Calculating ESR from tan delta -- tan delta's dependence on capacitance

[Junkrepair]

I'm finally recapping my Soyo K7VX6 motherboard (aka KT600 Dragon Ultra) and replacing Sacon SZ-series caps. The Sacon SZ datasheet provides a spec for tan delta, but not for ESR, while the candidate replacement caps are specified in terms of ESR.

I found this nice little description of the conversion:

Calculating capacitor ESR from Tan(delta)
https://forum.digikey.com/t/calculat...-from-tan/2633

It mentions that a general spec for tan delta has to be adjusted for the specific capacitance before plugging tan delta into the formula for ESR. It gives an example Rubycon datasheet that states:

"When capacitance is over 1000uF, tan delta shall be added 0.02 to the listed value with increase of every 1000uF"

The Sacon datasheet says something similar but even more ungrammatical:

"Note Above DF Specifications shall be 2% added for every 1000uF capacitor exceeding 1000uF."

https://www.badcaps.net/forum/attach...8&d=1686507774

The Sacon datasheet gives a tan delta of 0.22 for a 6.3V 1000uF cap.

I have these questions:

1) For a 6.3V 3300uF cap, would tan delta be increased by

a) ((3300-1000)/1000)*0.02

or by

b) ((3300-1000)/1000)*0.02*0.22

or by something else ?

2) For a capacitance less than 1000uF, say 470uF, would tan delta be decreased below the value for 1000uF?

3) What is "DF Specification" mentioned in the Sacon datasheet?

[Junkrepair]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

3) DF = dissipation factor

[lti]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

That datasheet does show ESR on page 5.

[Junkrepair]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

So you are saying that ESR and impedance (20 deg and 100 kHz) are the same? I'm not finding it stated that simply elsewhere.

[momaka]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

ESR and impedance are not the same, but they are more than close enough for these type of consumer electronics and thus can be considered equivalent. Same with most ATX SMPSs.

I can't give an answer to your specific questions in post one... but all I will say is, don't sweat it with reading too much into Sacon's datasheets. They were/are garbage caps to begin with and probably never met that spec anyways (or not for too long after leaving the factory, either way. ) By the looks of it, they are just "average" low ESR caps. Given the age of this motherboard, you can just use something like Panasonic FM/FR/FS series or equivalent from other manufacturers (Nichicon HV/HW, Rubycon ZLH/ZL/ZLG, United Chemicon KZH/KZM.) Actually, from experience, I can tell you that even "lower" grade low-impedance caps will work (the likes of Nichicon HE, United Chemicon KY/KZE, and Rubycon ZLQ.) As for caps around the CPU (particularly those filtering V_core), you can also go with polymers with down to half of the capacity of the originals... though if you can get closer to the capacity of the original caps, that would be better.

[lti]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

Yeah, people interchange impedance at 100kHz with ESR a lot. Caps usually specify impedance at 100kHz or 120Hz instead of ESR.

These are an ultra-low-ESR series similar to Nichicon HM or Rubycon MBZ. None of those are made anymore, so you'll have to pick something close. You can even go for polymer caps of similar capacitance at that point, but such large polymer caps are harder to find. I see a lot of people using slightly higher impedance caps, but still as low as they can find.

[AleXis6]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

an example impedance vs ESR (I found a datasheet with both)

[Junkrepair]

Re: Calculating ESR from tan delta -- tan delta's dependence on capacitance

Thanks for all the replies. You've cleared things up a lot. I'm working on selecting some specific caps. I'll have some more questions.