This is a very nice explanation of the capacitor value calculation, but it is misleading with respect to savings. In the USA, utility companies only bill small consumers for actual power, not apparent power.. Small consumers save nothing by power factor compensation, but they can free up circuit capacity. Large consumers have a more complicated billing structure that may include some charge for low power factor. I suspect the same is true in Canada and in other parts of the world. There is no cost to utilities to produce reactive power, but it does reduce their capacity and and the transmission losses have a cost. Utilities may install power factor compensation in substations and even on poles to reduce the transmission and capacity losses.
You really haven’t done anything, you should have checked the amps with the bell on and put the machine under load. You could’ve lost those amps just by taking the belt off and reducing the drag. Sounds like bullshit to me
sir good explanation kindly your wriitrn computation to share with me for my personal use and I am willing to give an incentive for kindness and productive explanation asson as possible. thank you so much.
Very good explanation and demonstration for power factor correction. It is always nice to see demonstrated with actual equipment instead of just on paper.
We recently bought an LG fridge, and there is an iPhone app that allows us to monitor the fridge electricity usage and cost. I checked the current usage and multiplied it by 120V, but the result didn't match what the iPhone app reports. It was actually higher. It turns out I overlooked the power factor (PF), which in this case is 0.73 or 73%. This led me to wonder how we could make the fridge more energy-efficient. I haven't taken any action on that front yet, and I'm not sure if I ever will, but I was curious about what value of a capacitor would be needed to correct the power factor. And then, I found Serge's video that answered all of my questions. I want to express my gratitude to Serge for explaining everything so beautifully! The RU-vid University.
What was the first capacitors size? Is the MFD higher of lower range? I'm assuming you are working with the RUN capacitor? Could changing the MFD help reduce even more amperage draw after completely finding the capacitance of the capacitor? Great instructional video!
In a lot of places, consumers don't pay extra for reactive power. The big industries that use large AC motors usually do. Also how much power does the capacitor draw when connected directly to mains?
It should draw very little because once the capacitor has been charged, that energy will circulate throughout the circuit, that is why they are being used. You are basically paying for the initial charge, but then the reactive power is oscillating back and forth between the inductive windings of the motor and the capacitor in synchronism with the sine wave of the applied voltage. It's an interesting concept, almost like a game of ping pong where energy is bouncing back and forth from one state to another.
What brands and types of capacitor should I use on an old 1940s transformer welder? There is no markings on the capacitor. The equipment plate has these specs, Primary volts, 230v 60hz, max 37 amps, output 180amps max at 25v, OCV 52v-65v, F.L.P.F. 75%.
Thank you for this! (I'll be back soon for 3Ph classes 🙂) Meanwhile, I have a diaphragm (inductive load) pond air-pump that at 120.8v meters at 78w (claimed) and 1.58a (claimed), but it didn't make sense to me. I have some homework to do and a plan. And now I can imagine how makers size run caps for CSCR vs CSIR motors. That said, It seems that any CSIR ought to be checked out.
I am in the process of replacing both start and run capacitors on a 5 hp 230VAC motor. The information tag does not provide all the discussed information nor does the mfg provide a data sheet. Neither do other mfgs of similar motors. The old caps are damaged such that they are not readable. So I am trying the figure out what capacitor values are needed with limited information. I'm frustrated.
Smart meters and analog meters charge extra for poor power factor, a parallel cap can save MONEY men. They are not true watt meters but just VA meters!
I'm trying to understand why the voltage drop across a start winding in a cap start cap run single phase AC induction motor rises so far above the supply voltage. Of course this is the principle of how a potential relay is used to drop the start capacitor out of these motors after a few seconds. Typically in a 240V fed motor, the drop across the start windings is about 360 V. The hand waving explanation in technical college is that back EMF is responsible for that rise. I'm wondering what happens to the inductance of a motor coil as the motor spools up. In an RLC series circuit, that kind of big drop is easy to explain because of the phase shift in the stretch of wire between the run cap and the inductor. Is back EMF phase-shifted compared to incoming voltage? Does motor inductance increase with rotor rpm, to explain this rise? How do you model back EMF in a circuit with classical complex number circuit analysis?
As asked by Muhammad 1year ago. Why are motors produced with this inefficiency in them? Are the motors with two capacitors on them corrected already. Im nowhere near a electrician just always trying to learn a bit of something. Thanks for the lesson.
It would be interesting to know the value of the original capacitor, I assume it was lower than your computed preferred capacity. Also, your HVAC or electronics guy could test a few of the 20% tolerance units and help you hit your target capacitance. I agree with other comment that raised efficiency should prolong motor life, etc.
