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Sealed acid batteries - properties and applications.

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  • Sealed acid batteries - properties and applications.
    Lead-acid batteries are still present in many devices, despite the availability of modern lithium polymer, lithium-ion or supercapacitors. The affordable price of lead-acid batteries and the simple design of the charger make them a popular source of energy for both buffer and cyclic operation. Sealed lead-acid batteries do not have to work only in the vertical position (they can work in any position except for the position with the pole terminals down). Maintenance-free batteries VRLA (Valve Regulated Lead Acid - i.e. with self-regulating safety valves and internal gas recombination) occur in the technology AGM (Absorbent Glass Mat - with electrolyte trapped in a glass mat separator) and GEL (with electrolyte in the form of a thick gel). Batteries in GEL technology can withstand more cycles than AGM and have greater resistance to deep discharge, while AGM batteries can deliver higher powers and have a lower internal resistance. GEL batteries dissipate the heat generated inside them well, they will work well, for example, in renewable energy installations. AGM batteries work better at higher currents, delivering higher power, they will work well, for example, in UPS devices. VRLA batteries do not require maintenance during operation, so there is no need to add fluids to them, the risk of electrolyte leakage has been reduced and the resistance to environmental conditions has been increased. Despite their tightness, VRLA batteries must not be sealed in a sealed casing, as overcharging and improper use may emit flammable gases that may explode without proper ventilation.

    Regardless of the technology used, you can meet the colloquial term "gel" in relation to AGM and GEL batteries. Batteries VRLA / SLA they come in different sizes (and capacities), the voltage usually specified as 6V (three cells) or 12V (six cells). There are also batteries with a voltage of 2V and a capacity of several hundred Ah (or even 1000Ah), intended for series connection into larger units. The stated battery capacity relates to specific operating conditions (e.g. discharge time, temperature), usually the given capacity relates to a discharge within 20 or 10 hours. Battery capacity will be different from the nominal for faster discharge (it will be lower for higher currents). Capacity is usually marked with the letter C and expressed in Ah.

    Operation - cyclical and buffer operation.
    The cyclical operation of the battery consists in its cyclical charging and discharging, e.g. in vehicle drives or energy storage systems obtained from renewable sources.
    In the case of buffer operation, fully charged batteries wait for a power failure, allowing for continuity of power supply to the loads (UPS, buffer power supplies, emergency lighting).
    VRLA batteries can be charged with an appropriately adapted charger, taking into account the charging current (usually 0.1C20HR, i.e. 10% of the (twenty-hour) capacity), limiting the charging current to 0.1C should ensure good battery life. For example, a 45Ah battery should be charged with max. 4.5A to keep long service life. VRLA batteries should not be charged with a current greater than 0.3C, the charging process will be faster, but the battery will wear out faster.
    In more advanced charging systems, the temperature of the batteries is taken into account, and techniques are used to increase the battery life (e.g. discontinuous charging in the case of buffer operation).
    Some manufacturers have products dedicated to buffer or cyclic operation, others provide universal batteries that should be charged to voltage for buffer operation. 13.5-13.8V (2.25-2.3V / cell), and for cyclic operation 14.4-15V (2.4-2.5V / cell).

    The conserving voltage for a single cell depends on the ambient temperature:

    Voltage V / cell temperature C battery voltage "12V" battery voltage "6V"
    2.35 0 14.1 7.05
    2.33 10 13.98 6.99
    2.27 twenty 13.62 6.81
    2.25 25 13.5 6.75
    2.23 35 13.38 6.69

    Cyclic charger should stop charging after reaching the assumed voltage threshold. You can see a drop in battery voltage when charging is interrupted. After 24 hours of resting the battery, you can determine the degree of its charge by measuring the voltage at the terminals.

