The Supco Redfish iDVM550 Power Quality Meter includes a function with which it can measure real-time power factor on a load. In this video, learn how using power factor to test capacitors under load is a valuable feature, and how to use the Redfish iDVM550 to do it!
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We're gon na have to check amperage and volts together at the same time set it to kilowatts, and I measure the voltage on the load side of the contactor on the outdoor unit. We would take our compressor common winding and our voltage on the top of the contactor here checking capacitors under load using the power factor feature of the meter in order to determine whether the capacitor is within the is rated capacitance or not. This has come in handy a lot for me, especially because there are certain manufacturers out there who have manufactured fan, coil systems with the capacitor for the blower motor mounted on the blower assembly, all the way up back into the back of the cabinet and the only Way you can get to it is to take the blower assembly out of the cabinet itself. It's a pain in the butt.

It adds extra time to maintenances, so this has actually been a pretty interesting and valid measurement to take, and it's been very helpful and I want to just real quick go through how to get to the power factor feature on the meter. We go to page 24 here in the user manual. This user manual is located on true tech tools. Comm.

If you search the IDB m5 50, you will see in the resources section of their website the online pdf version of the user manual. They don't have a print version that comes with the meter. You can of course, print this out anytime. You want, but it's always here available online to you, I'm a true tech tools comm.

So here page 24 we've got power, phase and power factor. They do a really great job explaining the power triangle which is depicted here. This power triangle here is depicted as an inductive load. If this were capacitive load would see an inverse triangle with the real power on the top.

The apparent power as the hypotenuse and the reactive power over here so here we're going to be looking at inductive loads because we're looking at an inductive motor, ie, condenser fan motors. So the apparent power here which is measured as VA volts, real power and watts and reactive power, volts, amps, reactive and then, of course, we have power factor which is this is notated as theta, but on the meter, it's notated as cosine theta. Essentially, what we're looking at is as it with an inductive load. They have to, they require a magnetic field, and in order to generate the magnetic field, you have to use reactive power as reactive power increases.

The apparent power becomes further away from the real power. So you can see that as the power factor decreases, the gap between apparent power and real power also increases. So power factor decreases. The gap between apparent power and real power increases apparent power is simply the amount of available power.

Real power is the amount of energy that is actually doing work. Reactive power is a part of this equation, but it's not doing any work. It's just creating the magnetic field, so it happens with an inductive load. Ie condenser fan motors.

It's going to be using more utility power to use reactive power to generate that magnetic field, and it's going to become extremely inefficient. It's going to heat up very quickly and we need a way to use less reactive power from the utility. That's when capacitors come into play, we're going to decrease the reactive power that is needed from the utility supply power, thereby increasing the power factor making this gap smaller, the epatha, the apparent power and real power will become closer and we're essentially trying to get a unity Power factor of cosine theta that power factor of 1 we're still gon na, have reactive power. So it's not going to be a true one.
If we had zero reactive power, we would have a resistive load and then which, in which case the apparent power and real power would be the same, but with an inductive load. We have to have that magnetic field. So that's what the capacitor is doing. It is considered a reactive power generator when tied into a circuit, so what it is going to do is rather than the inductive load itself, trying to draw all of the current from the utility to generate the reactive power.

The capacitor itself is going to provide that reactive power, thereby allowing the amount of real work done to increase. So we look here on page 26, power phase and power factor. This is the actual making of the measurements. So if you put your meter, the idv m to kilowatts you're going to see this screen here, the top of the display will be kilowatts.

The bottom left this voltage bottom right is amps current up here we see lag or lead so in an inductive load. The current is lagging behind the voltage if you were, if you looked at it on a graph and a capacitive load, you would see lead here, because the current is leading the the wave of the voltage as in this. In essence, the the peak of the sine wave for an inductive load here we're looking. If you press function once you're going to be looking at the kilovolt amps, the apparent power just volts times, amps, that's what you're looking at the apparent power, the amount of power that is available.

This is the real power, the amount of power that's doing the work. If you press function twice, you're gon na see cosine theta, which is power factor here, lag. That's indicating that you're measuring power factor on an inductive load - and this is your reactive power measurement down here on the bottom left. This is your volts, amps, reactive and up.

