Ron, You're absolutely correct. I deliberately avoided bringing the calculus into the discussion, simply because many lay persons are not familiar with it. The point I wanted to make is that true RMS power measurements require that the voltage and current measurements that are being integrated must be coincident in time. A four-quadrant multiplier chip, such as that contained in the WD-767 true-RMS power meter, performs this measurement and integration very well.
The latest solid-state kilowatthour meters being installed by some utility companies use the same four-quadrant multiplier technique to measure energy usage. Such meters have the additional capability of recording power factor and energy demand, and can document the time-of-use for billing purposes. One very interesting revenue meter, trade-marked as "The Turtle" uses a low-speed carrier current data stream to transmit meter readings over the power line to the utility. This eliminates the need to send a meter reader out to the boonies to read a few rural farmhouse meters. A major benefit of Turtle technology is that the data stream stops when the power fails at the meter location, so the utility knows within seconds who has a power outage. Pretty neat! 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Friday, June 13, 2008 11:16 AM To: [email protected] Subject: Re: [Repeater-Builder] RE: [msf5000] MSF5000 Forced Battery Revert The laymans equation for power is P=IE(cos(phase difference between I & E)) The cos of phase difference is the power factor. This could be hard to determine by most who do not have the proper equipment. However, power is not the voltage and current at a single point of time, but the product of the intergal of the IE wave giving the RMS power. This is the power we are most often concerned with. My home power meter was changed about a year ago to a digital one that can be read by a worker in a van passing by on the street. The old for over 70 years meter of a motor with rotor and stator in parrallel/series worked great and was simple. I wonder what method is being used with the new digital meters. 73, ron, n9ee/r >From: Eric Lemmon <[EMAIL PROTECTED] <mailto:wb6fly%40verizon.net> > >Date: 2008/06/13 Fri PM 12:36:02 EDT >To: [EMAIL PROTECTED] <mailto:msf5000%40yahoogroups.com> >Cc: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> >Subject: [Repeater-Builder] RE: [msf5000] MSF5000 Forced Battery Revert > >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:msf5000%40yahoogroups.com> [mailto:[EMAIL PROTECTED] <mailto:msf5000%40yahoogroups.com> ] On Behalf Of >Jesse Lloyd >Sent: Thursday, June 12, 2008 8:46 PM >To: [EMAIL PROTECTED] <mailto:msf5000%40yahoogroups.com> >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] <mailto:mcduffie%40ag0n.net> > 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 > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
