{"id":237735,"date":"2021-02-20T13:26:37","date_gmt":"2021-02-20T12:26:37","guid":{"rendered":"https:\/\/emariete.com\/?p=237735"},"modified":"2025-12-10T09:39:30","modified_gmt":"2025-12-10T08:39:30","slug":"esp8266-esp32-battery-charger-well-made","status":"publish","type":"post","link":"https:\/\/emariete.com\/en\/cargador-bateria-esp8266-esp32-bien-hecho\/","title":{"rendered":"Adding battery charger to ESP8266 and ESP32 (well done)"},"content":{"rendered":"

<\/p>\n\n\n\n

In this tutorial I will show you how to add battery and charger to any microcontroller based project, is based on Arduino, ESP8266, ESP32, or any other<\/strong>, correctly, safely, easily and for very little money.<\/strong><\/p>\n\n\n\n

The goal of this project is not just to build it<\/strong>, but also to highlight some key insights along the way\u2014especially for hobbyists who want to power their creations with a battery.<\/strong> After all, did you notice the \u201cwell done<\/span>\u201d in the title?<\/strong><\/p>\n\n\n\n

The uses are endless and, although I will be using as an example<\/strong> my project of Home CO2 Meter<\/a>you can use it in any other project.<\/strong><\/p>\n\n\n\n

There are more than a few occasions when we would like to use our battery-powered CO2 meter<\/strong> (at least it often happens to me). Even to calibrate it outdoors periodically, it is good for me that they are autonomous. Until now I have been using for this purpose a powerbank<\/strong> (rechargeable power supply with battery), commonly used for powering mobile phones,<\/strong> but I thought it was time for a slightly more integrated solution.<\/p>\n\n\n\n\n\n

And what's this about it being well done?<\/h2>\n\n\n\n

Adding a battery to a device that runs on 5V (or even 3.3V) might seem easy enough, right?<\/p>\n\n\n\n

Here\u2019s a secret<\/strong>: This article isn\u2019t just about showing you how<\/strong> to \u201chook up\u201d a battery\u2014it\u2019s about explaining why it\u2019s important to do it the right way<\/strong>. That\u2019s why it\u2019s so long (and believe me, it could be even longer if we went deeper into the details).

Do me a favour: Even if this seems simple and there\u2019s too much talk for something so basic, please read the whole article (don\u2019t just skip to the build). You might already know it all\u2014but then again, you might be surprised.<\/strong><\/p>\n\n\n\n

I think that by now everyone knows that Lithium-Ion (Li-Ion) and Lithium Polymer (Lithium Polymer) batteries<\/strong> o \"Lipo\") are delicate <\/span>and may even be dangerous<\/span><\/strong>. I'm sure many of you remember the scooters that went out on fire on their own in the street, not too long ago.<\/p>\n\n\n\n

We live with these batteries and nothing usually happens, but that's because the vast majority of commercial devices that use them know their risks and manage them appropriately<\/strong>.<\/p>\n\n\n\n

The danger does not come from the battery itself (well, it does a little) but, above all, from the way it is used.<\/p>\n\n\n\n

The problem often lies in the fact that the majority of the \"non-specialists<\/em>doesn't know (and it's logical, he doesn't have to know) what it is about \"...\".the use made of it<\/em>\"And even less so when they trust that if they take a battery and take a charger and plug them in carefully, nothing bad can happen.<\/p>\n\n\n\n

WRONG!<\/strong><\/p>\n\n\n\n

There is one type of use which is particularly sensitive and I am sick and tired of seeing projects with a design that puts your battery, your device and your home at risk<\/strong>.<\/p>\n\n\n\n

This type of use is mainly when You want to use the device and charge the battery at the same time.<\/strong>. <\/p>\n\n\n\n

Think about it, there are not that many devices that do that<\/strong>. We can think of the phones <\/strong>and, that they are really widespread, few others...<\/p>\n\n\n\n

We want the battery of our meter to be charged at all times, we want our device to work while the battery is charging<\/strong>. We do not want to have to turn the meter off for a few hours while the battery is charging.<\/p>\n\n\n\n

Essential rules for working with Li-ion and Li-po batteries<\/h2>\n\n\n\n

These are the ten most important commandments<\/strong> + 1 when working with Li-ion and Li-po batteries (and then others follow):<\/p>\n\n\n\n

