Upgrading My Old EDC Power Bank

For over 4 years I have carried this power bank in my pocket every day. For me the size is perfect because it is small enough to disappear in my pocket but large enough for a decent power boost. I carry it alongside an incharge cable on my keys so I (as well as my friends and family) am never without power! Lately however, I have noticed a drop in battery life and although I absolutely love the form factor, this particular power bank always had some featured I did not like... so I fixed them!

To start with, I always carry a powerful flashlight on my keys and everyone now has a flashlight on their phone. Hence I have never once needed to use the light on this powerbank. So although a UV LED is not much more useful, at least it is something I don't already carry two of!

Modification 1: Replace the white LED with a UV, blacklight LED

I also always disliked that the light from the four blue LEDs to show charge level would bleed into the next bar of the display making it near impossible to tell what battery level the pack was on. I actually tried to fix this when I first got the power bank by sticking some folded up black paper in there (which you will see in a later step) which hardly helped.

Modification 2: Replace the 4 blue LEDs with red, yellow, and green LEDs. As well, make proper dividers to stop the colour bleeding.

And finally, the main reason for going ahead with this project, the battery life.

Modification 3: Replace the two old 2,200mAh batteries with two brand spanking new 3,500mAh batteries!

This has been one of my favourite weekend projects in a while. It is just one of those rare projects for me where I had the idea, ordered the parts, and a week later it was all done exactly as I had planned. In fact, I have enjoyed the final product so much in the last week I have been carrying it that I built up another one and will probably give this older one to my father to keep in his car.

Like most of my other projects on here this is less a "how to" and more a "how I did it". Of course you could go out and buy all the same parts however I am more interested in just sharing broad ideas rather than exact instructions. This is a simple project so I will try my best to keep it short.

To take the power bank apart I started in the bottom corner and pried up just with my fingernail. Then I stuck the side of a plastic ruler in and slid it up to pop the case apart (a proper spudger tool probably would have worked better). Once the two halves of the case are apart there is just one screw to take the electronics out (takes a little wiggling thanks to the LED and button). I had already had the case apart to check if these mods were possible before buying the parts but I wish I could have shown you the layer of dust inside when I first opened it up.

The first thing I do once the electronics are separated is desolder the battery to prevent myself accidentally shorting the LiPo battery and starting a fire. I desolder the wires from the battery rather than from the circuit so there is no chance the battery can short out through the wires. Connecting the circuit to a power supply between about 3.2-4.2V (the voltage range of a standard LiPo battery) we can see that everything is still working as expected. From now until the final step I will be testing everything with the power supply instead of the final batteries as again, an accidental short circuit could very well be a disaster. However as long as you check for continuity before putting the battery back into the circuit and you don't try modify the circuit with the battery connected, you should be safe to test with the battery.

In the final photo you can see the second power bank I took apart. It had some funky white goo holding the batteries in place but carefully twisting the case back and forth, I slowly broke the case and batteries free.

I bought my UV LED from a small local LED supplier here in Australia. The part number is VAOL-5GUV8T4 and I found it on RS components as well for a little more so I assume it is a popular LED for these kind of applications.

I desoldered the original white LED and temporarily soldered the UV LED on for testing.

I was hoping that the UV LED would work without modifying anything else but it was very dim and my power supply showed the LED was drawing between 10-20mA which is not very much for an LED.

From the datasheet we can find that the LED is rated for a typical forward voltage of 3v at 20mA. As I didn't expect to use this torch very often I had no problems running the LED higher than 20mA. The datasheet recommends a maximum continuous current of 30mA and testing the LED at 25-30mA I was seeing a forward voltage drop of around 3.3V.

The entire original circuit is based around an IP5305 which is an integrated controller specifically designed for power banks. From the datasheet of the IP5305 I found that the recommended configuration is an LED in series with a 20ohm resistor coming out of pin 5 on the IP5305. Looking next to the LED I quickly found the 20ohm resistor labeled "R12".

Probing each side of R12 with an oscilloscope I saw a voltage of around 3.6V from pin 5 of the IP5305 and 3.3V across the LED (max voltage is labeled as Ma on my scope). The voltage was also not always on and had a duty cycle of ~75%. From here we can calculate using ohms law that the current flowing into the LED when the duty cycle was positive was (3.6-3.3)/20 = 15mA so for an average duty cycle of 75%, average current would be .75*15mA = 11.25mA.

If we wanted 30mA average, we would need a peak current of 30mA/0.75 = 40mA. Again using ohms law we can find the resistance necessary for this current by R = (3.6-3.3)/40mA = 7.5 ohm.

I decided to start by replacing R12 with a 10 ohm resistance. These are 0603 resistors and are quite small so for some advice soldering SMD components check out the procedure I mentioned in step 15 of my flashing PCB heart Instructable https://www.instructables.com/BEAM-Solar-Powered-P...

With a 10ohm resistance I expected an average current of 22.5mA but I was still getting less than 20mA. This is because the output impedance of pin 5 of the IP5305 would likely be quite bad so the more we load it, the less voltage we can get out of it. In fact, when I removed the resistor entirely and checked the voltage it is actually outputting 4V! Just for curiosities sake we can actually calculate the equivalent output impedance as we know that when we load the circuit up with 11.25mA we have a 0.4V drop from the 4V we expect to 3.6V so the output impedance is roughly 0.4/11.25mA = 35ohms. This impedance may not be the same for different output currents but it gives a good ballpark estimate for the impedance we can expect.

