18650 external camera battery
When directly powering cameras a 7.4V battery-pack is required. Sony NP-FW50 (and all related batteries) are two-cell Lithium-Ion battery packs (two-cell = two cells á 3.2V in series). If more capacity is required, either a 2S LiPo battery works well (up to 5000mAh is easy to get).
Another option is to use Lithium-Ion battery cells in standard sizes (for example the common 18650). Since I don’t want to spot weld and permanently connect the cells a battery holder on a PCB seems to be the better choice. To charge the cells they can either be removed and individually charged in a battery charger or the whole pack via a balancing charger for LiPo packs.
Idea taken from Jehu Garcias 7S powerwall packs: youtube link
Images
Deep discharge and overcharge protection for Li-Ion cells is done with an Hycontek HY2120 IC. This chip requires a charger to be connected before the pack can be used when the batteries have been changed. To circumvent this, battery ground can be shorted to a IC sense pin for a moment, that’s the reason why there is a button on the PCB.
Bill of Materials:
| Amount | Part | Details |
|---|---|---|
| 12 | 18650 cell | |
| Filament for 3D printing | PETG | |
| 4 | M3 screw 40mm | DIN912 |
| 4 | Heat insert M3 | |
| 6 | Keystone 1048 holder | |
| 1 | DC 5.5/2.1mm barrel jack | |
| 1 | PCB | |
| 1 | HY2120 2S-battery protection IC | |
| 2 | AOD514 N-channel mosfet | |
| 2 | 1206 330 Ohm resistor | |
| 1 | 1206 2k Ohm resistor | |
| 2 | 1206 0.1uF capacitor | |
| 1 | Omron pushbutton | |