Category: DIY

Solarstorm DX4S
September 22nd, 2018 by Chief

Some time ago I purchased a Solarstorm DX4S diving flashlight. Price was very tempting and I decided to give it a try. Got mine for 40 $ from Banggood. I must say I was quite skeptical since this was no proven manufacturer like Scubapro or Halcyon, but figured out that I needed a strong lamp for camping anyway so, I decided to order it and then inspect it a little bit. If it looks like it could actually survive high pressures underwater I would take it scuba diving. If it doesn’t look like solid built (no o-rings, plastic instead of the tempered glass protecting the reflector etc.) I would keep it as a home/car/camping lamp. So it would be a win-win experiment.

Solarstorm DX4S

Some useful info about the Solarstorm DX4S

The flashlight is powered by two 26650 or 18650  batteries. If you are going to use 18650, you have to put them into supplied adapters (yes they come in a box with the flashlight). It is a quite big flashlight and it fits the arm great. The switch is big enough, well placed and easy to operate even wearing 5mm neoprene gloves. It just slides up and down. One time up it is on, one more up the flashlight is off. If you hold it pulled up for a moment it will change mode. The flashlight has 3 modes, High, Low, and Blinking or Strobe mode. I have no equipment to measure output lumens. Only judgment was my subjective visual experience and from that part, I`m more than happy.  When you turn it on in a room at night, it scares the shit out of the dark, and the light level is almost like regular lights are on. At first, I could not believe that handheld lamp is producing so much light. The beam is not too wide, and yet not to narrow. It is perfectly balanced and I like it both underwater and on land.

Waterproof construction

At the bottom, there are two o-rings that take care of the keeping water out of the lamp. They do a perfect job since I never saw even a single drop of water between them. It means one ring is enough, the second one is just a safety precaution. Bottom cap has a gold plated contact spring, and I never had a problem with batteries losing contact. When operated on dry, it heats up much after few minutes of working so I think that it is ok to use it on short terms, but it should not be on for a long on dry because there is no water cooling it that way. It is definitely an underwater battery and should be treated that way – with respect.


The flashlight has four CREE L2 U2 emitters, each rated at 2 W, and that would be total  8 W of power. L2U2 has a working voltage of 2.85 volts. If we take in the calc that four of them is 8W / 2.85 V we will come to 2.8 A. Later I will display what I measured, and it will prove that all numbers are ok and real.

Product name: Solarstorm DX4S Diving LED Flashlight 60M
Brand: Solarstorm
Model: DX4S
Emitter Type: L2 U2
Material: Aluminum alloy
Total Emitters: 4X
Mode: High–Low-Strobe
Runtime: 1h53min,4h20min,7h10min (26650 battery)
Lumens: 3200lm-350lm-3200lm
Battery Configurations: 2 x 18650/26650 battery (not included)
Switch Type: Magnetic resetting switch (change the modes)
Switch Location: body side of the flashlight
Lens: Impact-resistant glass lens
Reflector:  Metal smooth reflector
Carrying Strap: included
Waterproof: 60 meters underwater.
Color: black
Weight: 374 g without battery
Size: 214mm x 55mm x 34mm(length x head x tail diameter)


Solarstorm DX4S

Water resistance

Its declaration says that it is 60 meters water resistant, and I took it to 58 meters. It survived so the manufacturer did not lie. I personally think that it can survive more than 7 bars of pressure but let’s be realistic here, what do you want from a 40 $ flashlight? 60 meters is deeper than most regular users will ever dive, and at that depth, you are entering the technical diving area so you need another kind of equipment. I have it now for two years, used it in APNEA and SCUBA diving, and in general have all positive experiences.

Underwater light performance

Here are a few pictures and video showing how it looks to dive with this lamp. There are pictures from day and night diving, so you can experience how much light it produces, how big it is in the arm, and what do you get underwater in general.

Solarstorm DX4S

Solarstorm DX4SSolarstorm DX4S

Solarstorm DX4S

Solarstorm DX4S

Solarstorm DX4S

Title of this paragraph may sound stupid and absurd, but on the sea bottom there are plenty masks, knives, lamps, and other objects that belonged to people that “knew how to do it”. I use a double-sided diving carabiner to secure the flashlight. One side I secure to battery hand strap and the other side to my wing`s harness. So it is locked near my right shoulder, and it has enough cord to freely use it, and move around. When not used, or in hand I just put the battery under the belt so it is not just hanging below me, hitting the bottom or making any other type of mess. It`s kind of DIR philosophy and makes a perfect sense.

