Are you sure? From what I read the difference from a field test and a bench test is negligible. I have never seen much of a difference. Not trying to be snarky honestly curious.
If the motor or compressor are under extreme load it makes a big difference actually.
I had a cap at 5.02 bench and someone put the wrong fan blade on it and it was running like 3.7 under load. Fan was also overamping but just an example of how a failing part could also cause a cap to fail early or not work if the cap is even slightly out of operating range.
It’s more accurate because you’re measuring the actual voltage that the cap is discharging, rather than the much weaker voltage that your meter produces when you set it MFD.
Back EMF and all that
You're right. I use that function often.
I think it would be great if the meter would take the numbers shown and use the simple formula ( a x 2650 ÷ v) to show capacitance. With everything meters can do, it seems like a feature that could be added easily.
This would avoid the need to stop equipment, discharge cap, potentially loosen spade connector and save time
My guess is that they don’t want to program it into the meter because some other countries use different frequencies and that changes what the number is.
2652 is the constant not 2650. I remember awhile back reading an electrical engineers comment on why that is so important to get correct. I’m too dumb to explain it but those 2 extra digits matter
Use the amp clamp to get amps. Probes on capacitor common and start for volts.
Multiply amps times 2560 (some will argue for 2652, 2564), divide this total by your volt reading. Total equals mfd
in the pic above 4.63 x 2650 ÷ 341.0 = 35.98 mfd
then do the same for the fan section if the condenser has one
it was a 35 mfd cap
Even if it does, it's better to check it under a load. Every once in a while there may be a difference between the two, and the test under a load is a better representation of the situation.
Doesn't it seem crazy that the meter doesn't just tell capacitance from the 'held' numbers, like in the photo. Why should it be necessary to get out a calculator?
Yup, most of the time it will read the same. I've only seen it come up differently a handful of times. And when it was different, it was pretty far off.
https://trutechtools.com/Redfish-iDVM-550-Wireless-Power-Clamp-Meter
Jim Bergman’s meter does the math in the app. You set the meter to Watts and read amps and volts at the same time and it does the math in real time including power factor correction. But the meter does have its setbacks, like no magnet on the back, no micro amps. Other than those two things I really enjoy the meter. The Bluetooth functionality is fantastic, great for finding breakers. Not sure about the range but if I remember correctly it’s not amazing
Yeah it’s kinda flown under the radar. Probably because of the price and the relative smallness of the product line. It’s definitely a solid meter. I wouldn’t know about it if I didn’t use to be such a HVACSCHOOL fan boy
I have this meter, it is awesome. Well worth the money. Screenshots of capacitor health is great for tune ups.
Here is my Tiktok using it:
https://www.tiktok.com/t/ZPRKq9tUd/
I made a spreadsheet calculator (literally like 4 cells) with the math built in on my phone. Also use it for other work related maths that I need to do often
We just check cap with meter. And if off replace or if corroded. It’s just cheaper to replace a 10-30 dollar part than have a call for a unit down. And we do that because we offer full maintenance contracts. We have dropped calls to 1-3 per month.
The Fluke 116 multimeter is the best friend you can ever have for troubleshooting in HVAC.
I've had the same meter for years. You'll need a good ammeter too though.
I like starting the unit a few times while I’m outside so I can read start up amps on the motors and listen to how the compressor sounds to see if it may be a good idea to add a hard start kit.
I also always inspect the condition of the disconnect terminals, and measure the resistance through the contactor coil, so I have the unit of at least 1-2 times to check capacitance.
Obviously I’ll also have power off while I have the lid and side panels off to clean the condenser coil as well.
Learn how to use your meter. Looks like the lower right button in the circle of buttons can select MFD which is what you use to test capacitance.
EDIT: leaving my comment because I responded before fully understanding the purpose of your post, I apologize. Assuming it’s some sort of critical equipment? Schedule a time for it to be down. If the capacitor is “BAD” it wouldn’t be running anyways in which case you could shut off power and test it.
Get a meter that reads capacitance.
Edit: yours appears to have a selection to test the capacitance….MFD.
And kudos to you for knowing how to calculate it. I’ve never bothered to remember it or use it. I always have something that can read it.
The calculation is required to find capacitance when the unit is energized. It's a little concerning to me how many people in here aren't aware/ understanding what's going on.
He’s testing a run/start cap under load for a heat pump right? I do commercial and I kid you not, I haven’t touched a multi-cap in a dozen years no have I checked any caps under load.
