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OT - Magical HF inverter
HF has a "700w" inverter that runs from a car battery. It is "700 watts
continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Bob |
Bob Engelhardt wrote:
HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". I've seen inverters that are supplied with cables that cannot handle the load, so are fused appropriately. Maybe the leads are replacable with 100A capable ones, and that's how it does 700W. |
Bob Engelhardt wrote:
HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Bob That's easy, it's a slooooooow-blo fuse of course. G Jeff -- Jeffry Wisnia (W1BSV + Brass Rat '57 EE) "As long as there are final exams, there will be prayer in public schools" |
On Thu, 06 Jan 2005 11:31:11 -0500, Bob Engelhardt
wrote: HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Bob My guess is that the 700W continuous is inflated. Perhaps you should play it safe and get this model http://www.harborfreight.com/cpi/cta...emnumber=47641, 400W, and a 40A fuse... Wayne |
"Bob Engelhardt" wrote in message ... HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Your average store-bought UPS has the same deal. In the outside of the box they are always rated in "VA" rather than in watts. If you bother to read the fine print, you will find that they assume a ridiculous power factor and your 500 VA UPS is actually a 250 Watt UPS. Vaughn Bob |
On Thu, 06 Jan 2005 11:31:11 -0500, Bob Engelhardt
wrote: HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Bob Is that watts RMS ? Watts Peak ?? Watts Peak to Peak ??? Watts Music Power ???? Watts Cambell Hausfield Compressor Motor HP * 748 ????? Enquiring Minds Want To Know- H. |
"Bob Engelhardt" wrote in message ... HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Bob I have one like this. It has three 30 amp internal fuses....Paul |
"Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) |
"Leo Lichtman" wrote in message ... "Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. Vaughn |
"Bob Engelhardt" wrote in message ... HF has a "700w" inverter that runs from a car battery. It is "700 watts continuous for up to 30 minutes" and has "Auto battery cables and 30 amp fuse". Is this new physics? Old physics held that 12v at 30a was 360w and you couldn't have more watts out than watts in. This is even worse than "Sears horsepower". Bob Is it possible the 30 amp fuse is on the secondary side? |
ATP wrote:
Is it possible the 30 amp fuse is on the secondary side? I hope not. It is rated for 1400w peak/surge, which would be about 12A. |
PJ wrote:
I have one like this. It has three 30 amp internal fuses....Paul In parallel, I assume. That's interesting - I don't think that I've seen fuses in parallel, but it might be practical. I.e., 30A fuses are a lot more readily available than 90A ones. Anyone know how balanced the current would be? Bob |
"Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. |
To be meaningful Watts RMS in audio also need a distortion, bandwith and a
load specification such as: 2500 Watts RMS at 4 Ohms with a THD (total harmonic distortion) of .001% from 20Hz to 20KHz. cheers T.Alan "Vaughn" wrote in message ... I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. Vaughn |
On Fri, 07 Jan 2005 19:18:57 GMT, "Leo Lichtman"
wrote: "Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. Agreed that average power is more useful and descriptive than RMS power. For unvarying power output they're the same. Peak output is also a useful measure, though. Two amps with identical average power ratings may differ in the peak power they can deliver without clipping on transients like rim shots on a snare drum. Average power rating is determined by the amp's efficiency and ability to dissipate heat. Peak power would be governed by available supply voltage and the output devices used. The length of time that it can deliver peak power without overheating is determined by the thermal mass of the heatsink. |
On Fri, 07 Jan 2005 05:49:13 GMT, "Leo Lichtman"
wrote: "Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) On the contrary actually, I consider RMS to be the most meaningful measurement of power, but that may be specific to the areas I use it in. As far audio goes I'd be more interested in THD, peak power/dymanic range & whether or not the dual isolated power supplies were built using oxygen free silver buss bars :). H. |
On Fri, 07 Jan 2005 20:53:13 GMT, the renowned Howard Eisenhauer
