It all sounds self-evident. The battery is empty, just turn on a battery charger, or turn off the engine of your car or boat and within a few hours the battery will be charged again. So that there is plenty of energy available again. A simple process and effective, but not always fast in case a lead-acid battery is installed, advantage is that standard charging equipment can be used. In 9 out of 10 cases you do not have to look at your battery and they are full again after a night’s sleep. With Lithium batteries this story does not apply and you will have to pay extra attention to the charging installation and the 12 or 24 VDC system in general. Because a Lithium battery can be dangerous when used incorrectly (read charging and discharging).
Why lithium batteries?
A Lithium-Ion battery is a battery where the Ions of the battery shift from the negative electrode, to the positive electrode, and vice versa. Lithium-Ion battery technology is widely used in consumer electronics such as phones, tablets and laptops. But also in other portable equipment, battery tools and in electric transport and internal transport systems etc. For the storage of larger amounts of energy lithium batteries are also increasingly used where previously standard open and closed lead acid, AGM or gel batteries were used. Most important reasons: Lithium batteries have a very high energy density and are therefore compact and lightweight, there is no memory effect which allows faster charging and have a very low self-discharge to name but a few advantages.
Different technologies lithium batteries
There are several types of technologies lithium batteries on the market, each with specific properties.
The most important ones are :
- Lithium Ion
- Lithium polymer (including Cobalt or Manganese or both such as NMC)
- Lithium Iron Phosphate (LFP - LiFePO4)
Lithium iron phosphate (LiFePO4 or LFP) is considered to be the safest on the market. This is precisely the reason why we at WhisperPower supply this type of battery in the various versions. We are aware that the other types have other advantages such as a slightly higher energy density, as is the case with the NMC battery, but these types are significantly less safe. At Whisper Power, safety comes first.
Application is decisive
It is extremely important to know what the application is before purchasing a lithium battery. In other words, where will the battery be placed, how will it be used, how many charge/discharge cycles will be planned, etc. The most important application we deal with at Lithium ION batteries is in hybrid systems for propulsion and / or power supply, which are increasingly being installed in a vehicle or vessel. The batteries are frequently used in the situation with many charge-discharge cycles, or high-cycle use. By cyclic use we mean that we deeply discharge the battery and then quickly charge it again, which will also be charged during discharge (use of the system). In an electric car, for example, the battery is discharged while driving. During charging the battery will not be driven. In other words, when charging, there is no use of energy from the battery in the system. All these parameters are taken into account when choosing the right battery and battery technology. You will see that for cars the compactness and weight are more important there is a conditioned pressure situation. So in this application we choose a different technology battery.
Back to choosing the right ION battery. After the right battery capacity and the total AC and DC system has been determined, the corresponding system components will have to be determined.
The nominal voltage of an LFP cell is 3.2V (with a standard lead-acid battery this is 2V per cell). A 12 Volt LFP battery is actually a 12.8 Volt consisting of 4 cells connected in series of 3.2 Volt = 12.8 Volt.
The voltage of a single battery cell is 3.2 Volt. This is called the rated voltage. However, the actual voltage during use can vary from 2.5 to 4.2 volts. When the voltage drops below 2.5 Volt, the cell will be damaged. The cell is then too deeply discharged and will be irreparably damaged. When the voltage exceeds 4.2 Volts the cell will also be damaged. The cell is then overcharged and will be irreparably damaged.
The cells of an LFP battery do not balance themselves, as is generally the case with lead acid. The cells in the battery are never 100% identical so over time the cells will be uneven in charge. To solve this it is necessary to balance the cells so that they are all equally charged. Whisper power lithium batteries have this balancing functionality built in. With cheaper lithium batteries this balancing function must be added. This is often through a loose circuit board that must be connected to the cells.
With lead-acid batteries there is always a current running during the maintenance charge. Because of this, cells that are less full will still be completely full and so the balancing is actually done automatically without us noticing.
With lithium batteries there is no power left when the battery is full. Because of this, balancing does not take place if the cells are uneven.
So it is very important that the batteries are properly conditioned and protected against deep discharge and overcharging and the cells will have to be balanced.
What we see in practice is that most lead-acid batteries fail prematurely due to sulphation, i.e. the hardening of the plates in the battery. This is because the user has left the battery partially or completely discharged for a longer period of time. This is often seen in applications where the batteries are only used part of the year, such as yachts, motorhomes and caravans.
Shortly below each other the advantages of a Li-Ion battery:
- Safe if the right Lithium technology (LFP) is used.
