1.0 Power Subsystem

1.0  Power Subsystem

1.1  System Overview

1.1.1  Description

The power system needs to distribute power from the solar arrays to all systems in the satellite. The voltage bus will be determined from the solar array configuration, voltage, and battery cell voltage. Our voltage bus will range from 15V to 22V. Note that the battery cells are directly connected to the solar array. A DC to DC converter will distribute this voltage among the sub-systems. Voltage limits need to be on the realm of standard values in order for the DC to DC converter to be efficient. Batteries will be used to provide power during eclipse conditions. These batteries will be charged during sun exposure.

1.1.2  Block Diagram

Figure 10.1 Power Subsystem Block Diagram

1.1.3  Components

Component / Purpose
Chargeable Batteries / To provide power to satellite during eclipse
DC to DC converter / To distribute voltages to all sub-systems
(To be built by VPT, Dan Sable)
UController/Chrg Controller / By switching on or off T-shunt, regulate and remove unwanted current. Prevent battery from being over charged. L limits the current overshoot when T-shunt turns on.

1.2  Component Overview

1.2.1  Batteries

Sanyo Cadnica model KR-1400AE

15 cells

1.4 A-hr

Nominal Voltage = 16.8V

45% DOD

Total mass: 465g, (1.0251lb)

1.2.2  Solar Cells

Figure 10.2 Solar Cell Dimensions

Desired:

§  Each string should have 12 cells.

§  13 strings

§  Total number of solar cells = 156

Solar cell characteristics:

§  Maximum average weight per 100 cells is 2.20 grams.

§  Isc = .35 A

§  Nominal current = 2.2 A

§  Avg. S/C load = 1.43 A

§  Voc = 2.4 V ≥ 2.4 V x 12 = 28.8 V

§  Vsa ~≤ 1.85V

§  Vbatt ≤ 22.2V – account for diode drop

By these characteristics, the battery is left with about .77A for charging during 54-minute periods. The battery can only replenish 0.69 A-hr, so the load should be less then 22 W (minus converter losses).

1.2.3  Power Requirements

Table 10.1: Power Requirements

Sub-System / Voltage / Power / Comment
Attitude
Torque Coils / 3.3 V / 0.25W / Can it take 5V
Magnet / 5V, ±0.25V / 0+.3W / (4A/1 usec pulse)
12V, -6/+3V
Computer / 5V and 3V / >3.0W (max)
A/D / Can it take +15V
S Band Xmit / 14W / Can it take 15.4-21V
UHF Rcvr / 11-15V / 5.4W – 15W / Can it take 15.4-21V
Cameras / +/- 5V / 0.85W ´ 3
Rate Gyro / +/- 5V / 1.2W ´ 3
PPT / 28 ±4V / 13W
Relays / 28V / Can it take 15.4-21 V
GPS / 5V / 1.4W

Table 10.2: Voltage Distribution from DC-DC Converters

T. Coil / DVHF283R3S + 3.3V
Cameras / DVHF2805D + 5V
Magnetom / DVSA2815S +15V, DVHF2805D +5V, Direct Bus 15V– 22V
Rate Gyro / DVHF2805D ± 5V
GPS / DVHF2805D +5V
Computer / DVHF283R3S + 3.3V
HV PS / Direct Bus 15V– 22V
Comm. / Direct Bus 15 V– 22V
UHF receiver
Relays / Direct Bus 15 V– 22V

1.2.4  Thermal Requirements

The DC-DC converters have an operating temperature range of –55°C to +125°C.

1.3 Schematic

Figure 10.3 Schematic of Power Board 1