|Re: HP-25 Battery Pack: A simple external charger|
Message #16 Posted by Andreas Grund on 19 Oct 2009, 5:35 a.m.,
in response to message #15 by Vieira, Luiz C. (Brazil)
The reasons are known why Woodstocks better should not be run with the AC Adaptor. Therefore I built a simple and low cost external charger, which uses as power source the existing AC Adaptor.
On a base plate of plywood 7.5x10.0x0.6cm I glued a box of wooden stripes (1.5x0.5cm) in exactly the dimensions of the battery compartment of an HP-25 (or any other Woodstock...)
In one end of this box I cut out an area of 1.5x0.8cm, which gives place to the retainer of the original battery pack and furthermore facilitates to remove the battery pack from the box. In the other end I drilled two 2.00mm holes in a distance of 14mm for the charging contacts. These contacts are M2x16mm screws.With nuts and washers the correct distance of 53.5mm can be easily adjusted.
As connector to the AC Adaptor's plug two screws (M2x12mm) are used (head removed with cutting pliers). Drill two holes, diameter 2.0mm in a small wood stripe (glued on the base plate) and fix the screws with a 2k adhesive in the bores.
Now, the electrical part comes. Connect left connector in the box with the left connector to the charger with a 8.2 Ohm resistor (white body in the photo), soldering tags may be helpful and connect correspondently the two right connectors with a diode (I used a standard 1N4001). The "positive" end of the diode is marked with a silver or white ring, this needs to direct to the connector in the box.
The AC voltage is 9.0V, at the charging contacts (idle) it 4.2V DC.
Finished - or continue with painting.
Materials: Plywood, wood stripes, 8.2 Ohm resistor (1W dissipation), diode 1N4001, soldering tags, 4 M2 screws with washers and nuts, wood glue, 2k adhesive, paint.
Tools: Jigsaw, sand paper, soldering iron, solder
Cost: approx. 1$
Time demand: 3hrs.
Edited: 19 Oct 2009, 6:20 a.m.