larger capacitance meter

[SGKent]

Had to decide whether to put this in lighting and electrical, general garage or heating. If you don't know the answer please don't guess.

Recently someone showed me their capacitance meter and they used it to test a starting capacitor. None of my many meters have that feature so I said have to get me one of those. I have multiple items around here that use starting caps and it would be nice to know one has lost capacitance rather than wait for that awful motor hum. So I started shopping for one.

Starting capacitors can be in the hundreds of MF, like 150 MF to 300 MF, or they can be 30 MF to 45 MF. All the meters I have seen save a couple top out at 20 MF including those advertised for testing starting capacitors. The BK 890 goes to 50 MF. There is a $30 unit at Amazon that goes to 470 MF but I think they show it as 470000 MF.

Do any of you who test starting caps have favorite meters that will test a starting cap as large as 200 - 250 MF or there abouts? Am I approaching this wrong? This is out of circuit testing.

Thanks in advance.

 

[Vicdog]

You may be confusing 50mf. That is millifarad as in 50,000 microfarad.

 

[SGKent]

perhaps. I thought (as in my mind) the cans labeled in MFD were large and therefore meaning millifarad. I am familar with the electronic ratings but not with the capacitance numbers on starting caps. Following your post I noticed that some starting caps online are labeled both as uF / MFD. Then there are the caps labeled only in MFD, and only those in uF. for example I am looking at one that is 233-280 MFD (dual can). The meters have a 20 mf scale. (without the D in MFD). I recognize that a farad would take up the size of a building. So if a meter reads say 500 uF is that the same as 500 MFD?

There are some non-verified articles out there I can find that say MFD is an old way of saying microfarad (uF). Can I trust that?

 

[samss]

This is what I use on the job: https://www.fieldpiece.com/products/detail/sc260-compact-clamp-meter-with-true-rms/clamp-meters-new/
Micro Fara D MFD is an acronym

 

[californiaHank]

There are some non-verified articles out there I can find that say MFD is an old way of saying microfarad (uF). Can I trust that?

Yes.

 

[MBfreak]

If you have access to a good DVM with input impedance of 10 MegaOhms, you can measure even quite large capacitors, as long as they are reasonably loss free.
Charge the capacitor to 12 V from your car battery.
Attach the DVM set at a range of two decimals.
Multiply the capacitance stated value in microF ( so often wrongly called mfd, which is milliFarads, 1000 times as much) with the DVM`s impedane, ie:
120 microF * 10 MegaOhm equals a time constant of 1200 seconds.
Connect the DVM to the capacitor and after around 1200 sec the DVM shoud read around 0,35*12V ie approx 4 Volts.

Ola

 

[Max]

Capacitors have a lot of characteristics beyond that of just capacitance. Many times you care about more than one attribute when you need to test one. As a simple example, for starting caps you care about the capcitance, but you also care about the working voltage. It is quite possible for a cap to look good on capcitance at low voltage (the DVM will use a volt or two at most to test) yet it breaks down at the much higher working voltage.

It’s been awhile since I looked at starting caps in any detail, but my recollection is that they are generally electrolytics. If so, a more reliable out of circuit test than capacitance would be checking ESR (equivalent series resistance). There are cheap testers for ESR available as well.

There is a school of thought that says due to the complexity of testing caps the best way to test is toss the cap in the trash can. If it goes “clunk” it was bad. . I am not in this school mostly because I have a lot of test equipment. YMMV.

If you do stick with measuring just capcitance, and the capcitors are electrolytic, note carefully the tolerance on the caps. Electrolytics can easily be -20% to + 100% tolerance so a wide range of values is good.

Max

 

[Bert_]

I have a cap tester than plugs into 120v. Not a fancy meter by any means but it has caught quite a few caps that a digital multi meter said was ok. The difference is the higher voltage used to test.

For starting caps that have a wide tolerance and the value isn't critical I often use a simple ohm meter with great success. Should start near 0 the swing over to infinite. The larger the cap the slower the reading should change.

 

[SGKent]

Thank you to all. I do know from days past that electrolytic caps are prone to leakage as well as drying out. There are workbench style testers and workbench style impedance meters from the 60's and 70's that can test for leakage and capacity. I was looking for something simple that would give me a general thumbs up or down without cluttering my workspace with more equipment. A lot of it will be Heathkit type stuff as well, where the assembly quality is unknown, and drift has occurred since then. A couple years ago I bought a DC voltage standard and was surprised that even my best meters that cost several hundred dollars were all over the place on DC voltage. After using the standard and tuning them they all read correct now up on DC. It does not speak highly of the equiment manufactures when someone pays $250 for a meter and it is 10% off out of the box. I won't turn this into a rant but I was thinking if I buy one more meter it has to be reliable and reasonably accurate on AC and it must offer features that I do not have. The Fieldstone SC260 shown does look nice. I have considered one like Bert's as well as I mentioned above because they often have a load test which is capacity and leakage at voltage combined.