wrote: On Fri, 07 Jan 2005 05:49:13 GMT, "Leo Lichtman" wrote: "Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) On the contrary actually, I consider RMS to be the most meaningful measurement of power, but that may be specific to the areas I use it in. "RMS watts", although mathematically possible to compute, would have no useful *physical* meaning that I can think of. Usually they are a misnomer for "true power". As far audio goes I'd be more interested in THD, peak power/dymanic range & whether or not the dual isolated power supplies were built using oxygen free silver buss bars :). H. You don't want to spend $500 on a wooden knob that prevents "microvibrations" from entering the delicate signal path? ;-) Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
"Bob Engelhardt" wrote in message ... PJ wrote: I have one like this. It has three 30 amp internal fuses....Paul In parallel, I assume. That's interesting - I don't think that I've seen fuses in parallel, but it might be practical. I.e., 30A fuses are a lot more readily available than 90A ones. Anyone know how balanced the current would be? Bob Now I have to tell you how I know about the three fuses. Bought the unit at a swap meet for $5. Being dead, I opened it up to find the three fuses blown. Someone had wired it up backwards. Turns out there are three separate inverter circuits. Wired in parallel on the output side. The inputs also have protection diodes, all three of which were cracked in half. Replaced fuses, diodes and repaired a burnt trace. I now have 700 mobile watts available....Paul |
On Fri, 07 Jan 2005 16:12:31 -0500, Spehro Pefhany
wrote: On Fri, 07 Jan 2005 20:53:13 GMT, the renowned Howard Eisenhauer wrote: On Fri, 07 Jan 2005 05:49:13 GMT, "Leo Lichtman" wrote: "Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) On the contrary actually, I consider RMS to be the most meaningful measurement of power, but that may be specific to the areas I use it in. "RMS watts", although mathematically possible to compute, would have no useful *physical* meaning that I can think of. Usually they are a misnomer for "true power". I can see your point however once you're away from DC or working outside narrow specialty fields where it's assumed everybody knows "Whats Watt" the term "watts" by itself can be mis-leading. If you say watts RMS everybody (at least in my experience) knows what you're talking about. For commercial power situations where you can run into power factor issues "VA" is a better concept. For audio I just buy the biggest amp I can afford & say the heck with the rest. So, anytime I set the power output on an AM or FM transmitter the ol' Bird 43 sez "Watt RMS". Same thing on the HP power meter when I'm doing micro wave links, except that when measuring at the directional coupler it generally comes out in "milli-watts RMS". And thats not even using the BIG Bucks "True RMS" meters they sell. SSB is, of course, Not to be Talked About Here :(. Anytime I set or measure a level on an analog audio line using a test tone I'm usually looking for a given level of dBM, where 0 dBM is, by definition, equal to 1 mW, RMS :). I recently designed an oil heater with a non-inductive load (duh). I calculated, using the resistance of the element and the 115 V RMS line level, the RMS power disapation in watts which I then cleverly converted (Convert.EXE- Gotta Luv It!) into calories to figure out how long it would take to heat up the oil under given conditions. When I actually tried the thing out I was pretty damn close :0. In point of fact, I find RMS usefull every day of the week, & sometimes twice on Sundays :). As far audio goes I'd be more interested in THD, peak power/dymanic range & whether or not the dual isolated power supplies were built using oxygen free silver buss bars :). H. You don't want to spend $500 on a wooden knob that prevents "microvibrations" from entering the delicate signal path? ;-) Only if it's one thats been lovingly hand crafted from select cuts of rare imported Outer Pangorian Swamp Palm. Anybody with half an ear can tell that a set of knobs made from it perceptually add to the acoustic colour depth as well as mellowing the harmonic relationships ;. Best regards, Spehro Pefhany Back At'cha, H. |
Leo Lichtman wrote:
"Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) Guess you don't remember the amplifiers that said 100 watts! 100/2 - 50/channel then that is peak to peak value - /2 (again) multiply by 0.7 and you find out the speakers you are using consume 10 watts before sound is heard from the big cones - take it back doesn't work! Peak to peak numbers and peak values were rampant. Finally standards were done. Had to be RMS voltage * RMS current. E*I. Liken it to the Horse power of power tools - one horse is a pony another is a Morgan. RMS is the effective heating power into a pure resistance = EMF voltage for same heating power. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
Leo Lichtman wrote:
"Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. Why was the RMS voltage developed ? It has meaning. Very good meaning. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
Spehro Pefhany wrote:
On Fri, 07 Jan 2005 20:53:13 GMT, the renowned Howard Eisenhauer wrote: On Fri, 07 Jan 2005 05:49:13 GMT, "Leo Lichtman" wrote: "Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) On the contrary actually, I consider RMS to be the most meaningful measurement of power, but that may be specific to the areas I use it in. "RMS watts", although mathematically possible to compute, would have no useful *physical* meaning that I can think of. Usually they are a misnomer for "true power". As far audio goes I'd be more interested in THD, peak power/dymanic range & whether or not the dual isolated power supplies were built using oxygen free silver buss bars :). H. You don't want to spend $500 on a wooden knob that prevents "microvibrations" from entering the delicate signal path? ;-) Best regards, Spehro Pefhany Remember - Power = I^2 * X where X is the reactive value of the system at a specific frequency, not all frequencies. So really one has to do a sum of I(@20hz)^2 * by Hz So in this case, the root of the mean square comes closer and closer. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
On Sat, 08 Jan 2005 05:49:24 GMT, the renowned "Martin H. Eastburn"
wrote: Leo Lichtman wrote: "Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. Why was the RMS voltage developed ? It has meaning. Very good meaning. Martin If you have a resistor, the average current into it is V(avg)/R. The average *power* is (Vrms^2)/R. You can really see the difference with pulsey waveforms. Imagine a 100V pulse at 10% duty cycle going into a 1 ohm load. 100V x----x x----x | | | | | | | | | | | | 0V ----x x----------------------------x x------- 0 1ms 10ms t- The average current is 10A. The average voltage across the resistor is 10V (what you'd measure with a DC voltmeter). But the RMS voltage is 31.6V, so the power is 1000W, not 100W. You can see this easily without the calculus stuff from the power when the pulse is high (10,000W), but it's only on for 10% of the time. Then you get into reactive loads (the cos-theta stuff really only makes sense for sine waves)... Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
"Howard Eisenhauer" wrote: Is that watts RMS? (clip)
^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. I think this is really a case of technical illiteracy on the part of the people who market power amplifiers. What gets called "watts RMS" is actually average (mean) power. To *calculate* this, they measure RMS voltage and then feed it into the standard V^2/R power formula. The whole point of using RMS voltage, instead of average voltage or peak voltage or any other measure is that it allows you to calculate mean power. But the actual number quoted is watts, not volts, and it is *mean* watts, not RMS watts. The name "watts RMS" is simply wrong, even when the number is right. RMS watts is well-defined mathematically, but it doesn't have any useful meaning for measuring an amplifier output. Dave |
"Martin H. Eastburn" writes:
Peak to peak numbers and peak values were rampant. Finally standards were done. Had to be RMS voltage * RMS current. E*I. Right. And assuming that the load is resistive (it is when testing amplifiers, but not when driving speakers), then RMS voltage * RMS current gives you *mean* power, not RMS power. RMS is the effective heating power into a pure resistance = EMF voltage for same heating power. Mean power is heating power. If you have a meter that reads power, you just average the output. It's only when you're calculating power from voltage and/or current that you need to use RMS measurements. Dave |
In article ,
Spehro Pefhany wrote: On Fri, 07 Jan 2005 20:53:13 GMT, the renowned Howard Eisenhauer wrote: On Fri, 07 Jan 2005 05:49:13 GMT, "Leo Lichtman" wrote: "Howard Eisenhauer" wrote: Is that watts RMS? (clip) ^^^^^^^^^^^^ Howard, I hope you did that on purpose. "Watts RMS," a term popular in advertising audio amplifiers, has always galled me. I can see no way for it to have any meaning, considering what RMS stands for, and what it is used for. :-) On the contrary actually, I consider RMS to be the most meaningful measurement of power, but that may be specific to the areas I use it in. "RMS watts", although mathematically possible to compute, would have no useful *physical* meaning that I can think of. Usually they are a misnomer for "true power". RMS Watts gives the actual power to do work. Assuming the signal is a sine wave, and assuming (for convenience) the load is a pure resistor acting as a heater to avoid needing to deal with imaginary current): 1) If the input power is 120 VAC (that voltage is *also* RMS, BTW. for 120 VRMS, the peak voltage is 1.414 (sqrt(2)) times the RMS voltage. So -- with that 120 VAC RMS, you get a peak voltage of 169.68 V 2) Now -- let's assume that the resistor is 100 Ohms, so at that peak voltage, it would be dissipating 287.91 Watts. 