A really simple circuit that I have used in a couple of repeaters uses three power diodes and a resistor. Select diodes that will carry the repeater load at about 50% of their rating.
Place one diode in series with the power supply to the repeater. This one keeps the voltage from backing up into the power supply when power is being supplied from the battery. Next, place a power diode in series from the battery to the repeater. Then place a power diode in series with a 10 ohm power resistor (50 watts or so) from the power supply to the battery. This keeps the battery charged. The resistor limits the inrush current from the power supply in case the battery gets discharged. It also limits the maximum current the power supply has to deliver when bringing up a discharged battery. Adjust the voltage from the power supply to float the battery at 13.5 VDC, or as close to that value as possible. Do this after the batteries are charged and power is being supplied to the repeater from the power supply and not the battery. This will minimize electrolyte loss while providing a reasonable capacity from the batteries. Hope this helps - 73 - Jim W5ZIT -----Original Message----- From: [EMAIL PROTECTED] To: [email protected] Sent: Mon, 8 Jan 2007 9:31 PM Subject: [Repeater-Builder] Battery backup Hi, New member here. Thanks for allowing me to join. Our club has acquired some large lead-acid 12v batteries we would like to use to back up our repeater in emergency situations. Does anyone know of a good (but simple and inexpensive [we are a very small group in a very small town]) circuit to accomplish this? Any input would be appreciated. Danny WM5C Heart Of Texas Ham Operators Group (HOTHOG) Brady, TX www.hothog.org ________________________________________________________________________ Check Out the new free AIM(R) Mail -- 2 GB of storage and industry-leading spam and email virus protection.
