopefully!

Step 2: Materials

At its most basic, all you really need is a cheap battery pack, a voltage booster, and a cable for charging your laptop.


There are a couple extra things that make building this a bit easier. For instance if you have an apple laptop, they sell really cheap cables for them that are already split out into two leads.

Helpful Accessories

Step 3: Assembly (easy) - Input

A lot of people might get scared once they start seeing wires, but it is really easy! You don't even have to solder, you can just use the screw terminals.

Input Hookup

  1. Chop your USB cable and isolate its positive and negative power leads (black and red) (or just use one of these USB connectors: https://www.sparkfun.com/products/437 )
  2. Connect the positive and negative USB leads to the Input side of the power-booster (to the + and - respectively)
  3. Plug the USB into the battery to see if it turns on (should light up with the display)
  4. Turn the small screw potentiometer until the output display shows around 19-20V (it will bounce around a bit, don't worry). Also check to see what voltage your laptop needs (most want about 18-20V)

Step 4: Assembly (easy) - Output

Output Hookup

  1. Now take that repair cable that charges your computer and connect its positive and negative ends to the + and - of the Output side (if you just have a spare AC adapter for your laptop, chop off the end leading to your computer and strip out its positive and negative ends)
  2. Connect to your laptop!

If all goes well, your laptop should start getting fed extra juice!

Now some laptops are much more power-hungry than others,and will react in different ways. For instance, my macbook retina 15inch will display the power connection as "Plugged in, not charging" and will still make the laptop last for 14+ hours. Other smaller laptops, like my macbook air, are much less power-hungry, and actually start charging from this. They also charge quicker (if that's what you are looking to do), while they are turned off.

Step 5: Use Case: 24-Hour Airplane Video Games

Just as an illustration of how awesome this is, I kept my power-hungry macbook pro retina running and playing SNES Zelda all the way from Atlanta GA, USA to Manila, Philippines. This means you have enough time to easily defeat all the castles in the Light-World, and 3 of the dungeons in the dark world in an otherwise really boring flight.

There was a guy sitting next to me who kept getting angry at me because he wanted to plug his laptop into the power plug where I was charging my laptop. I kept trying to explain that I wasn't using a power plug, and that there WAS NO POWER PLUG. I showed him the charger system, but he still kinda refused to believe me.

The only possible downside to this hack is if you use the one with a built-in voltage display, it might be alarming to others to see these bright numbers flickering on an airplane.

So i just kept it in the seat pocket :)

3 People Made This Project!


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17 Discussions

cool! thanks.... im sure you could pick up laptop chargers faaar cheaper than that though...?

3 replies

Not really, but then, those ones also have the built in protections necessary to not be damaging to the laptop battery.

There is no protection in the charger itself. When the laptop is fully charged, it'll draw less current and power itself from the DC input.

The protection isn't to stop it from overcharging the battery. It's to prevent it from pulling too much power and charging the pack too fast, making it heat up and damaging it.

That's simple math: 2A at 5V (maximum output from the pack), 10W. The conversion process is typically about 80% efficient, so 8W get through to the computer. At the 18.5V standard for laptops, that is 0.432A. Your computer comes with a 3-4A 18.5V supply, so this would be charging it at between 1/6 and 1/8 the rate it is designed for. The battery pack itself has (most likely) 2Ah (2100mAh average, 10Wh), of which 80% gets to the computer (1600-1700mAh, 8Wh). The computer draws on 11V batteries inside, which means another 80% loss to conversion from 18V-11V.

8Wh is the amount the computer can take in (0.432Ah at 18.5V), the batteries actually get 6.4Wh. By turning on a battery tracker, you can determine your power draw. From multiple computers tested, I've gotten an average of 30W. 6.4Wh will give an extra 0.213 hours, or 12.8 minutes. A bigger battery pack can obviously expand this range, but the FAA limits capacity to 100Wh per pack (or a 5V 20Ah/20000mAh.)

This system would have approximately a 64% efficiency, so the absolute maximum is 64Wh into the computer, or approximately 2 extra hours, for the absolute largest battery pack you can legally take onto a plane.

On a slight side slant, the batteries in those packs are actually 3.6V, run through another booster inside the case, which is why the packs have a larger listed capacity than actual capacity. That makes 25000 more likely to be the real maximum of the batteries, at 3.6V, which would have a maximum allowable 27Ah capacity.

The largest pack I was able to locate is only 20000mAh, and while it does say 4.2A output, that is divided between 2 2A ports.



2 years ago

Can it damage the laptop battery ?

nice and practical. Needs a proper enclosure tho. Also if you try to carry that on a plane for sure you gonna get pulled aside for some hard questions.


haha I dont think the airport security would let you take that on the plane lol.

What the heck you are using windows on MacBook :3

ooh manila i live there lol?

Are you wriying thay Instructables.com from Guantanamo?

I'm surprised TSA let you take something with exposed wires onto a plane. If it isn't mistaken for an IED, then it surely seems like a fire hazard.