    State of charge voltage V / cell voltage on the battery "12V" battery voltage "6V"
    100% 2.15 12.90 6.45
    80% 2.09 12.54 6.27
    60% 2.06 12.36 6.18
    40% 2.02 12.12 6.06
    twenty% 1.97 11.82 5.91

    For buffer operation, manufacturers offer battery models with a lifetime of ~ 5l, 10-12l, as well as specialized 15-20l. Recommended operating range for buffer operation is 20-25 C.
    For cyclical operation, some manufacturers provide an estimated number of cycles that the battery should withstand, but the actual number of cycles depends on the depth of discharge in the cycle (the shallower the more cycles can be achieved) and the temperature (the higher the battery, the shorter its lifetime).
    The battery can be discharged in cyclic operation in the temperature -20-50 C. Both low and high temperatures have a negative impact on the lifetime and parameters of the battery, one should take into account the capacity (low temperature) and lifetime (high temperature) limitation.

    For unused batteries, it is recommended to charge them once every 6 months, which allows you to compensate for self-discharge. The mentioned 6 months is the minimum time of keeping 50% of the stored energy at 20 C, for 30 C the time to the next charging is reduced to 4 months, and at 40 C 2 months.

    Storage time temperature
    6 months 20 C
    Four months 30 C
    2 months 40 C

    Batteries operating in series connection should be "equalized", that is, come from the same source and production period, have the same service history, and thus have similar internal resistance. The entire set of batteries in series should be replaced.

    Depending on the capacity, the batteries can be equipped with terminals in the form of "slides" or screws. When fastening with a thread, pay attention to the tightening force, indicative

    Diameter Thread pitch (mm) Screw tightening torque (Nm)
    M5 0.8 2.0-2.9
    M6 1 4.1-5.2
    M8 1.25 8.2-9.9
    M10 1.5 14.7-19.2

    During assembly, be careful not to lead to a short circuit. Resistanceinternal of the battery is very low (several to several dozen m?), the value of short-circuit current can reach several hundred A or even several kA (with higher battery capacity). In the case of series connected battery packs, the total voltage can be life-threatening.

    Final discharge voltage.
    The VRLA battery cannot be discharged "to zero". Often you can come across a voltage cut-off value of ~ 10.5V for a "12V" battery (1.75V / cell). Such a voltage value is usually set by the systems protecting the battery against excessive discharge. A discharged battery should be charged immediately so that it is not stored in a discharged state.
    In the event of a complete discharge, the sulfation of the plates is significant, which significantly increases the internal resistance of the battery. Fully discharged battery should be charged with a voltage of 2.27 V / cell with a current not greater than 0.1C20 in order to avoid excessive heating. The minimum charging time should be 96 hours.

    Cut-off voltage 10.5-10.8V for the "12V" battery it is a good generalization, allowing for example to build a module protecting the battery against excessive discharge. If we have control over the discharge rate of the battery, we can precisely control the cut-off voltage.

    Cut-off voltage V / cell Discharge time battery voltage "12V" battery voltage "6V"
    1.60 up to 15 minutes 9.6 4.8
    1.65 up to 1h 9.9 4.95
    1.70 up to 5h 10.2 5.1
    1.75 up to 8h 10.5 5.25
    1.80 up to 10-20h 10.8 5.4

    It is worth looking at the documentation of your VRLA battery, it will allow you to select the optimal operating conditions for the device.

    In which projects do you use VRLA batteries, what undisturbed parameters are important to you?

    Material prepared in cooperation with the company volty.pl

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  • #2
    Level 14  
    Editor, my sealed batteries have been pole-down for three years. Next to them are the batteries that work in the standard position, i.e. with the poles at the top. These batteries work under the supervision of an electronic system that protects against short-circuit, excessive discharge, overcharging and overvoltage, supervising the capacity of each single battery. Conclusions: sealed batteries can also work with the leads of the poles downwards and this does not affect their operating parameters.
  • #3
    Interesting confrontation of practice with theory, as you can see, what is not recommended sometimes has a chance to work properly under certain conditions.

    @dolby are these VRLA batteries AGM or GEL?

    What forced the reverse assembly? case size, original device wiring?

    How is the capacity of each battery monitored?
  • #4
    Level 37  
    VRLA is not mounted with the terminals facing down due to their design. These are not fully sealed Li-Ion batteries.

