I accidentally saw an article
with comments to it, and so the anger in me boiled over the illiteracy of people in the field of acid (lead in common) batteries, which could not stand it and decided to write "geeks" (to be a geek, as it turns out, it is not enough to buy an expensive phone) brief article about batteries. Consideration of the mistakes that I constantly tear off my eyes and cause the righteous desire to correct them.
Let's start with the name. I often see that in three letters A-K-B they call everything that can be charged, absolutely any battery. Especially in three letters, people like to call Li-ion type batteries. In fact, the battery is an abbreviation for the Battery Acid Battery. Under them means only one type of battery - lead acid. From the modern point of view, this name causes some cognitive dissonance. Currently, the meaning of the word "battery" i. A galvanic cell that can not be charged has passed to the word "battery". And it turns out as if due to the word “rechargeable” it is a battery that can be charged, but because of the word “battery” it’s as if the battery cannot be charged. In reality, the battery is just a circuit of electroplating cells and with the word “battery” it has only the root in common.
Next, we turn to some myths, namely the main myth - the battery for a car has some significant differences from the battery for UPS. And you can not use them here and there.
From a chemical point of view, any battery is exactly the same
. How are they arranged? Very briefly - if the battery is charged, then one electrode is a lead lattice with a paste of PbO 2
applied on it, the second is the same lattice with a paste of spongy lead. The electrolyte is a solution of sulfuric acid. In the process of discharge, PbO 2 is
reduced and interacting with sulfuric acid to form PbSO 4
. The lead on the other electrode is oxidized and again forms PbSO 4
. At the end of the discharge, we have both grid plates filled (more or less) with lead sulphate. When the battery is charged, electrolysis occurs and dioxide and metallic lead are again formed from lead sulfate. Of course, it must be emphasized here that the electrodes are not equal and you should not confuse their polarity because at the production stage, appropriate additives are added to the electrode spreads, which improve their performance properties. Moreover, additives useful for one electrode are harmful to another. In very old times, somewhere at the beginning of the last century, in conditions of simple batteries, it was likely that the battery was re-polarized by mistake or for some purpose and it worked for some time after that. The fact that it is valid now I doubt it.
Such cells in 12V battery 6 pcs, 6B - 3 pcs. etc. Many are misleading the value of the voltage on the batteries. Moreover, the values of the nominal voltage, charge, discharge. On the one hand, the batteries are called 12V (and 6V, 24V also exist, in my opinion, even 4V is occasionally found), but on the case of the same batteries for UPS, the manufacturer indicates voltage above 13.5V.
Here we see that in the forced mode the charge
voltage can be as much as 15V.
All explain the voltage curve on the battery:
On the left, we see the voltage for a battery of 12 cells (24V nominal), 6 (12V nominal) and, most useful, for one cell. There are also marked areas of unwanted voltages during discharge / charge. From the curve we can draw conclusions:
1 Voltage 12V, 24V, etc. are nominal and show only the number of galvanic cells (by dividing by two) in the battery. This is just a name for convenience.
2 Charging voltage can reach 2.5 V / cell, which for a 12V battery corresponds to 15V.
3 A charged battery voltage is considered acceptable when the value is 2.1-2.2 V / cell, which for 12V batteries corresponds to 12.6-13.2V.
Theoretically, the battery can be charged up to 2.4 V / cell or even slightly higher; however, such charging will adversely affect both the state of the electrodes and the electrolyte concentration. Once, before putting it into the scrap, I easily charged a 12V battery to a voltage of approx. 14.5B (I do not remember the exact value).
So, the author of the article with which I started, decided that the voltage of the charge of the automobile battery and battery from the UPS is different. This is not true, they have the same type of electrodes and the same concentration of sulfuric acid in the electrolyte (chosen long ago experimentally to provide the maximum voltage and minimum self-discharge). However, what is happening in the battery, why can not it be charged when the voltage is too high?
