10 yuan ultra-low-cost portable adjustable power supply (18650 battery) (can be used as a power bank)

10 yuan ultra-low-cost portable (power bank/adjustable power supply) (18650 battery)
Introduction:
    Adjustable power supply is an indispensable tool for both electronic engineers and electronics enthusiasts. However, although professional adjustable power supplies have strong performance, they are large, bulky, difficult to carry, and most importantly, expensive. Therefore, the adjustable power supply in this project sacrifices high performance in exchange for portability and ease of use with higher cost performance. (Although the original intention was to make a power bank, and now it is mainly used as a power bank, I found that it is also quite good to use as an adjustable power supply.)
Summary of features:
    ① Output voltage 4-30v, maximum current 2A, maximum power about 10w
Application scenarios:
    ① As an adjustable power supply
    ② As a power bank
    ③ As an 18650 battery charger
Advantages:
    ① The main circuits are replaced by modules purchased from Taobao, which is easy to make and suitable for novices.
    ②The cost is about 10R each (the price will be lower if you use coupons, see my b-station video for details on how to operate it), and the price is very close to the people.
    ③The output uses a USB-A female connector, and the charging input is Type C or Micro usb, with high compatibility.
    ④The charging module charging and output protection, the boost module also has high current shutdown protection, which is safer; Type C and Micro usb are deliberately placed very close to prevent someone from plugging in two heads at the same time, which is safer.
    ⑤Small and portable, it is not as big as a palm but has a large power of 2600mah 9.62wh (note that it is not so much in actual use, because it will heat up and lose a little), and can be easily carried in your pocket.
    ⑥The battery is removable and can be replaced at any time
. Disadvantages:
    ①The power is small, the maximum is about 10w (actually enough), the maximum current is 2A, depending on the output performance of the battery, good performance will also have high power.
    ② The voltage adjustment range is narrow, only 4-30v, and it is powerless for scenarios with higher or lower requirements. The same goes for power.
    ③The output ripple will be larger than that of a professional power supply (but unless a precise voltage is required, this is not required in normal use). In theory, adding a few electrolytic capacitors for filtering can improve this situation, but due to various considerations such as size and price, it is still not added.
Notes:
    ①The most important point! ! ! Never reverse polarity when soldering and installing batteries! ! ! Especially when welding the boost module and disassembling and installing the battery! ! ! Reverse connection will cause fire! ! ! When welding, be careful not to short-circuit the USB connector! ! !
    ②When welding, you can follow the following sequence:
        USB connector→→→→Boost module and charging module→→→→PCB and battery box connection
      (please cut the two wires of the battery box to a suitable length and stick them on In the gap between the PCB and both sides of the battery box, this is more convenient and beautiful)
    ③ You can add an appropriate amount of silica gel to the chip of the charging module and the inductor of the boost module, and add a small heat sink to the inductor to assist in heat dissipation. (The above two parts are the key heating parts during charging or discharging) Silicone must be used to connect the PCB and the battery box! ! Don't use hot glue! ! (Hot melt adhesive has low strength and may even melt)
    ④After everything is installed, apply conformal paint (the main component is resin) on the electronic components and PCB to prevent waterproofing and prevent contact with conductors during daily use. Short circuit, but be sure not to let the conformal paint enter the inside of the USB connector and other connections!
Material list and recommendations (search by product name):
    ①18650 lithium battery 2600mah (pdd search store Jiajia Electronics Store) 5R
    ②Boost module (Taobao) 2R
    ③Lithium battery charging module (Taobao) 1R
    ④USB connector (Taobao / Lichuang Mall) 0.5R (USB-A Lichuang Mall No. C404967, TypeC Lichuang Mall No. C709357, Micro usb Lichuang Mall No. C145793)
    ⑤ 18650 battery box single cell (Taobao) 0.5R
    ⑥ Heat sink (optional, small) Just click) 0.5R
    ⑦ (Select) 704 silicone rubber (Taobao)
    ⑧ (Select) conformal anti-paint (Taobao)