Here's your power factor: you want a power factor on an inductive load with a capacitor attached to it, like I said, we're trying to obtain a power factor of unity, one if I saw zero point, eight, six, nine or point eight seven. I would be looking at probably a weak capacitor. Maybe that capacitor is visually just blown up. We would be seeing higher amperage on the common winding of the inductive motor itself and with, of course, we have this lower power factor.
We would need to be taking a look at this capacitor a little bit more closely. Maybe take it out of a circuit to a bench test or do the capacitance calculation network that we're all used to maybe in the HVAC school lab click the function key. One more time we can actually measure phase negative is inductive load. Of course you would also be notated by lag positive without the negative sign here you would have a capacitive load and that's pretty much it.

The only other thing that I would say is mostly just a caveat. You can see here in the picture the way that they're measuring the currents on this particular wire here, these redfish meter clamps, are they can sometimes sensitive. You want to make sure that you're making a good measurement you want to be away from bundles of wires. You want to make sure that the wire that you're actually measuring is in the center of the clamp not off to the sides resting on the clamp itself, because it can alter the accuracy of the measurement going to make sure the the wire that you're measuring is In the center of the clamp and that the rest of the clamp and the wire you're measuring is away from bundles of wires for maximum accuracy, otherwise, let's go outside and let's take a look at how we measure this on a system that is running all right.

So we got the ID VM 550 meter here, we're gon na switch it to kilowatts, and you can see here. This is where we would be measuring real power with the kilowatts up here on the top display, volts and then amps. We hit the function. Key once see, this is where we would be measuring apparent power.

Twice we got power. Factor power factor would be displayed up here at the top kilovolt amps reactive down here at the bottom hit it one more time we can measure phase, remember positive negative. You could be measuring inductive or reactive loads, volts and amps hit it one more time. You can go back to real power or active power.

Let's go, let's go outside and measure it, and I did also want to show show you guys how to use the HVAC school app. You go to tools, you look up at the top under load, capacitor tests - and you just put in you input your readings voltage across the capacitor, which is your start and common on the capacitor, your amperage on the start winding and then what the capacitor is rated For and micro farad's we're gon na check volts across we've got 343 across the fan start winding and the run winding of the fan make sure we got here. 340, I'm sorry, 320, as looking like 343 now, if I switch to amps, we got a zero point. Six five six six input in here and it's rated for five.

You can see our calculated micro, farad's and the amount of variation is acceptable. This is matching the power factor test that we just did alright, so we're going to test this under load. We've got our compressor common winding and our condenser fan motor common winding. Remember we're gon na have to check amperage and volts together at the same time set it to kilowatts, and I measure the voltage on the load side of the contactor on the outdoor unit.
We would take our compressor common winding and our voltage on the top of the contactor here we're getting a power factor of about the same 0.97. Now, if I were to see this any lower than 0.94, I would say: let's go ahead and replace this capacitor, because it's probably it's probably weak and I would bench test and use the you - can also use the hvac school app to test it under load. Using the capacitance calculation, so there you are, that is checking the capacitor under load using the ID EVM 550. We're going to use the sub code, tech link app and we are going that comes in conjunction with the IDB M 550 sub-code power quality meter.

You can use it for the 510, I believe model meters that come from the redfish instruments or the sub cove instruments. You can go to your toolbox, you would simply just press add tool, it would scan, you would come up, you would just hit save and then you can connect or disconnects the meter. You're gon na connect our cars back together, real quick going into tests. You can see they have a lot of quick tests that you can do very easily capacitor check under load, single or dual run.

You can also do your your standard bench tests here and all while bluetooth connected to your meter. You got some guided tests. Capacitor bench test current imbalance fuse check, voltage, input tests, real quick, we're going to use the sub code. Tech link app so check the power factor on our compressor.

This way, we're going to indirectly by way of power, factor, determine the quality of our capacitor. As of right now in real time, so you can see right now we're pulling about one point: eight, five: kilowatts at two, forty five load voltage in seven point: seven, three amps the current being drawn by that particular motor of the compressor, and we got a power Factor of 0.98 - that's a pretty darn good power factor. I think I was measuring 0.7 a little a little while ago, so we got 0.98. Remember we're trying to obtain a power factor of unity in conjunction with the capacitor being applied to the circuit.

So I can confidently say that this capacitor is doing its job because we are just under a unity power factor. Now. If I wanted to check the fan side, I now have my amp clamp on the fan common winding we're pulling about point just under point 2. Kilowatts and we've still got just about a unity power factor.