Why do I need to add water to a car battery, but I don’t need a UPS battery? These questions allow us to smoothly move into the area of stress decomposition of water. As I wrote above, when charging the battery electrolysis occurs. However, not all of the current is spent on converting PbSO 4
to PbO 2
and Pb. Part of the current will inevitably be spent on the decomposition of water, which constitutes a significant part of the electrolyte:
O = 2H 2
+ O 2
A theoretical calculation gives a voltage value for this reaction of approx. 1.2V. I remind you that the voltage on the cell when charged is obviously more than 2V. Fortunately, water actively begins to decompose only above 2B, and in the industry for the production of hydrogen and oxygen from it, the process is carried out at all at 2.1-2.6V (at elevated temperature). Be that as it may, here we come to the conclusion that at the end of the process of charging the battery, there will inevitably
be a process of decomposition of water in the electrolyte into cells. The formed oxygen and hydrogen simply evaporate from the scope of the reaction. The following myths exist about them:1.
Hydrogen is extremely explosive! Recharge the battery and at least lose the room where it was!
In fact, hydrogen in the electrolysis process is allocated negligible compared to the volume of the room. Hydrogen explodes at a concentration of 4% in the air. If we assume that the electrolysis is conducted in a room measuring 3 * 3 * 3 meters or 27 meters cubic, then we will need to fill the room with 27 * 0.04 = 1.1 meters cubic. hydrogen. To obtain this amount of H2, it would be necessary to completely decompose approx. 49 moles of water or 884 grams of it. If someone has watched electrolysis, he will understand how much this is. Or try to go to the time. When the current in the standard charge for large battery 6A, Faraday equation gives the time required to obtain this amount of hydrogen, as much as 437 hours or 18.2 days. To fill the room with hydrogen to explosive concentration, you need to forget about charging for 2 and a half weeks! But even if this happens, the concentration of sulfuric acid will simply grow until its solution acquires too high resistance for a miserable 12V charge and the current becomes insignificant. Yes, and hydrogen will simply evaporate.
Very rarely do explosions occur directly in the housings of large-sized batteries due to the fact that the released hydrogen for some reason cannot leave the confined space. But even in this case there is nothing terrible - most often an explosion is enough only for a slight deformation of the upper part of the body, but not for breaking lead compounds. And the battery can still work even after such damage.2.
When electrolysis can be formed deadly poisonous and no less explosive than hydrogen, hydrogen sulfide!
Not ours, periodically came across a myth in the English-language posts. Theoretically, of course, it is possible to apply such a large voltage and create so such a large amperage that the sulfate ion recovery process begins at the cathode. The voltage for this will be sufficient, and the recovery products will not have time to diffuse away from the electrode and the recovery will go further. But charging within a dozen or three volts and with a current limit of 6A is hardly capable of that. Once, I observed the process of reducing sulfate to SO 2
, yes, it is possible; classmates by mistake did something wrong during the experience. But it is very rare because there the concentration of sulfuric acid was noticeably higher than that used in the battery, there was a different design of the electrode and its other material and, of course, the voltage and current were exorbitant. And SO 2 is
not H 2
During electrolysis, arsenic and antimony from the grate material will be reduced to poisonous arsine and stibine!
Indeed, the lattices contain relatively much antimony, and arsenic in modern lattices probably does not exist at all. During battery operation, the grating on which restoration takes place, i.e. cathode, cannot be destroyed. Stand out even somehow stibin, he would have interacted with PbSO4, restoring it to the metal.
However, there is some practical nuisance here. Gaseous hydrogen and oxygen can
entrain droplets of the electrolyte, creating an aerosol of sulfuric acid. Aerosol of sulfuric acid, even concentrated, is not dangerous for humans and simply causes a cough. However, sulfuric acid is a nightmare for fabrics and paper. It is worth even a small amount of sulfuric acid to get on the clothes and there will definitely appear holes or the fabric will rip in this place. In a few weeks, if there is a lot of acid, in a month, but the clothes will fade.
So you should not be afraid of gas emission from the household point of view or it is worth it, but you need to focus on the sulfuric acid aerosol.
So, water began to decompose oxygen into hydrogen, is it becoming less and less in the electrolyte, what next? If it is a battery in which the electrolyte is simply poured in the form of a layer of liquid, then an increase in self-discharge will begin due to an increase in the concentration of sulfuric acid. Interestingly, this will be accompanied by a slight increase in voltage (the concentration of acid increases) on the cell. That is why car owners must constantly monitor the concentration of sulfuric acid in their battery (using a hydrometer) and add water to it. The procedure for adding water is a necessary part of the process of servicing
any battery. In addition to one of their type, and we now talk about it.