You can't really determine the cap value from nameplate numbers. It is a function of motor loading. You put caps on & vary cap & note the current & go for minimum. You save nothing as far as utility is concerned. Home power is charged based on real power, not reactive power. The only "saving" is less current in your home's wiring. This would be useful only if heavy load is on the edge of tripping breaker. The cap you are using looks like "motor starting cap". These are AC nonpolarized caps designed for use a few seconds at a time only! You need AC oil caps if you plan on running the load for any significant period of time. They are large for the microfarads you get! You also need to deal with the surge on turn-on. This will tear up the appliance's on-off switch. A better thing to do with this motor (assuming it has either starting cap internally, in the bulge on the motor's top, or it is split-phase start, both with centrifugal switch cutout) is to put an AC cap on the "starting" winding permanently (smaller than the starting cap) sized to balance the 2 phases in the motor internally WHEN RUNNING. This will make the motor run cooler & consume less real power, & will reduce vibration.
@@bernardocisneros4402 An engineer that knows the internal workings of motors (what difference does it make?) The thing to understand is the purpose of a capacitor in regard to "single-phase" motor. For "straight" inductive load (such as the older "neon sign" transformers), the capacitor doesn't affect the transformer's function; it only boosts the power factor (I reduced the line current in neon sign transformer from 8 amps to 3. That permitted operating 3 of them on single 120V line circuit for Halloween "Jacob's ladder" display.) But for a "single-phase" induction motor (it is single phase externally only), the capacitor's function is to provide phase shift to produce a second phase internally. This is WAY more important than just reducing line current. It is connected in series with a separate (second phase) winding, causing current to lead the current in the main winding. The amount of capacitance required CHANGES with motor load. At instant of start, motor is effectively in "locked rotor" state. You need HUGE capacitance for this, which would be impractically large. So they use electrolytic AC capacitor inside that bump on the motor top. AC electrolytic cap is very "crappy", which doesn't matter if you use it for a few seconds at a time. DO NOT USE THESE FOR CONTINUOUS USE! They will fry & blow their top, spewing out what likes wet toilet paper soaked in (corrosive) chemical salts. The REAL way to determine the correct capacitance is to put a mark on the motor pulley & view with stroboscope set to "almost stop the motion". If the cap is correct, this motion will appear as slow UNIFORM rotation. If the cap is off, the motion will be alternating speed up & slow down because the 2nd phase will be too early or too late. Some (induction) motors have "permanent" cap on the 2nd phase, always connected. Common examples are refrigeration compressors & fans in outdoor A/C units & in refrigerators (can't put centrifugal switch inside). Starting torque is VERY weak & line current during the start is ~ 3X the full load current. (Look on A/C unit nameplate. There is "RLA", run load amps, & "LRA", locked rotor amps.) Designer banks on refrigerant leaking down when OFF so the starting load is light. Bad thing to do is to turn off compressor & then turn it back on before refrigerant can bleed down. That's why home A/C systems have "compressor delay". For things like power tools, the only starting load is usually the inertia of the motor rotor & the tool.
@@bpark10001 Thanks for taking the time to answer and write all this info. I understand about 80% of it. I will have to do more reading to understand the rest. That is a cool trick with the strobelight. Using it to find the correct capacitor. I was only asking if you were an engineer because I'm trying to get an idea of how much is expected of an engineer vs an electrician. I do know how start capacitors chancge the phase angle between voltage and current so the motor produces enough torque to start turning. I assume the run capacitor does the same thing, but instead of being used for producing more torque, it's used to improve the power factor. Thanks again!