Power supply

As mentioned before it can be powered by two 26650 or 18650  batteries. As logical 26650 are bigger and can have the larger Ah (Amper hours) capacity so they are the first choice. A good thing about 18650 cells is that you have them in every laptop battery.

18650 laptop cells

Maybe you can remove some of them from an old or damaged battery pack of a laptop computer. Usually, there are 6 or even more cells in a package, and one or a few of them is destroyed, but the rest is working and has the excellent capacity. You only need two of them so you have great chances to get lucky. I scavenged one nonworking Asus battery pack and got 5 out of 6 in working condition. They are in the picture above.


If you have any decent charger, it will do the job for you and test batteries. What I want to say is that if charger start and after some hours finish charging process, the cell is ok. If it displays any type of error, it means the cell is damaged, and you should throw it away and try the next one.

Nitecore Digicharger D2

And remember, there are marked places where it is ok to dispose of the batteries. Anyway there is one thing to be aware, or so to say beware, and that are scum batteries. There are many brands claiming insanely big capacities for just a few bucks. If it sounds too good to be the truth then in most cases it is not, so avoid buying the cheapest batteries. The same thing is a with a charger. I personally use this Nitecore Digicharger D2 ( D4 version has 4 batt slots) and it is a great charger. If you want the best for your batteries this charger will do a great job. Back to the lamp now.

Power consumption

What I measured on high setting is  2.7 A. On the low setting it is 0.86 A. It means that with 18650 cells you can get around 50 minutes of light at full power or a little bit over a 2 hours an low power mode. For 26650 battery type, with 4.2 Ah capacity, it is a little bit more than 90 minutes at high power mode or near 5 hours of light in low power mode. In both cases, it is quite ok for regular dives especially for day open water dives where you do not keep the lamp on the whole time.

 Solarstorm DX4S construction error

I noticed there is something wrong with the flashlight after having it for a few days. I would charge the batteries and put them into the flashlight. It worked like a charm. Then I would leave it be since it is not something I use on a daily basis. After a week or more, when I needed it there was no light coming out. I started to investigate what is wrong. Batteries had no juice. So I taught that I got junk batteries. Shit happens, right? I charged the batteries again, and everything looked fine. But this time I would not fall for the same trick again. I did some measuring and here is what I discovered.

When turned off, the lamp takes about 12.89 mA from the batteries. It must be a driver problem or a construction error, but I did not want to disassemble it. Now that I knew what the problem was it was possible to fight it. So basically it will drain 0.3 A / Day from batteries if you put them inside. For regular 18650 cells, it is draining around 13% of capacity per day. If you charge batteries just a few hours before the dive (and that is the best thing to do), you won’t feel the difference, but if for any reason you can’t do it that way, you need to do something about this problem.

Construction error workaround

The trick is to screw the bottom cap completely and then unscrew it for approximately one turn. When you try to turn it on it will not work, until you screw it back so it won’t drain batteries. Good thing is that at that position of the cap, both o-rings are actually covered inside the cap so water can`t get in. So you have something like safety switch and little more to think about, but it does the job. It is really not a big deal to do it. This is the only objection that I have found for DX4S.

What`s in the box


The flashlight has no hard case or carrying bag, it comes in the cardboard box, with two spare o-rings, adapters for 18650 batteries, and some kind of manual on one piece of paper, and in a Chinese language only. So, you can throw away manual, it is pretty much useless if you don`t eat plenty of rice every day. Let’s just say that it comes packed well enough to survive postal services and that is it. You do not buy a thing like this for its packing, so it`s not so important at the end. English manual would be a nice upgrade, but let us remember, it is just a lamp :). Just one more recommendation at the end. Get some silicone grease and put it on the o-rings. It is a good thing to do once in a while. Summa summarum, this is a great flashlight and you get decent quality for your money. Remember, wherever there is light, there is also something to see, and there are only two things that should come out to the surface from a dive, (except a diver of course 🙂 ) bubbles and photos. Happy diving 🙂


