Intro: DIY Power Bank!
I finished all my Spring/Summer projects, and needed a Fall project since September is rapidly approaching. I needed an idea and came across an old portable phone charger aka. power bank my wife got as a gift from her company. It stopped working, so it sat for a year until I found it. It charged when plugged in, but didn't charge the phone (no output). I took it apart, and it had a thin 7 mm thick LiPo battery inside and some boost/protection IC's on a board with SMD LED's for charge and capacity indicators. The battery said 4000 mAh. Cool project material!
I got a different one for Christmas, but I could only charge my phone once before it needed to be recharged again :( I wanted a better one, but didn't want to spend $30 or $40 for a high capacity one https://www.amazon.com/Anker-PowerCore-Ultra-Compa....
I came across these things (https://www.ebay.com/itm/Ultrathin-5000mAh-Externa...that looked like 2.5" external hard drive enclosures, but you put LiPo batteries in them and could turn them into portable chargers. I figured I could make one with the kit, but found out they were limited to 5000 mAh batteries. I wanted at least 6000 mAh, so I looked into custom fabricobbling something and decided it wasn't worth it without a 3D printer or other tooling.
Then I stumbled across more DIY power bank kits from China like these: https://www.ebay.com/itm/Power-Bank-Kit-LCD-Dual-U... that took 18650 lithium ion batteries as the power source, not LiPo's, which were kind of expensive for the thin ones that fit inside the enclosures.I ended up getting one more for the smaller liPo battery too and built that one. I had some 18650's lying around from salvaged laptop batteries of varying capacity, so I figured why not? How hard could it be? So I hit up my PayPal for $6.99. Parts in the mail! Let's get started!
Step 1: What You Need: Parts and Tools
Once I got the parts (from the USA this time), I realized that it's not plug and play like some of the others that have the spring connectors already installed so you just insert the 18650's like you would AA's in a TV remote. You had to build a battery pack in order for it to work. Not a problem since I've done it before, but for those who haven't, I'll help you out in this tutorial. I've made tutorials for homemade battery packs before, so check those out if you want to.
That said, you need some tools to make it happen.
Soldering iron. Has to be at least 30 watts! Less and you won't get good solder connections to the batteries. Holding the soldering iron on the battery terminals is not good. You want to minimize it as much as possible so the faster you melt the solder, the better.
Good solder. I use Kester 44 rosin core. It's the BEST solder for electronics. Period. Mine's .031, 63/37 Pb/Sn. Melts at 250 C, great flux and cleaning action. Do not use lead-free solder. It takes more heat to melt, leaves oxidization, and doesn't flow well.
Side cutters or flush cutters. Cheap ones, big or small are fine.
00 Phillips screwdriver for assembling the kit.
Lithium ion or polymer capable charger. You can use any that charge or analyze the batteries. I use a Zanflare C4, and my clone SkyRC iMax B6.
Sandpaper. For preparing the tabs and batteries for soldering. I'm using 500 grit, but 220 works too. Some tabs don't need to be prepped, but I still do since the solder sticks to it better.
Multimeter. Nothing fancy, you need it to measure battery voltage.
Utility knife or wire strippers. I live on the edge and use a utility knife. Be careful when using one to strip wires.
For the materials, you need:
Nickle strips or solder tabs for battery pack construction. I prefer nickle strips, but since I wasn't making a fancy, high output series/parallel battery pack with balance circuit, I used the tabs already on the cells leftover from the laptop battery connections. They work fine for this because we aren't putting a big load on it and it's only 3.7 volts.
Wire. I am using 24 gauge wire (.5.11 mm diameter). You don't need anything crazy like 18 gauge or 16 gauge. The most this will draw is 2 amps, and at the low voltages the wire can handle it, but I wouldn't go below that.
Masking tape. You can use electrical tape too for holding the batteries together while soldering them. If you want to be real fancy, you can use those battery spacers to position and align the batteries. I used my eyeballs and a flat surface.
Four (4) 18650 batteries. The more capacity the better.
Step 2: The Pack
So, we need to build a 4 cell pack with the cells in parallel. Usually these batteries are in a series/parallel configuration to have higher voltage and keep the capacity up. In a series connection, the voltage is combined across the batteries, but the capacity is the same as a single cell. My other Instructable explain this in detail, but basically we are connecting all the positive and all the negative terminals of the batteries together, with a positive and negative output going off each to the load.
