Big mod: I’m adding a perfboard so I can replace the USB charger circuit and the BMS, some filing, and a small modification to the audio circuit.
In my first post about TA7MNA battery and audio board, I added a USB PowerDelivery trigger module be able to charge the device with an USB-C PD charger. The problem is that it never worked properly. The 3S 1A Multi Cell Charger Board quickly failed, and the very compact BMS was not suitable for my recycled laptop batteries.
Space is limited on the circuit board due to the area occupied by the three batteries. Since I hadn’t had much success designing a brand new PCB for my choice of components with KiCAD (I had planned to export the batteries in their own box inserted under the top cover), I had to do with what I had.
The perfboard for the BMS and the charging circuit
So I decided to add another board and use connectors between the two. The origin board is used to establish connections with the QMX+ mainboard and to house the batteries and the audio amplifier. I am now using the large BMS that was installed in my original setup, and I found a charging circuit that is directly PowerDelivery and QuickCharge compatible. The second board is 100mm wide and slides inside the top cover of the QMX+ in the same way the mainboard slides in the bottom cover.
Detail of the connectors
With this new configuration, I can use a double switch to select between charging mode and operating mode. And it’s important for me to be able to completely cut off the power without having to remove the batteries.
The back of the rear panel with the 2P2T switch and the audio out jack
Since the BMS and charger board are on their own perfboard, this greatly simplifies the rear panel: there are only openings, with no need for brackets.
Rear view with the 2P2T switch and the USB PD charging port
Some people said they had better results with 22KΩ resistors in front of the audio amplifier instead of 1KΩ, so I put what I had in stock, aka 20KΩ. I had to file about 0.75 mm from the back of board next to the LM386 because it was too close of the QMX+ backup battery.
LM386 with 20K ohm and some filing
So far this is working well!
Affiliates links
2-pole male-female connectors with wires
https://s.click.aliexpress.com/e/_c2wJHZXn
4 pole male-female connectors with wires
https://s.click.aliexpress.com/e/_c3kOBHXR
Li-Ion/LiFePo4 2S-6S 45W Charger/Discharger module PD
https://s.click.aliexpress.com/e/_c3u1035x
3S 20A BMS
https://s.click.aliexpress.com/e/_c3gawLiH
2P2T rocker panel switch
https://s.click.aliexpress.com/e/_c45FEa9R
3.5 panel audio connector
https://s.click.aliexpress.com/e/_c39YkpWH
24AWG PTFE wire
https://s.click.aliexpress.com/e/_c42FEIrT
LM386 module
https://s.click.aliexpress.com/e/_c3KcStdT