Thank you for reading,


Posted in DIY, Tech Tavern, Video Tagged with: , , , , , , , , , ,

Battery pack with car charger
August 16th, 2017 by Chief

Battery pack changes from version I

This article is the continuation of the first one about diy power bank. After many field tests, I modified battery pack a little bit. I started with 3 S and ended up with 4 S pack. With 3 S voltage was a problem, since it was a little bit lower than most 12 V devices are expecting. For example, Blitzwolf USB charger would work when a pack is just disconnected from the charger, but it would start shutting down itself very soon. It was because the device was protecting the battery from over-discharge. It is logical since it is designed for use in the car, and this way it is protecting car`s battery. So I upgraded the battery pack from 11.1 V to 14.4 V. Connection of the cells is like on this scheme:


Battery pack of 32 cells, 8 cells in parallel, and then 4 times in series

Battery pack = power bank

The power bank is in the essence same device as the battery pack. Different names should not confuse you anymore. Modern marketing gurus just needed something new to sell. So they created a new name for the same device. The name is modern, strong and good sounding, and probably it boosted sales. You may call it however you like, the point is it is the same device.

Second edition

Power pack contains 32 old Nokia BL-5CT batteries. It is able to completely recharge smartphones from 8 to 15 times depending the phone type.
So at the end, it looks like this. It is 7 cm wide, 5 cm high and 11 cm long. It weights 800 grams.
I mounted standard car lighter plug. It means that battery pack can power many devices made for in car use directly. It`s not something that you can carry in your pocket since it is too big, but for longer off the grid occasions like camping it is a perfect. It can recharge your phones many times, power up your camping light, DC – AC converter and many other gadgets.

Battery pack

Final version with car lighter socket

Favorite usage scenario

This is my most used scenario for the pack. When on camping I plug in this great Blitzwolf charger, and the whole family is provided with enough juice to recharge phones for few days.This is the example of reusing technical waste. I had many of these old cell phone batteries and I put them to good use again. I ended up with the capacity of 8 Ah and voltage of 14.4 V. There is also a joy of using your own creation and that is the biggest of all rewards.

Once again, thank you for reading.


Posted in DIY

July 31st, 2017 by Chief

Wartime – how the darkness came.

I was ten years old when I noticed that people around me started talking about us and them. I remember clearly few situations when some older men asked me:”Kid, what are you?” It was at that time confusing and creepy question for me since I did not understand it. In most cases, I would ignore the question or just answer:”Human being”. When it happened few times, I asked my parents to explain to me what is the trick with older people asking that weird question. (Later I figured out it was a question about religion). They said that people always try to find reasons to divide among each other and that both my answers were correct. Very soon people became divided by other ways. For example, there were those with electricity and those without it. It was the wartime.

Life in a city without  electricity and heating

I lived in a city that had at the time around a quarter of million people. Infrastructure was ok, for example, there was a big heating plant providing everyone with heating and warm water. I lived on the eighth floor of the building with around 50 apartments. Just try to imagine how it looks to walk to the eighth floor by the staircase without any light! Yes, the building was designed that way, and it was not meant for living in a stone age and without the electricity. It had an elevator, but then again it also needs electricity to work. At the first, we had some flashlights, but soon we were in a situation that there were no batteries in stores to purchase. Very soon there was no money for them anyway so the first problem could be ignored….. It was a wartime.

 First of many problems – heating

The building had very bad insulation. It was hell during summer, and it was a fridge in winter. Without electricity, the fire was the only way of heating. Now that I`m thinking about it, it was the only way of cooking and heating water. So, in time when most of the mankind progressed at warp 9, we were solving problems from like a stone age. Parents bought us a wood cooker.

wood cooker


It looked just like this and even had an oven. Our greatest and only home appliance that actually worked. It provided us with heat, enabled us to cook and to heat up some water for bathing. We were almost ready to survive.