3) However, it is doing so only for a tiny part of the whole cycle. At other points, it has voltages much less than that peak, and even less than the 120 V which the RMS value has. 4) So -- if you actually measure the heat output, and do the necessary math, you will find that the actual average heat out of it is the same as though it had 120 VDC applied. 5) So -- RMS is a measurement of how much work you can get out of the signal, whatever it is doing. (In an audio system, that task happens to be moving air in specific patterns.) How much you can actually get out is also a function of the efficiency of the speakers, usually with the higher quality speakers being less efficient -- more of the power is going to controlling cone overshoot and other forms of mechanical distortion. As far audio goes I'd be more interested in THD, peak power/dymanic range & whether or not the dual isolated power supplies were built using oxygen free silver buss bars :). The "peak" power used in audio rating is not even that used in my explanation above, which at least has a basis in physics. Instead, it is what power you can get out of the amplifier for an instant before the power supply capacitors discharge to a lower voltage. So -- your peak power gives you an idea what a single castanet clack can produce (hopefully without distortion) -- but no promise that a rapid series of them will produce the same sound. The RMS power, instead, gives you a *real* measurement of how much power it can produce for a long sustained note. It is *defined* for a steady-state output. It can even give you an idea whether you can run a machine tool motor from the output. Any attempt to run a 100 W light bulb from an amplifier rated at 100W Peak will burn out the amplifier in fairly short order. An amplifier rated in RMS Watts will do the job -- assuming that it can produce enough output voltage (not a guarantee even with your preferred peak Watts). H. You don't want to spend $500 on a wooden knob that prevents "microvibrations" from entering the delicate signal path? ;-) It is beginning to sound as though that is the case. :-) Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
"DoN. Nichols" wrote: (clip) Any attempt to run a 100 W light bulb from an amplifier rated at 100W Peak will burn out the amplifier in fairly short order. ^^^^^^^^^^^^^^ Or, at the very least, produce distorted light. G |
Spehro Pefhany wrote:
On Sat, 08 Jan 2005 05:49:24 GMT, the renowned "Martin H. Eastburn" wrote: Leo Lichtman wrote: "Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. Why was the RMS voltage developed ? It has meaning. Very good meaning. Martin If you have a resistor, the average current into it is V(avg)/R. The average *power* is (Vrms^2)/R. You can really see the difference with pulsey waveforms. Imagine a 100V pulse at 10% duty cycle going into a 1 ohm load. 100V x----x x----x | | | | | | | | | | | | 0V ----x x----------------------------x x------- 0 1ms 10ms t- The average current is 10A. The average voltage across the resistor is 10V (what you'd measure with a DC voltmeter). But the RMS voltage is 31.6V, so the power is 1000W, not 100W. You can see this easily without the calculus stuff from the power when the pulse is high (10,000W), but it's only on for 10% of the time. Then you get into reactive loads (the cos-theta stuff really only makes sense for sine waves)... Best regards, Spehro Pefhany Now Spehro is pulling our legs again... No sin(t) or cos(t) - no time at all! But he uses a waveform. RMS was to match the heating ability of a battery. equal to equal. Duty cycle and even cycle begs the cos data. One needs to use an integral. Yave = 1/10ms Integral from 0 to 1ms of 100 dt Yrms = 1/10ms Integral from 0 to 1ms of 100^2 dt For square waves. DC is all together different. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
"DoN. Nichols" wrote in message ... -- assuming that it can produce enough output voltage (not a guarantee even with your preferred peak Watts). Or another way of saying the same thing..."assuming a proper impedance match between the load and the amplifier". Vaughn |
On Fri, 07 Jan 2005 19:18:57 GMT, "Leo Lichtman"