@@bernardocisneros4402 No. The run capacitor provides exactly the same function as the start capacitor: to make a second phase INTERNALLY in the motor. The motor doesn't give a @# what the external power factor is! The power factor inside induction motor internally MUST be low as the stator windings must carry lagging current to set up the rotating magnetic field, which conveys no energy, & also the inphase "running current" (coupled to the rotor short-circuited windings by induction) which is what acts against the magnetic field to make torque. But as I explained, the capacitance needs to be reduced from the proper value for starting (by a large factor!) (The purpose of the second phase is to make a rotating magnetic field, as 2 coils set at right angles IN SPACE & fed with currents "AT RIGHT ANGLES IN TIME" do so. This is the big invention that Tesla made & 99% of engineers don't understand!) Without the run capacitor (with the motor already running), the rotor currents create the 2nd phase by transformer action, but the torque is pulsating. You can hear this as a hum & feel it as a vibration of the motor body, especially if the motor is set on rubber mounts. (Tuning for minimum hum & vibration can also be used to determine run capacitance.) Yes, a run capacitor does improve line power factor, but its main object is to produce symmetrical winding currents INTERNAL to the motor. The only way to increase power factor INTERNALLY within the windings themselves is to put permanent magnets (or a separate set of windings fed with DC through sliprings) on the rotor. Now no current needs to be drawn by the stator windings to set up magnetic field & the power factor can approach 1, reducing heating in the windings. But said motor becomes synchronous, which requires complex electronics to generate variable frequency drive. You can see from the schematic diagram that both caps (in concert) feed the 2nd phase during start, & only the run cap does so when running giving the (desired) reduced capacitance. This connection is different from power factor correction cap, which is directly across the line & has NO EFFECT on motor performance. "run" winding "start" winding (2nd phase) line---------------o------------o--------------------------------------------o | 3 3 power | 3 3 factor = 3 3 correction | | run cap | cap | |--------------| |----------------------------| | | start sw start cap | line---------------o------------o--------o/o---------------| |------------o
This is a well articulated video, very rich and informative in its presentation.Added more insight to my understanding of the topic.Sir, please keep up the good work.Great thanks.
If the motor is only 54 percet etc efficient then it wonter matter what the va is because it can never give more than 54 percent etc, that means if we want the real power which in this case would be 95 percent efficient that means we will have to buy a motor with a bigger va ha ha ha ha....
Very nice explanation and really big difference after improving pf what about 3 phase motors is there any difference or only use 3 capacitors of the single phase case thanks
Is this taught in school to students training to be electricians and HVAC technicians or is this only taught to students studying to get a bachelor's degree in electrical engineering?
Would be nice to also clamp an ampmeter on the black capacitor wire to show the reactive current. And a killawatt device on the input to demonstrate an improved power factor.
Hi....at various location there has been a drop in voltage due to many reasons...hence there a rise in current which leads to rise in temp...so please advice how to tackle the issue ....??
Hi there! Now when I re-watched this, I realized there is something I'm missing : shouldn't TIP be voltage times FLA ? The final current draw, post-correction, is compared to FLA, but FLA appears nowwhere in the initial input calculations.
@@fxeconomist the procedure I use comes from documentation obtained directly from an electrical motor manufacturer. Most calculations of this type are based on using values of power instead of current because it gets away from series and parallel circuit rules and simplifies the process.
Thank you so much! I went along with your lesson and built a spreadsheet to do the calculations at the same time. I have a much better understanding and greatly appreciate the time you put into the video! Well done!
Excellent video first and foremost! Incredibly helpful and easy to follow along! Quick question for you though. After solving for the proper capacitor for the PF correction, you came up with the 82.xx mfd capacitor. I noticed that the capacitor you selected from the HVAC distributor was a plastic body capacitor. Normally in my trade (HVACR) the plastic body capacitors are used in the starting circuit applications and the metal body capacitors are used in the run circuit applications. I'm curious and would like to know if it would make a difference (if any at all) if A: there was a specific reason as to why you used a start capacitor style or B: could you use a run capacitor in lieu of a start capacitor so long as the mfd and voltage rating were matching?
You shouldn't use a start capacitor in lieu of run capacitor but you can use a run capacitor in lieu of a start capacitor. The start capacitor are only designed and manufactured for seconds of use at a time. They will burn up if used for extended periods.
Awesome content! You sir have a way to share very technical information in a way that's easy for me to understand. Got me to thinking though, I have a 7.5hp single phase 240 volt air compressor, would this work on a heavy start up load?
thanks for the knowledge sir , very helpful at our work , hope you have a 3phase calculation at one load and with different load at the same time , thanks again ,
Electronic variable speed controllers generally will not tolerate power factor correction at the motor. Power factor correction capacitors on the line side of the controller are likely to cause problems also. If such a system needs anything it will be a harmonic filter or inductance on the line side to prevent the controller from interfering with other equipment.
Likely due to calculation using supplied voltage at 115v and the demonstration in real time was metered using 124v. Higher voltage require lower current values to result at the same wattage usage
Like it’s very frustrating I understood and was learning until you jumped and didn’t explain what thr hell is varsc is and ever made any attempt to explain since
In mathematical terms: VarsC is the exact opposite to VArsL. they are both values of reactive power but can be easily confused so the electrical textbooks employ a subscript to clarify this fact. In more simple terms, the motor windings require reactive power to create a magnetic field to induce rotation in the motor. That reactive power can be obtained via a capacitor because they produce reactive power. The entire process is about calculating the amount of reactive power the motor requires to operate, but instead of obtaining it from the electrical outlet in your home, we can charge a capacitor and let that energy oscillate back and forth from the capacitor to the motor windings and back again in a perpetual loop when the motor is in operation. The benefit is that the homeowner does not have to bear the cost of that "Reactive power" to keep the motor running. We need an oscilloscope to show people that there is a difference in the voltage waveforms that the motor windings and capacitors produce, but the main thing to remember is that capacitors and inductors are the polar opposites to each other and we can use capacitors to cancel out the negative effects of what an inductor does inside an electrical circuit.