Of course, the building did not have a chimney so we drilled a hole in an outside wall and put smoke pipe outside at the building facade. It was the only way, and everyone did it. Soon building with white facade became almost brown, black and gray. It would actually look great in a cheap post apocalyptic movie. The whole city looked that way…. gray smoke and dark everywhere. But as I said before, now we got ourselves means of heating, cooking, baking bread and producing some hot water. If you would put big enough pot of water on a cooker and heat it near the boiling point, and then empty it in a bath tub and add some cold water, you could almost get a decent bath. In a great necessity, human ingenuity can be limitless.

Acquire a fire wood in the middle of the city

So the next problem was providing a fire wood, and stockpiling it somewhere. Well, we had a small storage room in the basement of the building and descent balcony, so some of the problems were solved. Next one was to buy firewood. It was very expensive, and there was little or no money at all. Anyway, very soon a new type of job and market arises from this trouble. There were horse wagons patrolling the city and selling firewood. Yes, I`m talking about 1993. year, it was not some western movie 🙂 . My parents would buy a wagon of wood and we would unload it in front of the building. Then, the fun would start, since it would need to be carried up to the eighth floor. We would start packing woods in a bags and carry some in the basement and some up the stairs. Great recreation huh?

Off and On ratio

At 1993. we were at the point where we would get electricity from the power grid for few hours every….. 45 days. Yes, that was the on and off ratio. At least for us unlucky enough not to live in the same building with a politician or military officer. Those with that kind of neighbors did not have any power restrictions. Most of the people used candles, and candle market was expanding one. Imagine the whole city in the complete dark, and few scattered buildings shining like a Las Vegas in the dark. It was already possible to conclude that this situation will not end up good. People were leaving their homes and going somewhere. I think it is the first time that I heard word refugees.

How did technology help in a wartime

The first and most common solution that did not involve light sources based on fire was a car battery (if you were lucky enough to have one) and a 12V light bulb. With a bulb from the car main light you would get very good light, but not for a long time, since it was 50 W lamp and that would give 2-3 evenings of light with a standard car battery. It was ok for the beginning of power restrictions when there was no power for few days. If you had a good charger you could recharge the battery in a few hours and it would do the job. But as it was getting worse and there was no power for a week, the main light bulb was not an option anymore, so the tail light bulb was more appropriate. It was 10 W, and it could last on a single charge for a week or more. It was a time of saving, and energy was the currency.

Neon tube as a life / light saver

Then came the best, most practical and greatest piece of technology of the ’90s – 12 V Neon tube driver, or 12 V CCFL inverter. It would make a standard neon tube shine on a 12 V with an acceptable power consumption. Usually, it would drive 10 – 20 W tube, and it would produce much more light for the same amount of current than an ordinary filament bulb. Another great thing was that the neon tube did not need to be in normal working condition. The ones that did not work on normal 220 V surrounding due to the broken filament, would work like a charm on this type of device. It was because of the different way of electrical gas discharge. Now you could create a decent amount of light for a current consumption around 1 A. There were many variations and sizes of this CCFL inverters, smallest I made worked on 6 V and took 200 mA to drive small 10 cm neon tube. It was great for the bathroom! I also made some big ones that drove 1,7-meter tubes at their full intensity. Big ones consumed up to 1.5 A but could produce enough light for a very big room or even a cafe bar.

How it was made

Most of the necessary parts could be salvaged from the old BW TVs. Remember, it was a war time and it was not possible to go to Radio Shack and by components. Transistor and ferrite were the most crucial parts and both were located in TV, and suddenly it was a great thing to have one that you did not throw away. Regarding ferrite, I experimented with stick shape, U shape, even pot shape. All worked, but the best was the U shape.

CFFL Inverter schematic


“U” shaped ferrite

Two of the U shapes were in high voltage cascade of the BW TV. I remember that we stripped CuL wire by unwinding old transformers. Capacitors and resistors could be scavenged by disassembling all sorts of electronic waste. Of course, there was improvisation also, right values were often created by combining multiple elements in series and parallel.You had to put all your ingenuity to work 🙂 . The casings could be made out of anything, from food cans to a wooden boxes.
Device creation could be a piece of cake. Only the transformer took time due to the big amount of windings in the secondary coil. And like always there is a “but” at the end. Soldering iron did not work without electricity either. There were some that could work @ 12 V but there was not even enough power for the light so soldering iron had to consume something else to get hot. My father ingenious as he is used one big old soldering iron in a very specific way. He would put its tip in a fire (we all ready had a wood cooker in our living room) to get it hot enough for soldering, then clean tip a little bit and use it to solder few wires or joints. Then back to fire again for heating up. That way he was able to create, repair and fix many devices even without electricity.



