Types of cells/batteries:
We call the electrical power supply the element responsible for generate the potential difference necessary for the electric current to flow through a circuit so that the devices connected to it can function. The sources that we will use more often in our projects will be of two types: batteries or cells and AC / DC adapters.
The term “battery” is used to refer to electricity generators based on normally non-reversible chemical processes and are therefore non-rechargeable generators; while the term “battery” applies generally to semi-reversible electrochemical devices that allow to be ornate, although these terms are not a strict formal definition.
The term “Accumulator” applies interchangeably to one type or another (as well as other types of voltage generators, such as electric capacitors) being thus a term neutral capable of encompassing and describing all of them.
If we distinguish cells/batteries by internal chemical dissolution responsible for the generation of the potential difference between its poles, we will find that the most widespread batteries (“non-rechargeable accumulators”) Currently on the market are the alkaline type, and batteries (“accumulators rechargeable ”) are, on the one hand, nickel-cadmium (Ni-Cd) and on all nickel-metal hydride (NiMH), and secondly those of ion-lithium (Li-ion) and those of lithium-ion polymer (LiPo). Of all these types of batteries, LiPo is the one that have a higher charge density (that is, being the lightest they are the which have, however, more autonomy) but are more expensive.
The international industry follows common standards of standardization for the manufacture of alkaline type batteries and Ni-Cd / NiMH type batteries that define certain preset sizes, shapes, and voltages, so that can be used without problems in any electrical appliance worldwide. In this sense, the most common types of batteries are type D (LR20), C (LR14), AA (LR06), and AAA (LR03), all of them 1.5 V generators and cylindrical in shape although different dimensions (in fact, they have been listed from largest to smallest). The PP3 type (6LR61), which generates 9 V and has the shape of a rectangular prism; and the 3R12 type (“pocket”) that generates 4.5 V and are shaped cylindrically flattened. In the following image you can see, from left to right, alkaline batteries of type D, C, AA, AAA, AAAA, and PP3, placed on a graph paper.
In the image below, two LiPo-type batteries are shown on the left and on the right, two packages made of cylindrical Li-ion batteries. The first usually comes in the form of thin rectangles inside a bag silver and the latter usually come inside a hard rectangular or cylindrical, although both really come in great versatility and flexibility of Shapes and sizes. LiPo is lighter than Li-ion but usually has a lower capacity, that is why the former is usually used in small devices such as mobile phones and the latter in laptop chargers and the like.
We must also indicate the existence of “button” type batteries. There are many types: if they are made with lithium manganese dioxide, their nomenclature starts with “CR” (thus, we can have the CR2032, CR2477, etc.) and, although each one of them have an encapsulation with different diameter and width, they all generate 3 V. If they are made of silver oxide, their nomenclature commonly begins with “SR” or “SG” (thus, we can have the SR44, SR58, etc., depending on your dimensions). There are also alkaline types, whose code commonly begins by “LR” or “AG”. Both silver oxide and alkaline ones generate 1.5 V. In In any case, whatever the type, in all button batteries the negative terminal is the cap and the positive terminal is the metal of the other side.
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Batteries or cells characteristics:
It must be taken into account that the voltage provided by the different batteries is a “nominal” value: that is, for example, a 1.5V AA battery actually at the beginning of its lifespan generates about 1.6 V, quickly drops to 1.5 V, and then little by little it goes down to 1 V, at which point we can consider the battery “Spent”. The same goes for the other types of battery; for example, a LiPo battery marked as “3.7 V / (4.2 V)” indicates that initially it is capable of supplying a voltage 4.2 V maximum but quickly drops to 3.7 V, which will be your average voltage for most of its useful life, until it finally drops rapidly to the 3V and automatically stops working. In this sense, it is useful to consult the official documentation offered by the manufacturer for each particular battery (the called “datasheet” of the battery) to know the variation of the voltage supplied in the function of operating time.
In addition to the voltage generated from a cell/battery (which we will assume from now always constant), you have to know another important characteristic: the load that it is capable of storing (sometimes called the “capacity” of the battery). This value is measured in amp-hours (Ah), or milliamp-hours (mAh) and allows us to know approximately how much current intensity can provide the battery/battery for a specified period of time. In this sense, you have to remember that while the voltage supplied by the cell/battery is ideally constant, the intensity provided, on the other hand, varies at each moment as it does the electrical consumption of the circuit to which we connect it. For example, 1 Ah means that in theory the cell/battery can offer an intensity of 1 A for one hour (if required by the circuit), or 0.1 A for 10 hours, or 0.01 A for 100 hours, etc., but always at the same voltage.
