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near one end of the cell, or the packaging may be printed with (+) and/or (-) designators (as
shown in Figure 6).
Place the bottom (negative) end of a cell against the springs in the CELL A holder, and then
gently slide it down and in at a slight angle into the holder until it snaps into place. Repeat for
the CELL B holder. Note: Cells without internal PCBs 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.
If you need to remove the cells (i.e. when the cells wear out), you can use a small, flat piece of
plastic (such as a comb or similar) or a small pair of needle-nose pliers with tape or heat-shrink
tubing attached to the ends (to prevent shorting) to gently pry them out.
Lithium cells come pre-charged, so treat them carefully—they already contain a significant
amount of energy. Handle with care and do not short the terminals!
Step 14. Re-mount your control board to the (4) standoffs on the top of the robot chassis.
Step 15. Connect a center-positive 2.1 mm wall transformer (such as Parallax #750-00009) to the
Charging Power Input jack as noted in Figure 4. 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 will not operate. Also, a lower current will not harm the cells; they'll just take
longer to charge.
Step 16. Upon application of charging power, the green LED (visible through the slot on the right rear)
will turn on. After a few moments, the blue status indicator LEDs should come on. Solid blue
means that the cells are being charged.
Copyright © Parallax Inc.
Figure 6
Li-ion Small Robot Power Pack-Charger (#28988)
v1.2 3/3/2015 Page 8 of 10
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