I wanted to create one for the means of this article, but I made or helped in the creation of so many of them as a kid that I almost puked even on the idea of winding a transformer again.
There is a great passion for electronics in my heart and joy of creating things, but that “survival mode” was a little too much. I think that we created more battery chargers, and CFF drivers than the small factory would do in a year. We traded them for food, wood, money, what ever possible. There is no such misery like the one in a city in times of crisis. When you live in the countryside and have some land, you can at least produce some food. Grow some vegetables and have some animals. On the asphalt and concrete in your 50 square meters, you can`t do anything but starve.

Radio over faucet 🙂

In a time like that even listening radio would help, and I was trying to find a way to power it.
I tried to create a little generator that would use water flowing from the faucet, but my great idea turned up not to be so great when finally it came to me that someone has to pay for that water also. I was so occupied with that project that I overlooked that fact. So, it was back to the drawing board again.

Radio over phone line

The next “great” idea came to me one time when the phone ringed in the dark. Yes, we had a phone, and it worked most of the time. I still wonder why, but phones worked. They let us use the phones, although you could call only the territory controlled by “ours”. Anyway, I asked my father, how the phone works, when there is no power almost anywhere, and he explained to me that in telecom, they had very big batteries, and generators, so their equipment is always powered up. I measured the voltage on the phone line and it was 9 Volts. The situation was promising! I figured out that I could drain up to 15 mA and telephone would still work. Great, I had a little radio that worked on 4,5 volts, found 3 AA NiCd accus, connected them in series and idea was to charge them from the phone line, and to let radio work taking power from them. That little radio could work with 10 mA current if it was on very low volume. 25 mA if it was decent volume. And I got to charge accus 24/7 so it would give me buffer to listen to the radio for let`s say 14 hours. Great, it would do the job. One time I was holding phone line wires in my hand and something very unpleasant happened. Somebody called us! It means that some 90 Volts or something like that ended up between my fingers. It was really a nasty feeling, and I threw everything away for a day or so, pissed off for what happened.Those days, the phone would ring once a week or something like that, and it had to happen while I had stripped wires in my hands! Murphy’s law! That is when I learned how telephone works, and rings 🙂 . Anyway, I ended up with that high voltage problem, and I think I used some Zener diodes and resistors to overcome it, but I can`t remember the details anymore. I used my great achievement for a while and enjoyed radio until parents started wondering why no one is calling us ever. Phone worked, and you could call, but it just did not ring. I knew it was my “genius” device and immediately went to guerilla mode. I would connect a device during the night to recharge my batteries for a little bit, and disconnect it in the morning. This worked, and although I had to make some compromise, I actually had a few hours of music every day. A little bit of happiness in the dark times. You know that special feeling when something is taken away from you by force and you finally get a piece of it back. That was it.

Washing machine bath trick

One more tech trick for a wartime. If you live in a building without warm water, and without water heater, you can use the washing machine to heat up some water for you. Here is my father`s genius solution:

Do not put any laundry in the machine.
Do not put any detergent or softener in the machine.
Take the drain hose and put it in your tub.
Set machine for highest possible temperature program.
When it spins up and get the water out, you will get much hot and clean water, just add some cold, and there is your bath, great huh?

Once every 45 days we would get those 3 hours of power, so it was a hurry to do what can be done, recharge some batteries, and of course, enjoy almost a real bath 🙂 .


No battery can last for 45 days

It was obvious that you can`t have a battery big enough to provide you with enough Amps to last you 45 days even just for a light.

This battery pack was a life saver and I must dedicate few sentences about it.
This was 10 NiCd cells pack for RT-20 military mobile radio unit. There is a great site about them at this link. So this battery pack was 12 V, 7 Ah and it was small enough to carry. Father worked at the local radio station as broadcast equipment specialist and since they had a diesel generator working 24/7 he would take the battery to work with him, recharge it there and then bring it back home again. Sounds crazy from today`s point of view right? Well, this worked, and we had a light problem solved. This was 4-5 Kg, 15 x 35 cm package, so it was not so hard to carry it around. I must say that these were most durable, rechargeable batteries I ever encountered. They were made for the military by factory “Krusik” in Valjevo, Serbia. Indeed they were a military grade technology.