    Under the cover there are recesses with projections with rubber caps attached. The increasing pressure inside the accumulator causes the gas to escape through the rubber band (which acts as a one-way valve) and is discharged through narrow channels into the environment. The entire magic absorbing mat is a piece of felt around this "valve" to absorb any small leakage.

    Now any position other than the terminals down ensures that any electrolyte, which is very little there, will not leak out. On the other hand, with the terminals down, any electrolyte accumulates in the rubber of the "valve" and pushes out of the electrolyte cell chamber by the resulting gases.

    Recently, I broke my teeth on batteries. Without going into details, as a curiosity, I will add that a short circuit of the battery, in particular VRLA, will not cause an explosion. Usually, the internal link between the cells will burn (but a fire from the battery hardware may start).
  • #5
    @mkpl the described short-circuit protection (fire protection in principle) is similar to those used in Li-Ion (a soldered metal spring / plate that pops off and disconnects the circuit when heated). Although after such a short circuit, the VRLA can be thrown out, but the risk of setting fire to the surroundings is limited.
    Usually in the charging / load circuits there is a fuse limiting the short-circuit current of the battery, also this internal protection can be treated as a gradation of protection, protection against short-circuit e.g. to a metal housing.
  • #6
    Level 37  
    @TechEkspert I will worry you there is no such thing in the battery itself.

    I did destructive tests on small batteries up to 18Ah, which were subjected to full short circuit at the level of internal resistance and the lead connector between the cells was always blown. The battery, of course, still had a charge in it, which after dismantling could be taken (about 2V for the purpose). The second experiment assumed such a short circuit not to exceed the breakdown current of the switch. The battery gave all the energy to "0" and only after discharging it began to emit heat. He warmed up to 70 * C and swollen.

    Wet acid batteries are more dangerous in this respect. In such an experiment, they evaporate profusely. A well-designed battery has the capacity of the "plugs" for this eventuality. Otherwise it could explode the battery. The explosion due to ignition of gases in the event of discharge will not occur because it is only water vapor.

    At the same time, it should be mentioned that each battery should have a fuse for the appropriate current, matched to the parameters of the collection system. Ie wires and devices. Otherwise, in the event of damage, the cables and the device will be powered by the source of fire.

    I will also mention that we do not use fuses like this:
    Our device uses a current of 5A and if something is damaged, it will take 30A, so we will use a 20A fuse. The 20A fuse at 30A will burn for an hour ...

    The value and type of the fuse are calculated from the Joule integral that the circuit is able to safely take over.

    Overall, the subject is wide and I could write about it for hours, so I will stop at this point :) and I will answer any specific questions you may have.
  • #7
    So the internal connections can disconnect the current (for the tested type of batteries 18Ah) in the event of a short circuit, e.g. to a metal housing, short circuit in a power socket, etc. cases where the resistance of the short circuit loop is very low.

    You have provided a useful observation regarding a lower current short circuit:
    "The second experiment assumed such a short circuit not to exceed the burnout current of the switch. The battery gave all its energy to" 0 "and only after discharging it began to emit heat from itself. It heated up to 70 C and swelled."

    "Wet acid batteries are more dangerous in this respect. In such an experiment, they evaporate abundantly. A well-designed battery has the capacity of drainage of" plugs "for such an eventuality. Otherwise, it would cause the battery to explode. The explosion due to ignition of gases in the event of discharge will not occur because it is only water vapor. "

    Have you carried out tests with simulated charger failure and overcharging of the battery?
    In addition to the aforementioned gassing and possibly electrolyte discharge to the "absorbing mat", have there been any other dangerous effects (eg risk of gas ignition?)?

    I had the opportunity to come across a module of a liquidated power plant, the module had a set of gel batteries working in series (4 units with a capacity of several dozen Ah + a buffer power supply with a power of several hundred watts). torn out and deformed (wavy) upper parts of the housing (swelling "sideways" was difficult because the space was limited by the module housing). There was no break in the serial connection (in the sense of complete disconnection, e.g. by burning the connections), the charger reported a charging error and the voltage on the battery pack was ~ 10V instead of> 50V.

