At 09:43 AM 4/8/05, you wrote: >can you do the battery backup mod that is found the repeater builder .com >site for the astron rs35 on the rs 50 or should one order the kit from >astron and mount in externally to the rs50
Your statement above is not too clear. I read it as you want a battery backup mod for the RS50. Why not just do the actual RS50 BB mod? <http://www.repeater-builder.com/astron/astron-rm50a-bbsmall.jpg> Remember to set the Astron voltage to the battery float voltage, and the float voltage for a sealed lead acid (i.e. gell cell) is different than that of a wet lead acid and is different than a nickel-cadmium bank. The Astron actually has to be set to the float voltage PLUS the voltage drop of the series diode. In my case I disconnected the internal voltage set potentiometer and wired in a replacement that I mounted on to the front panel of the Astron - and I used a screwdriver-adjust pot with a lock nut. See <http://www.net-doc.net/images/locking-pot-standard.jpg> The lower nut mounts the pot to the panel, the upper nut is the lock. Another version that work fine is at <http://www.net-doc.net/images/locking-pot-mini.jpg> As to the actual Astron BB mod, it's essentially a paid of high current diodes wired cathode to cathode. If you don't mind a "non-pretty" implementation, the diode array from a high-current alternator will work just fine. The normal automotive alternator diode array has six diodes in it (or sometimes 12 in 6 groups of 2 in parallel), and the arrays are usually tossed if one diode is dead. The last time I swapped out the 60 amp alternator in my old 1971 Dodge Dart DEA undercover chase car I paid $5 at the alternator shop for a dead array out of a 120 amp alternator. I cut the plate with a sawzall and scavenged a piece with two good diodes that had a common cathode and enough space around the diodes for mounting holes. Using that plate mounted on standoffs I ended up with the same circuit as the Astron BB option at a cost of $5 plus the standoffs... and in the proof-of-concept prototype they were pieces of leftover 2x2 wood. The final version used polystyrene rod. All of this was done before Astron came out with their BB option. Nowadays it may be easier to just buy the kit - but sometimes it's more fun to roll your own. The resistor that shunts one of the diodes in the Astron schematic creates the charging current for the battery. In that design the charging current is not limited - it's limited only by the voltage difference between the Astron output and the battery and a 1.6 ohm 15w resistor. Under conditions of a dead battery that initial charging current can be higher than the battery can take - 1.6 ohms at 14v is between 8 to 9 amps. The rule of thumb on max charging current is 1/10 of the amp-hour capacity. Therefore a 20ah battery has max charging current of 2 amps. And the BB charge current into a dead battery is 8 amps? Another flaw in the Astron design is that the 8 amps flowing through the charging resistors is over 100w.... oops, POOF ! There goes the three 5w resistor(s). Now in real life, the battery voltage is not going to be zero, so the difference voltage is not going to be the full Astron output of 14 volts, but still... there are better charging circuits out there than a 14v 50a power supply and a 1.6 ohm series resistor. In my case I left out that charging resistor and used an external charger. Automatic current limiting battery chargers are common at auto parts stores - just make sure that you get one with a good sized transformer rated for continuous duty. Add a decent series choke and a filter cap and you can tame the hum that in the automotive world is harmless. I used a 10a charger and the secondary of a 12amp 6 volt filament transformer as a choke. At one time I needed to loan out the battery charger so for a while the charger was a 2 amp solar panel and a solar charge controller. Backup batteries and solar panels are an industry all their own, and there are solar hobbyists just like there are ham radio hobbyists - it's just that the solar hobbyists take advantage of the fact that you can legally run the power meter backwards! Some installations have no batteries and run the meter backwards during the day and forwards at night, and the owner pays the power company only for the difference. And in the summer, where they make more than they use, the company has to pay them! (look up "net metering" in Google). Home Power magazine, run by a ham, is the major magazine of that community. See http://www.homepower.com Mike WA6ILQ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