Need to add that lower current means lower heat generated. Therefore, all heat exacerbated aging is slowed. Also, less heat generated in large industrial shops where there are more machines, therefore summer workspace cooling requirements are reduced.
I'm learning about PF correction online..you sir are the best teacher I have come across!!! That was excellent explanation of exactly how power factor works that it was so much easier to understand than my course I'm doing at the moment! Subbed and liked 👍 thank you so much and cheers from Australia 👍
A very interesting video showing the effects of reactive power and power factor correction. If you put the amp meter on the wires going to the motor after where the capacitor is connected, I bet the current would be about 5 amps. You are just getting the reactive power the motor requires from the capacitor and not from the power supply. The current on the circuit feeding the motor will be less, and the I square R loss in the circuit from the reactive part of the power will be slightly less (which loss is heating the wire), but in residential situations, the amount of I square R loss is not much so I doubt it would be worth to install such capacitors at motors to save that trivial amount of loss. As others have said, residential electric billing only bills for the real power used, not for any reactive power. But still an interesting exercise to demonstrate power factor correction!
New problem is that "smart meters" are now reading KVA hours not KWatt Hours. The story is that the power company is now charging for Reactive power at residents. I'll be checking my new meter once the sun comes up tomorrow.
Very nice. Well.ezplained. my question is. This is for one motor only. If i compute for let say 3 motors ac unit. Then only 1 ac is on. Will that 8ncrease my bills ?. Bec of the pf calculation is larger bec i used 3 motors 9n the calculqtion ?
I am building a rotary Three Phase converter. Can I apply the same process to this motor. I assume I would be adding similar capacitors between both legs of the three phase motor.
They can put that into an excel spreadsheet and it can grind out the numbers for you. The power will change if there is resistive force on the motor shaft. Current should increase. Will that change the capacitor value if there is a load on the motor? Here, you just used the numbers on the tag on the motor. Looks like you were just free wheeling the motor in the lab with no load on it.
Ok, I have a meter that gives a wattage and power factor reading. So with all these power terms bring thrown around, what would/should that wattage reading be? TIP, apparent?
I have a pedestal fan at my shop and it needs a new start cspscitor, only thing is that is very faded where it has the letters because of the sticky material between the cap and the metal cover, so i do not know the value of it. can i use a capacitor fora similar motor? i know harbor freight sells a very similar pedestal fan, i could order one for that motor and use it on mine, would it work?
Great set of videos Mr. Levesque. What a valuable resource for electricians in training. Some minor points because of my HVAC background. 1. That capacitor the guy at the HVAC store sold you is a "start" capacitor and will burn out in a few minutes if you use it for "run" duty as you have wired it. 2. We have to be careful in distinguishing between motor efficiency and power factor. They are NOT the same thing. 3. I don't know about Canada, but in the residential USA billing, the meters bill you by KW and not KVA. Although it is always good to have near unity power factor, the fact is that for an existing installation any improvement in PF benefits the Utility more than it does the homeowner. Unless of course if they have a low PF penalty, like in commercial billing rates. Keep the good stuff coming. Best wishes.
To clarify point 3 above a little more: If your T.I.P is 333W as you correctly compute in your video, then you are only paying for 333/120 = 2.7 Amps. This is because the utility meter is reading KWh and NOT KVAh. But the Utility has to provide you (and build their power plants) based on your KVA. If you compute your payback based on this 2.7 A, you will find it is hardly worth the hassle. (For a new installation of course the equipment size and wiring size benefits with high PFs.) And this is why the Utilities get so pissed if your PF is low :-)
I like your comment related to energy savings. This is where energy losses due to material imperfection comes in.. The higher the current drawn, the more the conductor heatsup, thus the more energy is lost. Just imagine the length of wire from utility meter to your motor. He just demonstrated the working principle of a power saving device...
The capacitor can only absorb a like amount of reactance, any surplus is redirected back into the supply and is redistributed to other devices within the same circuit that have the ability to absorb it. That is why it is important to accurately size a capacitor, the excess reactive power could register as an increase in current.
@@TreeHugg It depends on the Utility, penalty charges start to apply to commercial and industrial accounts where the power factor is below 90% as a general rule.