However, the above is not exactly the case, because the more quantity of current the cell/battery contributes, in fact, its operating time is it will reduce in a much greater proportion than that marked by its capacity. For example, a 1 Ah button cell is unable to deliver 1 A for a full hour (not even 0.1 A in 10 hours) because it runs out much sooner, but instead, no has trouble delivering 0.001 A for 1000 hours. To know the intensity of a specific current that enforces the Ah rating of a battery, we must consult the manufacturer’s documentation (the battery “datasheet”). This “optimal” current intensity in the case of LiPo batteries is often called “Capacity”, and is expressed in C units, where a C unit corresponds with the Ah value of that battery divided by one hour.
For example, the C unit of a battery with a 2 Ah charge will be 2 A, and its concrete capacity will be a certain number of C units, which can be consulted in the datasheet (1C, 2C…). If we then have, for example, a 2 Ah 0.5 C battery and another of 2 Ah and 2C, the first one will be able to provide a stable current of up to 1 A without being exhausted prematurely, and the second can provide a current of up to 4 A. Knowing this, it must be taken into account, for example, those button batteries have a very small capacitance (0.01C is a common value), so if they are forced to add a lot of intensity at any given time, your life will be drastically shortened.
On the other hand, we have already said that the one that a battery contributes in a certain moment one current intensity or another basically depends on consumption electrical power (measured in amps, or more typically milliamps) that performs the total set of devices that are currently connected to the circuit (and which logically can be very varied depending on the case). That is: the time of operation of a battery depends on the demand of the circuit to which it is connected. More specifically, we can obtain (very roughly) the battery discharge time using the expression: discharge time = battery capacity/circuit electrical consumption. For example, if a battery has an electrical load of 1000 mAh and a device consumes 20 mA, the battery will take 50 hours to discharge; yes instead the device consumes 100 mA, that battery will only take 10 hours to download. This is all theory, as the numerical mAh value printed on the battery should be taken only as an approximation, and should be taken into account only in the ranges of consumption levels (measured in C units) specified by the manufacturer since for high consumptions we already know that this value cannot be extrapolated accurately.
Multiple cell/battery connections:
We have already known the symbol that is usually used in the design of electronic circuits to represent a cell or battery is:
where the longest (and sometimes thickest painted) part of the drawing represents the pole source positive. The “+” symbol is often omitted.
When we talk about connecting batteries “in series” we mean that we connect the negative pole of one with the positive pole of another, and thus, in such a way that we finally have a global positive pole on one side and a negative pole global for another. In this figure you can better understand:
The series connection of batteries is useful when we need to have a battery that generates a certain relatively high voltage (for example, 12 V) and only We have batteries of lower voltage (for example, 1.5 V). In that case, we can connect these 1.5 V units in series to get the battery you want to “handy” provides the desired voltage, since the total voltage provided by batteries connected in series is the sum of their individual voltages. In our example, to get 12V at starting with 1.5 V batteries, we would need 8 units, because 1.5 V · 8 = 12 V. In fact, commercial batteries of 4.5 V and 9 V (and 6 V and 12 V, which are also available) usually manufactured by internally connecting 1.5 V batteries in series. For this reason, many times we will see the following symbol (instead of the one previously shown) representing a battery:
However, it must also be taken into account that the total capacity (is i.e. the mAh of the serial battery pack) does not increase: it will remain exactly the same as the one that has a battery of that set of form individual and independent. This fact is important because generally circuits that need to be supplied with large voltages have a higher electricity consumption, so (by virtue of the formula in the previous section) the operating time of a source consisting of batteries in series will be quite reduced.
Another way to connect different individual batteries together is in parallel: In this configuration, all the poles of the same sign are linked together. That is to say: on the one hand the negative poles of each battery are connected and on the other hand they have connected all positive poles, these two common points of union being the poles global negative and positive.
A set of batteries in parallel offers the same voltage as a single battery individual (that is, if we have for example four 1.5 V batteries connected in parallel, this set will also give a total voltage of 1.5 V). The advantage that we achieve is that the duration of the system maintaining that tension is greater than if we use a single battery because the capacity (mAh) of the set is the sum total capacities of each individual cell.
It is very important to make sure that the batteries connected in series or in parallel are of the same type (alkaline, NiMH, etc.), are of the same shape (AA, PP3, etc.), and provide the same voltage. If not, the operation of the assembly can be unstable and even dangerous: in the case of LiPo batteries, they can even explode if this rule is not followed. In fact, in this type of battery, it is recommended to purchase pre-assembled packs (in series or in parallel), that offers us the guarantee that their units have been selected to have the same capacity, internal resistance, etc., and not cause problems.