Copyright © Parallax Inc.

28986 Li-ion Power-Pack/Charger – 2 Cell

v1.0 6/21/2011 Page 4 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.