    \n
  1. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  2. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  3. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  4. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  5. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  6. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  7. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  8. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  9. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  10. Don't overcharge the battery<\/strong><\/li>\n\n\n\n
  11. No short circuits <\/strong>the battery (this is as important as the previous 10)<\/li>\n\n\n\n
  12. Don\u2019t discharge<\/strong> the battery below its safe threshold<\/li>\n\n\n\n
  13. Don\u2019t let the battery overheat<\/strong><\/li>\n\n\n\n
  14. Do not put batteries in parallel if they are not equal and have the same load<\/strong><\/li>\n<\/ol>\n\n\n\n

    They are not the only ones, but they are the ones you can do may your house go up in flames<\/strong> more easily.<\/strong><\/p>\n\n\n\n

    The sin of most projects<\/h2>\n\n\n\n

    Most of the projects you see on the internet commit the following mistakes a serious mistake<\/strong> and I am going to tell you what it is in a simple way so that you can quickly understand it.<\/p>\n\n\n\n

    If you remember, the first ten commandments said: \"Don't overcharge the battery\".<\/strong>. This means that, in the process of charging the battery, there is a certain point in the charging process at which you have to stop carrying it and go no further than that.<\/strong>. Continuing to charge the battery past this point is dangerous.<\/p>\n\n\n\n

    As you can imagine from the above paragraph, it follows that the charging process of a battery is very delicate<\/strong> and chargers for Li-ion and Li-po batteries (as opposed to lead-acid, nickel-cadmium or nickel-metal batteries, which can take more abuse) are very precise devices.<\/p>\n\n\n\n

    I am not going to explain in detail how the charging process of a Li-ion and Li-po battery works (maybe in another article) but I am going to give you the basics. main lines of what a charger does<\/strong>:<\/p>\n\n\n

    \n
    \"\"<\/a>
    Battery charging process with TP4056<\/figcaption><\/figure>\n<\/div>\n\n\n
      \n
    1. First the charger makes security checks<\/strong> to ensure that the battery is not connected the wrong way round, that it is within a certain voltage range, etc.<\/li>\n\n\n\n
    2. The charger then performs a \"pre-conditioning\".<\/strong>The battery is tested, in a very controlled way and by supplying low currents, that the battery \"absorbs\" the current it is expected to absorb, that its voltage rises when it is supplied with current, and so on.<\/li>\n\n\n\n
    3. The constant current load<\/strong>The charging process lasts almost the entire charging process. This means that the charger will keep changing the voltage<\/strong> supplying the battery as required, so that the battery always absorbs the same intensity<\/strong>.<\/li>\n\n\n\n
    4. When the charger detects that the battery is close to 4.2 volts, which marks its maximum voltage, starts to reduce the current intensity<\/strong> supplying the battery.<\/li>\n\n\n\n
    5. When the current is below a certain value, the charger stops charging.<\/strong>. It has ended.<\/li>\n<\/ol>\n\n\n\n

      Well, the problem is that in most projects, the last point is never reached and the battery charges, and charges, and charges....<\/strong> until... until the battery holds out.<\/p>\n\n\n\n

      Have you ever noticed how many battery-operated devices have problems with the battery? Well, that's a good reason.<\/p>\n\n\n\n

      And why doesn't it stop charging?<\/strong> Well, I will also explain it to you below.<\/p>\n\n\n\n

      The Hidden Damage: Micro-cycles and Chemical Stress<\/h2>\n\n\n\n

      In addition to the risk of overcharging that prevents safe termination (the \"deadly sin\" you have already covered), this common and poorly made power supply system introduces other problems that drastically shorten battery life:<\/p>\n\n\n\n

      A. Micro-Cycle Degradation<\/strong><\/h3>\n\n\n\n

      When the charger (e.g. TP4056) is connected in parallel with the battery and the load:<\/p>\n\n\n\n

        \n
      1. The charger attempts to keep the battery at its maximum voltage (\"4.2).<\/li>\n\n\n\n
      2. The ESP8266\/ESP32 circuitry, together with the converter step-up<\/em>is constantly active and its current consumption is variable (especially with WiFi).<\/li>\n\n\n\n
      3. Whenever the consumption of the device increases sharply (e.g. a WiFi transmission peak), the charger may not be able to react fast enough or the resistance of the cables\/components causes a voltage drop.<\/li>\n\n\n\n
      4. This drop causes the battery to supply the necessary peak current, which results in a micro-discharge<\/strong>.<\/li>\n\n\n\n
      5. Immediately after that, the charger detects the slightly lower voltage and reloads<\/strong> the battery.<\/li>\n<\/ol>\n\n\n\n

