Document the design of EPS module
EPS Design
Load Needs
Summing up load needs from COMMS there is
When in TX: --> (200ms/20sec) => DC 1%
COMMS 5v | |||||
---|---|---|---|---|---|
V4LOAD | IV4 | VBAT_LOAD | IBAT | VBAT_FLOAT | POUT |
4.47 V | 810 mA | 3.46 V | 1450 mA | 3.8 V | 30.7 dBm |
COMMS 3v3 | |||||
V4LOAD | IV4 | VBAT_LOAD | IBAT | VBAT_FLOAT | POUT |
3.15 V | 510 mA | 3.65 V | 590 mA | 3.75 V | 27.3 dBm |
In Idle state:
The estimation I used is
55 mA for both voltages on COMMS side and
80 mA for 5v on BAT side while
46 mA for 3v3 on BAT side respectively
@drid, @surligas / Please info on the estimation of the Idle state consumption?
The results were:
COMMS 5v | |
---|---|
PV4 | PBAT |
310.7 mW | 327 mW |
COMMS 3v3 | |
PV4 | PBAT |
198.1 mW | 202.1 mW |
min efficiency 95%
Power available on the Satellite
Based on @zisi and @papamat calculations the available Mean Power on the Satellite is:
787.184 mW for SM101K09L (We may go with this) and
737.302 mW for SM141K04LV (We shall go with this option due to MPPT IC availability)
!!! Important !!! as the design enables the use of 5 out of 6 sides of the Cube for solar panels (The side under the cube will accommodate the Kill Switches and the antenna equipment) and we cannot use the SM101K09L, our power availability is curtailed to 614.42 mW
Assuming a 90% efficiency to each of the 2 conversion step and a 25% safety this leads to almost 400 mW mean power production.
@surligas / Can you please check what we can perform with this power availability, and what could be the DC% of TX, RX, STM-operation, and Idle?
EPS Outline
Topology 1 | Topology 2 |
---|---|
+ Less components | - |
+ Stable PA Voltage | - |
- | + More efficient |
Note:
- They both rely on one switching element to supply the PA
Maybe we could add a 2nd for redundancy
I would also propose that we use connection in parallel for both the PV Arrays and the Batteries for redundancy. The only issue could be not manageable Voltages
Preferred Topology 1 as Simpler
Topology1.1 (details added)
Note:
- Still not sure about the TPS as a DC/DC unit
Components Selection
Solar Power Board
PV: 3x SM141K04LV in parallel on each side, x5 sides
MPPT: 5x SPV1040 one for each side
Battery Power Management System (BPMS)
Battery: 2x NP-BX1 / 1240mAh, Li-Ion, 3.6V, 4.5Wh, 25g
DC/DC: 1x TPS62086
Power Monitor: 1x MAX17261METD+
Note: On current monitoring we have used 2 x 20mΩ resistors for redundancy. In case that one of them is burnt, the voltage measurement on the resistors will be doubled - however the difference should be easy to spot in order to re-calibrate the MAX17261 scale!
(opional) -> FINALLY not used
Power Monitor: 5x INA226 ??? / @drid ???
IMU: 1x LSM6DSR ??? / @zisi ???
Documentation of BPMS-board characteristics
3v3 DC power supply
TPS62086 (step-down DCDC converter) can supply 3,3V DC on a mean efficiency of 85%
Vin = 3,6V The curtailed efficiency (orange line) is due to a 35mA minimum DC-Load current.
Pass Through: It can provide 3,3V Vout for a 100mA Load provided a 3,4V Vin
No Battery test
Finally, a test was performed on the system having the batteries unplugged (Power provided from the PVs on a light intensity where the top panel, almost perpendicular to the light source, would provide 500mW)
The system was capable to provide 3V Vout for a maximum Load of 350mW. If the load demands more than 350mW the system will loose the MPP setting and the Voltage will be driven at almost 2,3V The power demand then should get below 100mW so that the system will be able to spot again the MPP