Initial BMS Design
December 21, 2025
Design/Documentation
Due Date: December 19, 2025 → December 20, 2025 Projects: Ham Radio Powersupply (https://www.notion.so/Ham-Radio-Powersupply-2ccc50d201c2803da44de30d1e2cf3a4?pvs=21) Status: Ready for review
About the Radio
| Model | RT95 |
|---|---|
| Dimensions (mm) | 124 (W) x 163(D) x 39 (H) |
| Weight | about 0.64 kg |
| Manual | right here! |
Requirements
| Average Amperage | 1.735 A |
|---|---|
| Peak Amperage | 6 A |
| Recommended Current Capacity | 12 A |
| Minimum A/H Capacity | 10.35 Ah |
| A/H Capacity + Reserve | 20.7 Ah |
| Operating Voltage | 13.8V DC ±15% |
BMS must balance all cells. Pick BMS rated at least 12 A,
Pick a charger that matches the pack voltage and the charge current
Assumptions
To check max continuous and/or peak discharge (greater than or equal to 12 A), check cell discharge rating x parallel count, BMS continuous current rating, wire/fuse ratings.
Calculation
Configurations
| BMS | $16.00 |
|---|---|
| Overcharge voltage per cell | 4.2 V |
| Overdischarge voltage per cell | 2.8 V |
| Discharge Continuous Amps | 30 A |
| 10 second Discharge Burst | 60 A |
| Charge Continuous Amps | 30 A |
| Balancing Current | 50 mA |
| Li-Ion Cell | $2.50 per cell |
| Nominal Voltage | 3.6 V |
| Fully Charged Voltage | 4.2 V |
| Fully Discharged Voltage | 2.5 V |
| Capacity | 5 Ah |
| Max Continuous Charge | 1C / 5A |
| Max Continuous Discharge | 3C / 15A |
So, I propose a 3S3P (12.6 V, 15 Ah) configuration (with no accessories)
16 AWG
| Charger specs | |
|---|---|
| Chem & Series Ct. | Li-ion 3S, or 12.6 V CC/CV |
| Charge Current | 9 A (~1.3 hr charge time) |
t_ideal = [Ah]/[A]
~1.1 h = [10 Ah]/[9 A] | | Power connectors | Mini-Tamiya 2-pin connector |
| Fuse | i didnt realise there alr was a fuse |
|---|---|
| Current rating | 10 A |
| Voltage rating | > 12.6 V |
Fun Accessories!
TFT Screen (Sunlight Readable)
| Links: | Price | Notes |
|---|---|---|
| TFT Screen | $16.64 | |
| IDC Cable | $20.00 | |
| IDC Cable + 2x20 Pin Headers | $12.00 | most likely covers both the idc cable listing above, and the pin headers below. |
| 2x20 Pin Headers | $5.00 |
Note: I need some time to decide what accessories I want to use.
Personal Notes
| Current Capacity (A) | Ability to deliver # A of current at a point in time. |
|---|---|
| Ah or Wh | Like volume of fuel tank. |
| C-Rate | this is trying to tell you the CURRENT. |
C-rate is an expression for the allowable charge/discharge current relative to the battery’s capacity.
A_output= [C-Rate]*[Ah Rating]
This is a constraint for how fast the battery can be charged or discharged safely. |