davidw@lpi.UUCP (David Weisman) (04/24/87)
How do power factor controllers work? What types of devices/motors are they suitable for, and what are their typical payback periods for things like refrigerators?? Dave W.
henry@utzoo.UUCP (Henry Spencer) (05/02/87)
> How do power factor controllers work? What types of devices/motors > are they suitable for, and what are their typical payback periods > for things like refrigerators?? I'm not up on motors very much, but here goes... As I understand it, the only situation power-factor controllers help with is motors that run for substantial periods at less than full power. Things like refrigerators, which vary their output by cycling on and off rather than by running at lower output continuously, don't benefit at all. My impression is that power-factor controllers are really of very limited use to consumers, since few motorized consumer products run at partial power for long. -- "If you want PL/I, you know Henry Spencer @ U of Toronto Zoology where to find it." -- DMR {allegra,ihnp4,decvax,pyramid}!utzoo!henry
jans@stalker.gwd.tek.com (Jan Steinman) (05/04/87)
In article <7988@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes: >> What types of devices/motors are (power factor controllers) suitable for... > >.. the only situation power-factor controllers help with is motors that run >for substantial periods at less than full power. Things like refrigerators, >which vary their output by cycling on and off rather than by running at lower >output continuously, don't benefit at all. My impression is that power-factor >controllers are really of very limited use to consumers, since few motorized >consumer products run at partial power for long. A substantial portion of a "continuous duty" motor's capacitiy is used for starting it. Motors that must start at full load still present some reactance to the line. My experience is that PFC's can save 8% to 15% on older refrigerators and freezers, but late model ones have PFC's built into theier compressor motors. A refrigerator that burns $100 a year (not uncommon in high-rate areas, or with older motors) can then payback a $29.95 PFC in as little as two years. Henry's right, though. Where they really payback are on variable-load devices. Power tools and washing machines com immediately to mind. I've seen older washers save 30%. A table saw or drill press runs at nearly 50% without load. My dad sells PFC's, and I've got several in use. :::::: Software Productivity Technologies --- Smalltalk Project :::::: :::::: Jan Steinman N7JDB Box 1000, MS 60-405 (w)503/685-2956 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::
alab@ur-tut.UUCP (Daniel F. Luna) (05/08/87)
In article <7988@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes: > >I'm not up on motors very much, but here goes... As I understand it, the >only situation power-factor controllers help with is motors that run for >substantial periods at less than full power. Things like refrigerators, >which vary their output by cycling on and off rather than by running at >lower output continuously, don't benefit at all. My impression is that >power-factor controllers are really of very limited use to consumers, >since few motorized consumer products run at partial power for long. Power factor actually refers to "reactive power" on systems. Power factor is related to the phase difference between voltage and current through (usually) inductive devices, like motors. A capacitor will, if sized and placed correctly, correct the power factor. Power companies are unhappy when the power factor falls below 1. This leads to loss in transmission ability. Power factor is usually not a problem for small users, like residences. It is more a problem with industrial locations, where most of the power is operating "reactive" loads, like motors and transformers. (Transformers are in florescent lights, too.) Traditionally, power companies have capacitor banks on poles along the distribution path to offset the power factors of the reactive loads. Many power utilities require that the customer fix his power factor if it falls below a certain point, and I think that here it is 0.8 . Things like incandescant lamps have power factor of 1. Also toasters, electric stoves, etc. Your question brings to mind another device which was put on the market a while back. It does not control power factor, but "duty cycle". It's purpose was to cut "demand" costs in places by having air-conditioners, etc. run only part of the time. The problem I have with this is that it DRASTICALLY shortens the life of the compressor, because it does not let it warm up correctly, keep its fluids separate, etc., and also because the starting torque on the motor shortens the life of the motor each time it starts. Compressors like to "wind down" before restarting, typically a lot longer than these machines would allow. Demand is how the power company recovers costs for having all that equipment running at once (and built, for that matter). It again usually applies to only industrial customers, but doesn't have to. The idea is that they measure how much power used for a 15 minute period. The highest measurement for the month is called the demand power. Rates of 6 DOLLARS per kwh are common for the demand power. The power companies could provide all the power you needed from fewer generators if you didn't want it all at once (along with the rest of the world). So, since they have to build, man, operate, maintain, etc. these extra generators, they are compelled to recoup these costs. It also serves as a deterrent to wanton power consumption. -Hence the device above. (but i digress...) The idea of keeping the demand level down is OK, but using this brute- force method simply shifts costs from the energy column to the repair column, and multiplies it in the process. 'nuff said. -- Daniel F. Luna PC-Person. uucp: ...rochester!ur-tut!alab arpa: ur-tut!alab@rochester Standard Disclaimer here. If it don't work, it ain't my fault.