ESR (again)

[granddad]

I did not fully understand Equivalent Series Resistance until recent ETO posts about capacitors , and as my PIC24 projects sometimes need a 10uF low ESR for VCAP pin, I decided to build a meter as per the link , all seems to work OK, ( after I got the 2N2222 in correctly ! ) I have just set it up with 1% 1R,2.2R,5.6R,10R, resistors . Had to order 50uA meter other stuff I had in stock or recycled.

http://www.members.shaw.ca/swstuff/esrmeter.html

 

[Tony Stewart]

Good stuff.

Everything has ESR.
e.g. HCxx Logic drivers ( Vol/Iol=ESR) are about 300Ω @5V so with 680 in series it becomes ~1k then five invertors in parallel becomes 200Ω and 10Ω load, R7 becomes 250mVpp out of 5Vpp after harmonics of 5V square wave are low pass filtered. 74ALVxx CMOS logic is around 50 Ω...ALVC2xx logic in ARM chips are around 25Ω.

This R7 10Ω load becomes the source impedance to the Cap being tested in this ESR meter ~10 Ω, which becomes the mid-point of the meter, so no good for comparing low mΩ ESR electrolytic caps or e-caps where ESR is << 100mΩ but faulty standard e-caps might well be >> 1Ω. Each e-cap family usually has a constant ESR*uF product , so larger uF can have lower ESR but better material design can affect ESR greatly. ( e.g. silver content in plates or number of layers in MLM ceramic caps vs monolithic etc.)
Hint ... if you wanted to improve sensitivity of ESR, you might reduce all R values by 10x so you end up with 1Ω load and source impedance with 250mV signal. (1/16W pk) by changing 680's to 68 then changing 10Ω. to 1Ω. with some scope tuning of 1Ω. value, if you wanted more accuracy, (not essential as they use diodes to compress range on meter, instead of step range of source voltage, from which they measure current in the 2nd load R8 , which equals R7.

Inductors have ESR ... often called DCR

Batteries have ESR .. often measured in mΩ for ohmic loss.. as well as chemical saturation drop from float to load voltage.

Crystals have ESR , which affects Q = fc/fBW but cannot be measured in this tester.

Also Caps can have too low ESR for some LDO outputs as it shunts the feedback ripple too much to make it stable and actually introduces a phase shift in the unity gain frequency thus reducing stability or phase margin of some LDO's. They will tell you e-cap ESR range , if this applies.

here is an article on ceramic caps where too low an ESR can raise Q ( amplification of resonance from impulses)
https://media.digikey.com/resources/tdk/tdk-esr-control-multilayer.pdf) which might result in excess ripple.

When using ESR, think of source to load ESR ratio as the important figure to attenuate ripple.
Even LDO's have ESR which is the voltage drop with rise in load current... often observed by senior designers but never specified in design notes.

The series decoupling cap must also be improved if you wanted to reduce range of ESR to 1Ohm by using any plastic cap which have the lowest ESR but also largest size/uF. It's value must be much greater than D.U.T.

OK design but very limited use. I prefer a good LCR meter with 3 1/2 digits accuracy.

 

[Nigel Goodwin]

OK design but very limited use. I prefer a good LCR meter with 3 1/2 digits accuracy.

Which is completely useless for testing ESR - and high ESR is by FAR the biggest cause of electronic faults in the 21st Century (and the latter part of the last one).

 

[Tony Stewart]

Which is completely useless for testing ESR - and high ESR is by FAR the biggest cause of electronic faults in the 21st Century (and the latter part of the last one).

Speaking from experience, not only does an LCR meter easily measure defective caps but ones going to be defective going from 10 to 100 milliohms where with large 10A ripple currents(rms), ( the eye squared R =10 Watts in a small thermally insulated electrolytic causing a bulge to appear with the next year after it has failed.

Thus in my experience it is good for preventive maintenance on annual or whenever checkups.

But more importantly in large caps > 10uF it can measure the difference between a standard ESR and a low ESR cap where both are good, but one is better for some apps.

capiche?

It's also good for binning plastic caps typically 10% to < 1% or 0.5% for resonant circuit designs , which my clients have used from me. I also used it to measure RLC values in 5MVA transformers, the difference in SMTP chokes with inductance at 100Hz , 1kHz, 10kHz, 100kHz, or measuring the saturation current where value drops 50%... as well as measuring frequency tuning caps with 0.1pF resolution.

