The MaxTrac service manual states that 1.5 amperes is drawn during receive, and the M1225 service manual states that the 40-watt UHF radio draws 12.5 amperes during transmit. If we allow 1/2 ampere for the controller, the worst-case current load is about 14.5 amperes. The best choice for repeater service is a power supply rated for continuous load of 15 amperes, minimum, and an Astron RS-20 would be a good choice.
However, the M1225 will burn up in short order if run at 40 watts in repeater service, so it should be dialed back to perhaps 25 watts, with a fan blowing on its heat-sink fins. This will reduce its current draw to perhaps 9 amperes, but the fan will add perhaps 1/4 ampere. Even at the low power setting, you're still looking at a continuous load of perhaps 11 amperes, and again the Astron RS-20 is a good choice. Keep in mind that power supply ratings are usually based on intermittent loads, and the continuous load ratings are always lower and often are "fine print" specifications. If you are determined to build your own power supply from scratch, choose a design that can provide 20 amperes. I think you'll find that the parts costs of a home-brewed power supply in the 20-ampere class comes pretty close to what a commercial power supply costs. When you add the cost of a nice cabinet, you may not save a dime by building it yourself. Choose wisely... 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of agrimm0034 Sent: Friday, June 05, 2009 11:32 AM To: [email protected] Subject: [Repeater-Builder] Power Supply for Repeater GMRS home brewed repeater with a 25 watt maxtrac receiving and the transmit radio is a m1225 40 watt. The power supply on it now is around 6 amps and will not handle the load when radio transmits. Can anyone give me a approximate amp power supply I need. I found how to build a 10 amp power supply but I'm still not sure that will be enough.
