Power supply selection for mobile devices

To overcome power limitations in mobile devices, the usual approach is to use heavier batteries. New technologies such as fuel cells and supercapacitors provide us with a new option.

The key to optimizing system performance is to size the components in order to function most efficiently. Fuel cells are a good choice for providing continuous average power output, while supercapacitors are better suited for providing peak power. Supercapacitors like Maxwell's BOOSTCAP can provide ten times the power and life of batteries, and are lighter in weight. In addition, supercapacitors can work stably at extremely low and high temperatures.

A mobile industrial servo system provides an example of using supercapacitors and fuel cells instead of battery packs and non-self-contained power supplies. The system uses a small, low-cost fuel cell. In addition, supercapacitors are better suited to providing peak power than fuel cells. In a specific application, a 3.5A, 150V DC fuel cell provides a continuous current of 2A to the system and an additional 1.5A to charge the supercapacitor. According to requirements, the supercapacitor must provide a current of 30A for 500 milliseconds, and the voltage drop cannot exceed 25V. To determine the number of capacitors required, the device voltage (150V) can be divided by the voltage of each supercapacitor unit (2.5V) to obtain 60, which means that the device requires 60 of these units. If the total capacitance of the capacitor group is 3

50F, the single capacitor can be calculated to be 350F/60 = 5.8F/unit. The voltage drop of the capacitor group will be 500 milliseconds × 30A/5.8F = 2.6V; from the known ESR of the unit capacitor, the calculation formula for the impedance voltage drop can be obtained as follows: 30A × 0.0032 (resistance value of each unit) × 60 units = 5.76V, add the two together (2.6V + 5.76V = 8.36V), and the final total voltage drop of 30A current in 500 milliseconds is 8.36V. This value is much lower than the requirement of 25V. Therefore, if you need to optimize the configuration, you can choose a lower capacitor, which can reduce waste and reduce costs.

The total weight of the 60 supercapacitors is 3.6 kg. In order to meet the peak load requirements of the equipment, if only fuel cells are used, the battery volume will be large and the price will be too expensive. Compared with the previous solution of using only batteries, the use of supercapacitors and fuel cells has a longer operating time and is more reliable. In addition, the weight and volume of the supercapacitor pack are much smaller than the battery pack.

Power Combo

Fuel cells and supercapacitors can provide power for portable devices based on their unique capabilities: fuel cells provide continuous power, while supercapacitors provide peak power.