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email "Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. But if you use a standardised method of measurement (sine wave) the RMS is the same power dissipation as DC, isn't it? So you are measuring the ability of the amp to continuously dissipate heat, basically. Taking the square of a number that has _as part of its makeup_ a squaring process of only one constituent of that number is not "doing something that has already been done" at all. |
On Mon, 10 Jan 2005 06:53:04 +0800, the renowned Old Nick
wrote: On Fri, 07 Jan 2005 19:18:57 GMT, "Leo Lichtman" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email "Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY meaningful measurement of the power output capability of an amplifier. ^^^^^^^^^^^^^ Vaughn, lets look at this one step at a time. RMS stands for "root mean square." If you look at the equation for power, it is I^2 R, or E^2/R. For DC that is very simple, but for AC, it is necessary to use an average figure for E or I that gives the correct power. The way to get that average is to square the instantaneous voltage or current at every instant, take an average of the squared values, and take the square root of the average--hence: root (meaning square root) mean (same as average) square. The wattage rating or operating point of an amplifier is already in power units. It is perfectly OK to talk about "average power," or "peak power," but RMS power suggests doing something to the numbers that has already been done. To square, average, and take the square root again would produce a figure that has no meaning. That's my gripe. But if you use a standardised method of measurement (sine wave) the RMS is the same power dissipation as DC, isn't it? So you are measuring the ability of the amp to continuously dissipate heat, basically. x volts (RMS) voltage across a resistor will give you x^2/R watts dissipation (regardless of whether it's sine or not). x amperes (RMS) through a resistor will give you x^2*R watts dissipation (regardless of whether it's sine or not). The reason you want the square is that with a resistor (a very useful special case) the voltage and current are proportional. Hence, increasing the voltage also increases the current. If you only measure one of the two (with a resistive load) you can presume what the other one is: i = e/R or e= i*R. (I use lower case because both are functions of time) So, average power is the average of e*i = average of e^2/R (or the average of i^2*R). That's where the squaring comes from. Taking the square of a number that has _as part of its makeup_ a squaring process of only one constituent of that number is not "doing something that has already been done" at all. There is no squaring process in the most general measurement of power. Average power is the average value of (instantaneous voltage * instantaneous current). (NOT the average value of voltage * average voltage of current) If you were to actually calculate the average RMS watts, it would NOT be the same as the average power. For example. 100 Watts for 1 second, off for 9. Average watts is 10W. That's exactly how much power dissipation there will be in the load. But "RMS watts" would be about 32W. That has no useful physical meaning that I can imagine. It's just an erroneous term. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
On Sun, 09 Jan 2005 18:26:15 -0500, Spehro Pefhany
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email I am not a great quoter, but this guy saves me some time. http://www.bcae1.com/voltages.htm "RMS Voltage: RMS voltage is absolutely the most common way to measure/quantify AC voltage. It is also the most useful. ........ Its voltage level can be plugged directly into the formulas for power (on the Ohm's law page) and you will get an accurate image of its ability to do work. RMS voltage will give you the same ability to predict how much work will be done by an AC voltage." "For the Purists... RMS Power (PRMS): Throughout this site I will use the term 'RMS power'. Technically, as far as I know, there is no such thing as 'RMS' power. This section will help clarify and define a few terms. I will define RMS power as the power that's calculated when using an RMS voltage or current into a resistive load. Other ways to quantify power... Average power (Pave): Average power is defined as the RMS voltage multiplied by the RMS current. Peak power (Ppeak): Peak power is defined as the peak voltage multiplied by the peak current. " So we appear to be straining at gnats. Terminology. I am actually not sure how the arguiment started. There is no RMS power in physics. But there is RMS volts, and if you divide the square of that by the resistive load, you get a power figure by which things can be compared. It is _accepted_ to be "RMS power" in name. No harm done. It measures work and provides a standard. |
Snitched from sci.electronics.design...
