When I began tinkering with the arduino, one of the first things that I wanted to do was build a robot. Fortunately, building a beginner robot is pretty easy with a motor driver module(I used the l298), a couple of dc motors, and maybe even a few sensors.
But during the build, I got stuck in an unexpected place, which is almost always overlooked in youtube videos and articles - the power source. I needed not one, but two power sources to power both the Arduino Board(5V), and the motors(8-12V), and both needed to be light enough to not strain the chassis, and small enough to fit.
Almost all of the robots I saw on the net used either 6-8 AA batteries, or 9V batteries. Both these options had their own problems - AA rechargeable batteries are usually 1.2V each, so there was so no way I could fit into the chassis and charge 8 batteries. The small 9V batteries were not rechargeable, and one-use batteries are not only harmful towards the environment, but they also get expensive after a point of time(there are a few rechargeable 9V batteries you can buy, but the batteries and their own chargers are expensive, and they have a very low charge capacity).
So what was the right type of battery which does not take up too much space, provides high enough voltage and is easy to recharge? After much research and trial and error, I came up with the solution - lithium-ion batteries.
Although I began the article by talking about an arduino robot I was making, these batteries are the best option for almost any small to medium sized electronic project that requires mobility(and hence batteries) - not only for small dc motor robots.
Why lithium ion batteries?
Energy dense(high mAh and voltage per unit volume), and safe
Easily rechargeable
More energy dense than AA batteries, but safer than li-po batteries(which are even more energy dense than li-ion batteries! Li-po batteries are used to power drones)
As convenient to use as AA batteries.
Where to get them from?
Unfortunately, if you live in India like me, there aren’t places where you can get good quality li-ion batteries. In almost all websites where you can buy them, they’re either very expensive, or they’re knock-offs. I would never ever buy the knock-offs, whatever the case may be(you can spot them easily - if they have ridiculously high charge capacities like 6-10thousand mAh, or ridiculously low prices).
Knock-offs either have reasonable charge density, but may be very dangerous to use(as they were made from cheap means of manufacture), or they ARE safe, but do not have a good charge density. Either way, it rules out the advantages of using li-ion batteries in the first place.
Important: Lithium, which is the main substance used in these batteries, is one of the most corrosive elements known to man. Exposure to a leaked battery would prove fatal. That is why every appliance that uses li-ion batteries has the necessary circuitry and casing to protect the battery. In this article too, I’ve mentioned the explained the use of casing, and a module to charge and use the batteries, which you will see shortly.
That is why I think the best place from where you can acquire these batteries are old laptop batteries(almost all 2004-2009 Dell and HP laptops). Yes, many old laptop batteries had seperate battery compartments, which have li-ion cells inside of them. This was the best battery system technology had to offer at that time.
Take a look at the picture of this detached laptop battery(I will explain how to remove the laptop battery and the cells from inside it shortly).
The rating says ‘11.1V, 7200mAh’. This makes perfect sense, as all charged up li-ion cells have a voltage of exactly 3.7V. Therefore, it is clear that 3 cells are attached in series to get the voltage of 11.1 that the laptop requires. To get a higher charge capacity(so that the battery lasts longer), another set of 3 batteries in series is attached in parallel(keep in mind that when batteries are attached in series, voltage increases. When batteries are attached in parallel, charge capacity mAh increases).
Your old laptop battery may have a different voltage and a different arrangement of cells.
Advantages:
Guaranteed they are not knock-offs and they are of good quality, because they were used in good quality laptops at that time.
Disadvantages:
Chances are that you stopped using your old laptop because of some problems in the battery. In this case, few of the cells may be damaged and of no use
If the laptops were used for a very long time, the charge density of the batteries may reduce with time.
Getting the batteries out of the laptop:
Fortunately, most laptops like these have a separate battery, which can be clipped into and out of the laptop with ease.
Once you’ve removed the battery compartment, use a flathead screwdriver to pry it open by forcing the flat head into the crevice(weak point) lining the container. You could use a small heavy load(like a small hammer) to force a bit of the flat head into the container(but be careful not to force the flat head inside too much to strike the batteries that lay inside).
Batteries will now be attached in series and/or parallel with flat metal strips, that connect 3-4 batteries at a time. Remove, or rather, peel these carefully with pliers.
Now to store the batteries, the best option is to get some plastic cases(not more than 70-100 rupees)
Use these batteries while they are in the case, and try your best to keep them there at all times. These batteries may be safer than li-po batteries but, nevertheless, they’re still made of lithium. Any safety precaution that can be taken..should be taken.
Charging and using the batteries:
When it comes to charging and using the batteries, the tp4056 module is the best option.
It is extremely cheap, small, safe and very easy to use, even if you don’t understand all of the electronics behind it.
Reverse-polarity protection, over-charge protection, over-discharge protection
These safety features are very much necessary as you’re dealing with batteries with lithium inside it.
I will now give a brief summary of how the board charges and protects your batteries, and then explain the wiring up of the board to your batteries.
Takes in an input of 5V(from the micro-usb port) or 4-7V(from the input terminals beside the micro-usb port) and uses that to charge the batteries in a safe way
Various stages of charging(not going too deep into electronics inside the board) -
If the battery is below 2.9V, it trickle charges it until it reaches 2.9V, after which the charging current steadily increases for some time. Charging will continue until the battery reaches a voltage of 4.2V(at which point charging completely stops).
When the battery is in the process of charging, the red LED glows.Once charging is over, the green LED glows. Very. Simple.
Various stages of discharging:
When you’re using the battery(connected to a load), once the battery drains to 2.4V, the module will disconnect the battery from the load(over-discharge protection).
Now that you have an idea about what goes on with the board, you can begin to wire up the battery to it.
Connect the terminals of the battery(hopefully the wires coming out of the plastic case you’re using) to the ports labelled B+ and B-. These are the ports the module uses to charge the batteries.
Connect the OUT+ and OUT- terminals to your load. This is how you will use/discharge your battery. From here you can connect your battery to any other load like an LED or a dc motor.
You may have noticed the switch in the output wire. This is because the battery has to be disconnected from the load while the battery is charging. Do not charge the battery while the battery is discharging. It may lead to overcharging.
For power INPUT(which the board will use to charge the battery), you have two options:
Use the micro-usb port(any old phone charger can be used)
Use the input terminals beside the micro-usb port, supplying it with anywhere between 4v - 7V. (This option is favoured when you're charging many batteries with many of these tp4056 boards at the same time. You can use one power supply and connect all the boards in parallel, instead of using many micro-usb cables)
Well, now, you know the advantages of lithium-ion batteries, where you can use them, where you can get them from, and how to charge and use them!
I hope that you now have the knowledge to start incorporating li-ion power sources in whatever projects you require them for!