Tony, What's to "back up" at a site already supported by both solar and wind? Is there a temp below which the PV panels won't produce or the wind turbine won't turn? Deep snow covering the PV panels?
I guess my preference, for a number of reasons, would be to have a way to remotely invoke an operating mode for the repeater which could dramatically reduce standby current drain and/or transmitter power when the batteries were detected to be at any risk, or just massively bulk up on battery capacity. I had a solar powered UHF repeater in Florida once that used a 2-watt Repco RFID transmitter strip and companion receiver. Total current drain while repeating was about 700 mA. A standard 100 AH deep-cycle battery represented four days' reserve at 100% duty cycle. That would be expensive to replicate with normal repeater power levels, but maybe not as expensive as some less robust alternatives. If the PV panels get covered with snow, could you rig an automotive windshield wiper system to fire once an hour during snowstorms to keep them clear? If it's -40º, would the snow be dry and light enough to clear with a periodic blast from a cordless leaf-blower motor? The decent ones use 18-volt battery packs, but a small DC-to-DC converter could keep it charged, or switch two small 12V aux batteries charged off the main system into series, and run them through a dropping resistor to protect the motor. You'd only be running it for a few seconds at a time to keep the panels clear. What's the ground like? Could you dig deep enough to bury a battery storage locker below the frost line? Cave effect is a cheap battery temp regulator! If you're going to store fossil fuel at the site for use in protecting the batteries from freezing, what about just heating the batteries to keep them above 0ºC, and forget the moving parts involved in a generator scheme? Internal combustion engine generators are notorious for having starting problems when needed, because they sit much of the time. Interesting project and questions! 73, Paul, AE4KR ----- Original Message ----- From: Tony VE6MVP To: [email protected] Sent: Thursday, February 18, 2010 10:16 PM Subject: [Repeater-Builder] Low voltage disconnect in Alberta winters and more Folks I've been reading the low voltage disconnect thread with a great deal of interest. Thanks for the tips and suggestions. We're putting up a VHF repeater and two UHF link radios on a solar/wind power site. Given Alberta winters what would you folks suggest as a low voltage disconnect value to avoid the batteries freezing in winter? Which can hit -40 for a few days. Also we're thinking of having a backup power generator being a lawn mower motor hooked up to an auto style alternator and a rioughly eight or ten hour fuel tank. If the batteries get too low then we'll just attempt to get into the site, fire up that home made generator and walk away. We'll make sure it looks like a rusty piece of garbage so no one who wanders by is likely to steal it. Any comments? (Apparently the snow drifts can get quite bad so we might need to borrow a snowmobile for the last 400 yards or so.) We're thinking of putting the batteries in a chest freezer disguised by thin plywood so it just looks like a box. We're told by the site owner that a fridge looks way too much like trailer trash so disguising it with wood should work. I'm thinking we would put the charge controller in there for a little heat and the dump load in winter Are we nutz? Have I asked some stupid questions? Tony