 

[Nigel Goodwin]

Speaking from experience, not only does an LCR meter easily measure defective caps

Sorry, but that's utter nonsense - speaking as an experienced (and still practicing) service engineer an LCR meter tells you nothing useful about the vast majority of faulty electrolytics, as it doesn't measure the ESR and that's what you need.

Testing faulty capacitors on an LCR meter will almost always show them as within tolerance.

So what are you claiming an LCR meter tells you that's useful?.

 

[Tony Stewart]

that's exactly how I fixed my SMPS in my 43" TV monitor in five minutes.
My Extech LCR meter measures C,Q, Rp, Rs and L of any cap with >3 digit accuracy.
It's not a mickey mouse tester.

It can also do more if you want.

Like confirm these values

 

[Tony Stewart]

Here is an old photo of my LCR meter measuring the Q of a dielectric which is the ratio of impedance of C to ESR at a chosen frequency , in this case, the frequency of a rectifier cap current being twice the fundamental line frequency in North America.



the dielectric here was the oil in a large transformer from bushing to tank on a HV rated for 200kV BIL so that capacitor weighed 5 tons

 

[Nigel Goodwin]

that's exactly how I fixed my SMPS in my 43" TV monitor in five minutes.
My Extech LCR meter measures C,Q, Rp, Rs and L of any cap with >3 digit accuracy.

So it's NOT just an 'LCR' meter then, it can actually measure ESR as well - which makes it somewhat more useful for finding faulty capacitors.

However, presumably (unlike a proper ESR meter) it can't test them in circuit? (although to be fair there's a small number of circuits where ESR meters can't do that either.

Most ESR meters also tell you the capacitance as well, but not the simple analogue ones like the OP made.

 

[Les Jones]

Hi Nigel,
There was a design for an ESR meter in "Everyday Practical Electronics Magazine" September 2005 that works well testing capacitors in circuit. It uses a square wave current source through the capacitor and measures the voltage across the capacitor. I have built a slightly modified version (Added a lower range.) of this and found many high ESR capacitors. I have found it particularly useful around the line output stages of CRT monitors. It even found some tiny faulty electrolytics on a video camera module which got it working again.

EDIT.
Correction. The magazine was Elektor (Not EPE)

Les.

 

[MrAl]

Hi there,

Interesting difference of opinions here.

I know both Tony and Nigel have enough experience in the field, so my conclusion is that the type or quality of the meter(s) in question is different for each person. Tony obviously had good meters, while Nigel must have used the cheaper ones.

It's a known issue that many of the cheaper ones dont do that well for measuring ESR mainly because they dont use the right frequency. However, any schematic posted here is not too hard to test...either by hand using pure circuit analysis and the math that goes with it, or a simple simulator like LT Spice, Switchercad.

When i reviewed some of the schematics posted on the web a while back, i was unsatisfied with the circuits. I set out to build a better ESR tester for the hobbiest, but havent gotten to do that yet. Mostly because i use the only solid method i know: with scope and waveform generator, so i already have a method to test them and i've found it not only works it is a theoretically sound method as well as very straight forward. But building a better one would be very interesting, one that is nothing like the ones we see on the web.

Testing for Q is a nice way to do it and probably one of the best ways actually, but that is a little indirect. I believe Nigel was talking about the more run of the mill actual ESR testers which are made for measuring more directly.

For anyone here with a scope, i can help but recommend using it, and a waveform generator or square wave generator. the ESR value becomes more than obvious when you look at the scope results. What's more is you dont have to build anything or rely on some other designer's idea of how an ESR meter should work.
Can you test in circuit? As with any other in circuit test, it depends on the comparative values of the part under test and the other parts connected to it. If you are looking for a 10 ohm ESR and there is a 0.1 ohm resistor in parallel, it will be hard to discern if that resistor is 5 ohms or 10 ohms or 15 ohms because the exciting source is affected more by the 0.1 ohm than the 10 ohm. That goes with any in circuit test though.

With the scope and generator i've tested caps in computer power supplies and one TV set, and was always able to find the bad caps. It almost goes without saying though that all the caps should be changed when one or two are found to be bad, at least the ones that handle the power.

 

[spec]

Hi Nigel,
There was a design for an ESR meter in "Everyday Practical Electronics Magazine" September 2005 that works well testing capacitors in circuit. It uses a square wave current source through the capacitor and measures the voltage across the capacitor. I have built a slightly modified version (Added a lower range.) of this and found many high ESR capacitors. I have found it particularly useful around the line output stages of CRT monitors. It even found some tiny faulty electrolytics on a video camera module which got it working again.