In any case, I wanted more current still so I soldered the 20ohm resistor back on top of the 10ohm resistor to put them in parallel which created an equivalent resistance of around 6.67ohms. This gave me an average current of 25mA.

Before soldering the UV LED back in place I decided to do the SMD LED mods as it would be easier to solder some of the SMD components without the UV LED in the way

These new LEDs were quite a simple mod that has been such a game changer in the last week that I have been carrying the new power bank!

The LEDs are 0603 size and I bought a pack of 100 (20 of each of 5 different colours) from the same place I bought the UV LED for on $2.50.

To desolder the original LEDs I just heated both joints at the same time with a large, chisel tip on my soldering iron. The PCB designer in this case was nice enough to include marks for positive and negative side of the LEDs however you could always just remember the direction the original LEDs were, try to work it out from the datasheet, or just do trial and error. To solder the new LEDs I followed the same procedure I mentioned in step 15 of my flashing PCB heart Instructable https://www.instructables.com/BEAM-Solar-Powered-P....

I tested each new LED by replacing one LED at a time and then hooking the circuit up to my power supply at 4.2V.

Next I removed the old folded black paper spacers I tried to use to stop the LEDs bleeding into each other and laser cut some new spacers out of 1.3mm thick cardboard. The front 2 had to be cut at an angle to clear the USB and the back 2 could be a left little larger. I originally planned to have an extra bit of card on the very back but as you can see, it is absent as, otherwise it hit the negative wire coming from the LiPo.

Now we can solder back the UV LED. First we have to clear out the holes. To do this I usually first apply a bunch more fresh solder. Counterintuitively, more solder is often the easiest way to remove solder as a large blob of solder will hold heat and stay liquid longer than a small amount of solder. Then I hold my iron on the pad for a while and when it is hot enough I remove the iron and quickly blow very hard to blow out the liquid solder. This is obviously not the safest way and makes me quite light headed after a while. As well, one of the pads for this particular component is connected to the ground plane which sucks up heat from the soldering iron, making the solder solidify quicker. As such this trick only worked for one side and I had to use a regular solder sucker for the other.

Then I bend the LED legs at as sharp an angle as I could manage and roughly trimmed them before putting the LED and circuit in place. From here I applied a small amount of solder to the top of the pad just to keep the LED in the correct place, then I removed the circuit carefully and soldered the LED properly.

The light from the LED always bled into the charge indicator lights when on which never bothered me however I figured I should fix it while I was at it so I put black nail polish on the back of the LED and sides of the lens and then used to black heat shrink to mask of the rest of the side of the LED.

Next up, my main reason for modding the power bank in the first place!

I purchased 2x SANYO 3500mAh 18650 batteries from a reputable dealer here in Australia. I opted for the version with tabs already spot welded on as I have no means with which to spot weld myself. Though I have successfully soldered to 18650s in the past, watching some videos of how much heat is actually transferred to the battery during soldering prompted me to spend the extra $1 each for the tabs.

Next, I checked the polarity of each battery as we want to make sure we are connecting the batteries in parallel for this particular application. If we get this backwards and connect them in series, when we make the second soldered connection we will essentially be shorting out the 2 batteries which will inevitably lead to a fire. I then tinned the tabs before soldering them together. Next, I flattened everything down as there is very little room in the power bank for bulky connections. In retrospect, I doubt soldering the batteries together with a wire would have even worked at all in this case as there was not enough room.

Finally I tinned the tabs once more to accept the wires and soldered the whole thing back together, all the while being careful not to get any part of the 18650s too hot.

(Note: the batteries were indeed shipped at storage charge, I charged them up before the last photo)

As you may have gathered from the way I talk about them, I am quite cautious around LiPos as although I have not personally experienced a fire, the stories and videos I have seen are enough to scare me. Obviously you dont need to be scared of them as they are in almost every portable electronic device however I feel some amount of caution is warranted so for the first charging cycle of this new power pack, I dug up an old fire safe battery charging bag for charging quadcopter batteries and charged it in the bag just in case.

Finally I used a laser cutter to engrave "7,000mAh" in the case and filled the etched section in with some silver pen to match the rest of the lettering. I never did find a marking saying what plastic the power bank was made of and I am not so good at guessing plastics so this is actually the first time I have put something into my laser that I wasn't sure was safe. I figured it was such a small engraving and I wasn't burning away too much of it just doing engraving that it couldn't be the worst idea so I just left the extractor fan running for a while after engraving it.

Pop the cover back on and its all done! Like I said, nice and simple but I am super happy with this, especially as it is something I carry every day and it is now absolutely as good as I can make it.

My only closing thoughts are that maybe next time I need an upgrade I will put a laser module in place of UV LED but that will take a bit more modding. I also think this model power bank has already been discontinued by Cygnett so Im not sure what power bank I will buy if this new one breaks. If anyone knows a similar form factor charger I would love to know =)