Mark, There have been some good suggestions. However, there are two issues that you need to watch carefully for remote battery backup operation. The first, as some have mentioned, is the charge current if the battery is run down and AC power comes back.
For example, if you just tie a battery across your power supply (with a diode or whatever), it will be a great back up. But after it has run on the battery for many hours and the AC power comes back up, the power supply will send a bunch of current to try to charge the nearly dead battery. This will almost certainly blow the fuse between the power supply and battery as it could be 100 or more amps. A simple solution is to run the repeater off the battery and just use a charger to keep the battery happy (charged or uncharged). While this sounds good, it exposes a huge problem that is often overlooked. And that is what happens when the battery runs down. Running the battery completely down does two things, first it drastically reduces the number of times it can be charged and second it usually ends up in transmitter cycling mode for many hours or days. [Transmitter cycling mode is when the battery runs down far enough that it can't power the transmitter, but can barely power the controller. This ends up with the controller coming on, which keys the transmitter to ID, then the battery voltage drops (because of the transmitter) and the controller turns off because the voltage is too low. The transmitter goes off when the controller goes off and the battery voltage slowly increases back to the point to where the controller will come on. Repeat this for days and days or until the battery is completely dead and probably could never be charged again] To combat these two issues, there are two options. One is to power the system off the battery and use a small power supply to charge it, but then insert a battery controller system to handle the charging and Low Voltage Disconnect (LVD). The are plenty of 20 amp solar panel controllers for around $50 that will handle nearly everything for you. Larger ones are also available. The second method is to modify a simple Uninterruptible Power Supply (UPS). Just take the battery out and connect your larger external battery in its place. It will take care of the charging, LVD and give you 110 volts. Just be sure to pick one that is rated twice of your max watts. If your repeater draws 20 amps at 12 volts, that's 240 watts. So be sure to get a 600 watt UPS (or higher). Used 1200 watt UPSs are under $50 on ebay. Many of them that cheap may have a bad battery. Since you're going to use your own external 120 AH (or whatever) battery, it would not matter if the used one is bad. You get the better deal since no one else wants to buy a UPS with a dead battery. I have both types and while the solar controller method is more efficient, the UPS method is somewhat easier. Take your pick. Dwayne Kincaid WD8OYG > Willis, I have used a simple diode circuit in several > repeaters I have converted to battery backup. I like > the solid state solution more than a mechanical relay > for reliability. > > The circuit is as follows: > > Place a diode in series with the output of your power > supply. (it can be the internal supply) > > Place a diode in series with the battery output to > your repeater load. > > Place a diode and resistor (10 ohm 25 watt) in series > between the power supply output and the battery. > > All diodes have their cathode or bar pointed toward > the load. Choose the diodes to carry the current the > repeater is drawing. (the battery charging diode > needs to only handle a couple of amps) If the battery > goes down completely, the resistor limits the charging > current so the power supply is protected. Raising the > output of the power supply by .7 volts to overcome the > drop in the diodes would bring the power back up to > what it was. Another factor would be to adjust the > power supply output so that the battery floats at 13.5 > VDC for optimizing the battery charge vs electrolite > loss. > > 73 - Jim W5ZIT > > --- "Willis M. Hagler" <[EMAIL PROTECTED]> wrote: > > > 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 > > > > > > > > > > ______________________________________________________________________ ______________ > Never miss a thing. Make Yahoo your home page. > http://www.yahoo.com/r/hs >