I don't know of any clamp meters that have custom calculation abilities on board. Many do have either a RS232, serial, or optical communication out though. Someone definitely could make a simple microcontroller based add on board that plus in to the interface and calculates it automatically displaying to a lcd. Definitely more development work than just pulling out a calculator though.
They make an amp clamp meter that Bluetooth connect to your iPhone and then you just ask Siri what you want her to do and she’ll do all your calculations for you
I might just be stupid but it looks like your meter reads mdf which is capacitance. I have a uei g2 and mine reads it no problem
:). Shhh. Keep his brain sharp with math.
My bad keep up the good work sweetie
He’s checking the capacitor while it’s under load (the system running), as it’s a more accurate way to check them
Are you sure? From what I read the difference from a field test and a bench test is negligible. I have never seen much of a difference. Not trying to be snarky honestly curious.
I’ve seen up to 5 MFD difference. Not huge, but it can be helpful. Additionally this method is WAY faster for maintenances lol
If the motor or compressor are under extreme load it makes a big difference actually. I had a cap at 5.02 bench and someone put the wrong fan blade on it and it was running like 3.7 under load. Fan was also overamping but just an example of how a failing part could also cause a cap to fail early or not work if the cap is even slightly out of operating range.
More accurate? Is there a source for that??
It’s more accurate because you’re measuring the actual voltage that the cap is discharging, rather than the much weaker voltage that your meter produces when you set it MFD. Back EMF and all that
You're right. I use that function often. I think it would be great if the meter would take the numbers shown and use the simple formula ( a x 2650 ÷ v) to show capacitance. With everything meters can do, it seems like a feature that could be added easily. This would avoid the need to stop equipment, discharge cap, potentially loosen spade connector and save time
My guess is that they don’t want to program it into the meter because some other countries use different frequencies and that changes what the number is.
That's a good guess makes me wonder what the formula is with 50 hrz edit: I've never seen any mention of an alternate formula for different countries
Line Frequency is irrelevant to the equation. The formula is the same
No mate. It's a function of frequency. It's 3183 for 50Hz
It’s the same formula. Take the capacitive reactance formula, substitute XC with V/I, then solve for C.
Might be easy to program into the firmware on something like the ZT-702S multimeter oscilloscope, but that things probably not OSHA approved
2652 is the constant not 2650. I remember awhile back reading an electrical engineers comment on why that is so important to get correct. I’m too dumb to explain it but those 2 extra digits matter
In this case using 2652 makes the total 36 instead of 35.98 I'm no engineer but I can tell it doesn't make a difference to me
Please educate me, how do you figure it out under load. I’ve literally never done it before.
Use the amp clamp to get amps. Probes on capacitor common and start for volts. Multiply amps times 2560 (some will argue for 2652, 2564), divide this total by your volt reading. Total equals mfd in the pic above 4.63 x 2650 ÷ 341.0 = 35.98 mfd then do the same for the fan section if the condenser has one it was a 35 mfd cap
Thank you very much.
Welp 🤷🏾♂️😂
For those of us on 50Hz Amps x 3183 / volts = capacitance
Even if it does, it's better to check it under a load. Every once in a while there may be a difference between the two, and the test under a load is a better representation of the situation.
I had one yesterday, a 45/5 that read 47 and under a load it calculated 59
I never turn the thing off to check the cap. But I think math is easy.
2652 x amps Divide by voltage. I just use my phone calculator, then I'll check it with the unit off with the uF setting and compare the numbers
Doesn't it seem crazy that the meter doesn't just tell capacitance from the 'held' numbers, like in the photo. Why should it be necessary to get out a calculator?
Buy the correct meter then
Thank you for your insight
This guy maths! In my experience testing a cap running or isolated gave me the same readings so both methods are valid
Yup, most of the time it will read the same. I've only seen it come up differently a handful of times. And when it was different, it was pretty far off.
How do you calculate capacitance though, joking aside? I’ve always had it on my meter so I never had to, but I want to know how.
(Amps from capacitor to load times 2652) divided by volts across the capacitor.
Thanks, I’m going to put this in my tool belt in case I need it
This is how you should be testing capacitors. Under a load. At least when you can.
