Jesse, The short answer is that switching power supplies are significantly more efficient than either linear or ferro-resonant power supplies over most of their output range. At idle, switchers draw practically no current, whereas linear and ferro-resonant supplies are always generating some heat- and heat is wasted power.
Before we get too far into this discussion, I must remind our readers that measurement of AC power requires a true-RMS power meter; one cannot measure AC power by taking independent readings of voltage and current. When separate readings of AC voltage and AC current are made and then multiplied together, the product is volt-amperes not watts. Volt-amperes, or VA, is apparent power not real power, and it will be greater than real power in any inductive circuit. To measure real power accurately, an AC power meter uses a four-quadrant multiplier to make measurements of voltage and current at the same point in the cycle. The aluminum disc that spins in your kilowatthour meter is driven by two coils- one which is energized by the line voltage, and one which is energized by line current. The torque produced in the disc is the instantaneous product of voltage and current, and that torque is proportional to true power in watts. A permanent magnet "brake" controls the speed of the disc so that it is calibrated in watts and is geared to a dial that displays the accumulated energy consumed in kilowatthours. Your electric bill is for consumption of watts, not volt-amperes. I have just posted a number of power supply load test reports in the Files section of the Repeater-Builder site. Look for a folder entitled, Power Supplies. This is a work in progress, and I am collecting new data as time permits. I just upgraded my electronic load, and I can now load up to 50 amperes, so several of my load tests will be repeated. Also, I started my project using a fairly stiff 120 VAC branch circuit, but I soon realized that test results were affected by the droop in my line voltage caused by increasing voltage drop as the load on the UUT increased. More recent tests have been performed with an input maintained at exactly 120 VAC. Since the efficiency of any appliance is the ratio of power out to power in, the "Overall Efficiency" value is just that- the DC load in watts divided by the AC input power in watts. Ironically, the overall efficiency of some power supply designs will vary significantly as the AC input voltage varies. Linear power supplies, such as the Astron RS-35, become more efficient as the input voltage drops, because less heat is generated in the pass transistors. At a point just above the level where output regulation fails, the pass transistors are saturated and generating minimum heat. 73, Eric Lemmon WB6FLY -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd Sent: Thursday, June 12, 2008 8:46 PM To: [EMAIL PROTECTED] Subject: Re: [msf5000] MSF5000 Forced Battery Revert Eric, >From your study which power supplies did you find to be the most efficient, and also which have the least idle current? Jesse VE7LYD On Thu, Jun 12, 2008 at 8:07 PM, <[EMAIL PROTECTED]> wrote: > On Thu, 12 Jun 2008 18:59:46 -0700, Eric Lemmon wrote: > >> If your MSF5000 power supply consumes 500 watts when unloaded, it has a >> serious problem and needs repair. > > Interesting. I can't get to them now, but I checked them both after > getting them on the ham band and they both did it. Over the years, I've > also tested several constant voltage or ferro-resonant transformers and > they all drew just about the same current when loaded or unloaded. > That's why they run so hot when they have no load. I can't recheck now, > so will just let this float until such time as I can do so. Until then, > disregard what I said. > > Gary
