What are lead-acid batteries used for?

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Things to know about charging batteries

 

Lead acid batteries (lead acid, AGM, gel, etc.)

In our mobility behavior, batteries are becoming more and more important as electricity storage. They guarantee us independence and comfort.

This text is intended to provide information on how and with which sources batteries can be charged. Even if the primary focus is on lead batteries, other battery types are also described.

Lead-acid batteries are still the most common.

 

!DANGER!

Improper handling of batteries is dangerous and can lead to property damage and personal injury. Always use fuses as close as possible to the battery terminals and only use open lead-acid batteries in well-ventilated rooms.

In any case, the manufacturer's safety instructions must be observed.

 

 

How the battery is used

Basically, the battery systems can be divided into two different types of use. Accordingly, the charge is also different. Of course there are also mixed forms.

 

Battery in standby mode (buffer mode, float mode)

Typical applications are uninterruptible power supplies, emergency lights, battery-backed alarm systems, sliding doors, etc.

The battery is charged most of the time and is also attached to the charger. In special situations, the battery has to provide its energy in a relatively short time. Then it will be reloaded.

Since the battery is almost always charged, the charging voltage should not be selected too high. With a 12V lead-acid battery, the charging voltage is between 13.6 and 13.9V.

Batteries for general use (also called universal batteries) or batteries specially optimized for UPS systems are generally used for this application.

With these batteries, it is not the number of cycles but the expected service life in years that is an important criterion.

 

In most standby applications, electricity is drawn from the consumers while charging. This means that a current flows from the charger directly to the consumer. Classic chargers are therefore only partially suitable for this application. With most chargers, the battery is first charged to approx. 14.4V during the full charge cycle until the charging current falls below a defined value. If the consumer current is higher than the defined 'cut-off current', the charger remains fully charged at 14.4V. This can shorten the life of the battery.

So-called buffer power supplies are used as an alternative to the charger. These keep the battery at the usually adjustable charging voltage for float operation.

 

You can find more information at http://www.maurelma.ch/USV.htm or http://www.maurelma.ch/batterien.htm

 

Battery in cycle operation

Typical applications are electric vehicles, solar systems, mobile devices, etc.

The battery is fully charged and then discharged again, thus going through a cycle. With the solar system in the holiday home, for example, the battery is charged by the solar modules during the week and discharged again at the weekend.

In an electric vehicle, the battery is charged overnight and then discharged again while driving.

 

The classic chargers are suitable for cycle operation. The end-of-charge voltage for the 12V lead-acid battery is between 14.4 and 14.8V.

If the charger remains connected to the battery for a longer period of time, the charger must reduce the charging voltage when the battery is fully charged. It is even better if the charger can switch to pulse charging, as is the case with the Victron Energy chargers.

 

Mixed operation

The boundaries between standby operation and cyclic operation of the battery are not always so clear. In a car, the starter battery is more of a standby battery. In a truck, which also has a number of consumed batteries when the engine is not running, cycle operation is already approaching.

 

In an island system, in which e.g. a water turbine mostly covers the electricity requirement, the battery is more in standby and the battery voltage should be reduced a little.

 

 

Cycling batteries

Newly filled lead-acid batteries often still have not the full capacityt. This is because the battery fluid doesn't hit the plates anywhere optimally wetted or the fleece has not yet optimally saturated Has. With the first charges, the capacity even increases, sometimes even beyond the nominal capacity specified by the manufacturer.

If full capacity is required from the start, it makes sense to charge and discharge the battery a few times before using it for the first time. This is then called cycling.

This is used, for example, in batteries for electric wheelchairs or senior scooters. There you want to have the full range on the first exit.

 

Cycling the battery can also make sense before batteries are connected in series. Since the capacities can be quite different before the first cycles, the batteries are connected in series and charged differently, which can massively shorten the service life.

 

The cycling can be done in a simple way with a capacity measuring device, which measures the capacity of the battery by charging and discharging.

  

 

Charging characteristics

Every device, whether charger, charge regulator, alternator or fuel cell, which controls the charging of a battery, has a characteristic. This characteristic curve indicates the criteria according to which the charging current should flow. A not correct stored or set curve can to failure the battery or even the connected equipment to lead.

