I was wondering if there is a way to scale ESR values from a datasheet for frequency?
I am using a 680uF Cap at 20kHz and the datasheet claims a maximum ESR of 0.366Ohm at 120Hz.

It is the 687LBB200M2EC from Illinois Capacitor:
http://www.illinoiscapacitor.com/ic_search/seriesDocuments/LBB series.pdf

Thanks.

 

I don't think so. If ESR depends of frequency it most likely will be non-linear. It is also the case that capacitors stop being capacitors at higher frequencies, but you're a long way from that behavior.

 

It is my opinion that resistance is not frequency dependent. In a capacitor, you might get crazy at radio frequencies, but 20kHz is probably not a problem.

 

I was wondering if there is a way to scale ESR values from a datasheet for frequency?
I am using a 680uF Cap at 20kHz and the datasheet claims a maximum ESR of 0.366Ohm at 120Hz.

It is the 687LBB200M2EC from Illinois Capacitor:
http://www.illinoiscapacitor.com/ic_search/seriesDocuments/LBB series.pdf

Thanks.

Yes, the capacitor ESR depends on the frequency. Usually, they provide derating curves of ESR vs frequency in the datasheet. In this one they don't but you can try and find information on the company's website.

The ESR decreases as the frequency increases.

 

It is my opinion that resistance is not frequency dependent. In a capacitor, you might get crazy at radio frequencies, but 20kHz is probably not a problem.

It is. See the following article

http://wiki.xtronics.com/index.php/Capacitors_and_ESR

Scroll down to the section on dissipation factor

 

The specs show a ripple current multiplier at >10kHz of 1.45 with respect to 120 Hz. This means that the I^2*R losses are the same (approximately) with 1.45 times as much current for frequencies over 10 kHz.

Let ESR1 be the ESR at 120 Hz and ESR2 be the ESR at frequencies greater than 10kHz. If I^2*ESR1 at 120 Hz is the same as (1.45*I)^2*ESR2, you can calculate that ESR2 = ESR1/(1.45^2) = ESR1/2.1 = .174 Ohms.

The specs also give ripple current multipliers for different temperatures and you can make similar calculations to determine changes in ESR vs. temperature.

 

It is. See the following article

http://wiki.xtronics.com/index.php/Capacitors_and_ESR

Scroll down to the section on dissipation factor

Is there a scale to which you can compare the ESR of given capacitors of the same construction type?
I have had people ask me for lower ESR caps both polar and non polar electrolytic while building amps and speaker crossover circuits. I know there is a huge ESR difference from say tantalum to ceramic to electrolytic. But how to compare within the same type? How come the industry doesn't rate them except for "low esr" and just normal? That's sort of vague. How low is low? Do we know?
Given that you replaced one cap with another of the same type and several in the same spot in the circuit. Ergo, they would be operating at the same frequency.

Of course I see this as a passive aggressive attempt to market parts which might have cheaper manufacturing methods and seldom used standards or unknown properties. I got the gist from the hobbyist asking me he didn't know and by the time I got to the first few formulas explaining ESR, he flipped out in resignation.
I know a bit much on how ceramic chip caps are made as I did the manufacturing station rotation for each step at Kyocera, and made my own caps for Tesla coils, but this guy had a point, there is no easy comparison datapoint for same types of class of caps.

 

Is there a scale to which you can compare the ESR of given capacitors of the same construction type?

I did this study, many years ago (while working with the kind of audiophools that buy oxygen free copper wire) and found that the only answer is to get the datasheets for every capacitor you are considering. The manufacturers provide the data, but you have to dig for it. After days of digging, I arrived at dissipation factor for coupling capacitors as the only aspect that seemed relevant to the concerns. Poly-film caps like the Orange Drop had the best dissipation factor for coupling caps.

For filter caps, smaller caps in parallel is a workable method. Adding a 0.1 uf ceramic cap in parallel with an aluminum electrolytic extends the frequency range of the filter function. Bottom line: look up the datasheets. The information is in there, it just isn't fun to do the work (unless you're a nerd).

 

I was wondering if there is a way to scale ESR values from a datasheet for frequency?
I am using a 680uF Cap at 20kHz and the datasheet claims a maximum ESR of 0.366Ohm at 120Hz.

It is the 687LBB200M2EC from Illinois Capacitor:
http://www.illinoiscapacitor.com/ic_search/seriesDocuments/LBB series.pdf

Thanks.

If the datasheet quotes ESR at 120Hz - its not intended for use in a SMPSU.

 

I did this study, many years ago (while working with the kind of audiophools that buy oxygen free copper wire) and found that the only answer is to get the datasheets for every capacitor you are considering. The manufacturers provide the data, but you have to dig for it. After days of digging, I arrived at dissipation factor for coupling capacitors as the only aspect that seemed relevant to the concerns. Poly-film caps like the Orange Drop had the best dissipation factor for coupling caps.

For filter caps, smaller caps in parallel is a workable method. Adding a 0.1 uf ceramic cap in parallel with an aluminum electrolytic extends the frequency range of the filter function. Bottom line: look up the datasheets. The information is in there, it just isn't fun to do the work (unless you're a nerd).

The orange drops from Sprague I had in stock were great for smaller values, but this customer was adamant about being educated in data sheets that were just then beginning to become easily available on the internet. The values of capacitance were tens of microfarads, not pf range to .1 uf range like most orange drops typically used. I gave him some part numbers and said he could return what he didn't like once he got home and did his own investigation. As long as the parts were not soldered in of course.