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Li-ion Power Pack / Charger – 2 Cell (#28986)
The Li-Ion Power Pack-Charger – 2 Cell is an integrated storage cell and charging system on a single
3” x 4” printed circuit board. Compatible with most 18650-size Li-ion cells, the total power output
capability of the system is approximately 14–20 watt/hours, depending on the capacity of cells you
choose. Although this Power-Pack/Charger is compatible with both protected and unprotected Li-ion
18650 cells, Parallax highly recommends using the protected types, such as Parallax part #28987.
Features
PCB-mounted cell holders with on-board charging circuitry
Multiple power input/output options
On-board output fuse protection
Nominal 7.4 VDC output; 8.2 VDC maximum
Standard 3” x 4” PCB footprint integrates well with the Board of Education
Automatic charge/discharge switching circuitry
Holds two rechargeable 3.7 volt Li-ion 18650-size cells
(#28150), Propeller
™
Proto Board (#32212), or any application needing a reliable power supply with an integrated
charging system
®
Multiple LED indicators provide charge readiness information for each individual cell; a status key
for the LED indicators is printed on the board.
Aggressive holders retain cells in any board orientation and in moderate shock environments,
such as mobile robotic applications. Cells are not permanent, and can be replaced.
Dedicated circuitry continuously monitors the charging process to ensure safety, efficiency, and
to maximize the number of charge/discharge cycles of each cell.
Key Specifications
Charging Power Requirements:
supply (#750-00009 works well)
+5–12 VDC @ 1amp (min.); 2.1 mm barrel jack, center positive
Power Output: Unregulated nominal 7.4 VDC @ 1800—2600 mAh (depending on cells used)
Dimensions: 3.0 x 4.0 x 1.0 in; 7.6 x 10.2 x 2.54 cm
Charging Time: 1 – 6 hrs or more, depending upon the discharge level and capacity of the cells
Application Ideas
Portable power for data-logging applications
Mobile robots
Standby power / automatic power-switching
Automatic charging circuits
Stackable auxiliary power solutions
Boe-Bot / Board of Education / Propeller Proto Board Auxiliary Power Supplies
Stingray
™
Robot (#28980) battery pack upgrade
®
Copyright © Parallax Inc.
28986 Li-ion Power-Pack/Charger – 2 Cell
v1.0 6/21/2011 Page 1 of 7
Packing List
(1) Li-ion Power-Pack / Charger – 2 Cell PCB, 3” x 4”
(1) Li-ion Battery Cable (#802-00020)
(2) 2-amp fuses; 1 pre-installed, 1 spare (#452-00065)
(4) Black dome rubber feet (#700-00087)
(4) Clear square rubber feet (#700-00037)
Additional Items Required
(2) Li-ion 18650-size cells (#28987 or equivalent)
+5 to +12 VDC power supply, center positive, 2.1 mm barrel jack (#750-00009 or equiv.)
Safety glasses
Multi-meter (VOM)
Assembly Instructions
CAUTION: Before inserting the cells into the holder, two sets of rubber feet must be applied
to the correct places on the bottom of the PCB, following the steps below.
Aside from applying
the rubber feet and installing the cells into the holders, the PCB itself comes fully assembled and tested.
Lithium cells come pre-charged (to some extent), so treat them carefully—they already contain a
significant amount of energy. Handle with care and do not short the terminals!
Step 1: Turn the PCB over so that it’s oriented as shown in Figure 1 below.
Figure 1
Step 2: Place a clear flat rubber foot over each of the (4) soldered cell terminals as shown in Figure 1.
These feet protect the cell holder terminals from being accidentally shorted. Remember: Li-ion
cells have a lot of stored energy and rapid discharge can result in an unsafe condition. Even
though the output of the board is fuse protected, direct shorting of these solder points is not
within the fused portion of the circuit.
Copyright © Parallax Inc.
