ESR meters show different values

[gulftown17]

Hi,
I happen to have 2 ESR meters, the first is JINGYAN MESR-100 and the second one is Transistor L/C ESR Tester (you know that one with atmel microcontroller and it can measure resistance, capacitance, diodes, inductance, transistors etc). The problem is that they show different values. For example when I try to measure the ESR of 100uF 25V capacitor, the MESR 100 shows 0.19R and the Transistor L/C ESR Tester shows 0.30R. Just for your information I am using the pin headers and I dont use any wires to connect the caps. Which of these value is more accurate? You might recommend me to connect a small value resistor, but the problem is that the L/C ESR Tester detects it as a resistor a measures it differently than it would measure a capacitor. So which of these numbers can I trust?

Thank you

(I attach a picture of both of these meters)

 

[Colin Mitchell]

Buy a third meter.

 

[davenn]

Buy a third meter.

Doh, not likely to help

 

[gulftown17]

And the third meter would show another different value. This is not very helpful, I was hoping for some sort of a creative advise.

 

[davenn]

And the third meter would show another different value. This is not very helpful, I was hoping for some sort of a creative advise.

Yeah exactly hence my response to his post

I have never worried too much about ESR readings on capacitors, and so far has never got me into trouble
after 40+ years at this game
those 2 meters are only showing 0.11 difference and I would suspect that that is within the realms of reasonable tolerance anyway
if they were showing 0.7 or 1.0 difference, THEN I think you may have cause to wonder if there is a problem

Dave

 

[The Electrician]

Try measuring a much larger capacitor, such as 1000uF or 3300uF. The ESR should be much smaller; what do the two meters give you?

Also, don't measure a small resistor by itself; connect it in series with the various capacitors and see if the measured ESR increases by the amount of the small resistor's resistance.

 

[(*steve*)]

Try a couple of capacitors. See if there's a pattern. It may be that one reads 0.1 ohm more than the other or it may be that one reads 150% of the other.

If it's the former then relax, you're typically looking for large changes.

If it's the latter then you have a question of which to trust for absolute values, but all that means is that you need to use just one of these meters if you want to compare readings.

It is likely that the actual situation will not be so simple. It may also be that each use a different frequency and so the results may wander one with respect with the other.

What is most important is that the readings are reproducible and in the ballpark.

 

[gulftown17]

OK I have tried couple of different capacitors (look at the picture). The problem is that the Transistor L/C ESR Tester doesnt show consistent values, but they oscillate quite a bit. It seems like it depends if the leads make a good connection with the pin headers. When I apply pressure on the leads, so that they are better touching the ESR drops. So probably I should trust MESR-100 more even though it shows lower values in general, but they are at least consistent.

 

[(*steve*)]

All those figures seem to be in the ballpark for good capacitors. Try placing a 1 ohm resistor in series with those caps and measuring the ESR again.

You are right that the contact resistance is very important. However that becomes less of a factor as the ESR grows to a point where it becomes a problem.

Do you have a table of acceptable ESRs? These tables are pretty rough, but as I've said, when ESR is a problem, it's rarely a small change in ESR.

 

[gulftown17]

Hi, I tried to measure the caps again with 1R resistor in series. There was one issue though, MESR-100 couldnt automatically show the value of most of the caps. It has 3 ranges, which can be selected manually, 0-1R, 1-10R, 10-100R and then AUTO set. The problem was that it would show values from 0 to 1R then it showed OVERFLOW and then again values between 0-1R and OVERFLOW again ... I had to manually set it to 1-10R, then it would show the values, but I believe that this is not very precise. The L/C ESR Tester didnt have any problem and measured all the caps. I attach the table which I measured. A number to left of the / (slash) symbol means measuring AUTOmatically and number to the right of the slash means I selected manually 1-10R range.

Anyway I do have a table of maximal ESRs. Its a label on the MESR 100 meter, but also it could be found online.

 

[(*steve*)]

ESR can easily exceed 1 ohm when a cap goes bad.

The L/C meter seems to be the more accurate, but the other one is close enough. Both are fine in terms of the range of expected good values, just don't try to directly compare results from one to the other.

 

[HellasTechn]

ESR can easily exceed 1 ohm when a cap goes bad.

I do not agree.

The larger the value of capacitance a capacitor has the smaller the value of its ESR. does not mean that over 1 ohm a cap is not good.

second and most important is that we have to understand the capacitors behavior over frequency spectrum. the esr of a capacitor changes as the frequency of the signal going through changes. theese chineese ESR meters i think use a fixed frequency of 8MHZ. theese will only give you a taste about a capacitors status not that they are 100% accurate.

The difference between your two ESR meters is really not big i would use both of them there is no way to be sure which is more accurate wihtout useing more expensive gear.