Capacitor ESR ??

I did a quick look at some of our suppliers websites and I think this has some references to Al Cap ESR in it.

Jim

The ESR is a matter of technology. Have a look at the manufacturer's pages, eg

Rene

Thanks, At least that gives me some ball-park numbers.

...Jim Thompson

Just look up in LTspice's capacitor list to see what voltage/capacity/ESR ranges are viable?

aha

Jim,

Capacitor manufacturers no longer like to state ESR, because it depends on the frequency of interest. As you may have noticed, they do state Dissipation Factor (DF) instead. I had to do some poking around a few weeks ago to find the secret formula to convert DF into ESR, and here's what I learned.

DF/(2*pi*frequency*capacitance) = R

Assume a data sheet DF of .05% And assume you are doing some work at, say, 1kHz, and the capacitance is, say, 20uF.

So in this instance:

Wouldn't that mean you need DF given at a specific frequency so that you can work back to ESR (which should(?) be fairly constant)?

...Jim Thompson

At 0Hz, the ESR of a capacitor will be darn high. It drops as one goes up in frequency until inductance takes over.

When you do find specs for ESR in capacitor data sheets, they specify at which frequency (usually 120Hz in the US) they are providing the ESR for.

According to

1. Equivalent Series Resistance (ESR)

It's the sum of all the internal resistances of a capacitor measured in Ohms. It includes:

- Resistance due to aluminum oxide thickness

- Resistance due to electrolyte / spacer combination

- Resistance due to materials (Foil length; Tabbing; Lead wires; Ohmic contact resistance)

The lower the ESR the higher the current carrying ability the capacitor will have. The amount of heat generated by ripple current depends upon the ESR of the capacitor.

ESR is both frequency and temperature dependent, increasing either will cause a reduction in ESR. The ESR is an important parameter in calculating life expectancy as the power dissipation (internally generated heat) is directly proportional to its value.

I think dissipation factor includes several factors, one of which is ESR. The bigger factor at higher frequencies is a fairly constant per cycle loss. Your formula looks like it is interpreting those per cycle losses as ESR. Not very useful, I suspect.

Have you tried

They also have a spice manual. Have fun

You may be right. My formula was provided by the engineer at ASC, and I've also seen it on some online sites as well. I'll bet that the formula is useful for line-frequency based power supplies, though.

Jim, if you tell me what style capacitor (el cheapo, low-esr, ...), I might be able to measure the Z on our network analyzer. Z data varies quite a bit depending on capacitor construction. ESR can vary quite a bit over frequency, perhaps over 100 to 1 for some ceramic caps (as reported by AVX's SpiCap program.

FYI, AVX has good data on their ceramic and tantalum caps. Aloha, Mark

I've tried some of these AO caps, the A700 series, and one nice thing, unlike alot of tantalums and some niobium, is they don't go up in flames....ran a 4V version to 14V and held it there, and then back down, it nearly recovered all its original characteristics.

~25-15 mohm.

where DF=ESR/Xc=2xPIxFxCxR

Hmm, that looks so much like our Q-factor specs that we perform for our Mill Spec Mica Dips. and D40's etc. :) At least that is what we do at Semco.

Jim Thomps> >

Au contraire- if you look at that so-called formula it is the definition of DF which is the cotangent of the impedance angle of a simple series R-C equivalent circuit. The DF being small allows the identity between ratio and tangent function. The small in-phase component of voltage with current is exactly that fraction of the VA producing dissipated versus stored energy per cycle and is the equivalent resistance at the measurement conditions, where resistance is abstracted from being just a chunk material of finite conductivity to an energy-to-heat conversion element. It will be non-linear, a functional dependence on temperature, frequency, and signal level.

On Thu, 12 Feb 2004 14:06:57 GMT, Fred Bloggs Gave us:

Nice catch!

If you want to interpret all losses as if they were a result of an actual series resistance, and the total losses are low, the formula is fine. If you want to know what the parallel losses, the series losses and the hysterisis losses are, it is not much use. I think the best way to measure the actual series resistance is to subject the cap to its series resonant frequency and and measure its impedance.

Are you saying that the best model would be a series R-L-C evaluated at resonance?

...Jim Thompson

Yes. I think ESR shows up most clearly under those conditions.

Jim,

Maybe I should interject here that the equivalent circuit of an AL electrolytic is really a ladder network:

---/\/\/\---o---/\/\/\---o---/\/\/\---o... | | | --+-- --+-- --+-- --+-- --+-- --+-- | | |

------------o------------o------------o...

LTspice's capacitor database just uses 1 R and 1 C as an quick and effective approximation. But if you use 2 R's and C's, you can model the phase angle of the impedance correct within a few degrees over many decades of freq. Three 3 R's and 3 C's should let you model more accurately than you can measure with any component analyzer I know of.

--Mike