28986 Li-ion Power-Pack/Charger – 2 Cell
v1.0 6/21/2011 Page 2 of 7
Step 3: Place a black domed rubber foot in each of the four locations designated by the dashed circles on
the silk screen. These provide stability for the board if you set it on a flat surface. If you will be
mounting this device on standoffs where the board traces cannot be shorted, then you can skip
this step.
Figure 2
Step 4: Carefully remove the cells from their packaging. Note the
positive cell polarity. Various brands of cells are marked
differently. The positive terminal may be indicated by a
ringed indentation near one end of the cell, or the packaging
may be printed with “+” and/or “-” designators (as shown in
Figure 2).
Step 5: Using a multi-meter (VOM), measure the voltage of each
cell. Write down the sum total of the two voltages. If either
cell measures less than 3 volts, it may be defective.
Step 6: Turn the board right-side up as shown in Figure 3.
Step 7: Carefully place the bottom (negative) end of a cell against
the spring in Cell Holder “A”, and then gently slide it down
and in at a slight angle into the holder until it snaps into
place. Repeat for Cell Holder “B.”
Note: Cells without internal PCB’s will snap into the holders easily.
Higher quality cells (those that have internal PCB protection such as Parallax #28987), are slightly longer.
They will fit into the holder, but they are a very tight fit. The holder’s ends will flex a bit as you insert the
cell. Sight along the sides of the cells to make sure that they are completely seated into the cell holders.
CAUTION: Removing the cells once they have been inserted into the holders is NOT
recommended.
The holders are tight by design, and so the cells do not come out easily. Be aware
that the body of a Li-ion cell is usually covered by a thin plastic wrapper that can be easily pierced.
Furthermore, the negative terminal of a Li-Ion cell actually encompasses the entire body of the cell, to
right up near the top of the Positive terminal of the cell itself. Attempting to pry a cell out of a holder
with a sharp-edged screwdriver blade could pierce the cell’s wrapper and short out the cell, damaging it.
However, if you ever do need to remove the cell, (i.e. when the cells wear out), a dull-edged, non-
conducting prying tool, such as a chip-puller, is recommended. If such a tool isn’t available, you can use
a small, flat-bladed screwdriver covered in heat-shrink tubing or electrical tape. A small pair of needle-
nose pliers (also covered in insulated material) works well too.
Initial Testing
Step 8: Measure the voltage by placing your VOM’s probes on the top two screw terminals on the green
Cell Power Output terminal block. You should measure the same voltage as the sum of the two
cells you measured in Step 5 (above).
Step 9: Plug the Battery Cable into the Cell Power Output jack (See Figure 3). Now measure the output
voltage by inserting the positive VOM probe into the inside of the barrel plug on the end of the
adapter cable, and touching the negative VOM probe to the outside ring of the barrel plug.
Again, you should measure very close to the same voltage as the sum of the two cells you
measured in Step 5 (above).
Copyright © Parallax Inc.
28986 Li-ion Power-Pack/Charger – 2 Cell
v1.0 6/21/2011 Page 3 of 7
Step 10: Connect a “center positive” 2.1mm wall transformer (such as Parallax #750-00009) to the
Charging Power Input jack as noted in Figure 3. The power supply should have a voltage output
between +5 VDC and +12 VDC. The amount of current necessary to charge the cells is
controlled automatically by the circuitry; however your wall transformer should be rated at 1 amp
or more to minimize charging time. If the charging current supply is too low, the charging
circuits may not operate. In addition, a lower current will not harm the cells; they’ll just take
longer to charge.
Step 11: Upon application of charging power, the green LED (next to the barrel jack) will turn on. After a
few moments, the blue status indicator LEDs should come on. Solid blue means that the cells are
being charged.
Figure 3
Circuit Description and Operation
CAUTION: Due to the nature of the charging circuitry and the size and very high capacity of
the cells, the heat-sinks near the cell holders may get hot!
The amount of heat generated
depends on the length of charging time, the amount of charge on each of the cells, and the voltage input
of the charging power source. For example, a 12 VDC transformer and/or completely drained cells will
generate more heat than a 7.5 VDC charge input or near-fully charged cells.
