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#1
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Power factor question
Hi all,
I have a question about the term "power factor". A number of years ago I was an install tech. for a company that sold Nortel phone systems. I noticed that almost all the small units were sold with a plug-in device that weighed about 25 pounds and I first thought it was a very heavy-duty filter/surge suppressor but I was amazed to find out that such a large unit was only rated for 6 amps. When I opened one up I found it to have only two components, a HUGE doughnut coil (that made up about 4/5th. the weight) and a HUGE capacitor, it was simply an L-C circuit. I asked one of the tech's what it was and he told me it was a power factor device. I ended up with two "spare" units and used one for my A/V system and the other for my computer network. After finding out that nothing had changed with either application I gave them away to a, at the time, friend of mine who designs and tests battery backup and power supply units for ships and private jets - thinking he might find a use for them. Tonight I was in another NG and read a post about surge suppressors and they were talking about power factor correction and that reminded me about this so I looked at wikipedia for an explanation of power factor. What I got was a little over my level of understanding. I know a little about electronics, I did TV repair in the late 1980's but didn't get too far into the theory of electronics so I would say that my understanding is about at a 1st to 2nd semester level of electronics understanding. Sorry for the long winded intro. My questions are . . . 1. is there an easy way to understand power factor and power factor correction? 2. is there any reason a person would want one of these units for home use? |
#2
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Power factor question
On Thu, 27 Mar 2008 23:16:42 -0700, "Caveat"
wrote: ... My questions are . . . 1. is there an easy way to understand power factor and power factor correction? Maybe not... It may be one of those things that just 'comes' to you one night at 3 AM... 2. is there any reason a person would want one of these units for home use? None that I know of... |
#3
Posted to alt.electronics
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Power factor question
"Caveat" wrote in message ... Hi all, I have a question about the term "power factor". A number of years ago I was an install tech. for a company that sold Nortel phone systems. I noticed that almost all the small units were sold with a plug-in device that weighed about 25 pounds and I first thought it was a very heavy-duty filter/surge suppressor but I was amazed to find out that such a large unit was only rated for 6 amps. When I opened one up I found it to have only two components, a HUGE doughnut coil (that made up about 4/5th. the weight) and a HUGE capacitor, it was simply an L-C circuit. I asked one of the tech's what it was and he told me it was a power factor device. I ended up with two "spare" units and used one for my A/V system and the other for my computer network. After finding out that nothing had changed with either application I gave them away to a, at the time, friend of mine who designs and tests battery backup and power supply units for ships and private jets - thinking he might find a use for them. Tonight I was in another NG and read a post about surge suppressors and they were talking about power factor correction and that reminded me about this so I looked at wikipedia for an explanation of power factor. What I got was a little over my level of understanding. I know a little about electronics, I did TV repair in the late 1980's but didn't get too far into the theory of electronics so I would say that my understanding is about at a 1st to 2nd semester level of electronics understanding. Sorry for the long winded intro. My questions are . . . 1. is there an easy way to understand power factor and power factor correction? Sure. When the voltage and current are 90 degrees out of phase, the energy transfer is 0 because the power factor is 0. What is happening in this case is that the load is storing the energy and then returning it to the source. That is the extreme case and seldom happens in reality. When the voltage and current are in phase, the power factor is 1 and VA = watts ... often happens in reality with resistive loads. Motors (inductive loads) and switch-mode power supplies (capacitive loads) have power factors between 0 and 1. This means that volts times amps do not equal real power. The cosine of the phase shift between current and voltage (on the input side) is the power factor. Power factor correction is the use of capacitors with inductive loads to shift the phase back towards 0. Often used when lots of motors are on line. 2. is there any reason a person would want one of these units for home use? Power factor correction is not an issue for residential consumer, but can be a big issue for commercial/industrial consumers. The energy supplier will often penalize a commercial user for a bad power factor (charge a higher rate based on kWh). The user can save money by using correction capacitors or power supplies designed to increase the power factor. |
#4
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Power factor question
Thank you both for your answers.
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#5
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Power factor question
On Mar 28, 10:01*pm, "caveat" wrote:
Thank you both for your answers. Expanding on what Charles said. Idea is to get both current and voltage to 'sine wave' simultaneously so that all power is useable. Many ways of doing this. For example, one reason why both peaks don't occur simultaneously and clean is other harmonic frequencies combined with the 60 Hz frequency. That LC filter simply removes harmonic frequencies. Capacitor and coil will shift 60 Hz sine wavest back towards each other (if properly designed). Today, power supplies are required (not everywhere) to have dynamic power factor correction. Some reasons for bad power factor are devices that create an inductive load (motors and fluorescent bulbs) or electronic devices that only take power from part of the wave. Later devices have or will have dynamic power factor correction. A circuit that some might confuse as a line filter. Electric distribution systems also install power factor correction on some telephone poles in their distribution. These cylinder devices (smaller than transformers) are nothing more than capacitors to compensate for neighborhood inductive loads from motors, et al. Another trick too complex to explain here is to setup a synchronous motor that simply runs with no load. That motors is setup to perform like a varying capacitor so that factory power is power factor corrected. |
#6
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Power factor question
Power factor correction is not an issue for residential consumer. This is seriously untrue these days with EMC. Any device drawing current must do it in a steady way. You cant use simple diodes and capacitors as this only takes current at the peaks of the waveform. This means you need either a SMPS or some front end filtering to ensure the current flow is steady. |
#7
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Power factor question
On Mon, 31 Mar 2008 15:53:57 -0700 (PDT), cadman
wrote: Power factor correction is not an issue for residential consumer. This is seriously untrue these days with EMC. Any device drawing current must do it in a steady way. You cant use simple diodes and capacitors as this only takes current at the peaks of the waveform. This means you need either a SMPS or some front end filtering to ensure the current flow is steady. WTF? Oh, I get it, it is April 1! Ok... |
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