Rechargeable A/B Battery Power Supply

This is the final leg in the portable "GlowBug" project. The entire project consists of a 3 tube Qrp transceiver for 40 meters, an AC power supply/charger, and finally this battery supply for field use.

The design parameters for the supply were to provide for an adjustable filament voltage of 1 to 6 volts and capable of supplying approximately 500ma of current. The HV supply was to be adjustable as well, with fixed stops at 22, 45, 67.5, and 90 volts. Current requirements are on the order of 100 to 125 ma. maximum. In addition, a fixed supply of 18 volts was added to enable operation of the low plate voltage receivers of which I have been experimenting. This was necessary as many of the Qrp Tube type transmitters use cathode keying, requiring an isolated ground from the receiver ground. Otherwise the ground paths are completed through the power supply causing the transmitter to be keyed all of the time.

The filament and HV supplies were to be metered for both voltage and current. The current meter was to monitor both discharge and charging conditions.I chose to use one meter for both supplies by switching in the appropriate resistors for the intended purpose.
 

For the HV supply, I chose to use two parallel banks of 25, 3.6v Nickel Hydride batteries. I obtained these from B.G. Micro, at a cost of $0.99 ea. Although it may seem expensive at first glance, the decision to build such a supply came about because of the high cost of replacing standard "B" Batteries on a regular basis. If you look closely at the battery bank, you can see the taps for the various supply voltages.
  For the Filament and 22v supplies, a higher current capacity battery was chosen. These are surplus batteries I found at $0.25 ea. They supply 360ma/h per battery. The 18V supply is wired in series whereas the filament supply is wored in parallel. Eventually I will use two of the filament battery banks wired in series and passed through an LM317 variable regulator, for a constantly variable filament supply of 1 to 6 volts.
 

This shows the interior construction of the Power Supply. Note all of the controls are on the back of the unit, necessary to accomodate the rather large (proportionately) meter that occupies the entire front panel. By the way, the chassis' for all of the individual units used in this project are standard Radio Shack cabinets that measure approximately 3"H x 3"W x 6" deep. The cabinets are reasonably priced at $6.95. Working with them can be trying as the material is a VERY soft aluminum.
  This is the completed Power Supply shown with the companion Rig and AC Power supply/charger. For more information on the custom meters, click here. For further data on the Rig, click here.