Recently, I got a Nokia Lumia 820 mobile phone, but unexpectedly, it also came with a set of third-party Qi standard wireless charging package. While lamenting that the threshold for wireless charging of mobile phones is so low that mobile phones less than 2000 yuan can be used, the author also has a strong interest in wireless charging. After the wireless charging function is added, what is the impact on product design, and what are the differences in actual use? A study was conducted with Lumia 820 as a sample.

Qi wireless charging experience

Easy shell replacement, body weight increased by 1/3

From the previous technical analysis, it can be seen that to enable the mobile phone to support Qi wireless charging, a series of devices must be added to the mobile phone, including receiving coils, chips for converting electromagnetic signals, etc. In this way, how does it affect the design of mobile phones?

After removing the back cover of Lumia820, the author found that there was no integrated Qi system equipment inside the phone, but the receiver coil, chip, etc. were integrated on the special back cover, and only four metal contacts were reserved on the back of the phone for battery charging. This is a common practice at present, which has the advantage of reducing the design difficulty without considering the placement of charging components and the interference of electromagnetic signals on internal components. For a mid-range phone like the Lumia 820, considering the cost, it is only equipped with an ordinary back cover when leaving the factory. If you want to use the wireless charging function, you have to purchase a Nokia Wireless Charging Kit (about 738 yuan) or a third-party wireless charging kit (less than 200 yuan). When using the wireless charging function, just replace the cover. This operation is not difficult for Nokia phones that "technology is based on changing the cover".

For a mobile phone with a 4.3 inch screen, the Lumia 820's own weight of 160g is too heavy. After replacing the wireless charging back cover, the author obviously felt that the phone was heavier when picked up. After all, the back cover was integrated with coils, chips and other devices, and the weight increase was also expected. However, the overall weight of the phone reached 214g, an increase of 54g, equivalent to 1/3 of the original weight. You should know that the 5.5 inch Note2 is 185g. In this state, it is equivalent to holding two iPhones 5 (a single 112g), which is really heavy. In addition, the workmanship of the third-party wireless charging shell is really rough, and there are obvious problems in the details. After the author installed it, there was a problem with the volume button. The phone automatically turned the volume to the maximum. There was always a volume bar on the top of the interface, which was very depressing.

All charging devices are designed into the back cover of the phone, and only four metal contacts are left on the phone to connect with the back cover for charging

Comparison between original housing (left) and wireless charging housing

Wired/wireless charging time comparison failed

The next step is the actual charging process. The author first tested with Nokia's original charger. The 1650mAh battery started to charge when there were 5% left. It took 135 minutes to fully charge the battery. Then there is the wireless charger. After connecting the connecting cable to the charging base, the indicator on the base will show red. As long as you put your mobile phone on it, the indicator light turns green immediately, which means you start charging. The whole process took 203 minutes, 68 minutes more, and half the time. In terms of charging time, wireless charging failed completely.

Why does wireless charging take so long? The author also tested the power consumption of wired/wireless charging with a power consumption meter. The final result is that the power consumption of wired charging is 7.5W, while that of wireless charging is slightly lower, only 7.1W. However, considering that the conversion efficiency of Qi wireless charging is only 70% of that of wired charging, and this third-party wireless charging package with rough workmanship should not reach this efficiency. Therefore, when the power consumption efficiency of wired/wireless charging is the same, the charging efficiency of wired charging with higher conversion efficiency is much higher, which is why the wireless charging time will be extended by half.

Very close use distance

It is known that the use distance of wireless charging is very close, so to what extent? When I put the center of the back cover (receiving coil) of the phone on the charging base (transmitting coil), the sensitivity was OK, and I started charging immediately. However, if you move the position of the receiver coil of the mobile phone slightly, it is not facing the transmitter coil, and the mobile phone can not sense the signal from the transmitter coil at all. Put the phone against the base and try it around. It's the same. It can't sense the signal at all. Then the author tried to pick up the phone, and just got it about 3cm away from the base, it showed that the charging had been disconnected.