Other handy things

There were few more helpful things in the DIY department.
Alcohol stove made of a can was great for cooking coffee and tea, and even boiling some eggs. Soon there was no coffee and no alcohol for the stove. So it did not last much 🙂 .
The diy candle was another useful thing to create. You put some oil in a glass and use a piece of cotton as a wick. Wick would go thru a bung and piece of metal over it so bung does not burn. Great diy candle, but it smells bad as it burns.


Eggs of war

I don`t know precisely why, but there is some special connection between wartime and chicken eggs. Sounds crazy? Well as soon as the city was without electricity egg market expanded rapidly. Why? I suppose it was because they are cheap and easy to transport, and do not require much energy to prepare. You could boil an egg even over a candle. It means you would not starve. Eggs were being sold in front of the already closed stores, on the sidewalks, on improvised market places, literally anywhere. I ate so many eggs in those years that I can not look a chicken in the eyes anymore :). So if you ever notice that eggs are selling rapidly around you, it`s time to run away. Try to leave your country and do not look back. War is coming, or it already came. And if you want to be a normal person ever again, then it is not a surrounding for you to be in, or you may end up writing articles like this 🙂 .

Money for nothing

We also had our own currency, and it was something to tell about. What better way to enslave citizens than to take control over the money. How to do it? Invent your own currency and print it yourself. That way you control how much money is out there, and how much does it actually worth. That is also a great way to exchange worthless paper for stable foreign currencies that you will need when you take everything you can and leave the country for a some far away place without an extradition treaty. All that you can do if you are a government or in our case few man show. Another great thing was inflation. If by any case you would get some money you would need to run to buy something for it or change it to foreign currency asap. Why? Literally, over night, you would need one more zero for it to be as worth as yesterday.


5000 to 500 millions

Our Monopoly money 5000 to 500 million.

For example today 1 DM (Deutsche Mark, most popular currency of the time) would be exchanged for 5000 Dinars (Our new patriotic money was called “Dinar”), but tomorrow one Mark would be 50000 dinars. I remember that one time my mother got her monthly salary in those dinars and she could buy a box of matches for it. In that time she at least still had a job. It was a real life Monopoly money, or as Dire Straits would say Money for nothing. Unfortunately, the technology could not help here, but at least we used it to stay in a connection with the rest of the normal world.



I started writing this article in hope to evoke some old memories regarding my early electronic projects. I also shared some stone age ideas and memories. Necessity created them, nothing big, great or revolutionary. They made a life a little bit easier. Now I`m thinking what would I give at that time for one of the today’s led`s? Well, time was different and darkens did not come from the lack of the technology but the lack of the sanity and humanity. And if you notice that eggs are being sold everywhere, and whenever you see a bill, you begin thinking about Dire Straits, it may be a time to found yourself a new country, because yours may be coming into a war.


Once again thank you for reading.















Posted in *.*, DIY, Tech Tavern

Nokia batteries
May 13th, 2017 by Chief

Electric age is driven by batteries

Most things around us are now powered by batteries. Many devices are powered by similar type of batteries considering voltage and capacity, but only packed in different casings. When a device stops working, or there is no need for it anymore you can salvage some parts. In this example we will use some old Nokia batteries to create home made power bank. Not a big deal, finished housings  can be purchased for standard laptop cells  in order to create a power bank. You would even  get charging electronic and connectors  built in. Well, we will create something different this time. Our approach will be more geek and less conventional duo to nature of this article.

Why power bank?

Short to say it`s because the batteries are still to inefficient to provide enough juice for today`s devices. Manufacturers sacrificed battery autonomy in order to keep devices as small as possible, retain mobility and keep the performance. Best comparison is between today’s cell phones and the ones from ten or fifteen years ago. Today in most cases you must charge your phone on a daily basis, and back then you would do it once a week. So if you want more autonomy you need a power source, and if located somewhere without access to thee power grid , power bank jumps in.
Basically it is a pack of batteries in witch you store some energy for a latter use.