If, for example, a GEL battery is charged with the characteristic curve of an OPzS battery, the GEL battery suffers very much from overvoltage and an early failure is inevitable.

 

IU characteristic

Chargers, charge controllers or alternators with this characteristic curve first charge the battery with the maximum for the device Current [I]. The current is usually constant except for the alternator, where it is also dependent on the speed of the alternator itself.

When the battery dies End of charge voltage [U] reached, this is always held or for a certain period of time and the charging current is reduced.

If only the designation IU characteristic is given, it is not clear what happens after the end of charge voltage has been reached.

 

Inexpensive small chargers, especially for Li-Ion batteries in the drive area, e.g. switch off the charge completely after the end of charge voltage has been reached. In addition to the end-of-charge voltage, the switch-off criterion is when the charge current falls below a predefined value. This Cut-off current will also be Cut OFF Current called. With Li-Ion chargers, this current is often set to 5% of the nominal current.

 

Alternators (alternators) or, in some cases, parallel charge controllers for small hydropower plants hold this voltage after the end of charge voltage has been reached. The advantage is that electricity consumed by consumers can be delivered again immediately.

The disadvantage is that the battery is either always operated at a relatively high voltage and thus loses water, or is charged too deeply and a sulphate layer can form.

 

 

IU0U characteristic

Devices with this characteristic behave similarly to the devices with the IU characteristic, only these devices do not switch off but on one lower end-of-charge voltage. For example, a 12V lead-acid battery is first reduced to 14.6V and after a certain time or below the Cut OFF Current to 13.7V.

This characteristic curve can often be found in price-optimized chargers that are supplied with battery-operated applications. Even small chargers for Li-ion cells often work this way.

This characteristic is also programmed into many solar charge controllers. It is advantageous if the characteristic curve in the values ​​of the charging voltages U0 and U can be adapted to the battery used.

With this characteristic curve, load units can be built, which too parallel to the consumer can be used. That means the charger (or charge regulator, etc.) feeds the consumer and charges the battery at the same time. The Switching from U0 to U via one timer and not just via the Cut OFF Current. There should also be no timeout for the main charging phase and charge retention.

 

Mostly it is with these charging characteristics poorly described, Which criteria must be fulfilled that again a Main charging phase to the higher charging voltage.

 

The IU0U characteristic is quite good-natured. If the charging voltages are reasonably correct, the battery will be charged properly.

 

 

IUI0U characteristic

Typical characteristic curve for charging traction batteries (drive batteries).

Again, first with one maximum charging current loaded until the End of charge voltage is reached.

After that, however, it is not simply lowered to a lower float charge voltage, but it is continued over a certain period of time with a predetermined one constant recharge current loaded. The charging voltage can rise higher than the end-of-charge voltage.

 

!DANGER!: 

If the parameters of this characteristic curve (final charging voltage, in particular recharging current) are not matched to the battery, the battery can be used within a short time get damaged. Particular attention should be paid to GEL batteries or AGM batteries. If the end-of-charge voltage is too high, these batteries will sooner or later fail. Open lead-acid batteries are less sensitive. Too large a recharge current, respectively. Charging voltage leads to the battery gassing and thus to a loss of water. This loss of water can be compensated for with distilled water.

 

Ri characteristic

The Fronius company has developed a charging algorithm for the larger traction chargers, which is based on the internal resistance of the drive battery.

 

 

The condition of the battery is determined based on the internal resistance.
The charging characteristic is adjusted depending on the age, temperature and state of charge of the battery. The optimum current is supplied to the battery in every charging phase. Each individual charging cycle is therefore unique with an individual characteristic. By adapting the current to the battery, charging losses can occur at the beginning of charging as well as in the reload phase. The battery only gets the power it really needs, so the new Ri charging process guarantees the coolest and gentlest possible charge. This ensures maximum battery life.

 

Serial charge regulator

The serial charge regulator is used in photovoltaics. Here it is also known under the name of solar charge controller or solar battery charge controller. It is placed in series with the battery. As long as the battery is charged, the solar module is simply connected to the battery. When the battery is full, the power supply is interrupted. Instead of interrupting the supply line in the plus or minus conductor, the solar cell can be short-circuited even when the battery is full. A series charge regulator should not be used if the energy source consists of a rotating generator. The inductance of the generator coil can generate a considerable voltage peak when interrupted, which can destroy the switching element in the controller immediately or gradually.