We can confidently say that this this capacitor is okay, and this is just another way to measure it. Using the manufacturers supplied subcode tech link app, it's a fantastic map. You can use it to record your readings. You can see the timeline here, the line graph.

You can expand this so that you're not longer seeing the gauge. If I were in a test say, for example, the capacitor under load test. I would finish the test. I would hit complete and then all of my tests would be located in the results tab.
It's very similar to the layout that we have in measure quick, Jim Bergman has designed a fantastic app in that as well. So there you go, that is using the sub code. Tech link app as well in conjunction with the I've ID EVM 550 of power quality meter.

17 thoughts on “Using power factor to check capacitors under load”
  1. Avataaar/Circle Created with python_avatars q zorn says:

    a wonderful PF-cap video… also, the solar inverters and VFD motor drives can create 5th and 7th harmonics that can burnout equipment on the grid…. thanks… 🙂

  2. Avataaar/Circle Created with python_avatars Sam Andrew says:

    How does the app connect to the meter?

  3. Avataaar/Circle Created with python_avatars Simon Watson says:

    I have an 04 condenser, my compressor's power factor is 0.75. The rated capacitor is 80MFD, and installed Cap is well in range , at 78MFD. I can only assume that the loss is due to compressor wear. Is that correct? I imputed my data into the calculations provided on The Engineering Mindset's video 'Power Factor Explained' and converted that to MFD and I got 92MFD. Would that increase due more harm than good to my compressor?

  4. Avataaar/Circle Created with python_avatars Richard Segui says:

    Don’t you mean SYSTEM Power Factor vs Capacitor Power Factor? Please advise!

  5. Avataaar/Circle Created with python_avatars Big Nasty HVAC says:

    .94 and you're concerned? Come on man that's a bit egregious isn't it? Even Emerson says correcting to 90% .90 is more than acceptable….. Emerson AE9-1249 sec.8

  6. Avataaar/Circle Created with python_avatars Daniel says:

    do power factor really safe money am using 10 motor in wood work shop can power factor cut my bill

  7. Avataaar/Circle Created with python_avatars Richard Segui says:

    Please clarify something for me.
    If the power factor is less than 0.94 and indicates a weak cap, what does a power factor of 1.5 indicate?
    Great video!

  8. Avataaar/Circle Created with python_avatars Mark E Pugliano says:

    I ate a power bar after this video. Are you in Ottawa ?

  9. Avataaar/Circle Created with python_avatars RJ_Make says:

    I don't think it was mentioned, but doesn't the load play a roll? If you inadvertently use this testing method with say a compressor or fan that is unloaded (staged) won't that skew the results?

  10. Avataaar/Circle Created with python_avatars Glen Schmidt says:

    This type of test is done during R&D of a motor to confirm engineers math and capacitor choice. In the field a normal clamp-on multi-meter using voltage and amps is all that is required. Amps X 2652 ÷ Volts = uF. This is under real world load for given conditions. Mr. Psychometrics correctly pointed this formula out. Have done it hundreds of times. No apps or fancy meters required. Your overcomplicating something for what reason, your forgetting K.I.S.S. principle, unless your trying to sell meters.

  11. Avataaar/Circle Created with python_avatars Jose Guerrero says:

    Another great video and explanation to

  12. Avataaar/Circle Created with python_avatars Hozer HVAC says:

    great video!!!

  13. Avataaar/Circle Created with python_avatars JT H says:

    At what power factor would you start to suspect the capacitors. Since the manufactures dont put out power factor specs wouldn't you need a baseline reading to be able to determine that there was a change?? And since the voltage is an integral element in the power factor computation would a change in voltage from your baseline reading cause a change in power factor? Are you in Orleans ?

  14. Avataaar/Circle Created with python_avatars Silvio Atejedor says:

    Hi can you do this with other meters

  15. Avataaar/Circle Created with python_avatars Mr Green says:

    Ah yes 2552 × Amps ÷ Voltage = MuF

  16. Avataaar/Circle Created with python_avatars Susie Dunn says:

    Thank you. I was just telling my husband this morning that I didn't know how to use all the functions of my redfish. Are yall Mind readers? Do you diagnose systems from your office chair too?

  17. Avataaar/Circle Created with python_avatars InsideOfMyOwnMind says:

    So if you have a known good cap and the measurement says otherwise is that an indicator that the inductive load may be in early failure? Service area Kanata??

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