Should you buy or DIY?

PB`s are quite useful to have due to it`s function and portability. It is possible to buy one in almost every consumer electronic shop or order it online. If you have some tools, basic  knowledge about electronics  and want to have some fun, you can even make it yourself.
Here is BOM for the job:

Some old batteries (I had 12 pieces of Nokia BL-5 batteries),
Soldering iron ,
Soldering wire,
Some wire,
Insulation Tape


Schematic diagram

Block diagram of generic power bank

This is the block diagram of mostly used design for power banks. Manufacturers mainly use laptop cells , 18650 connected in parallel. Capacity of one cell, times number of cells is what they advertise as PB capacity. For example if inside of a PB are four 2500 mAh cells, it is advertised as  10000 mAh PB.
If you have a PB of 10000 mAh capacity, and your smartphone has a 2500 battery inside, it does not mean that you can charge it from 0 to 100 % of capacity 4 times as logic would suggest. It is closer to say that you will charge it two to three times at most.

Important to know:

Cells in diagram are connected in parallel. These cells are typically Li-Ion batteries with 3.7 declared Voltage. Most devices have same 3.7 V batteries. Charger must have higher potential than battery. It means that for charging 3.7 V battery you need at least  4 V or 5V source. This is where 5V step up comes in.  If we charge our phone with 5V 1A it means that we are using P=U*I 5W of power. If we take 5 W from a source of 3.7 V it will be 5 W / 3.7 V = 1.35 A. To keep it simple it means that from 10000 mAh PB you get around 7000 mAh of charging. To get back to example of the phone battery of 2500 mAh it means that you will be able to charge it from 0 to 100 % at most 2.8 times, not considering any losses.











Here is what we did:

12 Batt.

Our Schematic

















We took twelve BL-5CT batteries and connected them by schematic above. So it was four in parallel and than three times that in series.




BL-5 is declared as 3.7 V 1050 mAh , so we connected four in parallel and got 3.7 V 4200 mAh. Connecting three times that in series  got us 11.1 V 4200 mAh battery pack. Now let`s look at the Wh or Working Hours. You get that number by multiplying voltage and capacity. 11.1 * 4.2 = 46.6 Wh. If we look at a case from our example of commercial PB it would be: 3.7 * 10 = 37 Wh. Since the Wh is amount of energy that can be stored in to the battery , it is clear that numbers are in favor of our PB and considering we got it from junk and it costed almost nothing, it is a great result, right?









Alltogether connected

Finished PB

Measuring batteries

Voltage of fully charged PB












What to do with it now?

You can power up many things with this power bank,  portable radio, car phone charger, camping light and many other gadgets and therefore enjoy using them off the grid.

Charging phones


Car phone charger  connected to a PB, and charging two smartphones.










Great camping gadget, and works like a charm when powerd by our PB

12 V 15 W led camping light

This Led provides enough light for descent camping area when hanged at 3 meters hight.

LED Powered by PB, consumes 0.67A










Anyone interested  can purchase similar LED  on Ebay for under 5 $. Here is the link for starting point so feel free to explore if you are interested. Just replace wires and alligator clips when you get it since original ones are to short and to thin.



These batteries have a built in charging control and when full they will stop taking current. What I usually do is feed them with 12 V power source in series with a 12V 5W light bulb from a car interior light. Light bulb is there for over current protection and you can buy it almost anywhere. You can use any DC charger, or adapter,for example from old external hard hard drive, in general anything that outputs 12 – 18 Volts and 1 A or more.

Charging batteries by 12 18 V power source in series with light bulb for current limiting

Charging batteries


Word of a author:

I just had some of these old Nokia batteries and therefore did something better than throw them to waste. Since in deed I was in need of a power bank this was a logical choice. It is interesting that these batteries were old and much used , but still found in a great shape. I measured that they still have more than 80 % of their stated capacity and that is awesome. I will later install cigarette lighter socket, like in every car so I can plug in things directly and avoid wires and alligator clips.

Well, it is time to end this story, I hope you find it useful and interesting, and if you have any comments, thoughts, or simply want me to test something , please leave a comment and we will get in touch.
Once again, thank you for reading.



Posted in DIY