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Lecture
19: Electric Systems / Power Supply
Electric Power Overview
• Primary Power: 28 VDC
• Secondary Power:
– Isolated from primary power (28VDC)
– CGBA/PGBA: 5VDC, 12VDC, 24VDC, AC-ballasts
• Isolation: = > 1 MegaOhm
– Between different electric circuits to avoid ground loops
– Between video, primary power, secondary power, chassis ground, communication lines
• Bonding:
– Class C: fault wire (green wire), max. current capable.
– Class H: all electric components / boxes: < 0.1 Ohm
– Class R: < 2.5 milli-Ohm
– Class S: < 1 Ohm
• Grounding:
– Chassis ground (similar ‘green wire’)
– Single Point Ground (SPG) – avoid ground loops / EMI / power loops.
· Spacecraft: power return is grounded to chassis ground
· Payload: primary power return must be isolated from chassis, otherwise: ground loops
· Payload isolated secondary power: must be chassis grounded at single point ground.
• AC / High Voltage Shock Hazard:
– Separation (insulation, potting, inaccessible)
– Current limits (very low)
– Ground Fault Interrupt (or equivalent for space – no ‘ground’).
• Batteries:
– Stored energy, toxic electrolytes
– Leak test with vacuum exposure 6 hrs,
– Current limits / fuses
• Start-up Current
– Inrush current can be very high (charge current for capacitors 100 Amps…..)
· Soft-start required (short-circuit protection, solid state fuse trips)
· power supply may trip, or experiment circuit may not start properly – test compatibility.
• Switching power:
– Current: on-resistance of switches: loss = heat = I2 R. very good MOSFET: 0.05W / 10 Amp. = 5 Watt loss
– Voltage: arcing; most consumer electronics: < 30 VDC delta.
Power Conversion
DC Supplies on Spacecraft typical (28VDC Shuttle, 120VDC ISS)
· Supply may vary (28VDC = 24-32 VDC), but user may need stable voltage à regulation.
· Voltage loss in lines: 28VDC nominal drops to 19-24V at end of 12 ft cable.
o MDK Ceiling (10 Amp cb limiting – thermal derating) =19.1 VDC at 9.5 Amp. MAX (182 Watt max.)
o MDK 10 Amp MUP (10 Amp cb limiting) = 24.0 VDC at 9.5 Amp. MAX (227 Watt max.)
· DC Regulators: waste heat: input current = output current, input voltage > output voltage. Loss = heat = (Vin-Vout) * I
· DC-DC converters: 80-90% efficient; Loss = heat = power used / efficiency = Vout * Iout / n.
o DC – switched = AC – transformer – rectified to DC – regulated to desired voltage
· DC-AC Inverters: provide AC voltage (fluorescent lamps, backlighting,….)
o DC – switched = AC - transformer
· Isolation between different power circuits may require use of DCDC converters.