Modern solar charge controllers do not simply interrupt the power supply but regulate the power supply by means of pulse width modulation when the battery voltage approaches the end-of-charge voltage. In this way, more optimal charging cycles can be run for the battery.

Thanks to the large quantities, solar charge controllers are nowadays quite cheap and available in various expansion stages:

  • The simple charge controller has only one solar input and one battery output and can only be used for the corresponding battery voltage.

  • If the discharge currents are not too high, e.g. for a lighting system without an inverter, it is worth using a solar charge controller that can switch off the loads as soon as the battery is empty. This can significantly extend the life of the battery. Depending on the intelligence of the solar charge controller, the consumers can be switched off via the battery voltage or via the remaining charge.

  • If the battery voltage is not yet known during project planning, or if the system should be modified later, a serial charge controller can also be used, which automatically detects the battery voltage.

With the simple solar charge controller, make sure that the solar module voltage matches the battery voltage. This means that the optimal working voltage of the solar module (voltage at max. Power) should only be slightly higher than the end-of-charge voltage of the battery. Since the solar module is connected directly to the battery during charging, the module voltage is 'pulled down' to the battery voltage. The module voltage above the battery voltage is not used and the efficiency of the system is reduced. If the module voltage is much higher than the battery voltage, it is worth using an MPPT charge controller.

 

Parallel charge controller (load regulator)

When using rotating generators, neither the generator must be short-circuited nor the supply line simply interrupted. Short-circuiting the generator would sooner or later burn the winding.

Since the winding of the generator is inductive, opening the supply line leads to impermissibly high voltage peaks on the generator and thus also on the charge regulator. The switching element of the controller only has a very limited service life.

In many applications such as Pelton turbines, waterwheels, etc., it is to be avoided that the system is operated without load, because otherwise the speed will reach an impermissible level.

 

The only sensible alternative is to burn off the excess power in a load resistor when the battery is full.

 

Whether the battery is charged with solar cells, with a wind generator, a water turbine or a similar energy source, the principle of the load regulator can always be used. However, the series charge regulator should only be used with solar cells.

 

The disadvantage of the load regulator is that it still needs a substitute load (resistor). This also has to be adapted in part to the needs, which is associated with additional costs. Any heat from the load resistor must also be dissipated.

The load resistor is often also used as a heater. For example in mountain huts, where the load resistance helps to heat the hut.

 

The disadvantage of the simple parallel charge controller is that only one IU charging curve is possible. This means that only two charging levels are possible:

 

1) Charging with the charging current supplied by the source.

2) Maintain end-of-charge voltage.

 

The energy manager from Energy manager from Phocos is an exception. The voltage of the trickle charge can be set here to protect the battery.

Some Tristar from Morningstar also offer charging characteristics and can be used as parallel charge controllers.

 

So far, no MPPT charge controller has been known as a parallel charge controller.

 

 

 

Charge controller with MPPT

The MPPT charge controller (M.aximum-Power-Point-Tracker) is in principle an intelligent DC / DC converter, which adapts the input voltage from the solar module or turbine so that the optimal operating point is reached. The adaptation is done by adapting the input current until the maximum power (and thus the maximum battery charging current) is reached. The input voltage must always be higher than the battery voltage, as the MPPT charger can only convert the voltage down.

With such charge controllers, the efficiency of the system can be increased considerably and solar modules can also be used, which are actually intended for network systems. Such modules are often cheaper thanks to the larger numbers in production.

The MPPT charge controllers are a lot more expensive than the simple series charge controllers. However, because solar modules for grid-parallel operation are only half as expensive, a system with MPPT charge controller is usually cheaper and also has better efficiency.

 

MPPT charge controllers are also available for wind turbines and water turbines.

 

 

Battery charger

You can find more information about battery chargers at https://www.maurelma.ch/batterieladegeraet.htm  

 

Charging with a charger from a diesel or gasoline generator

Since combustion engines usually generate an unpleasant background noise, they should run as little as possible. This means that the battery should be charged with a high current.

