Dwayne, I have done exactly as you said with a relay and a second pot. It works well.
The only problem one does not realize the power savings one might think although it is a noticable amount. The reason is if you look at a MII PA running 100 W its current draw is about 20 Amps. by reducing the power out to 60 W the PA still draws about 15 Amps. Reducing it to 20 W would probably give a current draw of 8 Amp. Just have to try with the pot now in place. It would improve your battery life. If you use a smaller PA as you suggested, MII or Exec II (both can be driven by the MII exciter just fine) a 35 W PA turned down to 20 W the current draw will be noticably lower than 20 W with the 100 W PA. Of course this is more work with the RF switching. 73, ron, n9ee/r >From: ldgelectronics <[EMAIL PROTECTED]> >Date: 2007/10/16 Tue PM 06:11:14 CDT >To: [email protected] >Subject: [Repeater-Builder] Reducing power out when on battery backup. > >Hello All, > >I have a requirement to install a battery backup system at a local >ham repeater. It's a GE Mastr II running about 100 watts. With that >much RF power, a couple of 100 AH batteries is only going to last a >few hours. > >My first thought was to add a second lower power RF amp (something >like 20 watts or so) and use coax switches tied to the AC mains to >switch to the smaller amp when the AC power was out. This should give >me a factor of 4 or 5 more amount of time on the backup batteries. > >The second thought (and here is where I need input), was to bring the >variable resistor (R8 on the VHF version) from the 10 watt driver >board to a smaller external board. Then add a second variable >resistor and a relay to switch between the two. This should give me >two independent amp settings that can be controlled by a single >control. > >Is there any reason why this should not work? It would save the cost >of the second smaller amp and two fairly expensive coaxial relays. > >The relay could be controlled from the repeater controller or >automatically with just a 12v DC wall wart. > >Dwayne Kincaid >WD8OYG > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
