University of Leicester
PLUME
Ref: PLM-PSU-ChargeDischTest-307-2
Date: 09/04/2009
Charging/Discharging test of the PSU
Matthew Cro
Date
Updated Reference Number
change
09/04/2009
06/11/2009
PLM-PSU-ChargeDischTest-307-1
PLM-PSU-ChargeDischTest-307-1
13/01/2010
PLM-PSU-ChargeDischTest-307-2
first version issued
Addition of: ‘2.3.1 Alternate
Experimental Set-up’ –
inclusion of battery board.
Added references and
detailed steps to 2.3 –
Experimental Setup.
Added 4.1 - Safety
1. Abstract
The PSU of the CubeSat Plume is a fundamental piece of equipment and requires rigorous
testing. This report documents a series of tests to determine firstly that the battery
purchased from Clyde Space works, and secondly to determine its functional characteristics
and estimate charging and discharging times. Unlike standard batteries, Lithium Polymer
batteries used in our PSU do not suffer from the ‘memory effect’ but can still loose their total
capacity overtime therefore these tests will be conducted with a test battery which will be
replaced with an identical unit for actual flight hardware.
2. Charging
2.1 Power Production
When testing the PSU and batteries during charging and discharging, different power values
need to be used as the total power produced by the solar array can vary from a maximum
and minimum value depending on the CubeSat’s orientation in space1. These values as well
as an average are:
Maximum Power: 8.78W
Average Power: 4.60W
Minimum Power: 2.34W
2.2 Charging Time Estimate
The battery capacity is listed as 1250mWh which is equal to 10.25Wh at 8.2V. Using the
value above estimates for maximum, minimum and average charging times can be made.
These are:
Maximum Charging Time: 4.38 hours
Average Charging Time: 2.23 hours
Minimum Charging Time: 1.17 hours
1
Power Production Calculations – Ariana Stlianidi Christdoulou
Page 1 of 6
University of Leicester
PLUME
Ref: PLM-PSU-ChargeDischTest-307-2
Date: 09/04/2009
2.3 Experimental Set-up (Charging the Battery)
The battery board is carefully removed from storage and made sure that it is connected
properly to the EPS board. The voltage across the unregulated power bus is checked by
touching a multimeter to the relevant PC104 pins. This is to check the charge condition of
the battery prior to performing any experiments.
The push pin connector is attached to the PC104 bus. This contains soldered connections
which short several pins (see Test Plan) to simulate the closing of the separation switch and
removal of the pull pin as well as connections for the I2C bus. These are push connected
onto the I2C bus adaptor (again see Test Plan for specific pins) which is then connected via
USB to a laptop with the appropriate interface software to act as the Master. Specific pins
include H2.41, H2.42, H2.43 and H2.442 for the I2C bus.
As the solar panels have not yet been purchased they must be simulated using the solar
array equivalent circuit shown in Figure 1. In order to simulate the power values above the
current limiter is set to 500mA and the voltage raised to 9.2Vfor the average value 3. The
ammeter and voltmeter are placed after the solar array equivalent circuit to monitor the
current and voltages into the Battery Charge Regulator (BCR) to check the values given on
the power supply:
Figure 1: Test circuit set-up with voltmeter and ammeter.
At this point the battery will begin charging at a rate determined by the power supply. The
voltage and current across the battery are periodically monitored via the I2C bus. The
process is timed until the battery is completely charged. Below is a detailed setup of the
power supply to the I2C bus for charging.
1. To begin with, the BCRs function should be tested by connecting the battery to the
BCR with the removal of the shorting pin. Or shorting pins H2.33 – 34 with H2.41 –
44 to simulate the removal of the pull pin. This is critical before attaching any input to
the array connectors to prevent damage to the power stage.
2. To activate the +BatBus/5Vbus/+3.3Vbus H2.35-36 should also be shorted to H2.3334 and H2.41-44, simulating the closing of the separation switch.
3. The power supply should then be interfaced to the USB connector for charging.
Depending on the setup, this can be achieved two ways:
a. By using a 5.0V power supply connecting the SUB H1.32 and limiting the
current to 0.5A.
b. If the EPS is mounted (in this this is preferable) in the power supply, the USB
cable can be inserted into the USB socket.
2
3
The exact positions of these pins can be found on page 8 of the CubeSat Power System User Manual.
For the correct Header SA pins, see page 12 of the CubeSat Power System User Manual.
Page 2 of 6
University of Leicester
PLUME
Ref: PLM-PSU-ChargeDischTest-307-2
Date: 09/04/2009
4. This is then connected to pin H2.29 to ground the connection. Below in figure 2
shows a block diagram for this connection:
Figure 2: Block diagram for USB and power supply connection
5. Connect to the power supply as shown in figure 1, connecting the positive and
negative connections of the power supply to pins 1 and 2 respectively to each
respective SA Header Pin.