It is therefore ideal if the battery has a very low internal resistance.

Li-ion batteries certainly have an advantage here.

 

The Lifeline AGM batteries are also suitable for such an application. Compared to other lead-acid batteries, these batteries have a very low internal resistance and can therefore be charged with a comparably high charging current.

 

 

 

Charging with an alternator

In vehicles such as mobile homes, campers or sales vehicles, as well as in boats, the battery is often charged via an alternator. Depending on the industry, the alternator is also called an alternator.

The alternator was developed for charging starter batteries and has relatively simple charging properties.First, a charging current dependent on the speed of the alternator is charged until the end-of-charge voltage specified in the alternator is reached. After that, this final charge voltage is simply maintained.

If a battery isolating relay or a battery splitter is used for the consumer battery, this second battery is charged with the same charging properties.

Especially for gel or AGM batteries which were built for cycle operation, this is not ideal. These batteries are then partly not fully charged, which can lead to sulphation, or because they are constantly attached to a high end-of-charge voltage, the internal oxidation is greater and the service life is shorter.

In order to improve the charging of the second battery, a charging converter can be used instead of an isolating relay or battery splitter (see also below for charging booster).

As an alternative, the alternator can also be equipped with an intelligent alternator regulator. This alternator controller then controls the alternator in such a way that the battery is charged like a 4-stage charger.

The installation of an alternator regulator requires the Intervention in the Vehicle electrics. Therefore, this should be done by a vehicle electrician

In modern vehicles, the alternator is already controlled in such a way that a switch is made from full charge (14.4V) to trickle charge (13.6V).
This has the disadvantage that only a relatively low input voltage is available for a charging converter.

Charging multiple batteries

Two battery systems are often used, especially in special vehicles. One system is used to start the engine, the other e.g. as a passenger information system in the bus, as a supply system in the boat or camper, etc.

Both batteries are fed by the same alternator, the same solar cells or the same wind generator.

The starter battery should now always be charged so that the engine can be started even when the supply battery is discharged and the supply battery can be recharged via the alternator.

 

In order to be able to charge both batteries without closing them in parallel, there are different solutions:

 

Battery splinters

Both batteries are charged in parallel via a 'diode' each. The diode prevents that only the corresponding battery is loaded during discharge.

However, since the classic diodes have a voltage drop of 0.7V, which, for example, would result in a power loss of 70W at 100A, Mosfets are sometimes used today

 

The disadvantage of this solution is that both batteries are charged the same. The starter battery cannot be given first priority.

 

 

 

 

Battery isolating relay

The supply battery is separated from the starter battery by a relay. The charge is connected to the starter battery. As soon as the voltage at the starter battery has reached a corresponding value, the isolating relay detects that the battery is being charged and also switches the supply battery to charging. As soon as the charging voltage drops again, the second battery is disconnected from the starter battery. This ensures that only the supply battery is loaded by the consumers without charging.

The advantage is that with deep discharge and low charging currents (e.g. from chargers, solar modules or wind generators) the starter battery is always charged first.

The disadvantage is that significant current peaks can occur when the batteries are switched on if the batteries are still charged differently.

With the battery isolating relay, the starter battery and consumer battery are charged with the same voltage. Often, however, the starter and consumer batteries are not of the same type. The strater battery is mostly a wet cell battery. In the case of consumer batteries, maintenance-free and sealed gel batteries or AGM batteries are often used. Starter batteries and supply batteries should therefore also be charged differently. So that the consumer battery can now be optimally charged, a charging converter (also called a charging booster) should be used instead of the battery isolating relay.

 

If the supply battery is a Li-Ion battery, a charging converter should be used instead of the isolating relay. Because the Resting tension the Li-Ion battery is higher, it can happen that the cut-off relay only disconnects when the supply battery has lost some of its charge.

 

 

Charging booster

Now it may be that the supply battery is far away from the alternator and the starter battery or was even placed on a trailer.

The voltage drop across the lines can mean that the supply battery is never properly charged and thus fails prematurely.

In the meantime, device booster chargers are offered which have an internal DC / DC converter. With this converter, the voltage on the supply line that is too low is raised to the battery charging voltage. If the voltage on the supply line falls too low that there is a risk that the other battery could discharge, the booster charger switches off. This means that no isolating relay is required.

