> Darren King wrote: > > I'm trying to build in UPS protection into a circuit I'm working on > and I was wondering if anybody had done this already and had some > circuit tips for me. I want to charge batteries all the time and then > switch to them when mains is disconnected. For error checking I want > to check battery level. I guess I will use AD for this and if it > starts to drop when charging then I will automatically assume the > batteries are going bad. But I also want to know when I'm on the > batteries and when I'm on the charge... > > Any help? Thanks guys. > > Darren King Do you need 117VAC, or could you just have a "trickle" charging (with perhaps faster charging when they're too discharged) these batteries, then a pair of diodes, one to +V on the batteries, one to another AC-powered power supply set about 1/2 volt higher than the batteries' voltage, so that switching is done automatically? Or, if you "float" charge Lead-Acid batteries (and the circuit can run with a multiple of 2V or so as Vcc - or you regulate down from the Battery / AC voltage), just regulate the voltage across the batteries (with the AC-powered charger), keeping them topped off - that's what security/alarm systems do. A couple LM317's will do nicely for Voltage and current limiting (National web pages for datasheets, I can give a URL if you need, ask off-list.) Are we on AC or batteries? If (Optoisolator across the transformer, is not flashing at 60 Hz) then (We're on the batteries), else (Either we're on AC and happy, OR, power's gone, we're not running at all!) Mark -- I do small package shipping for small businesses, world-wide.