EDIT.
Correction. The magazine was Elektor (Not EPE)

Les.

Hy Les,

I was interested in the EPE ESR meter that you mention, but cant find it in any 2005 issues- did you have the year wrong?

spec

 

[Les Jones]

Hi spec,
I made a mistake. The magazine was Elektor. I did add a correction some time later when I realised.

Les.

 

[Nigel Goodwin]

I know both Tony and Nigel have enough experience in the field, so my conclusion is that the type or quality of the meter(s) in question is different for each person. Tony obviously had good meters, while Nigel must have used the cheaper ones.

Not really, Tony claimed that all you need is an LCR meter to test for faulty electrolytics - which is patently untrue. He later added the extra information that it tests ESR as well. A normal LCR meter wouldn't detect 95+% of faulty electrolytics.

As for home made meters, the now defunkt 'Television' magazine published two designs for them, I used the first type for a number of years.

The frequency you need to use is 100KHz, as that's what the capacitor specs use for testing.

Incidentally, the AVR based component testers from Bangood also test ESR as well as capacitance - with some of the newer versions adding in-circuit ESR testing.

 

[granddad]

After reading your posts ( thanks) seems I still don't fully comprehend ESR that much. Test wise , I have an LCR, a couple of DMMs a DIY Freqency counter ( via ETO ) an old 2235 Techtronix Scope, that I had to repair.. no focus. I just wanted to have some idea of the caps I was using for PIC24 were the ESR money ( you can pay silly $ for a low ESR 10uF )(you never know theses days) and I have some caps that are decades old ! and I read somewhere they can become deformed over time .
My little black box seems to fit the bill.

Now what can I build with this.....

 

[spec]

After reading your posts ( thanks) seems I still don't fully comprehend ESR that much. Test wise , I have an LCR, a couple of DMMs a DIY Freqency counter ( via ETO ) an old 2235 Techtronix Scope, that I had to repair.. no focus. I just wanted to have some idea of the caps I was using for PIC24 were the ESR money ( you can pay silly $ for a low ESR 10uF )(you never know theses days) and I have some caps that are decades old ! and I read somewhere they can become deformed over time .
My little black box seems to fit the bill.

Now what can I build with this.....


View attachment 98750

The first thing to do with old aluminum electrolytics is to reform them and check their leakage current:

SET UP
(1) Set a power supply to the capacitor's maximum voltage (Vmax).
(2) Connect the negative of the PSU to the negative terminal of the capacitor
(3) Connect a resistor of Vmax/20ma to the positive of the PSU
(4) Connect the free end of the resistor to the positive of an ammeter
(5) Connect the negative terminal of the ammeter to the positive terminal of the capacitor

READING
Normally the indicated current will be 20mA and will tail off to a steady value.
Leave the test set up for 15 minutes. The current reading should not be more than the leakage current specified for the capacitor.

If the electrolyte has dried out too much, no current will flow and the capacitor will be scrap.
You may not notice any current on a low value capacitor.

Once the capacitor has been initially reformed and tested as above, you can check the value with a capacitance meter designed for electrolytics and then check the ESR

I had some 20 year old caps, similar to yours, and they were all OK.

The capacitor in your picture is 30V, 12mF (12,000uf) and is a high quality, heavy duty type from Vishay (Sprauge), one of the best cap manufacturers. It would make an ideal reservoir capacitor in mains power supplies up to 30V peak (0V to peak of voltage ripple). They would be expensive to replace. https://www.vishay.com/docs/42066/36ddedx.pdf

I know you are experienced, but just a word of caution about capacitors, especially high capacity and or high voltage types: they store a lot of energy at a very low impedance (ESR), so always discharge them with a Vmax/20ma resistor (approx) before handling them. Also, they will often recover some voltage after being discharged due to dielectric absorption, a phenomena that is not fully understood.

spec

 

[Nigel Goodwin]

After reading your posts ( thanks) seems I still don't fully comprehend ESR that much. Test wise , I have an LCR, a couple of DMMs a DIY Freqency counter ( via ETO ) an old 2235 Techtronix Scope, that I had to repair.. no focus. I just wanted to have some idea of the caps I was using for PIC24 were the ESR money ( you can pay silly $ for a low ESR 10uF )(you never know theses days) and I have some caps that are decades old ! and I read somewhere they can become deformed over time .
My little black box seems to fit the bill.