- Very high energy density making them very compact and up to a factor 30-50 % smaller compared to lead acid batteries.
- An extremely low weight up to 70% less than lead acid batteries.
- Durable: many charge and discharge cycles possible, up to 6000 cycles which is more times more than lead-acid batteries.
- Very high efficiency 92% compared to 80% of a lead-acid battery. Even at low discharge, the efficiency remains high. With lead-acid the efficiency drops dramatically when used between 80 and 100% battery capacity. Therefore we recommend the use of LFP batteries in solar and generator applications where significant savings of fuel and CO2 emissions are realized.
- No memory effect, no recharging vab 80 to 100% with decreasing charging current as with tanning batteries.
The purchase price is higher than a lead-acid battery, but keep in mind that the battery has a much longer lifespan. Because of this the lithium battery will be more economical over the entire life counted.
What is important
We have seen that the Lithium battery can be dangerous when used incorrectly. So it is important to work with a reliable supplier who can configure the right systems for the user’s application. This may cost a little more to purchase, but the advantage is that the system is guaranteed to work, be reliable and above all be safe. So that you can make optimal use of the energy where and when you need it.
That’s why LFP lithium batteries (LiFe PO4) are the only right choice for systems in demanding conditions and where weight, size, performance and energy efficiency are important. Whisper Power supplies the following lithium batteries:
- We offer our customers our Li-Ion Basic range, suitable for the smaller power systems, for 12 and 24 VDC.
- With the ION Power Plus we supply a heavy duty "system" battery for larger system configurations, especially 24 and 48 VDC.
The Li Ion Basic batteries are extremely suitable for use in vehicles and vessels where the discharge current is limited between 50A and 100A depending on the exact battery type.
It is necessary to take a moment to consider the charging and discharging process of such a battery. Nothing is as annoying as an empty battery when you need power. That’s why it is important to make sure that the battery is fully charged again immediately after it has been discharged. But what is the best way to do that?
As mentioned before, a Li-Ion battery should never be overcharged. If this happens, the battery will start to ‘stress’ and in the worst case it can catch fire with all the consequences. Therefore, always use the right Whisper Power Lithium battery for the right application with the corresponding WhisperPower charging system.
The Lithium ION battery has a special protection circuit (BMS , Battery Management System), which ensures that the battery does not exceed the maximum voltage. This BMS also ensures that your battery is not too deeply discharged. If the voltage is too low or too high, the BMS ensures that the battery is not damaged.
How do we protect the battery
With the ION Basic we have an internal disconnect technology we always recommend an external DC disconnect option such as the Remote Battery Switch type 12-500A or the 24-500A for 24 Volt battery systems.
The DC Modular Remote Battery Switch (the switch) is a smart high current magnetic closing switch, which can handle continuous DC currents up to 500 Amps. The switch can easily be installed in a motor room or battery compartment, while being controlled from a more convenient location by a small panel mounted switch. But the switch can also be controlled by a battery monitor or a lithium battery, for example, as a discharge/overcharge protection.
With the ION Power Plus we have the WIB that takes care of the disconnection in the next Tip we explain that more specifically.
Lifespan Whisper Power Lithium
The service life of a battery decreases with age and the number of charging and discharging cycles is specified. In other words, the more often the battery is charged and discharged, the shorter its service life. In short: the life of the battery depends on the degree of charging and discharging. For the ION power basic this is more than 2000 cycles with a 1C and 100% DoD (depth of discharge). 1C discharge means with an LFP battery that a 100Ah battery can be discharged with 100A for 1 hour. This is considerably longer than a lead-acid battery with a cycle life of 200-300 cycles with a DoD of 50%. So we see that with lead-acid batteries the discharge current is often many times lower than the battery capacity is a much used battery than C20. C20 is a 20 hour desalination, so a 100Ah lead-acid with C20, means a 5A discharge for 20 hours. Where we can only discharge the battery for 50%. In many cases, the lithium battery is the best choice in terms of long life and the lowest cost over the entire life span.
As mentioned before, Li-Ion batteries have a minimum self-discharge. The BMS needs a small current so some energy is consumed anyway. This will have to be taken into account, the battery needs to be maintained by means of the right battery charger, solar panel windmill or another charging source. In case the battery will not be used for a longer period of time, you will have to take this into account. The more charged the battery is, the faster the battery starts to oxidize from the inside and thus the life span decreases. If you don’t use the battery for a longer period of time, make sure that there is still about 60-70% capacity left in it and take measures that the battery will not be discharged by the BMS.
So it is not entirely unwise to monitor the battery with a battery monitor.