Power X-Change - Episode 4: Ladetechnologie (mit Dr. Markus Thannhuber)

Dear e-Community, in this Power Exchange episode I would like to give you some information about charging technology and especially about safe charging of Power Exchange. My name is Dr. Markus Thannhuber, I am responsible at Einhell for the areas of technology, development, innovations and quality management.

Generally speaking, lithium-ion cells, due to their very high cell voltage of 3.6 volts resulting from the physical pairing of lithium and carbon, have enormous potential for operating power tools and power garden tools. With these cells it is actually possible to replace large corded devices with battery-powered devices. This was not possible with other battery technologies, e.g., nickel-cadmium or nickel-metal hydride. However, the physical properties of lithium-ion cells require more careful discharging and even more careful charging of the cells or the battery pack to ensure performance, longevity and safety in operation.

In the last video episode 'Packs and Safety' I already showed you the inner workings of our Power Exchange packs. With our battery management system, the SSB technology, our FETs and many other components, we ensure maximum safety and performance of our battery packs under all conditions. All components ensure, among other things, that our power tool, e.g., the hand-held circular saw, always receives the maximum power available at the given time. But what actually happens when charging our packs? What should be considered? And above all, what exactly do we at Einhell do to perfectly charge our Power Exchange packs, regardless of their age and which Power Exchange charger we use?

Let's take a look inside our lithium-ion cells. During charging, due to the applied charging voltages, lithium ions are driven from the cathode (the positive electrode connected to the positive pole) through the separator to the anode (the negative electrode). At the anode, the lithium ions are embedded in a carbon lattice. The speed of charging is of great relevance here. Properly guided, lithium always occurs only bound in metal oxide at the cathode as an ion or intercalated in carbon at the anode, but never metallic. This could happen if charging is done with incorrect, e.g., too high charging currents. Metallic lithium, due to its reactivity, poses a significant safety risk for lithium-ion cells. Therefore, our charging processes, our individual cell monitoring and cell balancing strictly prevent lithium metal deposition.

Let's look at how we charge our Power Exchange batteries. The standard charging program for lithium-ion cells is the CCCV program, i.e., constant current (CC) and constant voltage (CV). It works as follows: The cells are charged with constant current (CC) until a voltage threshold is reached, and then the charging process is continued with constant voltage (CV) until the cells are fully charged. The controlled CV charging at the end of the charging process ensures that the cells are really fully charged and the pack voltage remains stable when the battery pack is put into operation, so that the power tool can offer maximum performance. Without CV charging, battery packs are not fully charged during fast charging processes. Therefore, at Einhell we exclusively use the CC-CV charging method for maximum performance of our Power Exchange batteries.

The CC-CV charging method may only be used if it can be guaranteed that the lithium-ion cells are not overloaded by the CC charging currents. But how exactly do we guarantee that? We initially charge the cells with currents that bring the cells into the correct temperature window, e.g., warming up, i.e., very carefully. As soon as the cells have reached the appropriate temperature, we adjust the charging currents. This is called temperature-guided charging. This charging method is based on the absorption capacity of the anode, where the lithium ions pass through a boundary layer and are intercalated in the carbon, i.e., embedded there. The advantages of the temperature-guided CCCV charging program that we use for the Power Exchange platform are: first, the cells are fully charged and thus activated; second, fully charged cells guarantee maximum performance of the pack; third, the individual cells are charged quickly but gently, ensuring optimal longevity; and fourth, the temperature-guided CCCV method results in maximum safety.

Now we have not just a single lithium-ion cell installed in the battery pack; we have five or ten cells in the pack, whose individual safety and performance are critical for a battery pack. In addition to temperature-guided charging, our individual cell monitoring and cell balancing ensure maximum safety when charging and discharging the battery pack. Through individual cell monitoring, we monitor the voltage level of each individual cell during charging and discharging. This prevents, among other things, an aged or weaker individual cell from being overloaded during charging and thereby causing problems. This is ruled out with us because we permanently monitor each cell separately with our battery management system. In the event of non-conforming cell voltages, our battery pack switches itself off immediately. This is one of the many Power Exchange technology features that contribute to maximum safety.

All Power Exchange batteries are charged in a balanced manner. During balancing or balanced charging, each cell in the pack can be individually supplied with charge. This ensures that each cell in the pack reaches its maximum state of charge after charging and balancing. This makes the battery particularly voltage-stable and powerful. So to summarize: temperature-controlled charging plus individual cell monitoring plus cell balancing – that is the be-all and end-all for powerful and safe charging. We guarantee this with our Power Exchange technology.

In addition to the mentioned features, our Power Exchange charging technology includes other important safety functions, such as critical state of charge detection, low state of charge detection, recovery charge programs, no trickle charging, and independent timebase. The interplay of intelligent cells, the safest battery pack configuration, and intelligent charging programs make our Power Exchange batteries certainly among the safest on the market. As of 2018, we have three chargers in our range: the quick charger, the twin charger, and the boost charger.

The Power Exchange quick charger is our all-rounder and charges all Power Exchange batteries. We charge a 1.5 Ah battery with this charger in just 30 minutes. This charging time varies depending on the capacity of the inserted battery. As already mentioned, we charge with temperature control, individual cell monitoring, and cell balancing. Before and during the charging process, our charging technology constantly checks whether all cells and voltages are in order. If a cell in a pack has an over- or under-temperature, e.g., due to sunlight, winter temperatures, or excessive work, the charger indicates this on the display by constant illumination of the red and green LEDs, and it waits until the temperature inside the battery pack has returned to a permissible range. Then a very slow charging process begins first to avoid stressing the cells. If the cells in the Power Exchange battery do not react properly, both LEDs on the display flash simultaneously; then the charger does not charge the battery. This means that our chargers do not simply send current into the battery to charge it; we only charge when all parameters are right, and we only charge quickly when all parameters have been assessed as good for it.

Our Power Exchange twin charger works on the same principle as the single quick charger and is of course suitable for all Power Exchange batteries. The twin charger has the great advantage of being able to charge two batteries simultaneously and independently of each other, in parallel. And this is not limited to two batteries of the same capacity. Moreover, it does not matter what state of charge they are in. Basically, the twin charger differs from the quick charger only in its ability to charge two batteries at the same time, and this with just one cable that then occupies only one power outlet. Importantly, many chargers available on the market that can accommodate multiple batteries simultaneously cannot actually charge them at the same time. The standard in the industry up to now is different; usually only sequential charging is done. At Einhell, we charge in parallel, i.e., simultaneously, with our Power Exchange twin charger, so that both packs are available to you again in the shortest possible time.

Our new boost charger is based on the same technology as our quick charger. Additionally, this charger has a boost function. It automatically recognizes which battery is currently inserted. With our smaller batteries (1.5 Ah, 2 Ah), this does not make a significant time difference, but with our larger batteries from 3 Ah, we have the possibility with the boost button to charge the battery in nearly half the time. For example, the 5.2 Ah battery takes about 50 minutes to be fully charged with the boost charger. That is of course a great advantage. However, one should not overlook at this point that fast charging with the boost function stresses the cells in the battery pack more. Slow charging is best for a lithium-ion battery. Therefore, we recommend using the boost function only when your battery really needs to be ready for use again very quickly.

That was the fourth episode of our Power Exchange series on charging technology. Look forward to the next episode, where we will briefly cover practical tips and advice. Thank you for your attention.