    The whole thing was already out of service and I did not have the opportunity to do more detailed research. I wonder what could have caused such damage: short circuit on the battery pack / overcharging / blocking the vents or damage to the fans and overheating with the buffer power supply?

    The question of selecting fuses is actually a separate topic, often the term "10A" fuse may be confusing to a person who is just starting to research this topic.

    Here, a very basic test showing the operation of a fuse with a value much lower than the aforementioned 30A, an test with a current twice as high as the symbol on the fuse.
  • #8
    Level 37  
    As I wrote, it can be different with these fuses. Manufacturers produce several types, e.g. 4F fuse (4A fast). They differ only in their catalog number and, most importantly, in the Joule integral (I ^ * t) that I describe. It determines the amount of heat needed to blow the fuse. This value depends on the current in time according to the previously mentioned formula i ^ 2 * T. As can be seen, for small current values, time has a significant influence, but with larger overloads the current plays an increasingly important role.

    I think that fuses are a topic for a separate article because you can write a small book about them :) .

    When it comes to overcharging, VRLE batteries are damaged by swelling. Balloons are made of them and that's it. The risk of electrolyte leakage is very low. Absorbent mats are only slightly damp (electrolyte is minimum). There is no "free" liquid electrolyte there to run out (in classical understanding of a battery leak).

    Therefore, any attempt to "add" water above the plates to such a battery, according to the descriptions available on the Internet, is a trap. It damages it irreversibly. The water evaporates from them, of course, and this is related to the storage conditions of the battery. But in order for the water to escape into the atmosphere, the battery needs to be heated up so that the steam pressure overcomes the bleed valve I described in previous posts.

    These types of batteries wear down by transferring material from the plates to the parator (electrolyte-soaked separation mats).

    In the case of wet batteries, an explosion is very real, they contain a large amount of liquid electrolyte (which also translates into a much lower internal resistance and a much higher current), which will boil and break down chemically when overcharged, creating highly explosive vapors.

    In the case of UPS, where there are batteries connected in series of 20 pcs, shorting one cell or even disconnecting one battery from the series does not cause any damaging effects. The batteries will take over the excess voltage and will wear out sooner.
  • #9
    Level 28  
    TechEkspert wrote:
    The question of selecting fuses is actually a separate topic, often the term "10A" fuse may be confusing to a person who is just starting to research this topic.

    Therefore, you should first follow the golden rule: "Read That Fine Manual" (RTFM for short) - normal fuse manufacturers indicate for which currents, how the fuse operation time is shortened and sometimes what is the influence of temperature. Generally in most cases at 25 C the breaking current is around 2x the rated current and the time goes in seconds. But the temperature also does its job - the fuse burned in with the rated current will burn faster than the one that was cold when switching occurs.

    When charging acid batteries, remember that with increasing temperature, the maximum voltage in which gassing and / or overheating occurs drops. Therefore, it is dangerous to use CC / CV chargers for lead acid batteries and high current charging.

    Added after 4 [minutes]:

    mkpl wrote:
    As I wrote, it can be different with these fuses. Manufacturers produce several types, e.g. 4F fuse (4A fast). They differ only in their catalog number and, most importantly, in the Joule integral (I ^ * t) that I describe. It determines the amount of heat needed to blow the fuse. This value depends on the current in time according to the previously mentioned formula i ^ 2 * T. As can be seen, for small current values, time has a significant influence, but with larger overloads the current plays an increasingly important role.

    Exactly yes, but you need to remember about such a parameter as the breaking capacity - that is, the current (usually very large) above which the given I ^ 2 * t does not work and the shutdown takes longer.
  • #10
    Level 37  
    @OldSkull CC / CV is an accelerated loading method and if used properly it is safe. What's this all about:

    Classic charging with 10-hour current is charged all the time with 0.1C current forcing the battery and after some time disconnect the battery. It is safe because it is the battery that forces the final charging voltage and the charging time.

    Buffer charging is charging with a DC voltage source, the value of which is dependent on the battery voltage versus temperature curve. The charging current limitation is 0.1C, which is classic.