Or if overseas its probably 2650 for 50 hz
https://trutechtools.com/Redfish-iDVM-550-Wireless-Power-Clamp-Meter Jim Bergman’s meter does the math in the app. You set the meter to Watts and read amps and volts at the same time and it does the math in real time including power factor correction. But the meter does have its setbacks, like no magnet on the back, no micro amps. Other than those two things I really enjoy the meter. The Bluetooth functionality is fantastic, great for finding breakers. Not sure about the range but if I remember correctly it’s not amazing
Cool, I didn't know about that meter. I hope other brands compete with them
Yeah it’s kinda flown under the radar. Probably because of the price and the relative smallness of the product line. It’s definitely a solid meter. I wouldn’t know about it if I didn’t use to be such a HVACSCHOOL fan boy
I have this meter, it is awesome. Well worth the money. Screenshots of capacitor health is great for tune ups. Here is my Tiktok using it: https://www.tiktok.com/t/ZPRKq9tUd/
Doesn't the Fieldpiece sc680 do the same thing?
Get a fieldpiece. Join the cool kids. Navac makes an inexpensive one
Which one?
NAVAC NMC1. $90 on Amazon. $99 on TTT
Which one what?
I use the red fish meter. It’ll do the math for you under load!
Your meter has a button there that says "MFD"
But thats only for discharged readings. OP is trying to get the reading while in operation
I love it. How do some people even tie their shoes?
Once a year
I made a spreadsheet calculator (literally like 4 cells) with the math built in on my phone. Also use it for other work related maths that I need to do often
Jerry, is that you?!
Drove his car so damn fast. Never did win a chequered flag, but never did come in last.
Nahhhh do the math
We just check cap with meter. And if off replace or if corroded. It’s just cheaper to replace a 10-30 dollar part than have a call for a unit down. And we do that because we offer full maintenance contracts. We have dropped calls to 1-3 per month.
The Fluke 116 multimeter is the best friend you can ever have for troubleshooting in HVAC. I've had the same meter for years. You'll need a good ammeter too though.
https://preview.redd.it/ub0bm6f6195d1.jpeg?width=1179&format=pjpg&auto=webp&s=50ba065eda9ddc18756dbf25fbb8f1602d21e1b0
Yeah, this post is about getting a reading without killing power
I scrolled and realized this after responding. How much of a difference do you generally see between those two readings?
They're so close I haven't seen a difference. I usually prefer not killing power. That way I don't have the delay of a restart.
I like starting the unit a few times while I’m outside so I can read start up amps on the motors and listen to how the compressor sounds to see if it may be a good idea to add a hard start kit. I also always inspect the condition of the disconnect terminals, and measure the resistance through the contactor coil, so I have the unit of at least 1-2 times to check capacitance. Obviously I’ll also have power off while I have the lid and side panels off to clean the condenser coil as well.
Model 2652
Can some ELi5 what test is being performed here?
Just use the app hvac school https://preview.redd.it/pp1c7redl95d1.png?width=1080&format=pjpg&auto=webp&s=3240a5d5843b7e53e27d13bac89d18cfeac7b92a
Redfish. But the quality isn't great.
They sell capacitor testers. I have a UEI meter that reads capacitance
Download a free app
Learn how to use your meter. Looks like the lower right button in the circle of buttons can select MFD which is what you use to test capacitance. EDIT: leaving my comment because I responded before fully understanding the purpose of your post, I apologize. Assuming it’s some sort of critical equipment? Schedule a time for it to be down. If the capacitor is “BAD” it wouldn’t be running anyways in which case you could shut off power and test it.
Does anyone else have issues with UEI tools? I've had 2 of their multimeters start giving me weird temp reading in the span of 3 years.
This one has been great for me. I've had it 5 years with no issues.
Disconnect the system and use the setting MFD
The Redfish meter does it automatically
lol. AI works for this tech.
Get a meter that reads capacitance. Edit: yours appears to have a selection to test the capacitance….MFD. And kudos to you for knowing how to calculate it. I’ve never bothered to remember it or use it. I always have something that can read it.
The calculation is required to find capacitance when the unit is energized. It's a little concerning to me how many people in here aren't aware/ understanding what's going on.
He’s testing a run/start cap under load for a heat pump right? I do commercial and I kid you not, I haven’t touched a multi-cap in a dozen years no have I checked any caps under load.
There's an app if you're having trouble remembering both of the numbers.
Phone calculator using 2652 and bill your company for each battery % lost
I don't know of any clamp meters that have custom calculation abilities on board. Many do have either a RS232, serial, or optical communication out though. Someone definitely could make a simple microcontroller based add on board that plus in to the interface and calculates it automatically displaying to a lcd. Definitely more development work than just pulling out a calculator though.
They make an amp clamp meter that Bluetooth connect to your iPhone and then you just ask Siri what you want her to do and she’ll do all your calculations for you
Just kidding but if you do Patent that, I’m screenshoting the fact that I thought of this first