  

 

 

 

Battery life

Type of use

How long a battery can be used depends heavily on use and maintenance. That is why guarantee promises for batteries are always a tricky thing

First of all, it is important that the battery is not used for purposes other than intended. This means that the battery should be used for what it was developed for. A car starter battery is less suitable for a solar system. Or cycle-proof batteries and not batteries for general use should be used for an electric wheelchair, golf caddy or electric scooter. The other way round is more likely. General purpose batteries are more suitable as backup batteries for emergency power supplies, where the battery is not discharged and recharged as often.

 

Cycle operation

Every deep discharge gnaws at the life of the battery. The deeper the battery is discharged, the more damaging it is for the battery. In the case of deep cycle batteries, the manufacturer's information on the number of cycles must be observed. It is important not to compare apples with oranges. Many manufacturers state the number of cycles at 80% discharge, others at 100% discharge. The number at 100% discharge is usually much smaller.

 

It is important for cycle operation that the battery is not discharged too deeply. Especially with golf trolleys, electric bicycles, electric wheelchairs, etc., it is important to ensure that the device switches off at the lower discharge voltage. In the case of golf trolleys in particular, it has been observed that many batteries have already lost an excessive amount of capacity after one year.

 

It is also important to ensure that the batteries are correctly charged before use. It is not worth saving on the charger. For such applications we recommend a charger from Victron Energy NOCO or Powerfirst.

 

Depending on whether one or two charging cycles are only carried out on the weekend or whether the battery performs a charging cycle every day, the corresponding battery should also be used.

We recommend OPzS batteries, OPzV batteries or the newly developed lead-carbon batteries for daily use.

 

In the micro power plant (solar system / wind turbine / water turbine)

Most of the time, the battery is used stationary in a pico power plant. If it is a battery whose acid is not bound in a glass mat (AGM) or gel, the acid can separate from the water over time. This is because the specific weight (density) of the acid is greater than that of water. Therefore, such batteries should be overcharged from time to time in a controlled manner. The hydrogen-oxygen bubbles, which arise when overcharging, mix the electrolyte again. This is less of a problem for mobile applications.

 

ATTENTION: Completely sealed batteries (GEL, AGM, VRLA) must never be overcharged to such an extent. The resulting oxygen-hydrogen mixture could no longer be sufficiently broken down. This creates a strong overpressure in the cell, which is discharged through the valves. This leads to the failure of the battery.

 

Overcharging of the battery may only be carried out in well-ventilated rooms, as the oxygen-hydrogen mixture (oxyhydrogen) is highly explosive.

 

Overloading should be the exception, not the rule. Overcharging of the battery is prevented by a charge controller during operation. There are also intelligent charge controllers, such as the PL20 energy manager, which can control overcharging that can be parameterized.

 

Batteries that are overcharged from time to time should have their acid level checked more often.

 

When used in wind, hydro or solar power plants, there is also a great danger that the battery will never be fully charged. You are drawing energy again, although the final charge voltage has not been reached. The state of charge is always in the balance and one speaks of starvation of the battery. A sulphate layer forms on the plates, which has a negative effect on the capacitance and internal resistance. Experiments have shown that this sulphate layer can be reduced by pulse-like discharge and thus the service life can be increased. In the meantime, devices such as the Megapuls are available on the market, which carry out this pulse-like discharge autonomously.

 

Deep discharging of the battery should also be prevented in the smallest power plant. If no other loads apart from an intelligent inverter are connected, the inverter itself will switch off in the event of undervoltage. Otherwise, it must be ensured that the discharge voltage is not undershot.

 

 

 

General

Regardless of whether it is charged with a pico power station or with a charger, it is important that the lead-acid battery is really fully charged.

If a battery is never fully charged, the service life is shortened enormously.

 

In contrast to Ni-Cd batteries, a complete discharge should be avoided with lead batteries. A so-called deep discharge has a negative effect on the service life.

 

A battery should also not be overcharged, i.e. charged higher than the final charge voltage. If a lead battery is overcharged, heat is generated and the water in the battery is broken down into hydrogen and oxygen. Overpressure can arise in maintenance-free (closed) cells and the gases flow out of the battery via safety valves.