An ESR meter is really for finding faulty components in faulty equipment, and almost exclusively in SMPSU's - for the vast majority of other capacitor uses it's not so important.

One point to bear in mind, high voltage capacitors often have ESR's - it's fairly common (or was) to have something like 1uF to 10uF 450V in the primary side of SMPSU's, these test higher ESR than you would think, even when new, and it's not a fault.

 

[The Electrician]

Not really, Tony claimed that all you need is an LCR meter to test for faulty electrolytics - which is patently untrue. He later added the extra information that it tests ESR as well. A normal LCR meter wouldn't detect 95+% of faulty electrolytics.

Nigel, apparently you haven't kept up on the names manufacturers give to meters than can measure more than just the value of an inductance or capacitance. It is common nowadays to use the name "LCR meter" for meters that can measure all the parameters of a capacitor: capacitance, ESR, Q, DF, etc.

For example, here are a number of so-called LCR meters that can measure ESR as well as L and C. I'll link to them on eBay because it's easier to find many of them there. These meters measure using sine wave excitation, typically at several frequencies. Note that even high end Agilent meters that would be expected to measure all parameters are only called "LCR meter"; they aren't called "ESR meters" even though they can measure ESR.

https://www.ebay.com/itm/Agilent-Ke...628993?hash=item20fdc6f901:g:o-YAAOSw-vlVgwAv

**broken link removed**

**broken link removed**

**broken link removed**

https://www.ebay.com/itm/Quadtech-7...822981?hash=item51de5a7c45:g:9yoAAOSwkNZUofqS

https://www.ebay.com/itm/HP-Agilent...hash=item5647dd2239:m:mRTTBlq_MHHXMDlFwK7x7uw

https://www.ebay.com/itm/New-DER-EE...593192?hash=item2c8c3129a8:g:y~MAAOSw-jhUFnvW

**broken link removed**

https://www.ebay.com/itm/AT826-Hand...561158?hash=item2c8c30ac86:g:C7UAAOSwd4tUFnDW

Every one of these meters is called an "LCR meter", and all of them can measure ESR. They can all measure inductance as well.


There are, of course, meters that are specifically made for measuring ESR, such as these:

https://www.ebay.com/itm/Peak-Atlas...636687?hash=item2a406ee84f:g:oO4AAOSwPTlTymDO

**broken link removed**

These "ESR meters" are lower cost than most of the "LCR meters" (although the DE-5000 is a good performance, low cost, LCR meter), but cannot measure inductance. They don't usually measure using a sine wave excitation, but rather a square or pulse, usually at 100 kHz.

No meter can measure "in-circuit" under all conditions. Other components in parallel with a particular capacitor can make it impossible to make an "in-circuit" measurement, but the "LCR meters" can measure in-circuit just as well as the "ESR meters".

 

[dr pepper]

I still have a psu I buitl 25 years ago with a a sprague powerlytic in it that I salvaged from a typewriter, still runs on for 20 seconds after power off.
My cap esr tester is a thrown together affair, mine has a ferrite from a pc psu to transform the test voltage right down below the conduction voltage of a silicon junction so I can test cap esr's in circuit, its been a really good tool, I didnt even bother callibrating the scale, I just go off experience with it.
This is the project I used to build mine, its more or less the same:
https://ludens.cl/Electron/esr/esr.html

 

[spec]

I still have a psu I buitl 25 years ago with a a sprague powerlytic in it that I salvaged from a typewriter, still runs on for 20 seconds after power off.
My cap esr tester is a thrown together affair, mine has a ferrite from a pc psu to transform the test voltage right down below the conduction voltage of a silicon junction so I can test cap esr's in circuit, its been a really good tool, I didnt even bother callibrating the scale, I just go off experience with it.
This is the project I used to build mine, its more or less the same:
https://ludens.cl/Electron/esr/esr.html

Interesting post doc,
especially the bit in the attachment about fixing the scope and the radically different value ESRs from two 'identical' bead tants.

On a general note, one thing I am not sure about is testing electrolytic capacitors. I would have thought that a polarizing voltage of around VCmax would be needed before any testing could be fully representative of the capacitors performance, but it seems that this is not the case as most LCR/ESR meters do not apply a polarizing voltage. Are there any views on this?

spec

 

[granddad]

This is the project I used to build mine, its more or less the same:

Thanks Doc , I did see this design but had parts for build "In stock"
spec, thanks for reform post , I tried it on the 12,000 uF cap ( only 20v) and it would appear OK .