Figure 3 shows a basic block diagram of the charging process:
1. Set-up solar array equivalent circuit, incorporating in ammeter
and voltmeter to measure voltage and current across circuit. Follow
any further steps needed from footnote 2.
2. Connect to I2C bus to monitor
current and voltage using
previously mentioned pins.
3. Set power supply current limiter to 500mA
and start initially at 0V.
4. Slowly increase voltage to value required for
power input (see above), monitoring voltage and
current across circuit.
5. Continue until battery is fully charged (8.2V)
using the I2C bus to monitor the charging process
of the battery every few minutes at fist to check if
it is working then every 10 minutes.
Figure 3: Block diagram of the charging process.
Page 3 of 6
University of Leicester
PLUME
Ref: PLM-PSU-ChargeDischTest-307-2
Date: 09/04/2009
This is to be repeated several times to gain an accurate estimate of the total time taken to
charge the battery, as well as repeats made with different power values, particularly the
values stated earlier.
2.3.1 Alternate Experimental Set-up
Alternately, the battery can be charged (or discharged) through the battery board itself by
replacing the battery equivalent with the Clydespace battery itself. Image 1 below shows the
connected battery and battery board:
Screw
connectors
Image 1: Top down view of battery, battery board and screw connectors.
The battery itself is secured to the battery board via 4 screws (labelled ‘screw connectors’).
The battery is connected via a black pin (labelled) as shown in image 2, allowing for power
to flow from the battery to the board and vice versa:
Screw
connectors
Pin
connector
Image 2: Connection between battery and battery board
Once both battery and board are connected, the completed power supply can be connected
to the I2C bus for testing following the original test plan. Again, when discharging, a similar
set up can be used by replacing the battery equivalent circuit with the Clydespace battery.
Page 4 of 6
University of Leicester
PLUME
Ref: PLM-PSU-ChargeDischTest-307-2
Date: 09/04/2009
3. Discharging
After the battery is charged, it will then be discharged by a combination of subsystems.
Table 1 below gives the total maximum power drawn from each subsystem (including
contingencies and taking a worst case ‘everything on’ scenario) and from which bus it will be
drawing current:
Subsystem
Power Bus Max Power Drawn (mW)
OBDH
3.3V
66
ADCS
3.3V
80
PAYLOAD
5.0V
1190
COMMS
5.0V
1292
Table 1: Max power/current consumption from each subsystem and power bus
From table 1, the total power across the 3.3V bus is 146mW and across the 5V is 2482mW
and so the total power drawn by all the CubeSat subsystems is 2.628W. At this rate the
battery would take 3.9 hours to completely discharge.
Using these values, it is possible to replace the load on each power bus with a resistor.
Using the following equation:
R Bus
V2

PTotal
the total resistance needed for each power bus can be calculated. These values are:
Resistor value for 3.3V Bus: 74.589 Ω = 74 Ω = 65 Ω + 18 Ω
Resistor value for 5.0V Bus: 10.073 Ω = 10 Ω 4
3.1 Experimental Set-up (Discharging the Battery)
The solar array simulation circuit is disconnected and a discharge circuit shown in figure 4 is
attached to each of the 3.3V and 5V buses. The battery is allowed to completely discharge
to its end of discharge voltage (3.2V) through these circuits so that an estimate of how long it
will take for the battery to completely drain can be made, assuming maximum power drawn
whilst not in direct sunlight.
Figure 4: Discharge circuit connected to one of the battery buses. The resistor value is
chosen to reflect the maximum power drawn by the other CubeSat subsystems (see above).
4
It should be noted that ADCS will run off the 5.0V bus every time during start-up but switch to 3.3V straight
after. For this calculation, this has not been taken into consideration, however if it is, the value is reduced by
roughly 2 Ω; a negligible amount.
Page 5 of 6
University of Leicester
PLUME
Ref: PLM-PSU-ChargeDischTest-307-2
Date: 09/04/2009
Figure 5 shows a basic block diagram of the discharging process:
1. Connect to I2C bus to monitor battery
current and voltage.
2. Connect to required resistor value and
discharge through resistor, monitoring the
current and voltage until completely discharged
to end of discharge voltage (3.2V).
4.1 Safety Procedures
The following produces should be followed:





The exterior surface of the cells is covered with space grade Kapton adhesive tape;
this provides insulation for the cells and is not to be removed.
The battery should not be charged above 8.2V.
The battery should not be discharged below 6.4V.
The battery should not be connected to the charging system in reverse polarity
The peak discharge current should not be exceeded.
Page 6 of 6