ESR Confusion

[wraper]

Low ESR one are designed for high frequency SMPS uses, where the other ones would be ineffective and would quickly overheat.

It's less about frequency and more about ripple current. General purpose capacitors can work at the same frequencies completely fine, it's just they won't survive high ripple current for long. Say if you place several general purpose caps in parallel instead of one LOW ESR, they'd work just fine. A few decades ago, there were SMPS but nobody heard about such thing as LOW ESR capacitors.

[Terry01]

If that graph is not for ESR did they just make it for a laugh or does BK not know nothing?

BK is fine, something wrong on your side. READ again, LCR measurement guidelines, not ESR. LOW ESR capacitor ESR usually is specified at 100kHz, be it small or big capacitor. General purpose capacitor ESR may be specified either at 120/100Hz or 100kHz. In both cases capacitance is usually specified at 120Hz or 100Hz. In practice there is no need to check ESR at 120Hz when checking components, unless you want compare apples vs apples with figure in a datasheet.
Here you go, up to 18000uF with ESR specified at 100kHz. http://www.chemi-con.com/upload/files/5/1/74811667552d6c4d41a84c.pdf

When would a large electrolytic be used @ 100kHz?

Say SMPS.

If your LCR meter allows it, measure the impedance
at the application frequency if you can. Seeing the
impedance magnitude in ohms helps you use your
intuition—and the phase angle tells you quickly if
you have a pure reactance or a mixture of resistance
and reactance.

Nope! I am fine, no problems here. English is my 1st language so no help needed thanks.

Just for fun I did a couple caps @ 100 Hz, 120 Hz, 1 kHz, 10 kHz and 100 kHz and just between just 120 Hz and 1 kHz the ESR measurement is half or more "less" at the higher frequency. Before you say meter is wrong or some other waffle I did a few.

A big electrolytic may well/defo is! used in a SMPS, but it won't be working @ 100 kHz or the rest of the circuit wouldn't like it very much. Not at all in fact. Nice try but come on. Your getting deeper.

That's all I won't reply no more.

(@Terry01) Just for the avoidance of any confusion. The only way to confirm the health of a capacitor (or any other component come to that) is to measure it against the specification set out in its datasheet. If the datasheet specifies measurement at 100 or 120Hz then you should confirm the ESR at that frequency, however if the datasheet specifies a measurement 100kHz then the value needs to be measured at that frequency. Electrolytic capacitors are manufactured in many different families, some 'higher' ESR ones are intended for simple mains transformer/rectifier applications. Low ESR one are designed for high frequency SMPS uses, where the other ones would be ineffective and would quickly overheat.

If you adhere to the datasheet figures specified for that specific part then there can be no confusion and no dispute.

I agree 100%.

The data sheet is the way to go..... but I doubt very much BK thought we'll make a graph to help users get the best results from our instruments but we'll feed them a load of shite just to confuse them in the instructions. I get it's more a "rule of thumb" thing than "it applies to EVERY capacitor".

What happens if for some reason you can't get the data sheet for the part you need to test? You don't take a measure because you can't use your head and think. You must stick to the data sheet 1000%! Come on??

There's no confusion here.

[Gyro]

While that "rule of thumb" might have some relevance to signal level components, BK themselves clarify this in the text:

Measurement frequency: Since the reactance is a function of frequency, your choice of measurement frequency should reflect the usage of the component. For capacitors, larger values (tens to hundreds of μF or more) are often used in power supply filtering applications, so should be tested at twice the line frequency. Smaller capacitors (fractions of a µF) tend to be used at higher frequencies, so should be tested at 1kHz or more.

In the case of SMPSs the 'line', ie. switching frequency is normally 50kHz or more, so their words are completely in line with 100kHz testing of these higher capacitance parts. You can't simply rely on that straight line graph without paying attention to the accompanying text.


The trouble is, these days, there are several "rules of thumb". A capacitor with, say, 0.5R may be perfectly fine for a gentle rectified mains transformer based supply, it would be totally ineffective (Faulty) in an SMPS application with high frequency, high peak currents.

Sadly there is no non-application-specific simple single rule of thumb.

[wraper]

BTW if you think that in linear power supply capacitors work only at double of the mains frequency, you are wrong. They work at frequency which is consumed by the load. Say if it is an audio amplifier, expect up to 20 kHz.

[Terry01]

While that "rule of thumb" might have some relevance to signal level components, BK themselves clarify this in the text:

Measurement frequency: Since the reactance is a function of frequency, your choice of measurement frequency should reflect the usage of the component. For capacitors, larger values (tens to hundreds of μF or more) are often used in power supply filtering applications, so should be tested at twice the line frequency. Smaller capacitors (fractions of a µF) tend to be used at higher frequencies, so should be tested at 1kHz or more.

In the case of SMPSs the 'line', ie. switching frequency is normally 50kHz or more, so their words are completely in line with 100kHz testing of these higher capacitance parts. You can't simply rely on that straight line graph without paying attention to the accompanying text.


The trouble is, these days, there are several "rules of thumb". A capacitor with, say, 0.5R may be perfectly fine for a gentle rectified mains transformer based supply, it would be totally ineffective (Faulty) in an SMPS application with high frequency, high peak currents.

Sadly there is no non-application-specific simple single rule of thumb.

Eh?? 

Are we looking at the same thing?

You've got it all the paddy way round about neeb! I think you need a pair of spectacles!

[Gyro]

  I have no idea what you're talking about, what I said seems perfectly clear and the quote is from the BK document you linked.