http://www.machinadynamica.com/machina27.htm http://www.machinadynamica.com/machina28.htm http://www.machinadynamica.com/machina29.htm And I bet they sleep well despite selling such bogus rubbish for a living. -- Terry Pinnell Hobbyist, West Sussex, UK God, to think of the money I could be making if only I was a crook at heart :(. Howard. |
On Tue, 11 Jan 2005 21:54:22 GMT, Howard Eisenhauer
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email Snitched from sci.electronics.design... http://www.machinadynamica.com/machina27.htm http://www.machinadynamica.com/machina28.htm http://www.machinadynamica.com/machina29.htm And I bet they sleep well despite selling such bogus rubbish for a living. -- Terry Pinnell Hobbyist, West Sussex, UK God, to think of the money I could be making if only I was a crook at heart :(. Did you check out the rest of the site? |
On Tue, 11 Jan 2005 21:54:22 GMT, Howard Eisenhauer
calmly ranted: Snitched from sci.electronics.design... http://www.machinadynamica.com/machina27.htm http://www.machinadynamica.com/machina28.htm http://www.machinadynamica.com/machina29.htm And I bet they sleep well despite selling such bogus rubbish for a living. God, to think of the money I could be making if only I was a crook at heart :(. One guy had Pet Rocks, these guys have Brilliant Pebbles. They reference a photon absorbtion white paper for their sound absorbing rocks. Brilliant x2, eh? ================================================== ======== Save the ||| http://diversify.com Endangered SKEETS! ||| Web Application Programming ================================================== ======== |
well, umm, whaa, ya mean those pebbles[gulp] don't make my video look
better? But when I use that gizmo...okay I'm too lazy to even go back and look at the name .....what a bunch of hooey. Anyone remember green magic marker on the edge of your CD??? Larry Jaques wrote: On Tue, 11 Jan 2005 21:54:22 GMT, Howard Eisenhauer calmly ranted: Snitched from sci.electronics.design... http://www.machinadynamica.com/machina27.htm http://www.machinadynamica.com/machina28.htm http://www.machinadynamica.com/machina29.htm And I bet they sleep well despite selling such bogus rubbish for a living. God, to think of the money I could be making if only I was a crook at heart :(. One guy had Pet Rocks, these guys have Brilliant Pebbles. They reference a photon absorbtion white paper for their sound absorbing rocks. Brilliant x2, eh? ================================================== ======== Save the ||| http://diversify.com Endangered SKEETS! ||| Web Application Programming ================================================== ======== |
On Wed, 12 Jan 2005 10:27:02 +0800, Old Nick
wrote: On Tue, 11 Jan 2005 21:54:22 GMT, Howard Eisenhauer vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email Snitched from sci.electronics.design... http://www.machinadynamica.com/machina27.htm http://www.machinadynamica.com/machina28.htm http://www.machinadynamica.com/machina29.htm And I bet they sleep well despite selling such bogus rubbish for a living. -- Terry Pinnell Hobbyist, West Sussex, UK God, to think of the money I could be making if only I was a crook at heart :(. Did you check out the rest of the site? Yes I did. Uncharacteristicly I find myself commentless, that is to say unable to come up with any statement that would even come close to expressing 1% of what should be said about the subject. Too bad, I'm sure that if I could it'uld be a real Zinger :). H. |
On Wed, 12 Jan 2005 16:20:46 GMT, Howard Eisenhauer
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email Did you check out the rest of the site? Yes I did. Uncharacteristicly I find myself commentless, that is to say unable to come up with any statement that would even come close to expressing 1% of what should be said about the subject. Too bad, I'm sure that if I could it'uld be a real Zinger :). I loved the magazine reviews. My subscription to those magazines, if they exist, would require a lot of thought. Makes Monster Cable look like god's truth personified. |
On Thu, 13 Jan 2005 06:37:46 +0800, Old Nick