 

 

 

Batteries connected in series

Batteries are connected in series to increase the usable voltage. This means that the positive pole of one battery is connected to the negative pole of the other battery.

If the batteries have already been discharged in the series connection, they can also be charged again in series. Usual nominal voltages are 24V, 36V and 48V. You rarely go higher. The 36V system can be found in railways and in some cases in electric scooters. 36V chargers are rarely found on the market.

With a 48V system, make sure that the charging voltage rises above the 50V limit, which can lead to electric shocks if touched. The poles should therefore no longer be openly accessible.

 

Only batteries are allowed same capacity in with same oldr can be connected in series. Batteries should never be connected in series that are not equally charged. The batteries must always be charged individually (or in parallel) before being connected in series.

 

With new AGM (fleece) batteries or GEL batteries, it is advisable to connect the batteries before connecting them in series cycle. The batteries are individually charged, discharged and recharged several times. The number of cycles for cycling should be the same for all batteries.

 

With the series connection, the voltage only doubles. The capacity remains the same. If, for example, you connect two 12V batteries with 20Ah each in series, you have a battery system with 24V, but still with 20Ah.

Since a greater variety of cheaper chargers for 12 volts are available, one is tempted to connect the batteries in parallel for charging. Experience has shown that this disrupts the concept of modern chargers and that they can develop into different charging states over time. It is therefore advisable to also charge batteries connected in series in series or individually when discharging.

 

Even if you make sure that the series batteries are of the same type and age, asymmetries can arise and one battery will be overcharged when the other is not yet full.

 

It makes sense to use a charge equalizer, also known as an equalizer.

The equalizer measures the total voltage of the 24V system and calculates the mean value. If the voltage of the individual battery deviates from the mean value, an equalizing current flows until the battery voltages are equal. This is only carried out if the total voltage is above 26V, i.e. the battery is being charged.
This increases the service life of the batteries and, thanks to better charging, also the overall capacity.

 

 

 

 

 

 

Batteries connected in parallel

In order to increase the storage capacity, batteries are also connected in parallel. This means that the positive pole of one battery is connected to the positive pole of the other battery. Same thing with the negative pole. It is very important that the batteries are of the same type so that the voltages are identical. The batteries should also be charged more or less equally when they are connected, as considerable equalizing currents can arise. When connected in parallel, the capacity is doubled.

It should also be ensured that the same cable lengths and transition resistances apply to all batteries. The batteries should therefore be connected 'crosswise'. Place the connection from the positive pole of one battery and the connection from the negative pole to the other battery. The connection cables should also be of the same length.

Whenever possible, however, it is advisable to avoid parallel connection and instead to connect individual 2V cells with a larger capacity in series.

 

 

Gas formation

Lead-acid batteries should always be placed in a well-ventilated area.

Batteries that are not locked (maintenance-free) must not be charged in locked rooms. When the battery voltage is in the range of the end of charge voltage during charging, the charging current begins to split the water in the battery into hydrogen and oxygen. The mixture of hydrogen and oxygen is called oxyhydrogen. With the appropriate concentration and ignition source, this gas leads to an explosion.

Sealed, maintenance-free batteries are designed in such a way that the oxyhydrogen gas inside the battery turns back into water. If the charging currents are too high, however, the catalytic converter is no longer sufficient. The generated oxyhydrogen leads to an overpressure in the battery and to the opening of the overpressure valves.

With the classic lead batteries, which are mounted stationary, the formation of oxyhydrogen is resp. intentional overcharging of the battery from time to time. If you stand for a long time, the acid can separate from the water in the wet cells, as the acid has a higher density. Overcharging causes gas bubbles to form, which mix the electrolyte again.

If wet cells are installed for the solar systems or the wind system, the charge controller should be able, e.g. to overcharge the battery once a month, or, as the saying goes, to bring it to a boil. For such cases, Maurer Elektromaschinen recommends, for example, a controller from the PLX energy manager family.

