Many Repeater sites are in remote locations and rely on a solar/battery power source. One such repeater installation is VK2RAY, located near Albury, NSW, Asutralia. Repeaters can draw a substantial (>10A) amount of current and will flatten a battery very quickly it there isn't sufficient capacity, like after a few overcast days. Draining a battery below it's minimum voltage will, at best shorten the battery life span, at worst destroy the battery completely. The VK2RAY installation comprises 2 repeaters (2mt & 70cm) plus some ancillary equipment which provides an internet link,digital interface for various digital modes and a Raspberry Pi system to log data to APRS telemetry.
With such an array of equipment the low power shutdown process needs to be well considered and is not just a matter of "remove power from everything". For example, as the battery voltage drops to the largest power consumer should be shut down first, then the next lowest and at the telemetry should be the last system to loose power so we can monitor the battery state. Once the power has nearly run out and the telemetry is off the air, battery monitoring needs to continue, at a minimal power expense, bring systems back online when the solar has provided sufficient charge to restore reasonable battery capacity.
With these thoughts in mind I set out to design a repeater power management system for VK2RAY and this pages documents the power management system.
Step 1
Design and manufacture a Printed Circuit Board - whilst I normally use EagleCad, I decided to use AutoCAD for this task as it was mainly about component layout, substantial tracks to carry lots of current and fitting the board into a plastic enclosure.
The circuit layers (red and cyan) were laser printed onto Press-n-Peel PCB transfer film from Techniks Inc. (Jaycar HG9980), ironed onto a single sided copper clad board, touched up with a blue Staedtler Lumocolor permanent marker and etched using Ammonium Persulphate (Jaycar NC4258). The result was a reasonable quality board which turned out quite usable.
After a few [not so successful] trials of toner transfer another sheet of Print-N-Peel film was used to produce the silk screen on the component side of the board. Unfortunately the iron was a bit too hot so produced some messy results as it melted the blue PnP film!
The end result of the transfer was still acceptable and was fixed in place with a coat of clear varnish from a spray can.