    Accelerated loading eliminates the problems of classic and buffer loading. The point is that the battery, reaching the buffer voltage, is less eager to consume the current, which decreases with the degree of charge, which significantly extends the full charge.
    Accelerated charging is done in such a way that the battery is charged with a current forcing of 0.1C to the floating operation voltage (taking into account the temperature). At this point, the battery current begins to drop and, below a certain threshold, a permanent voltage source is connected with a value according to the ambient temperature.

    It is difficult to explain it with the text, charts would be useful, but unfortunately I have nothing at hand.
  • #11
    Level 38  
    On the occasion of the topic, I will ask about something that I once observed. Worn-out AGM battery (voltage below 8V, practically no current) and plugs in it. It was visible (cork lid concave), and when removing the cork with the pliers you could feel a slight force holding it.
  • #12
    Level 37  
    It is difficult to predict what happened in the battery. This is chemistry and has its own rules (sometimes an electronic person has a hard time understanding it)

    I suppose the battery was charged cyclically with 0.1C current for 10 hours. After the loss of capacity (decrease to 50%), it was gradually reloaded to the capacity it should have nominally, which resulted in gassing and heating. After the "exposure" ceased, the gases condense and the pressure in the cell dropped below atmospheric pressure.

    A similar situation could occur when one of the cells is damaged, during charging it causes overcharging the others and when discharged it lowers the voltage of the battery which then seems to be discharged.

    It is difficult for me to determine exactly what could have happened without looking at the battery, but I would bet on one of the above.
  • #13
    Level 28  
    @mkpl Yes, I know what's going on, but the problem is when the charger doesn't know what temperature the battery is at. I encountered a situation where the charger gave over 0.25C and even had a built-in smart cut-off algorithm that was supposed to detect that the battery is less willing to accept current - and switch to another mode. The problem was that before this happened, the battery was warming up to such a temperature that its maximum voltage dropped significantly - so much that the algorithm failed. Effect? Hundreds of swollen cells around the world.
    And the problem would not be at all if the battery was cooled or the charger measured the temperature of the cells instead of its surroundings. So applying voltage due to the ambient temperature is not enough.
    I am writing to warn people against mindless loading.
  • #14
    Level 37  
    I have seen situations when the batteries were charged directly from the mains. People do such systems (the voltage in the network is stabilized). I do not trust it, but I also do not play UPS with several kW. Up to 3kW, Mean Well inverters can be used in 24V systems with appropriate power supplies. Such systems are the object of my professional work and in such cases I can express my opinion.

    The battery is a component to be used with awareness, including all applications and their disadvantages. Despite its simplicity of operation and application, I believe that most beginners should consult with experienced people on this matter. Lack of literature and appropriate knowledge is unfortunately a problem that cannot be overcome in a simple way and the topic itself is quite dangerous.

    For my part, I would like to say that a "festive" one-time recharging of the battery with electricity and even 0.4C will not do him much harm. It is more important to monitor the floating operation voltage. This can cut battery life by up to half.
  • #15
    Level 21  
    I have 2 questions about the above. batteries:
    1) The text includes a table for assessing the battery charge based on the daily voltage drop. How does this relate to several years old batteries with a significant decrease in capacity? For example, I have a battery with a factory capacity of 100Ah, after a few years its capacity is 60Ah, from the table I can read its 60% charge. The question is whether I have 60% of the factory capacity, i.e. 60 Ah, or maybe 60% of the reduced value, i.e. 60% * 60Ah = 36Ah

    2) Caution against charging frozen batteries, what values are alarming? i.e. below what voltage and below what temperature should special care be taken?
  • #16
    Level 37  
    Ad.1 Of course, the charge level depends on the current state of the battery. For new, the capacity has a tolerance of -20 / + 5%

    Ad.2 It is absolutely forbidden to charge the battery below 0 C, in practice it is safe to 10 C (these values do not apply to car batteries).
  • #17
    Level 11  
    Hello dear colleagues,

    The lead battery is our old friend from the car. Construction, operation and diagnostics known for years. We have also known its weaknesses for years (large mass and rapid degradation of cells if we leave them discharged for some time). For electronics, it is an energy store to power his devices.