It’s of course inconvenient to have a battery in which a layer of caustic dangles with respect to metals, and therefore attempts to get rid of the liquid directly were made a long time ago, began almost in the first half of the 20th century. By the way, it’s not that the layer of sulfuric acid was directly splashing around the electrodes. In reality, it is not badly distributed between the electrodes and the separators surrounding them, even in low-cost models. So the first option was to use fiberglass. It is enough just to surround the electrodes with fiberglass which is impregnated with sulfuric acid and most of the problems will be solved. This type of battery is called AGM (absorbent glass mat) and the majority of such batteries for UPS. Although such small form factor batteries are often positioned as those that can be operated in any position, one cannot fully agree with this. Opening the lid of a standard low-cost AGM battery shows that there are no special lids, and consequently, only capillary forces hold back the electrolyte from leaking out. I’m pretty sure that if you drive an AGM battery upside down, then after one charge, sulfuric acid will flow from it under the pressure of gases.
The second common type is more interesting. gel batteries. And they turn out thanks to the following. If acidified silicates are soluble, then silicic acid will be released:
+ H 2
= Na 2
+ SiO 2
+ H 2
If the initial solution of silicate does not differ in quality, then the silicic acid will be released in the form of a glassy mass, but if it is sufficiently pure, then the silicic acid will precipitate in the form of a beautiful piece of a uniform translucent gel. This is the basis for the method of obtaining gel batteries - the simple addition of silicates to the electrolyte causes it to harden into a gel-like mass. Accordingly, there is nothing left to flow from there and the battery can indeed be operated in any position. By itself, the process of formation of the gel does not increase the capacity of the battery and does not improve its qualities, however, manufacturers use it in the production of high-quality models, and therefore these batteries are of high quality and greater capacity. It is interesting that in both cases the carrier of the electrolyte is SiO2 in one form or another.
Both types of batteries are combined into a glorious type of VRLA - a valve-regulated lead-acid battery which is used in UPS. Formally, they are considered unattended and endurable in any position, but this is not the case. Moreover, many have already met with the effect, when literally a few ml of water return to life, it would seem, a dead battery from the UPS. So it turns out, because these batteries are not a drop insured from the electrolysis of water in the electrolyte, and consequently, drying. Everything is exactly the same as in a large battery. But the most expensive and steep maintenance-free batteries contain a catalyst for the recombination of the released gases back into the water and now their case is really made completely sealed. I draw your attention to the fact that a battery of the type AGM and GEL can be truly sealed and maintenance-free, but they may also not contain a catalyst for recombination of oxygen and hydrogen. Then, despite the seemingly advanced design, the user will either have to buy new batteries more often, or add water with a syringe.
I would like to add a few words about the discharge modes. Battery manufacturers indicate which current is maximum permissible for a particular model, but you need to understand that a battery is just a mixture of chemicals and EMF is generated exclusively by chemical means. This is not a capacitor which, by electro-hydraulic analogy, can be compared with a kind of mechanical vessel (with a flexible membrane). Although batteries can produce very large values of current, in reality, they are best operated just at low currents, which is in the discharge, which is in charge. Therefore, UPS, designed for charges of small batteries, when working with large-sized will charge them in the most gentle mode. However, in the course of far from one day. It is interesting to note that the higher the power of the UPS, the more batteries the manufacturer consistently prefers to assemble. Everything is logical here - the small batteries withstand very high discharge currents very poorly.
1. Small-sized and large-sized batteries are identical in device.
2. For the vast majority of batteries of any size, adding water is a necessary part of ongoing maintenance.
3. Only a few of the expensive battery models contain a gas recombination mechanism and can be called truly unattended.
4. By itself, the hydrogen that is released during the charge (and this is equal to the constant work in the UPS) battery, is not a significant threat or problem.
5. It is necessary to work very carefully with the battery, carefully avoiding spilling even the smallest electrolyte droplets, or lose your clothes.
6. Discharge and charge with small currents are the most preferred battery operation modes.