LiPo cell based 9v battery (NEDA1604) with USB C charger.
This is a case to make a 9V battery replacement, based on a 3.7 Volts LiPo rechargeable battery and a breakout board to charge and step up the battery voltage up to 9V.
To get the best off this design, you will need good skills in micro-electronics manipulation, soldering and assembling; or get involved some pal who is proficient in that field. It´s a very trying project; safely fitting all the components in the restricted form factor of a NEDA 9V battery is no easy task.
You will need then, apart from the 3D printed parts:
- a 3.7 volts LiPo battery type 501540, 300mAh (see attached image)
- A TP4056-MT3608 breakout board (see attached image), providing a USB C connector for recharging
- a 9V battery snap connector (you can get one from a spent battery)
- a pair of 1.6x13mm screws (I've used Märklin 74990 screws, cause I have plenty)
- you would like to provide a method to disconnect Li-Po battery when not in use as the step up circuit will be
always drawing some current from the battery; I am using a simple jumper accessible from outside the case, mounted on a little strip of multipoint PCB.
As it's a very constrained design, care should be taken when assembling in order to avoid shortcircuits (remember LiPo cells have a big discharge capacity, hence risk of overheating and potential fire!!); especially isolating the top snap connector from the top of the LiPo cell (my cell has a Kapton tape on the top but nonetheless I added an extra layer.
Depending on the thickness of the scrapped snap connector you will have to trim the upper part of the bottom piece (the one that holds the electronic. Make sure the snap connector is firmly glued to the top piece, as you will be pressing against it when connecting the battery to the appliance.
IMPORTANT NOTE: the charger section of the breakout board (TP4056) includes an SMD resistor (typically 1200 ohms)
to set the charging current value (1000 mA @1200 ohms). We need to decrease the current to a safe value
for our LiPo cell (60 mA for slow charging, up to 150 mA for a fast charge in my case). Again check Li-Po cell
datasheet and TP4056 datasheet in order to replace this resistor with a suitable value one.
The step-up section of the breakout board has a tiny variable resistor in order to adjust the output voltage, in our case, to 9.00 volts.
Adjust and test before connecting the 9V battery to the application circuit.
DISCLAIMER: we are contributing the design to the experimenting community. If you decide to reproduce it, you do it at your own risk regarding your own security and any possible damage that this experimental project may cause. Always read and apply any safety guidance provided by battery manufacturers and providers and make sure to duly understand the functions and ratings of all electronics involved.
Caution is mandatory when working with LiPo cells so be sure to read and understand the manufacturer's datasheet and operating conditions.
I'm providing the skp file in case you need to modify/adjust anything.