Announcement

Collapse
No announcement yet.

Watts vs Volt-Amps - huh ??

Collapse
This topic is closed.
X
This is a sticky topic.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    Originally posted by inetdog View Post
    Which unfortunately gives the individual homeowner no economic incentive to reduce their PF.

    BTW, since the problems an inverter has with low PF loads are most noticeable near full rated output, the thing you have to watch is the PF of your largest (usually motor) loads. If the only thing you are powering is CFLs and computer power supplies, you are probably nowhere near the full output of your inverter [I]unless that is the entire load that you have planned for[/I].
    There is so much BS surrounding the PF - urban myths supported by loony sites and all the average homeowner is screwed anyway. I have written to manufacturers asking for the info for CFL lamps and been told they don't give that information out.

    That would be one place regulation would be useful - even if just a penalty for the abusing lamp/fridge or whatever - make it cost more upfront to make the crao less attractive.
    [SIGPIC][/SIGPIC]

    Comment


    • #32
      Originally posted by inetdog View Post
      Which unfortunately gives the individual homeowner no economic incentive to reduce their PF.

      BTW, since the problems an inverter has with low PF loads are most noticeable near full rated output, the thing you have to watch is the PF of your largest (usually motor) loads. If the only thing you are powering is CFLs and computer power supplies, you are probably nowhere near the full output of your inverter [I]unless that is the entire load that you have planned for[/I].
      With that said I need to make sure the small frig I want to get is efficient and does not have a poor PF. Too bad I didn't know enough about the difference between a TSW and MSW inverter before I purchased my Whistler. At least I know I have to stay below the 2500watt rating.

      I gotta read more of the posts in here so I can learn as much as possible about building my own PV system

      Comment


      • #33
        Originally posted by SunEagle View Post
        Sunking. Thanks. I didn't know about the difference between a TSW and MSW inverter.

        You are also correct about the non linear switching loads. They cause harmonics which increases both Voltage and Current distortion which can cause bigger losses than a low PF.

        Actually that is my job to help our customers eliminate these harmonics by installing HMI type transformers. By putting in transformers with higher efficiencies that also mitigates the triplet harmonics there is a good change of reducing their electric bills by 4 to 6% as well as eliminate issues caused by the harmonics.
        Well here is the deal. You had better know if you sell the stuff and fully understand the subject.

        You need to know a TSW = True Sine Wave Inverter., and MSW = Modified Sine Wave Inverter.

        TSW inverters can run Motors loads (reactive) and Non Linear loads (switch mode electronic power supplies) up to a limit.

        MSW may but not likely to do so.

        It matters.
        MSEE, PE

        Comment


        • #34
          Originally posted by Sunking View Post
          Well here is the deal. You had better know if you sell the stuff and fully understand the subject.

          You need to know a TSW = True Sine Wave Inverter., and MSW = Modified Sine Wave Inverter.

          TSW inverters can run Motors loads (reactive) and Non Linear loads (switch mode electronic power supplies) up to a limit.

          MSW may but not likely to do so.

          It matters.
          LOL. Care to make me an offer for my whistler? The good thing is that I don't sell inverters. I am just trying to build a personnel portable solar power system.

          It's funny that I have a number of years experience in the electrical engineering field for industrial and commercial complexes as well as studying the design and fabrication of Cadmium-Sulfide Solar cells back in the 70's but when it comes to these DYI solar power systems I am still learning and really appreciate your advise as well as the other experts on this website.

          I will pay attention and learn as much as I can. That is why I am asking for help with the purchase of a 30A Charge Controller. Right now I have learned that MPPT is better than PMW and that going less expensive gets you less quality. I just don't know which charger I need to get since there are so many different manufacturers as well as knock-offs that sound and look as good as the real thing. If someone can point me to the right brand and model I would really appreciate it. Thank you.

          Vince

          Comment


          • #35
            SunEagle do not get to wrapped up into it. It only becomes a problem when you are pushing the inverter to the limits.
            MSEE, PE

            Comment


            • #36
              Why the persistence in using the totally incorrect term MSW to mean Modified Sine Wave?? No one in their right mind or left mind would ever modify a sine wave to get a Modified Sinewave.

              The correct term is MSW .Modified Square Wave.