· EMI electromagnetic interference / EMC electromagnetic compatibility: filtering / protection / shielding necessary:
o radiation / conduction out = emissions
o radiation / conduction out = susceptibility
o sample report for PGBA plant chamber (big PDF)
Measurement Instruments:
• Isolation: > 1 MegaOhm
– Any multimeter with setting > 1 Mohm (10 Mohm)
– Open circuit indication depends on Multimeter
• Grounding / Bonding: < 2.5 mOhm
– Milliohm meter with 4-wire test leads
– 6 digit meter with 4-wire test leads
– Multimeter (only check, insufficient resolution)
Design Examples - CGBA Incubator
Plant Growth Chamber
Sample EMI Tests: PGBA Emissions Summary
|
PGBA Conducted E-Field Emissions |
Range |
Limits |
PVP |
Pass/Fail |
Plot |
|
CE01-postive lead |
30 Hz to 15 kHz |
110 @ 30-200 Hz
74 @ 15kHz |
EL-ER-015 2 EL-MD-005 |
Ö Pass |
1 |
|
CE01-negative lead |
Ö Pass |
2 |
|||
|
CE03-positive lead |
15 kHz to 50MHz |
74 @ 15 kHz
45 @ 500 kHz
45 @ 50 MHz |
Ö Pass |
3 |
|
|
CE03-negative lead |
Ö Pass |
4 |
|||
|
CE07 (TT01) |
Spikes, time domain |
|
EL-ER-015 #5, #6, #7 |
Ö Pass |
See fig. |
|
PGBA Radiated E-Field Emissions |
|
|
|
|
|
|
RE02 NB (SSP52000 and NSST21000) at
1 meter: |
14 kHz to 20 GHz |
ISS and NSTS: |
|
|
|
|
RE02NB Narrow Band, vertical polarization, |
14k to 1.0GHz |
56 @ 14k to 10M 86 @ 259M 46 @ 259M 72 @ 10G 76 @ 13.5 - 15.5G NSTS: 75 @ 14k 66 @ 200M 77 @ 10G |
EL-ER-015: #8, #9 @ 1 meter |
Ö Pass |
5 |
|
RE02NB Narrow Band, horizontal polarization,
|
30M to 200MHz |
Ö Pass |
6 |
||
|
RE02NB Narrow Band, vertical polarization, |
1.0GHz to 10GHz |
Ö Pass |
7 |
||
|
RE02NB Narrow Band, horizontal polarization,
|
1.0GHz to 10GHz |
Ö Pass |
8 |
||
|
RE02NB Narrow Band, vertical polarization, |
13.5G – 15.5GHz |
Ö Pass |
9 |
||
|
RE02NB Narrow Band, horizontal polarization,
|
13.5G – 15.5GHz |
Ö Pass |
10 |
||
|
RE02 BB (NSTS21000 only) at 1 meter: |
|
NSTS Only: |
|
|
|
|
RE02BB Broad Band, vertical polarization, |
14kHz to 1.0GHz |
110 @ 14k
65 @ 200M 100 @ 10G
70 @ 1.7-2.3G |
|
Ö Pass |
11 |
|
RE02BB Broad Band, horizontal polarization, |
30MHz to 200MHz |
Ö Pass |
12 |
||
|
RE02BB Broad Band, vertical polarization, |
1.0GHz to 10GHz |
Ö Pass |
13 |
||
|
RE02BB Broad Band, horizontal polarization, |
1.0GHz to 10GHz |
Ö Pass |
14 |
||
|
PGBA AC Magnetic Field Emissions |
|
|
|
|
|
|
RE04, at 1 meter (NSTS only) |
30 Hz to 50 kHz |
130 @ 30 to 1k
63 @ 50k |
|
Ö Pass |
15 |
|
RE101 scan for maximum emissions and
spectral analysis to locate test locations (Front, top, left, right).
Following tests at PEAK for each surface ! |
30 Hz to 50 kHz |
140 @ 30 Hz
85 @ 3.5k
85 @ 50kHz measured at 7cm. If exceedances, Re-measure at 50 cm to pass. |
EL-ER-019 #1 |
PGBA peaks at 30, 50 kHz Ambient |
16 |
|
RE101, Front at LCD screen, 7 cm from faceplate |
10,20,30kHz |
17 |
|||
|
RE101, Front at LCD screen, 50 cm
from faceplate |
Ö Pass |
18 |
|||
|
RE101, Left Side, 7 cm from enclosure
at peak |
Ö Pass |
21 |
|||
|
RE101, Left Side, 50 cm from enclosure at peak |
Ö Pass |
22 |
|||
|
RE101, Right Side, 7 cm from enclosure at peak |
Ö Pass. |
23 |
|||
|
RE101, Right Side, 50 cm from
enclosure at peak |
Ö Pass |
24 |
|||
|
RE101, |
Ö Pass |
25 |
|||
|
PGBA DC Magnetic Field Emissions |
|
|
|
|
|
|
NSTS: measured at 1 meter |
DC |
< 170dBpT |
EL-MD-006 #2 |
Ö Pass |
N/A |
|
ISS: measured at 7 cm, if fail, measure at 10, 20, 30 cm until below limits. |
DC |
< 170dBpT |
EL-ER-019 #2 |