The power bank outputs 5 volts which is regulated by the circuit board to increase the battery pack's voltage beyond 3.7 volts.This is how we can get away with a parallel configuration, where the positive and negative terminals of the batteries are joined together. This makes for a very high capacity, which we want! I am shooting for at least 6000 or 9000 mAh, which is why I am making two packs. One is out of 1500 mAh cells, the other is 2400 mAh cells.
Step 3: The Batteries
We know to connect the positive and negative terminals of the batteries together, so let's get going.
My packs will be made from some batteries I salvaged from two HP laptop battery packs I got at my thrift depot for around $4 for both. That's 12 cells total. I made an Instructable on how to get and salvage these type of batteries. I have two models of Moli Energy Company 18650 ICR cells. Moli Energy used to be in Canada, but are now owned by a Taiwanese company and make batteries for all kinds of companies and OEM's, so they are good quality. The teal color ones weren't clearly marked and data was near impossible to find, but I presume they were 1500 mAh capacity and good for 2'ish amps discharge (like most all ICR-type chemistry) since they came out of an old HP ProBook laptop battery rated at 3 Ah and 11.1 volts. I ran them on my charger analyzer, and they came out to be average of 1455 mAh, so pretty close to the 1500 figure. The blue ones are newer ICR-18650J and I found the datasheet for those easily. 2400 mAh at 2.2 amps discharge, so pretty good! I tested them and they actually came out over their rating at an average of 2453 mAh.
Test the batteries. Make sure their voltages are really close together, within -/+ .03 volts. These are pretty good since I had tested, charged, and discharged them previously. Plus, they've always been used together in the battery pack. As a rule of thumb, it's ideal to use batteries that were previously in a battery pack since they are conditioned together and will be roughly the same voltage since there's usually a balance circuit in laptop batteries or multiple cell lithium packs. If you're using random cells, make sure they are around the same voltage and the same capacity and condition. Test them first. Having a weak cell in a parallel pack isn't as bad as in a series pack, but it's still not good as it hurts capacity.
If the voltages look good, we're ready to move on.
Step 4: Building the Pack(s)
Usually you use solder tabs or nickle strips with a spot welder to make battery pack connections, but I don't have a spot welder and don't need one as they cost about $250 USD for a Chinese one, so we will be soldering them together. Not the recommended way, but it should be fine if you're careful.
Start by figuring out the size of the strips you need to connect the cells together. These batteries already had the remnants of the tabs from the laptop battery intact that were already spot welded on, so I figured I'd just solder them back together. The remaining strips were long enough to just solder together, and where I needed more, I just cut one to length and soldered it on.
Prep the surfaces you will be soldering by scuffing them with the sandpaper where the connection will be made. Since the tabs from the laptop battery pack were still welded to the terminals, I trimmed the tabs to length and soldered them together to avoid having to solder directly on the battery terminal, which isn't good for the cells. It can cause heat buildup and capacity loss, or damage the battery. I connected two cells, then taped the rest together to keep them aligned and level.
If you need to make a strip to fill a gap, scuff and add solder to both ends and solder to the tabs on the battery, and solder the strip on.
When finished, the connections should be strong. Add a tab to the positive ad negative side so you can add the output wires. I also taped the sides to protect the exposed terminals. I had some thick paper pieces desined for this, but didn't have enough for both. Measure the voltage of the pack and it should equal the same across all cells. +/- .02 volts is fine. Eventually, they will equalize in voltage as they sort of self balance.
I built two packs, one with the 1500 mAh cells, and another with the 2400 mAh cells, so one is 6000 mAh, and the other is 9600 mAh, so pretty high capacity! I tossed them on my charger and put it in discharge mode, and charged the other. It has a 5000 mAh limit for capacity and a 300 minute safety timer, and it maxed out, so I can safely assume that it's well over that. I say that's a win.
Now we're ready to add them to our power bank kit!
Step 5: The Kit!
In the package was the two halves of the enclosure/case, the PCB, a button assembly, and a reflector for the built-in LED flashlight, two tiny self-tapping Philips screws, and two clear plastic lenses to cover the LCD display and flashlight reflector openings. The case halves were covered in a plastic film, and I figured out why quick. The case is a very shiny plastic finish made from rigid plastic. It's an absolute fingerprint magnet, and the slightest scratch shows up. Trust me, it was scratched within seconds of the plastic coming off. Kind of a bummer, but it is what it is.
