Build a multi purpose external battery that works with macbook air for 19$ dollars or more
Finished product is a 14.8 V battery at 8800+ miliamps approximately capacity that will run you for only about ? dollars. Here is how I did it.
Before you build this you need to be very careful and responsible for all your actions. I am sharing a how I did it, but I am not an expert.
Things you will need:
1. Soldering iron, solder, soldering holding devices.
2. Pliers, cutting tools, wire stripers
3. Electric tape
5. Lipo Charger
Materials and their cost:
1. Your macbook adapter(Free, since you can still use it after conversion)
2. Laptop batteries you will need to get 12-20 cells from laptop batteries - 15$+
3. Extension cable from adapter will be consumed.(assuming you already have it, other wise get a coil of wires for 5 bucks at awl mart and this project should consume less than 1/10 of that coil. - 50cents
4. A roll a electric tape 57 cents.(I prefer to buy a whole sleeve at home depot for about 5.70, and this will use close to a roll. - 57cents.
5. A roll of double sided foam mounting tape - 1$(Optional)
6. Cut off button - 1$ (optional)
7. Voltage warning device - 1.5$(optional)
8. CCTV male and female plugs 1$(buy 2 sets if you want to keep using your adapter)
9. Balance cable -1$
10. 2 strip ties - 10 cents
11. 2 18 cube or 20 cube conduit boxes - 1$ at home depot.
12. Heat shrinks(optional)
So, adding up the must haves Batteries 15$ + tape 57 cents + CCTV plugs 1$ + balance cord 1$ + strip ties 10 cents + conduit boxes 1$ + 30 cents worth of wires
So if we really went cheap on this, 19$ of materials will do the trick.
I will try to write this one precise.
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Step 1: Pick the Right Battery Cells
Buy laptop batteries, carefully and safely harvest(salvage) them, check voltage. solder in wires in opposite direction and between all steps, always tape off.
Step 2: Solder Batteries in Groups.
Form your groups, tape together and test fit in conduit boxes, then tape groups well. I used foam double side for my project but electric tape will do.
Step 3: Assmble Half at a Time.
Use NASA standard flat soldering techniques and join two groups + to - and their control wire together(control wire is for balance charge.)
Tape or heat shrink and then fold to complete half.
Step 4: Solder Harness and Fuse
Cut a piece of your extension cable slightly longer than how long you want your cable to be, counting the conduits' heights.
Solder a detachable connection to your final output. First strip some extension cable carefully, solder male dc plug to white and grey wires in extension cord, white to red and grey to black. Solder female plug to the none power bearing adapter, in this case the mag safe connector or a cig lighter socket.
Feed the wire into one corner port of conduit box. Solder a fuse holder or a weakest link I call a cheapo fuse to the positive, and hold wire in position with some adhesive.
Step 5: Final Assembly
Install the two halves into conduit box, choose one positive side to solder a control wire(balance wire 5)to it and also solder harness positive fuse to it. Next, pull up the control wire from between the two groups and solder that to balance 4, solder thw other half's control to balance 2, solder other side neg to harness neg and a control wire which goes to balance 1. Solder an new control wire to balance 3 and hold the last connection s close to each other to see if the fuse blows or if there's spark（there should be no spark, but if there is then there's a short. I blame ebay product in that case. It did happen to me once）
If no spark and all is working, taking your voltmeter to test the voltage between the two groups, should be 14.8+or-.
solder those connections together and be good to go.
Step 6: Final
Zip tie down your case and enjoy.