Astron Battery Back-Up (Float) Modification

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Back to Home A Battery Back-Up Modification
of Astron Linear Power Supplies
By Kevin K. Custer W3KKC
Maintained by Mike Morris WA6ILQ

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 commercial AC power mains voltage is removed or applied.

Caution: This mod just adds a current limiting resistor in line with the voltage feed back of the regulator chip, otherwise destruction of the chip will result.

Modification: Installation is straight forward:
A) Cut the trace on the PCB between Pin 4 of IC UA723 and the wiper of R5.
B) Bridge the cut trace with a 10K ohm 1/4 or 1/2 watt resistor
C) Set the output voltage by adjusting R5 to desired "float" voltage with no load or battery connected to the power supply.

Voltage settings:
A) For standard deep cycle marine batteries, set voltage to 13.50 vdc. ( Do not forget to periodically check the water level in battery! )
B) For sealed gel cell batteries, set voltage to 13.80 vdc.
!! Use of standard car batteries is 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:
1.) Hook the equipment to the battery through a fuse.
2.) Hook battery to power supply through a second fuse.

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.

Update 2015 – Two things:
1) If you are going to have a situation where the Astron loses power and has a +12 volt source across it's output (like if you have a battery connected) then you will want to make sure that your Astron has CR7 installed (it was left out of a number of units). Look at the RS-35M schematic. It's a 10 amp 100 volt diode. This wil protect your pass transistors.

2) Bob Meister WA1MIK authored an article on adding voltage and current adjust potentiometers and discuses the current limiting method in his article. Worth reading.

If you have enjoyed this construction article please e-mail me at kuggie //at// kuggie//dot//com and let me know.
I may take the time to do more quality construction projects in the future.

The Astron Corporation Irvine, California 92618
949-458-7277 8a-5p Pacific Time.

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