The board has two USB A outputs, one for 5 volts 1A output, and a second for 5 volts, 2A output (for charging iPads, tablets, devices that use 2A output, and a Micro USB B input for charging the power bank's battery. I tried charging it with my phone's high output charger (9 watts), but I couldn't tell if it charged it any faster than a standard 5 watt charger. It's a big battery, so it did take a long time to charge! About 9 hours. The LCD has a nice blue backlight, and shows you overall battery capacity, status (charge in/discharge out), and the type of output being used (1A or 2A). I can only presume what the IC's do, but there's probably a gas gauge IC, one for regulating voltage output, and another for battery protection/charging.
Step 6: Assemble the Electronics
Putting it all together was pretty straightforward. It did require some finaggling, but I eventually got it together. Just so you know, instructions are nowhere to be found! Start by preparing the PCB. You need your soldering iron and some solder for this. Add solder to the two battery input solder pads. Next, solder the battery output wires to their respective pads, positive and negative. DO NOT reverse the polarity, or you will probably cause the board to release the magic blue smoke, at which point it won't work anymore as there is usually no input protection on these cheap Chinese boards. I had to shorten the output wires of my battery to get it to fit, which I expected. The board will power up at this point as well, so you should see it display the battery level.
Step 7: Add the Bits
We need to add some of the parts to the case next including the button, it's housing/trim, and the LED's reflector. There are mounting posts for the button trim piece, and it snaps into place. The fit was pretty good. The button itself goes on first, and you can secure it with glue, or use a hot piece of metal to melt the two posts down so it secures the button and trim in place. I used some CA glue (aka. super glue). The reflector for the LED just sets in place and is held in by a little divider. It's mostly held in place by the LED itself pressing on it, which was pretty wonky, so I put a little super glue on the case where the reflector sits and put the lens on. You can add the plastic lenses now or later. They have a backing covering the pre applied adhesive. Peel it off to expose the adhesive. There was strangely another adhesive pad on the lens itself that I had to carefully peel off too. I used the point of my utility knife to do it. Oddly, there's another protective film on the outside of the lens too. I peeled that off last. The adhesive is pretty strong, so I don't think the lenses will come off.
Step 8: Add the Board and Battery
Now you can add the board and the battery. It's a tight fit, so you may need to test fit first. Make sure you don't crimp any wires too badly to prevent future breakage or bad connections. I put the board in first, sliding the LED into the reflector first, the gently pressing it on the right side until it snapped into place. It might take a couple of tries to get it right, so be patient. Once it's in place, add the screws. You need a 00 Philips screwdriver, by the way.
Step 9: Put It All Together
Now that the electronics are in, you can snap the case together. I added some 2 mm microcell foam strip scraps I had lying around to the top of my battery to cushion it from jolts and to keep it from flopping in the case if dropped or banged around.This is optional, but I highly recommend it. Set the top half of the case on the bottom to make sure it's aligned right. Then Press down on the sides, moving your way around the outside to engage the snaps on the front, sides, and rear until it's all secure and the tops and bottom are flush. Note this thing isn't water proof or splash proof/resistant. You could add clear silicone to the board around the outputs and switch to help, but that would make it a pain to fix in the event the battery connections went bad, or it ever needed replacing.
Step 10: Test, and You're Done!
It's all together, now you test it to activate the circuit. It needs a 5 volt signal, so plug it into any wall charger through the micro USB input. Once you get that, you're done! Plug in your cable of choice and charge something! The LCD displays the percentage of battery life remaining and the status, input (charging the internal battery) and output (charging a device), and the type of output 5 volt 1A, or 5 volt 2A. I think the battery gauge is a little off, since my phone battery is 3200 mAh, and at 71% charge it shows 68% battery capacity, which isn't anywhere near the actual battery capacity of around 9600 mAh +/- 150-200 mAh. If I can get 3 charges or 2.5 full charges off it, I call it a success though. I might get a second one of these for my other battery as well.
I used it to also charge my Bluetooth speaker and it worked great.
The LED light is very useful and a welcomed addition. It's not super-bright, but not dim either. Good for an emergency or for finding that elusive charging port at night or a lost charger under the dresser. To activate it, just press the power button twice quickly, and again to turn it off.
I tried the phone on the 2A output, and didn't notice a difference in charge speed. It's dependent on the device's charging ability for that, and this phone wasn't designed for that. No biggie!
I hope you liked this Instructable. I tried to do a topic that there's not many guides on, so if you found it helpful, let me know, or let me know if I could do better!