Do you know about batteries and rechargeable batteries? The livestream “Keysight: Live from the Lab” provides a good introduction to the topic. In this livestream series, which is Keysight Hosted by , each event explores different electronic processes or events. The individual presentations attempt to convey electrical engineering knowledge in a simple and humorous way. For example, in a previous livestream, a 50Ω cable was cooled using liquid nitrogen to measure the temperature influence on its high-frequency properties.
Drill batteries and lithium cells
The current presentation focused on the topic of "Power for IoT." The measurement of an old drill battery formed the basis for this. For an initial unscientific test, screws were driven into a board until the cordless screwdriver gave up. Nevertheless, the first lesson was already learned: Batteries lose capacity through charging cycles and their internal resistance increases. In the test mentioned, the old battery performed worse than a new 37%.
Since almost all batteries have similar problems, measurements on this battery can be transferred to other batteries. To avoid unnecessary battery consumption, Keysight developed a virtual model from the measurements of these batteries, which explains the following properties in more detail. The following tests address the three most significant problems of batteries. The respective core essence is also included.
- Aging processes (charging cycles)
- Influence the internal resistance of the battery, whereby less power on the device arrives.
- Influence the capacity of the battery, which means Battery can only be used for a shorter period of time between charging cycles.
- Solution: Use a slightly oversized battery so that there is still enough capacity after a few cycles!
- (Ambient) temperature
- Affects the capacity of the battery and causes a Nonlinearity of the internal resistance.
- At low temperatures ~10% lower capacity and possible failure of individual cells
- At higher temperatures ~15% lower capacity
- Solution: Use the battery in a constant temperature environment if possible to ensure consistent overall capacity!
- Electricity or power consumption
- Influences the capacity of the battery. If the withdrawal is lower, the cycle duration is longer.
- Solution: Use the battery with adjusted current draw to extend its service life!
The same tests were subsequently conducted with a lithium-ion battery. It was found that this battery was less sensitive to cold, but exhibited less severe aging effects (~41% less than its nominal capacity at colder ambient temperatures).
Experiments on DC-DC converters
The second major part of the event focused on the characteristics of DC-DC converters, which play a key role in most devices for implementing different supply voltages. Here, too, two converters were compared using various tests, focusing in particular on the specifications provided by the manufacturer:
- Load Regulation (Change in output voltage depending on the load current)
- The Voltage of the converter collapses suddenly at a certain current consumption.
- Line Regulation (Change in output voltage depending on input voltage)
- The converter has upwards and downwards a limit voltage before/after which it can no longer deliver the required output voltage.
- Turn-on time (Time until a stable output voltage is reached after switching on the converter)
- Here we must good ratio between edge steepness and possible overshoot the voltage must be taken into account.
- Turn-off time (Time how quickly the voltage is disconnected from the load after the converter is switched off)
- When switching off, Voltage peaks arise, which can damage the load.
- Ripple Output (Parasitic noise generated by switching operations in the converter)
- The Ripple Factor = Ripple/(Average Output) should be below 1/3 lay
- Efficiency (Efficiency of the converter)
- At higher operating voltage of the converter is the Efficiency better, at the same time sinks this with higher power consumption.
Despite my prior knowledge, I consider the livestream to be very informative, as it stimulates thought in an entertaining way. In particular, the electrical properties of the components under consideration were explored in depth, and the important design parameters for powering portable devices were discussed. You can watch the recording of the livestream for free here.
Do you need help selecting rechargeable batteries, batteries, or general power supplies for portable medical devices? Then feel free to contact us. You can find an example of a past project we implemented in the following blog post: Interview about start-ups in medical technology with Ralph Steidl