United States Air Force Auxiliary
CAP National Technology Center

Battery Back Up Modification for Astron Power Supplies

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Modification or service of Civil Air Patrol owned equipment should only be performed by qualified technicians approved by the Wing/Region Director of Communications. 

This modification allows a battery to be floated on the Astron power supplies for battery back up while protecting the regulator chip from damage when the ac power is removed.

It essentially is adding a current limiting resistor in line with the voltage feed back of the regulator chip.

Installation is straight forward:

Cut the trace on the PCB between Pin 4 of IC UA723 and the wiper of R5

Install a 10K ohm 1/2 watt resistor to bridge the cut trace between Pin 4 and R5

Set the output voltage by adjusting R5 to desired voltage with no load or battery connected to the power supply.

Voltage settings:

a- for standard deep cycle marine batteries, set voltage to 13.5 vdc. ( Do not forget to periodically check water level in battery )

b- for sealed gel cell batteries, set voltage to 13.8 vdc

Use of standard car batteries are not recommended.

It is HIGHLY recommended that a fuse rated at equal to or less than the maximum current rating of the power supply be installed between the battery and the power supply. This will protect your system in the event that the power supply's crowbar circuit fires and tries to pull the current of the battery to ground.

Recommended hook up should be:

a- Hook equipment to the battery

b- Hook battery to power supply

In this configuration your equipment is being powered by the battery and the power supply is serving two functions. One is keeping the battery charged, and second to aid during high current draws. It will also allow the battery to act as a surge protector adding some additional protection to your equipment from line surges.

Astron Power Supply Schematic
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