With cells installed in their respective holders, and with no external connections to the input/output jacks,
the circuitry is inactive and there is no current flow (other than some very, very small leakage current
through the inactive charging circuits).
Upon application of +5 to +12 VDC to the Charging Power Input jack (J1), the following happens:
a) The Charging Power Input (Green LED) is activated.
b) The Auxiliary Raw Power Output has power that is directly from the charging source (wall
transformer, solar panel, car battery, etc.). This power can be used to operate another circuit
or application using the (included) Battery Cable.
c) Each cell is electrically disconnected and isolated from the other.
d) The Cell Power Output jacks are disconnected from the cells, and disabled.
e) The dual charging circuits begin a qualification mode to determine each cell’s characteristics.
f) After checking the cells, LED status indicators are activated. If required, each cell begins
charging their respective cells.
Copyright © Parallax Inc.
28986 Li-ion Power-Pack/Charger – 2 Cell
v1.0 6/21/2011 Page 4 of 7
When Charging Power is removed, it results in the following:
a)
b)
c)
d)
The Auxiliary Raw Power Output jack is disabled.
Cell charging circuits are disabled and Status indicator LEDs are disabled.
The cells are electrically connected into a series configuration.
Cell Power Output jacks connect to the cells, resulting in a 7.4 to 8.2 VDC output.
Jack/Plug/Indicators Functional Descriptions
Green LED:
Charge Power Indicator—whenever charging power is applied to the Charging Power Input
barrel jack, the board is receiving power.
Charge Power Input:
2.1mm barrel jack, center positive. +5 to +12 VDC input. Do not reverse the
input voltage as this may damage the charging circuitry. Charging time is dependent on the
amperage available from the power supply you choose, as well as the capacity of the cells you
choose.
Aux. Raw Power Output:
Polarized, right angle, female, bottom pin positive. This connection can be
used to power another device. For example, you can charge the Li-ion cells and operate another
device from the same power supply. When you plug in wall-transformer (to charge the Li-ion
cells), you can use the Molex/barrel jack cable to provide power to another device (such as a
Board of Education, Propeller Proto Board, etc.) This is not power from the cells. This is the
same power that is charging the cells, via your charging supply input on the Charge Power Input
barrel jack.
Cell B Red Status:
This LED indicates a fault condition in Cell B.
Solid = There is/was a fault in the cell, or there was a glitch during the charging process.
Remove and then re-apply power to the board, to see if the condition persists.
Blinking = The temperature of the cell is outside the safe charging zone. The safe charging
zone is typically set for between 32 and 113 °F (0 to 45 °C).
Off = There is no fault condition detected with Cell B, or there is no cell in the holder.
Cell B Blue Status:
This LED indicates the charging status of Cell B.
Solid = The cell is charging.
Blinking = The cell is fully charged.
Off = The cell was already fully charged and no charging was needed, there is no cell in the
holder, or the cell is not fully-seated into the holder.
Cell Power Output:
Polarized, right angle, female, bottom pin positive.
This Power Output jack is the output from the cells.
When there is no Charge Power Input (i.e. When the wall charger is disconnected from the PCB),
the two 3.7 volt cells are electrically connected together in a series configuration, and the
resulting power (3.7 VDC x 2 cells = 7.4 VDC) is available at this jack.
Upon application of Charge Power, Cell Power Output is disconnected from the on-board cells,
and this jack is disabled.
Cell A Red Status:
This LED indicates a fault condition in Cell A.
Solid = There is/was a fault in the cell, or there was a glitch during the charging process.
Remove and then re-apply power to the board, to see if the condition persists.
Blinking = The temperature of the cell is outside the safe charging zone. The safe charging
zone is typically set for between 32 and 113 °F (0 to 45 °C).
Off = There is no fault condition detected with Cell A, or there is no cell in the holder.
Copyright © Parallax Inc.
28986 Li-ion Power-Pack/Charger – 2 Cell
v1.0 6/21/2011 Page 5 of 7
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