wrote: On Wed, 12 Jan 2005 16:20:46 GMT, Howard Eisenhauer vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email Did you check out the rest of the site? Yes I did. Uncharacteristicly I find myself commentless, that is to say unable to come up with any statement that would even come close to expressing 1% of what should be said about the subject. Too bad, I'm sure that if I could it'uld be a real Zinger :). I loved the magazine reviews. My subscription to those magazines, if they exist, would require a lot of thought. Makes Monster Cable look like god's truth personified. Personaly, I'm a firm believer in the superior acoustic properties of Zip Cord :). As for the other sentiment, I really don't believe the concept of "thought" in any way belongs in a sentence discussing a subscription to any of those rags :(. H. |
Old Nick wrote (or quoted):
Throughout this site I will use the term 'RMS power'. Technically, as far as I know, there is no such thing as 'RMS' power. This section will help clarify and define a few terms. I will define RMS power as the power that's calculated when using an RMS voltage or current into a resistive load. Then you/he are/is wrong - dead wrong. You simply do not understand the term RMS and the reasons for its use. How's your calculus? If it's not up to snuff, the following will do you no good - don't take offence, just take the word of someone who knows and don't worry about it or try to make the facts fit your misconceptions. If you _can_ handle calculus then: The time average (or mean) of a continuous integrable function of time, f(t) over a time interval from t1 to t2 is DEFINED as _ 1 t2 F = -------- Integral f(t)dt t2-t1 t1 Note: For discrete quantities, we replace the integral with a sum and t2-t1 with the count and get the familiar definition of average. These definitions agree with "Reference Data for Radio Engineers", pg 982 published by IT&T. My copy is the 1957 edition but that part of mathematics and electrical engineering is beyond even Kalifornu to change. Now, supose we want AVERAGE power. Given voltage, v(t), and current, i(t), themselves continuous integrable functions of time, INSTANTANEOUS power is DEFINED as p(t)= v(t) i(t) IF the load is linear and purely resistive then v(t) and i(t) look the same except for a constant, R. Thus v(t) = R i(t) and two frequently useful substitutions are possible. Namely 2 2 p(t) = R i(t) or p(t) = v(t) ----- R What's more, if these functions, v(t) and i(t), are periodic (i.e. repeat exactly every (say) T seconds) then the long term average is the same as the average over a single period (cycle) and things get even simpler. We can then say the average (or mean) power is 2 _ 1 T v(t) P = --- Integral ---- dt T 0 R Since R is a constant, we can take it outside the integral to get _ 1 1 T 2 P = - - Integral v(t) dt R T 0 Thus AVERAGE power is the mean square voltage divided by R. Now, except that I have natural gas heat, if I were to switch my electric heater over to DC when the power failed, what DC VOLTAGE would I have to apply to it to get the same heat output? Obviously I want the AVERAGE POWER to be the same and at DC _ 2 P = V / R for some appropriately chosen voltage, V. For the same heat, I want 2 V 1 1 T 2 - = - - Integral v(t) dt R R T 0 The R's cancel and we have 2 1 T 2 V = - Integral v(t) dt T 0 or ( 1 T 2 ) V = SQRT ( - Integral v(t) dt ) ( T 0 ) "root" "mean" "square" This is the RMS voltage associated with a time varying voltage, v(t). This is how the term arises and the reason it's useful is it relates the AVERAGE power in a resistor load when ac applied voltage and dc applied voltage are compared. The same argument can be applied to derive Irms from i(t) and, for any periodic waveform into a pure resistor load Pavg = Vrms Irms And only the media and the hi-fi industry can manage to screw that up as badly as they have. Oh, sure, I can define an RMS power mathematically using the integral but it has absolutely nothing to do with the ac voltage that is equivalent in heating power to a dc voltage when fed into the same resistance heater. |
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