Travel Battery Pack
This photograph shows the power supply I used with the K1 on the last overseas trip. The battery is an 1800 mAh NiCd pack donated by Dr. Megacycle, KK6MC. Thanks Jim, the battery worked like a charm! I believe that it was a recycled pack that was removed from medical equipment during a scheduled replacement cycle. It has a date code from 1997. Some postings on QRP-L suggested that free used batteries can sometimes be obtained from the local medical electronics department at your local hospital or medical center.
I removed the original battery connector and added an in-line fuse (2 amp) plus the radio power plug. The coaxial power plug is a Radio Shack 274-1569A (5.5mm OD by 2.1 mm ID), which is the most common size used on QRP radio kits.
The wall-wart is a Radio Shack 44-1141 rated at 12 VDC at 500 mA. To connect the wall-wart to the battery for charging, I built a short adapter cable with two Radio Shack in-line coaxial power connectors wired back to back.
The radio was operated from the battery at 4 to 5 watts of RF output power. After the operating session, the battery was connected to the wall-wart to bring it back to full charge. This is a very simple and compact system.
The recommended charging current for NiCd packs is a steady current of 10 percent of the mAh rating, or 180 mA in this case. The current measured from the Radio Shack wall-wart starts out closer to 270 MA when the battery is discharged and decreases as the battery comes up to full charge. A further desirable refinement of this battery system would be a current regulator.