              Comment


              • #37
                John along those lines you could call it Modified Stair Wave as that is a more accurate description of what it looks like on a scope. However the question becomes how many STEPS are used. Really cheap inverters is just a plain ole square wave and more robust units may be several hundred steps.
                MSEE, PE

                Comment


                • #38
                  Originally posted by SunEagle View Post
                  With that said I need to make sure the small frig I want to get is efficient and does not have a poor PF. Too bad I didn't know enough about the difference between a TSW and MSW inverter before I purchased my Whistler. At least I know I have to stay below the 2500watt rating.

                  I gotta read more of the posts in here so I can learn as much as possible about building my own PV system
                  In trying to figure out why some appliances or motors have a poor PF and others do not I have formed the idea that PF is related to the design, construction and quality of the components. Is this a correct assumption? If so the old adage, "you get what you pay for" certainly rings true once again but as per everything that I read on this site the respondents will show me that its not that simple!
                  Further to the last comment made in the above quote, do the contributors to this site have a page where they might recommend certain products or brands for use in an renewable energy System?
                  Last edited by Beanyboy57; 10-28-2012, 12:26 AM. Reason: spell check

                  Comment


                  • #39
                    Sunking its not the point if there is only one step or 2,376 steps The inverter is first designed??to produce a SQUARE WAVE. Because thats the cheapest way to make an inverter.
                    So after the square wave gets modified you could call it a stair wave a step wave or anything similar but the fact remains the first conversion from DC to AC is done with a square wave.

                    And no matter how you cut and slice it its ALWAYS going to be wrong to call it a Modified Sine Wave.
                    IE You cant have a modified Ford vehicle unless you first start with a Ford vehicle.

                    Beanyboy its not always easy to recommend items by brand or even by a particular model as to what is best or "worstest"
                    Very often an item made for one countries market can be very different to the "same" model marketed in another country.
                    Another problem can occur if some one on here buys a very early version and it has problems ,and they say its c..p but the second version many be great.And you would not be buying it because of reading on here it was a so so product.
                    Also some of us in this industry get pre production items that may have features that dont end up on the retail version. Then you will be complaining we gave bad advice. This certainly applies to me I get to test many panels,batteries ,charge controllers and inverters that in many cases dont have the same features as the final versions will. And could never give results on here as all testing is highly confidential. Much as I would like to tell you some of the real shonky items that never come close to their claimed specs. This holds especially true for many MPPT controllers.Many cant even equal let alone beat a good PWM controller .
                    Mabe there are some others that will give you some advices as to what to buy.. But it usually comes down to MONEY you buy rubbish 10 times you buy good once.

                    Comment


                    • #40
                      You tube videos of off-grid setup

                      Originally posted by Sunny Solar View Post
                      . Much as I would like to tell you some of the real shonky items that never come close to their claimed specs. This holds especially true for many MPPT controllers.Many cant even equal let alone beat a good PWM controller .
                      Mabe there are some others that will give you some advices as to what to buy.. But it usually comes down to MONEY you buy rubbish 10 times you buy good once.
                      What would be nice to see is a Youtube or similar video make by someone reputable, qualified and experienced, showing the components, the wiring, the location, the battery bank setup, of an off-grid solar/wind energy system that is in current operation, with the data about the day to day function. Many DIY'ers gain advice from not so reliable sources for their first off grid attempt and make some costly mistakes as you can read for yourself from the postings on this site.
                      I wish I had seen all the advice that I have gained from this site demonstrated in a ready made system before I ventured into this 'world' and wasted some of my hard earned cash, although I must say that it has certainly been useful to make some mistakes and increase my knowledge base.

                      Comment


                      • #41
                        Originally posted by Beanyboy57 View Post
                        In trying to figure out why some appliances or motors have a poor PF and others do not I have formed the idea that PF is related to the design, construction and quality of the components. Is this a correct assumption?
                        Sort of but not really. Any motor is a reactive circuit because of the windings, and any reactive circuit will have a PF. Any AC to DC power supply is a non linear circuit.
                        MSEE, PE

                        Comment


                        • #42
                          Originally posted by Sunking View Post
                          Sort of but not really. Any motor is a reactive circuit because of the windings, and any reactive circuit will have a PF. Any AC to DC power supply is a non linear circuit.
                          +1. Different types of motors will inherently have different typical power factors, and the PF will often vary with the load on the motor.
                          When looking at non-linear circuits like CFL ballasts, the ones with better PF do not (just) use better components, they use [B]additional[/B] components which reduct the amount of the non-linearity which is seen at the input. In that sense, it is a difference in design, and designing for better PF will usually increase the cost.
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

                          Comment


                          • #43
                            Originally posted by Sunking View Post
                            SunEagle do not get to wrapped up into it. It only becomes a problem when you are pushing the inverter to the limits.
                            Thanks I won't.