        Consequence:<\/strong> The battery undergoes constant tiny charge\/discharge cycles (micro-cycling<\/em>) while connected to the power supply. This continuous work in a state of High State-of-Charge (SoC)<\/strong> generates a chemical stress that destroys the lithium cells more quickly than if it were simply at rest or if the charger could prioritise charging power.<\/p>\n\n\n\n

        B. Voltage and Temperature Accelerated Chemical Stress<\/strong><\/h3>\n\n\n\n

        This system also adds two factors that kill the battery in the long run:<\/p>\n\n\n\n

        Factor<\/strong><\/td>Problem in the usual System (TP4056 in parallel)<\/strong><\/td>Consequence on the Battery<\/strong><\/td><\/tr><\/thead>
        High SoC Constant<\/strong><\/td>The battery is constantly floating at \"4.2.<\/td>Degradation of the calendar:<\/strong> Maintaining a lithium-ion battery at 100% charge (the maximum voltage) is the most destructive factor to its chemical longevity, even without cycling. A good system power path<\/em> prevents the battery from charging to 100% until the main load is disconnected, or keeps it at a safer level (e.g. 80%).<\/td><\/tr>
        Heat Generation<\/strong><\/td>1. The battery is in constant activity (micro-cycles). 2. The charger chip itself (TP4056) dissipates heat that radiates to the battery, especially if they are in close proximity.<\/td>Premature Death:<\/strong> The high temperature exponentially accelerates unwanted chemical reactions within the cell. Every \"10 increase of more than \"25 can halve its service life.<\/strong><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

        The usual and (very) poorly made feeding system<\/h2>\n\n\n\n

        What they do in many (very many) projects is the following:<\/p>\n\n\n\n

        We start from a project, which is powered normally at 5 volts.<\/p>\n\n\n\n

        \"\"<\/a><\/figure>\n\n\n\n

        The next step would be to add a battery with its charger (a small board based on the TP4056 integrated circuit, which works very well and is able to charge the battery with an accuracy of 1.5%), and which could be left connected at all times to keep the battery permanently charged:<\/p>\n\n\n\n

        \"\"<\/a><\/figure>\n\n\n\n

        Of course, in the above example we would have a charged battery but that battery would give us a voltage of between about 3 and 4.2 volts, depending on how charged it is, and we would not be able to use it directly to power our circuit.<\/strong> (which needs 3.3 or 5 volts to operate).<\/p>\n\n\n\n

        What our clever designer does is to connect, in parallel with the battery, a circuit called \"step up down\" (among other curious combinations of words such as booster or SEPIC), to which we can apply any voltage at the input (within limits that depend on the exact circuit we use, say between 2.5 and 30 volts) and that at the output will always give a nice 3.3 or 5 volts stabilised.<\/strong>:<\/p>\n\n\n\n

        \"\"<\/a><\/figure>\n\n\n\n

        But, alas, our amateur designer soon realises that he is not alone (when the battery dies or disaster strikes<\/strong>The first thing that happens, but it won't take long), that things are missing here to make your circuit work properly, and can sleep peacefully at night<\/strong>.<\/p>\n\n\n\n

          \n
        1. A protection against overload<\/strong>If you leave your device plugged in for too long and the battery discharges below a certain point, the battery will die (some batteries have this protection built in).<\/li>\n\n\n\n
        2. A protection against short circuits<\/strong>because, let's be serious, at any moment (and more so in an amateur circuit, which is what we are) a cable can touch another one, ... and then the magic smoke escapes\u2014every electronics enthusiast knows what that means.<\/li>\n\n\n\n
        3. Other protections<\/strong> which may not cause the assembly or the house to burn down, but which are convenient to have.<\/li>\n<\/ol>\n\n\n\n

          So he goes back to the design board and changes the simple loader he had been using for a more complete charger<\/strong>The device must be equipped with the necessary protections (pay attention to the connections to the charger), are very similar, but not the same:<\/strong> the previous one had only two terminals<\/strong> and it has four terminals<\/strong> two for the battery and two for the output):<\/p>\n\n\n\n

          \"\"<\/a><\/figure>\n\n\n\n

          At this point, our amateur designer has got what he wanted. A battery-operated power supply system that can charge the battery and power the device at the same time and has the necessary protections...<\/p>\n\n\n\n