 

Lithium-ion batteries (Li-Ion)

The Li-Ion batteries impress with their energy density. A LieFePO4 has almost the same volume, but is at most half as heavy. Furthermore, with Li-ion batteries, cycles can be increased by a factor. Furthermore, in contrast to lead batteries, the capacity does not decrease with high discharge currents. This is why this battery is very popular in traction applications such as electric vehicles, electric boats, etc.

 

 

There are countless variants of lithium-ion batteries. The cells also have different end-of-charge voltages depending on the chemistry. Therefore, the chargers cannot simply be exchanged with one another. The correct charger must be used for each battery.

 

The batteries are also not as good-natured as the lead-acid batteries. For example, with some types, fires or detonations can occur if they are overloaded or discharged too quickly. Li-ion batteries connected in series are also unable to adjust the charging voltage by converting the energy into heat when the cell is full, as is the case with lead-acid batteries.

When a lead acid battery is overcharged, hydrogen and oxygen are released, which in the worst case scenario can lead to explosions. If a Li-Ion battery is overcharged, it emits corrosive and poisonous gas and carcinogenic dust. The gases can contain hydrofluoric acid, which can lead to irreparable lung damage.

To prevent this from happening, a battery management system (also called BMS) should be used.

 

A BMS monitors the voltage and current of each individual cell. If a value is outside the permissible range, at least one warning is issued. Better ones are able to control the battery charger in accordance with the battery.

In terms of production, the individual cells can have slightly different capacities. It is advantageous if the BMS is able to balance the charge of the cells so that no cell receives an overvoltage while charging, although the final charge voltage of the battery has not yet been reached.

Depending on the battery management, individual values ​​are saved during charging and discharging and can be read out later.

 

The optimal temperature range for Li-Ion batteries is between 20 ° C and 40 ° C

Li-Ion batteries should be used at low Temperatures (below 0 ° C) cannot be charged or only with a low charging current. Special aging mechanisms can lead to irreparable damage to lead.

The most important of this type is the so-called Lithium plating. When charging at low temperatures, pure lithium is deposited on the anode. This leads to a reduction in the cell capacity and, in the worst case, to a short circuit if the lithium is deposited as dendrites.

 

 

 

Battery management system

A large number of different circuits are now available under the name of battery management system (BMS).

But not all BMSs are the same:

 

Over and under voltage protection

The simplest form would be to protect the battery against overcharging and deep discharge, similar to a battery monitor in the lead area.

However, since the individual cells can still have different states of charge (because the cells have slightly different capacities due to the manufacturing process or age differently), this type of BMS does not offer much protection.

 

Battery monitor

Some manufacturers offer a system called BMS that only provides information about the condition of the battery. For example, it shows the remaining charge in the battery and provides information about any malfunctions such as overcharging or deep discharge of individual cells. The devices are not equipped with power electronics and cannot interrupt the charging or discharging of the battery. These battery monitors offer at most one digital output, with which a high-performance relay or power electronics could possibly be influenced.

Battery monitors do not offer any protection, but in addition to a BMS they are of great help when it comes to displaying the charge status of the battery.

 

Protecting board

Many Chinese battery manufacturers already offer this protective circuit as a battery management system. The system monitors the individual cells and interrupts the charging process or switches off the consumer if a cell is outside the permissible voltage.

Such systems protect the battery effectively.

In contrast to the lead-acid battery, however, with this system you do not notice when there is only a small residual charge. As soon as a cell is empty, switch off the board abruptly and you have no reserve left.

These protecting boards are usually not able to compensate for different charge states of the cells by so-called 'balancing'. If the states of charge of the cells drift apart due to aging and charging processes, the capacity of the entire battery decreases, although the individual cells still have their full capacity. This is because the cell, which was not yet discharged when the discharge was switched off, prematurely reaches the end-of-charge voltage during charging.

 

Cells print

With a small number of cells, the use of cell prints is worthwhile.

Good cell prints are capable of balancing the charge states and also offer the option of interrupting charging and discharging via a contact.

Make sure that the charger is matched to the cell prints. If the equalizing current from the balancing is greater than the cut-off current from the charger, the charger never switches to the 'battery charged' mode.

 

 

High-end BMS

A good BMS monitors every cell and can interrupt the charging process or disconnect the load from the battery if impermissible voltages occur.

When charging, the individual charge states are matched by balancing in order to obtain maximum charge.