 

[MBfreak]

Yes, bipolar electrolytics, ie two units connected in series with one reverse polarized.
Since starting caps are used on AC, a single electrolytic cap will blow up.
As to voltage withstand, for this test it seems extravagant to try to establish a value.
If the unit has been in service and not let the magic smoke out, it can be taken for granted that the voltage withstand is sufficient for the application, even if the capacitance may be far too low for the starting duty
ESR and frequency dependent parameters are of little significance for starting caps.
However, being in Europe I am quite ignorant wrt starting capacitors. We use three phase motors.

Ola

 

[rlitman]

...

ESR and frequency dependent parameters are of little significance for starting caps. ...

My personal experience says otherwise.
ESR is a good measurement of the thermal load a cap has, which tells you how hot it will be running, which is a good predictor of failure.

 

[SGKent]

A friend in electronics since birth I think gave me this. It isn't field practical but it appears to be workbench friendly if one avoids the wires.

The terms "MFD" and "uf" are the same - microfarads. MFD is an old term.

For large caps, like motor starter caps, I use a 26 volt surplus utility transformer and an AC ammeter. Caps in the 20 uf and up range draw measurable current when connected to 60 hz AC voltage:

Xc = impedance of capacitor (ohms)
Ic = current through capacitor (amps)
Vc = voltage across capacitor (volts)
C = capacitance (farads)
f = 60 (hz)
pi = 3.14159


Xc = 1 / (2 x pi x f x C)

but 2 x pi x 60 = 377

Xc = 1 / (377 x C)

Ic = Vc / Xc
Ic = 377 x Vc x C

e.g. the more applied voltage and the more capacitance, the greater the current flow.

Example:
Let C = 100 uf = 100 x 10e-6 = 10e-4
Let Vc = 26 vac

Ic = 377 x 26 x 10e-4
Ic = 980 ma

In general, for 60 hz and 26 vac,

C = Ic / (377 x Vc)

C = Ic / 9,802

Now if you use a variac to set the transformer output to 26.53 volts, then the meter will read numerically in capacitance: 1 amp per 100 uf.

C = Ic / (377 x 26.53) = Ic / 10,000

For C= 270 uf,

Ic = 270 x 10e-6 x 10,000 = 2.7 amp


For C = 20 uf

Ic = 20 x 10e-6 x 10,000 = 200 ma

Hope this helps.

Regards,

 

[BillK]

The appliance repair guys used to have standalone capacitor checkers. Now days all of the good DVM's have the capability. You can probably buy a standalone one on e-bay for cheap

https://www.ebay.com/itm/Supco-mfd1...940158?hash=item1cd209c5fe:g:G3UAAOSwwVtc69n6

 

[dogdog]

most capacitance meter capabilities on multi meters are only good for certain ranges... and definitely very limited, don't matter if it is a Fluke or what nots.

Not sure what OP is looking for or what that impedance calculation for... in relationship to this topic...

Keeping with the topic maybe the OP is looking for these LCR meter.... but still not big enough doe the MegaFerrad range he is looking for .. only at 9999 F and can't make it to the Mega Range... .... pretty sure you can find a HP/ keySight Agilent brands if you don't want BK Precision brand.... don't think fluke makes them though...

https://www.tequipment.net/BK/891/LCR-Meters/?v=0

 

[SGKent]

most capacitance meter capabilities on multi meters are only good for certain ranges... and definitely very limited, don't matter if it is a Fluke or what nots.

Not sure what OP is looking for or what that impedance calculation for... in relationship to this topic...

Keeping with the topic maybe the OP is looking for these LCR meter.... but still not big enough doe the MegaFerrad range he is looking for .. only at 9999 F and can't make it to the Mega Range... .... pretty sure you can find a HP/ keySight Agilent brands if you don't want BK Precision brand.... don't think fluke makes them though...

https://www.tequipment.net/BK/891/LCR-Meters/?v=0

starting caps mostly. They are expensive enough that it is cheaper to test them than replace them. The method my friend gave me tests them under a load which gives a more accurate result. Frankly I have enough junk already and will just get a BK or something now that I know that MFD is the old way of saying uF. A 45 MFD starting cap is the same as a 45 uF cap.