          He tests it and it works! and he is so happy he publishes it...<\/p>\n\n\n\n

          But that design (so extremely widespread, Google it if you want and you'll see hundreds of them) hides a dark secret, a deadly sin<\/strong> that can put us in danger:<\/p>\n\n\n\n

          THE CHARGER NEVER FINISHES CHARGING THE BATTERY, THUS BREAKING THE FIRST 10 COMMANDMENTS!<\/strong><\/p>\n\n\n\n

          Why is this happening? <\/strong><\/p>\n\n\n\n

          The key to this can be found in the first point of the TP4056 integrated circuit datasheet:<\/strong><\/p>\n\n\n\n

          \"\"<\/a><\/figure>\n\n\n\n

          \"The TP4056 automatically terminates the charge cycle when the charge current drops to 1\/10 of the programmed value after reaching the final float voltage.\"<\/em><\/strong><\/p>\n\n\n\n

          This means that the TP4056 will stop charging the battery. only when the final voltage has reached 4.2V and the charge current drops to one tenth of the programmed charge current<\/span>.<\/strong><\/p>\n\n\n\n

          By default, most boards using the TP4056 (and similar chips) have a programmed charging current of 1 Ampere (which can be adjusted by changing a resistor). This means that the charging process won\u2019t stop until the current draw drops below 100mA<\/span>. Since we have an additional circuit connected\u2014hanging off the charger<\/em>\u2014the charger gets confused<\/em> by this extra consumption and never stops charging the battery<\/span>.<\/strong><\/p>\n\n\n\n

          If the programmed charging current was 500mA. the charger would only finish charging the battery when the voltage had reached 4.2V and the consumption was less than 50mA<\/strong>.<\/p>\n\n\n\n

          The basic solution<\/h2>\n\n\n\n

          The solution to the above problem is to achieve that the battery charging and power supply circuits of our device are independent of each other.<\/strong>.<\/p>\n\n\n\n

          Look at the diagram below, imagine if we had that switch in our circuit and it switched automatically. depending on whether the external power supply is connected or not<\/strong>.<\/p>\n\n\n\n

          \"\"<\/figure>\n\n\n\n

          Here it is with the external power connected<\/strong>. As you can see the battery continues to charge, but has no connection to our circuit<\/strong>:<\/p>\n\n\n\n

          \"\"<\/figure>\n\n\n\n

          And here it is only with the battery<\/strong>:<\/p>\n\n\n\n

          \"\"<\/figure>\n\n\n\n

          This, electronically, is usually done by a MOSFET transistor and a diode<\/strong>The two are working together, so that between them they are capable of directing the current in the right direction<\/strong>depending on whether external power is available or not:<\/p>\n\n\n\n

          \"\"<\/figure>\n\n\n\n

          Basically we have the same forbidden circuit as before<\/strong>but now we have this \"automatic switch<\/strong>\"who chooses the right path for the current<\/strong>.<\/p>\n\n\n\n

          This is the path the current takes when the external power supply is connected. As you can see the charging of the battery and the power supply of our device are completely independent<\/strong>:<\/p>\n\n\n\n

          \"\"<\/figure>\n\n\n\n

          When there is no external power supply, our device is powered by of the battery only<\/strong>:<\/p>\n\n\n\n

          \"\"<\/figure>\n\n\n\n

          In addition, this also allows you to we prioritize external power over the battery<\/strong> on the battery when the device is powered by cable, so that we will avoid our circuit causing continuous charging and discharging of the battery <\/strong>(which would greatly shorten its life).<\/p>\n\n\n\n

          The above images are of an excellent manufacturer's application note Microchip<\/strong>where he talks about the design of Li-Ion battery chargers and circuits\".load sharing<\/strong>\"(load sharing) or \"power path<\/strong>\"(path of the current). If you are interested in finding out more I recommend you to read it, here<\/a><\/strong>.<\/p>\n\n\n\n

          And how do we get it right?<\/h2>\n\n\n\n

          A few years ago we would have needed a lot of components: Several for battery protections, several for the charger, several for load sharing. Now we have on the market integrated circuits that do all of these functions in a quarter of a square centimetre<\/strong>.<\/p>\n\n\n\n

          The solution I bring you this time is based on one of these integrated circuits. The integrated circuit MCP73871<\/strong>.<\/p>\n\n\n\n

          Here is the datasheet of the MCP73871.<\/p>\n\n\n\n