    Importantly for the storage of renewable energy:
    to remove 1 kWh from the lead battery, insert approx. 1.6 Ah during charging.

    Each cell is an individual electrochemical "kitchen", during charging and discharging, the cell temperature rises, the cell voltage reaches the threshold voltage above which forcing the current flow no longer transfers ions and begins to decompose water from the electrolyte into oxygen and hydrogen.

    In most of our applications, we need supply voltages much higher than 2 V. A traditional car is 12 and 24 V, the telecommunications world uses 48V, UPSs of higher power are already in the area of network voltages of 300-600 VDC.
    Lead acid battery cells are connected in series. Unbalances in capacity and the state of charge are compensated by intensive overcharging at low current intensity, and the resulting water losses are filled up manually or automatically.

    In the second half of the last century, a fantastic and user-friendly and environment-friendly technical solution appeared. The electrolyte was bound in glass felt or gel, and seasoned with additives facilitating recombination, i.e. reverse conversion of the resulting gases into water. Everything is closed in a sealed chamber equipped with a pressure relief valve (hence the name VRLA). It is enough to swallow the distributor's marketing fairy tale and we become convinced that we have the perfect battery.

    And these are really good batteries!
    But the practice of their operation, especially when charging, requires discipline and does not tolerate exceeding temperature-dependent charging voltages.

    And now, my dear colleagues, I am going to share with you some of my modest experiences with VRLA batteries.

    As soon as the Optima batteries appeared in Poland among the technological innovations (coiled cells in the fight against the AGM electrolyte / glass wool), when I had some free money, I bought my father an Optima for a small Toyota bus. The feeling was amazing, even in winter with frosts of minus 15 degrees, this battery spun the cold diesel engine like a fan. Something amazing. We have already got used to the fact that it always fires. After a year or so, the battery died (ran out) overnight. Traditional charging with voltage from a typical alternator slowly, insidiously and silently deprived the electrolyte of water!

    Later, for a few years I dealt with servicing and diagnostics of stationary batteries. It was then that new technologies were poured out in our area and closed batteries appeared. So my life forced me to switch from the "trumpet - pump and jack" technology (full charge, electrolyte density test, water refilling, full battery discharge control, recharging, control, adjustment and repair of buffer power supplies) to technologies and new knowledge giving the possibility to control over a new type of battery.

    It is practically impossible to add water to this type of accumulator! If we have a series of cells or battery blocks on a rack and some of them are near the radiator or air conditioning or the sun shines on a part of the row in summer, then there will be an asymmetrical distribution of cell temperature in the series being charged.. And then our battery will get a virus called "Thermal run away". The voltage thresholds above which the cell will begin to decompose the electrolyte water decrease with increasing temperature. Even with a perfectly symmetrical distribution of charging voltages on the cells, these cells or this one "black sheep" a bit warmer, on the principle of positive feedback, it will start to heat up even more, the electrochemical threshold voltages will drop even more and the weakest cells start to diverge more and more in parameters . Until then, this phenomenon of symmetry of cells / rechargeable batteries in the battery is not showing any symptoms. Well, we even have a slight margin for self-correction, because with a very low equalizing current (C / 50 - C / 100) and fairly operating overpressure plugs, the buffer power supply is able to pull up "laggards", some of the asymmetrically appearing gases will "return" to the electrolyte .

    With an already asymmetrical situation between the cells, intensive and deep cycles, e.g. traditional diagnostic discharge to determine the battery capacity, and then intensive full charging can completely delete a working battery the next day!

    With old type buffer power supplies, it is worth measuring the pulsation level at the output of the power supply (AC component). All peaks above the threshold voltage can now initiate gassing. I had a case in a heat and power plant, where 220V gel battery batteries died regularly despite theoretically correctly set and measured charging voltages with multimeters. The power supply was French, the documentation was also in this language and it was not noticed during the installation that the A output was powered by a three-phase rectifier bridge (and it was powered by batteries), and at the B output (to receivers) there was an additional half-tone inductor blocking pulsations. I caught it from the device schematic, swapped the outputs as intended by the designer and the AGM batteries stopped raining.