                            I tested my inverter today on the small 4 cu ft frig we own. It's name plate has it rated at 115 volts, 120 watts and 1.5amp max. It drew about 15 dc amps when the compressor was on so the PF is probably between 65 and 70. Since the inverter is rated 2500 watts I don't see a problem overloading it.

                            I appreciate your support. By the way you can call me Vince.

                            Comment


                            • #44
                              Originally posted by Sunking View Post
                              Well if you are a Carpenter, I can teach you AC theory in 5 minutes or less.

                              Any good carpenter knows how to make a perfect Right Triangle with a simple cosine equation. Bet you are not even aware you knew trig. Ready 3 + 4 = 5 Every carpenter knows this is a true statement and is cosine law you can prove to yourself right now with a piece of paper, a ruler, a compass, and a pencil


                              So now just replace [B][I]a[/I][/B] with Resistance, and [I][B]b[/B][/I] with Reactance, and the result [B][I]c[/I][/B] is the Impedance. Oh the power factor is simple PF = a/c
                              Also called: The pythagorean theorem. I never thought of using it in AC calculations. Good to know.
                              Also reminds me of the time when a Capt. in the Army thought he would give me (a lowly E4) a lesson in geometry. As we sat under a tin roof shed doing the latter part of "hurry up and wait" which the Army is so famous for he pointed to the rafters and says, "See this." He was a nice enough guy so I let him go on about measuring the sides in order to get the length of the longer side. The funny thing was that he didn't seem to know what I was talking about when I said, " 3, 4, 5".
                              No need to elaborate on the Pythagorean deal on my part. I just enjoyed the rest of my day.
                              North Florida Solar Newbie

                              Comment


                              • #45
                                Power Factor correction

                                I am new to solar and very interested in off grid systems.
                                I could not calculate impedance or power factor without referring to books.
                                However, an old timer explained it to me this way.
                                Electrons flowing through a wire create a magnetic field surrounding the wire. When you make hundreds of coils from the same wire (an inductor) and pass current through it the magnetic field produced by the flowing electrons [I]induces[/I] an equal but opposite (flowing the other direction) current in the adjacent turns of wire. This [I][B]inductive reactance[/B][/I] (as it is called in an AC circuit) or [B][/B][I]inductance[/I] as it is called in a dc circuit tends to oppose the current being delivered from a power source to the load. In the case of an ac induction motor (most motors being used in the average home are single phase induction motors) this opposing force is referred to as CEMF or counter electromotive force. Large factories and industrial plants tend to have many inductive loads and induction motors, causing the low power factor. This low power factor is why the power companies charge more for the power, because it requires more power to run a load. This is incentive for the factory to [I]do something about it[/I]. So what do the factories [I]do[/I] about it? If a person were running a synchronous motor, as opposed to an induction motor, there would be no CEMF in the circuit.
                                At this point it should be noted that in a purely capacitive load (power factor greater than 1), the current leads the voltage instead of lagging, as in the inductive load. So, if a plant or factory has the incentive to do so they can introduce capacitive loads in some manner.
                                In a oil refinery where I once worked they had a huge compressor motor with a wound rotor (dc voltage could be applied to the rotating element) which could be operated at a leading power factor (current leading the voltage) in order to help correct for the large number of induction motors which were operating at a lagging power factor.
                                Another place I worked was a hospital in Anguin California which had an emergency generator.
                                During times when the utility power was out (which happened frequently) they ran their generator. Power was at a premium as you might imagine since it was a hospital.
                                In this place I noticed they had very large capacitors connected across some very large induction motors connected to the elevators. This, I was told was to help correct power factor for when they were running on their emergency generator power source.

                                The purpose of my post is to determine the following:

                                Are any of the veteran off grid solar people taking steps to correct their load(s) by perhaps adding capacitance to their systems? I read all of the 44 posts above but it was not mentioned.
                                As my handle states, I am just a hobbyist. I have just purchased a set of cells, and intend to make my own panel as a project with my kids. This panel will be used to charge my travel trailer batteries when we are dry camping. I am, however very interested in off grid power and I'm considering going off grid for my mother in law unit, or just for an emergency back up.
                                Love the idea!

                                Comment

                                Working...
                                X