jeffr@sri-spam.UUCP (02/09/87)
Can someone give me a diagram of one of those "power conservation" gizmos,
for example "Dr. Watt ?" ("You can cut power usage in appliances up to
60% with new Dr. Watt, the power factor controller from EnerCon, developed
under license from NASA") I'd like to build one and experiment with it.
T'anks watts !mth@ihnp3.UUCP (02/19/87)
To: ihnp4!cbatt!gatech!lll-lcc!mordor!sri-spam!jeffr Subject: Re: What is inside Dr. Watt ? Newsgroups: sci.electronics In-Reply-To: <9861@sri-spam.istc.sri.com> Organization: ATT Bell Labs Cc: Bcc: I believe that the technical name for this device is the Nola Converter, named after Frank Nola of NASA, who invented this technique. My understanding is that these devices measure the phase shift (read power factor) between V and I, and then clip a part of the cycle to reduce the time that the current is actually supplied to the motor, thus reducing the total energy cost. I seem to remember that this works because common (most?) AC motors draw the same amount of current regardless of the mechanical load they are asked to rotate. They do, however, exhibit a different power factor (read phase difference between V and I), when subjected to different loads. In some cases, if the motors are oversized, their power consumption can actually be in excess of the amount actually needed to do the work. I believe that the device senses this, presumably (only a guess) by looking at both the E and I waveforms, determining the phase shift, and clipping some part of the AC cycle. I would imagine that relatively little of this is happening when the motor is starting and needs all the current it can get, but there may be room once things reach a fixed velocity. It would stand to reason that in some applications motors would be sized to be able to accelerate the load within a specified time, rather than for steady-state operation, hence there should be ample room for power savings in such cases. Also, since motors come in certain sizes, they are freqently matched to their application by choosing the next-larger-size technique, with the same result. Hope that this helps. Now for a QUESTION: What is the simplest circuit that you can think of that would measure both the voltage across an AC line, as well as the current passing through it and do the A/D conversion into 7 or 8 bits, to be read by a microprocessor? The conversion should take no more than 1/2 of a 60HZ cycle, or about 8ms. I envision some sort of inductive pickup followed by a cheap A/D ultimately winding up at a 8-bit input port of a micro, the whole conversion triggered at some know angle of the cycle. Any ideas? Please respond directly, since I don't read this newsgroup often. I will post responses. Thanks in advance. Mark Horbal @ Bell Labs ...ihnp4!ihnp3!mth