Mark, I once helped maintain three of the older Icom repeaters for a club. They had a similar arrangement to what you describe...built-in 12V supply, with binding posts for direct 12 VDC input, but not an adequate charging system.
All our sites featured well-maintained generator back-up, so we never did an emergency DC supply, but we did kick some ideas around. One was a separate charger with a DPDT relay. The relay's coil was powered by the AC line; the normally closed contacts were connected to the (+) and (-) binding posts on the back of the repeater; the normally open contacts to the (+) and (-) from the charger, and the common contacts to the (+) and (-) from the battery. Most linear power supplies have big enough capacitors to keep the repeater up, even in transmit, for the few milliseconds it takes the relay to switch, and the closer that decaying voltage is to the 13.6 or so volts of a floating lead-acid battery, the less current is switched by the relay contacts. 20-amp relays with coils set up for 117 VAC are common. I didn't like this idea because it didn't provide any protection from brownouts. (Like dropping a phase on the 440 3-phase coming into a broadcast transmitter facility.) Another reasonable approach might be a switching supply which could output a regulated 13.6 VDC with inputs from 10.5V (death's door for a six-cell lead-acid battery) to, say, 20V (from an unregulated charger capable of 13.6 VDC during transmit.) Just parallel the charger's output (thru a diode to isolate it during blackouts or brownouts), the battery and the switching supply's input, and the repeater would never see anything other than perfect 13.6 VDC unless the battery ran all the way down before power returned. I've since been spoiled by a whole different approach. I built a UHF repeater that was completely "off the grid." It used Repco RFID data boards rescued from a dumpster and repaired. The 2-watt transmitter, receiver, adapted Motrac helical preselector and S-com 5K drew a total of under 1 amp, key-down. That meant a group-27 size deep-cycle marine battery, rated for 100 amp-hours, would run the repeater key down for more than four days with no charging whatsoever. The system was charged by a single solar panel which made 3 amps at 13.6 volts or better for much of each day. The charge controller was a simple relay which took the solar panel offline when the battery hit 14 volts each day, and reset at sunset. This system was crude, but worked great in Orlando, FL. Even if the repeater had been busy for hours the night before, the battery generally reached full charge by 11am the next morning. (I knew because the 5K was programmed with a macro to switch to a different CWID and longer tail when the charge relay had energized to drop the panel offline.) I only tell you all this because the experience got me very interested in using solar to augment or replace commercial AC power for charging batteries. Even when I replaced the Repco boards with a GE Mastr II mobile conversion and a 7K, there might have been enough power available to keep the repeater up indefinitely in light usage. Four panels like the one I used, more battery capacity and a more sophisticated charge controller would probably have been enough to cover a 100% duty cycle for at least a day-long emergency net or public service event. I don't know what your budget is, but the cost of panels has come down. A more sophisticated shunt-type charge controller could leave the battery at full charge at sundown each day, rather than shutting down for the day at 11am like my one-shot relay did. (I later connected a logic output from the controller to allow restarting the charger in the afternoon using a DTMF command or a start-of-activity macro, to leave the battery closer to 100% at sundown.) I've also been amazed lately by the new, small wind turbines. Many repeater sites have consistent enough winds to make this a viable option. A hybrid system combining part-solar and part-wind would be almost infallible. Neither sun nor wind are 100% reliable, but there are few moments at most hilltop repeater sites when you don't have at least one of the two. 73, Paul, AE4KR ----- Original Message ----- From: Willis M. Hagler To: Repeater-Builder@yahoogroups.com Sent: Wednesday, December 12, 2007 10:49 PM Subject: [Repeater-Builder] power supply / battery system for repeater site Hello Everyone, I am wondering what repeater operators commonly use when a 12v power supply as well as a battery charging and switching system is needed at a repeater site. My repeater has an internal 120v power transformer that feeds a 12v regulator box, and also has a battery circuit on the back of the repeater that will allow it to draw from batteries when the main power is lost. It supplies a very low current trickle to keep the batteries charged up, however if the batteries drain due to extended power outage it does not provide any sort of reasonable facility to charge them back up again. The manufacturer recommends to take the batteries off, charge them externally, and then return them to float charge... however that's not very feasible if the repeater is located on a mountain or some other location that's not easily accessible on short notice. I'm thinking of just ditching the internal power supply and building a more robust off-board power supply and battery charging system that can switch onto the batteries and charge them up again when the main power returns. For use at home I like the PWRGate units which maintain the batteries nicely but I am wondering if others have used those at repeater sites with no trouble? Thanks anybody who has information to provide. This group is a wonderful resource for all things repeater-related. Yours, Mark Hagler W7WMH Seattle