 

[dogdog]

starting caps mostly. They are expensive enough that it is cheaper to test them than replace them. The method my friend gave me tests them under a load which gives a more accurate result. Frankly I have enough junk already and will just get a BK or something now that I know that MFD is the old way of saying uF. A 45 MFD starting cap is the same as a 45 uF cap.

LOL starting caps, I think most multi meter capable of measuring capacitance will be able to handle it... if not a generic ESC/LCR combo meter would do, I still have to go get one myself, just can't justify for one.., a good one is not that expensive..... that BK... is just messing with you... but it is one of the rare one that can measure in 9999 Farad range, that is about 99% of the LCR meter out there can't do it even a Farad.... I have a bunch of 5V1.5F that I can't even measure... bought them from Ebay Evils...



I think that calculation is for measuring large voltage AC caps... only. Not sure if I would ever remember that in the field at all or would carry a variac around... even though I have few in various size and form laying around...

There was one method I have seen that some one build a known resistance bridge and looking at the charging curve with the oscilloscope... never tried it... never came across the needed for it, but I think your friend might know it....

 

[MBfreak]

Q I have a bunch of 5V1.5F that I can't even measure... bought them from Ebay Evils... UQ
Most likely not a capacitor in the sense that the energy is stored by two metal foils separated by a dielectric membrane.
Guess yo mean supercaps, which are mor like a battery.

A meter that measures up to 9999F would be a sight to behold. Do you have a pic or a mfr designation?


Ola

 

[dogdog]

Q I have a bunch of 5V1.5F that I can't even measure... bought them from Ebay Evils... UQ
Most likely not a capacitor in the sense that the energy is stored by two metal foils separated by a dielectric membrane.
Guess yo mean supercaps, which are mor like a battery.

A meter that measures up to 9999F would be a sight to behold. Do you have a pic or a mfr designation?


Ola

yea I have them will post later not sure why you wanted to know... but sure... I got this bunch of 150 Avx brand by Kyocera group... for about $50 think... DC caps... there are also few 3v3000F ones for $80-ish each... and NO, I don't have that 9999F meter (but aparently they do exist, I have order from TEquiptments all the time, don't think they are trolling with that listing) or any meter capable of measuring 1F... Just can't justify for one or afford one as fun toys...




Super Capacitors are very common these days...

http://www.avx.com/products/supercapacitors/scm-series/

 

[dogdog]

I didn't realized you were asking for the Meter...
The link have the info on the meter "BK 891"

https://www.tequipment.net/BK/891/LCR-Meters/?v=0

Their spec on the docs also have it... not too sure.... wayyyy to high end for me.

This datasheet revision is 08042015
https://res.cloudinary.com/iwh/imag...1/26/BK_891_Benchtop_LCR_Meter_Data_Sheet.pdf

on page 4 of 6... measurement parameters...

Their later revision 08222018 edited out the ranges not sure why.
https://bkpmedia.s3.amazonaws.com/downloads/datasheets/en-us/891_datasheet.pdf

But it is just an example to keep on the topic Probably other manufactures have better specs than BK.

 

[nsula_country]

Fluke 26III is what I use for checking caps. Don't know what range it has, but will test any motor cap that I have came across.

Fluke 87 and 187 will test them also.

CT

 

[MattT]

Fluke 26III is what I use for checking caps. Don't know what range it has, but will test any motor cap that I have came across.

9,999 uF and I can't recall ever seeing a cap that came close to that large.

BTW I thought I was the only one still using a 26 III. Haven't seen anyone else with one in years.

 

[dogdog]

9,999 uF and I can't recall ever seeing a cap that came close to that large.

BTW I thought I was the only one still using a 26 III. Haven't seen anyone else with one in years.

No not, 9,999uF it's 9,999F, if you search ebay for ultracapacitors, they have boat load of them around, name brand and unknown brand.... 3000F is the biggest ... but if you parallel them together you get the sum..

 

[SGKent]

No not, 9,999uF it's 9,999F, if you search ebay for ultracapacitors, they have boat load of them around, name brand and unknown brand.... 3000F is the biggest ... but if you parallel them together you get the sum..

re sum - and if you arc them you get the sun.

 

[dogdog]

re sum - and if you arc them you get the sun.

LOL I am not that smart and don't trust my self not to get killed.... but I do have quite collection of non super caps.. industrial DC caps .. don't know why I had them... as a kid I think we charge those 470uf ones and throw them across the classroom for some one to catch but then they used to call them condensers in the aviation industries... .....