    Battery manufacturers' specifications show the battery life dependence on temperature in the form of a curve resembling a Gaussian bell curve. The declared and promised service life can be achieved only when maintaining the optimal buffer voltage (corrected according to the temperature). Above or slightly below the battery life drops quickly.

    How is it in practice?

    My subjective observations are as follows:
    I had a period of time when in the country a bit further south of us (on average 5-10 degrees warmer) for a few years serviced battery batteries and installed there very cultured buffer power supplies from the Warsaw Medcom (with temperature compensation of battery charging voltages). The local cement plants, like ours, were swallowed by the Germans and blindly transferred the German practice and settings of buffer power supplies and charging in industrial ups. And when it happened in Datenblatt that there had to be so much Volt, then as much or a bit more in banking was set up. Supply voltages as for the German climate, and operating temperatures on average 10 degrees higher. The result was frequent replacement of entire batteries. It was enough to lower the charging voltage properly and the batteries suddenly regained their useful life and the client was convinced of my knowledge.

    And a similar observation, but the other way around: I was servicing somewhat exotic industrial UPSs from Israel. Completely different technical mentality, a bit clunky design, but very solid workmanship and significantly lower charging voltages. They just left a much larger margin of voltage tolerance for the asymmetry between the cells. So only theoretically, they consciously moved away from the optimal battery life towards lower voltage levels, obtaining a much greater reserve for asymmetries in charging voltages! And yet in the banking and insurance industry, Panasonic brand batteries with a 12-year service life are replaced with new ones every year!

    There is one more important thing to remember when working with VRLA batteries. For a technician, a battery is primarily its capacity, recommended charging parameters, and sometimes its service life given in duty cycles. Everything else supporting the operation and obtaining these parameters was previously done solidly according to good engineering practice (solid housing, connections and internal connections, reliable plugs / pressure relief valves).

    I got to know the gel batteries through the traditionally designed Sonnenschein batteries (They probably even added gel to the fillings to the A600 family gel cells, the valve plugs were unscrewed, when at night the Bester rectifier in melex boiled the entire electrolyte, I could experiment with adding water and the battery came back to life) and Deta traction batteries (engineers from the German Deta talked proudly about the production of batteries for all Ubots and for Deutsche Telekom).
    And then the roller of globalization came and leveled it. The future global company and battery manufacturing had to undergo a slimming value analysis. The technical value system had to conform to the cash register management and the creators of marketing legends.

    What has this changed in my service practice?
    "standing or lying ..." The battery is now designed for a specific product life cycle. When it is new, it has capacity and works, but ... the redundant metal has been optimized from the internal connections. Whether it is working or not, ordinary chemical corrosion will eat them, well, maybe when it is under the optimal buffer voltage all the time, a bit slower.
    The ability to maintain a positive pressure to support water recombination is very important, but if you dear colleagues see the current "excess pressure valves" in VRLA batteries (eg a small condom with a cracked black rubber on the plastic end of the tube), the operation of this solution becomes questionable.

    I set the charging voltages lower than the optimal ones according to the specification (e.g. 13.6 V for 12 V batteries) It often happens that the batteries inside the ups swell and can only be removed in pieces. This is the effect of an increased temperature in a cramped chamber, the Thermal run away phenomenon accelerating a catastrophe, drying out and overheating of already dry batteries.

    The American company Midtronic was one of the pioneers in non-invasive diagnostics of VRLA batteries. It was found that the conductance, i.e. the cell's conductivity (Siemens unit = 1 / Ohm), is approximately 80% concurrent / correlated with the total surface area of the plates and the state of the electrolyte, i.e. with the capacity expressed in Ah that can be removed from the battery. Of course, the values measured in this way also depend on the temperature, state of charge, etc., but in the field, with a specific battery, it makes it possible to quickly detect asymmetry and cells "after transitions".
    Practically, these are dedicated devices for measuring resistance in the mOhm range with DC insulation, so that the cell voltage does not falsify the measurement.
    It was difficult for me to negotiate with Midtronik,so I bought a dedicated Hioki instrument back then and during all my years of active work with lead batteries, I always had it in my car. After a few years, my own database of measurement values allowed for very quick and reliable battery diagnostics without discharging them.

    What can I advise on how to use VRLA batteries today?

    An analog solution of a good VRLA battery charging algorithm is the Unitrode (now TI) UC2906 chip, already with temperature compensation of the charging voltage.


    Application note very briefly and specifically presenting the current knowledge on how to charge VRLA batteries


    On any of the popular digital controllers, the algorithms presented in the above links can be easily applied to control a smart charger. It is important that the temperature sensor is pressed against the battery housing and covered with thermal insulation from the outside.

    best regards

  • #18
    Administrator of HydePark
    A very interesting article. I already knew a lot on this subject, but I must admit that you shed new light on my knowledge. I also learned a few little things.

    Fules wrote:
    Fallen batteries inside the ups swell and can only be removed in pieces

    I know something about this. In fact, I do not deal with UPSs above 5kVA, but more than once I have drilled rivets or even cut the housing to get out the batteries that have swollen and "filled" the construction holes :)

    Best regards.
  • #19
    Level 37  
    I will still develop how such Hioki measures (such an algorithm has many fire protection power supplies).
    It is a sinusoidal wave generator which forces a 1kHz current into the battery through a series capacitor.
    The voltage on the battery is measured (AC selectively 1kHz) and the current in the series resistor sewn in the device (also selectively 1kHz). Simple and it works great.
  • #20
    Level 10  
    CMS wrote:
    A very interesting article. I already knew a lot on this subject, but I must admit that you shed new light on my knowledge. I also learned a few little things.
    Fules wrote:
    Fallen batteries inside the ups swell and can only be removed in pieces

    I know something about this. In fact, I do not deal with UPSs above 5kVA, but more than once I have drilled rivets or even cut the housing to get out the batteries that have swollen and "filled" the construction holes :)
    Best regards.

    I would like to add something to the battery life in cyclic operation. I have (or rather had) SSB-SBL 200-12i (VRLA) batteries connected in series to power lighting / sockets via an inverter. They were charged cyclically from photovoltaic panels. Working temperature - attic 15-30 degrees depending on the season. The batteries lasted 2.5 years of operation and then stopped holding voltage. The charging voltage was regulated by the Stecy Tarom 4545 regulator - about 27V for charging and slightly less for maintenance (floating). The protection against deep discharge was a limit on the inverter, which put it into stand-by mode at 22V. I do not recommend VRLA batteries for cyclic operation, max 800 cycles and drop dead. Similarly, in the company I work for, we use AGM 12 V 7Ah "long life" batteries. On average, 3 years of service life and to be replaced at the nearest service point. If I were smarter, for the same price I would choose wet batteries and topping up electrolyte once a week.
  • #21
    Level 30  
    Wet is a very wide range. Traction batteries will work best.
  • #22
    Administrator of HydePark
    When it comes to inexpensive and good batteries, look for SSBs with green lettering.
  • #23
    Level 38  
    CMS wrote:
    When it comes to inexpensive and good batteries, look for SSBs with green lettering.

    I have two 90Ah in a 12VDC installation. Source - Astec power supply modified to 13.8V, batteries connected in parallel, buffer. About two years of work without fear. From the same series, two 18Ah units under the APC Smart-UPS 700 UPS died halfway through the same time. At the beginning, I calibrated the UPS and the backup time was more than 90 minutes, now it is not even 40. However, I blame the UPS, which charged the batteries with too high voltage. Either way, I won't be buying any Vipow inventions, just SSB SBL with an 'i' at the end :)
  • #24
    Level 12  
    Hello, I asked a question under the video but I couldn't get the answer so I wanted to ask that question again here. Or maybe someone has knowledge about what safe current can be used to discharge batteries? Yes, I know it can depend on many things like manufacturing technology, capacity etc. I'm just wondering how you deal with it, is there any sweet measure like 0.1C loading, or are there any tables with generally accepted values for that?
  • #25
    Administrator of HydePark
    It all depends on the type of battery. For some it will be fractions of C, for others it will be tens of C.
    It is best to look at the catalog note of a specific battery.