ESR (again)

[MrAl]

Hi Tony,

Wow that is quite a capacitance swing there. With the scope and wave generator method though the swing in capacitance would not matter, as long as the voltage was kept low and of course there is no ESR swing to worry about.
The basic equation is of course:
Z=R-j/wC

where R is the internal resistance and C is the internal capacitance, and they are connected in series.

Since the capacitance effect is still imaginary it wont affect the real resistance. This would still happen because the voltage across the internal cap C does not get a chance to change before the measurement of the resistance R is made. This is part of the beauty of a time domain approach and it is really the very reason it works. I dont think a single frequency frequency domain approach can show this as clearly unless maybe the amplitude is also limited. But in any case, the time domain approach is a measurement of what actually happens in the real application anyway, which is nice in itself.

 

[Tony Stewart]

Hi Tony,

Wow that is quite a capacitance swing

Since the capacitance effect is still imaginary it wont affect the real resistance

...But in any case, the time domain approach is a measurement of what actually happens in the real application anyway, which is nice in itself.

That's debatable .
Ceramic caps of this size are often used in fixed frequency SMPS, but with high harmonic content so neither test method is purely accurate. But CC sine @f is the standard used by testers and MFG's.

Also dielectric layers with many non -homogeneous and variable diameter ratios of laminations with metallic interface affects ESR, Rp and C simultaneously with different test conditions.

Thus C and ESR both change.

 

[MrAl]

That's debatable .
Ceramic caps of this size are often used in fixed frequency SMPS, but with high harmonic content so neither test method is purely accurate. But CC sine @f is the standard used by testers and MFG's.

Also dielectric layers with many non -homogeneous and variable diameter ratios of laminations with metallic interface affects ESR, Rp and C simultaneously with different test conditions.

Thus C and ESR both change.

Hi again Tony,

Well if the ESR is going to change much then we have to know what is causing that and then test accordingly. The power supply caps are easier to test i guess because they either have low ESR or the ESR is much higher than expected. For a little historical data, my devices never actually failed before the cap ESR changed pretty drastically, which is easy to detect with either method. If we want more explicit data on a cap then we really have to be willing to test more carefully. That's only if that kind of exacting data is really needed at the time, such as when specifying the capacitor for the first time.

When we do a simple test on a resistor, we can apply a DC voltage and measure the current. We then calculate R=E/I and we're done. If we have to test a potentiometer we might still apply a DC voltage, but then we'd have to plot the curve of the current in order to calculate the curve of the resistance.
So if the ESR changes much then we have to know what makes it change and then test accordingly. If it changes with voltage, then we have to test with different bias voltages, if it changes with frequency, then we have to test with different frequencies. If if changes with both, then we have to test with different bias voltages and different frequencies, then we'd have to use a 3d plot to plot the variations due to both parameters. If we also wanted to plot with temperature (a good thing too) then we'd want to do the test with bias voltage and frequency over several different temperatures, so we'd get several different 3d plots.

The main idea here is that if we want to go beyond the basic test for ESR, then we have to be willing to go the distance just like with any other test.
So i do agree that if the ESR changes (second sentence, first paragraph of previous post) then we have to take steps to test more rigorously.

Very good point BTW, especially if we start to take temperature effects into account. Temperature is such a pain sometimes and everything heats up at one time or another

 

[granddad]

Think I'm going to have to click "unwatch thread " you clever people lost me about #14 , Not planning to use 12000 uF , found it in my garage junk that wife says I must chuck out , after 30 Yr . Now I have good 10uF Tant on PIC24 VCAP pin I am battling MPLABX 3.25. I want to open / close my greenhouse door from 250m away. have pair nRF24L01 ( perhaps a new thread looms)

 

[spec]

Think I'm going to have to click "unwatch thread " you clever people lost me about #14 , Not planning to use 12000 uF , found it in my garage junk that wife says I must chuck out , after 30 Yr . Now I have good 10uF Tant on PIC24 VCAP pin I am battling MPLABX 3.25. I want to open / close my greenhouse door from 250m away. have pair nRF24L01 ( perhaps a new thread looms)

grand

Throwing out a good 12,000uF capacitor is a criminal offence.

spec

 

[Nigel Goodwin]

Now I have good 10uF Tant on PIC24 VCAP pin I am battling MPLABX 3.25. I want to open / close my greenhouse door from 250m away. have pair nRF24L01 ( perhaps a new thread looms)

I think you might be struggling at 250m, but how about these instead:

https://www.banggood.com/5Pcs-HC-12...odule-Remote-1000M-With-Antenna-p-980288.html

Up to 1000m, and far easier to use than the nRF24L01 - just simple serial commands.

I've got some on order

 

[Tony Stewart]

In order to understand the effects of the "double-charge"charge layer in e-caps and piezo-electric effects in ceramic caps or the aging effects or hydroscopic effects or thermal effects, which can introduce variations in current levels from different excitation voltages, one needs to upgrade their test equipment to something like a Network Analyzer or something that measures Multi-frequency electro-chemical impedance spectroscopy (EIS).

The result is a variety of resonant frequencies. THe characteristics are also influenced by conductor materials where silver mica have extremely good qualities and dipped tantalum, not so good as well as the shape of the conductors which exhibit ESL or inductance and various resonant frequencies.

Historically for ac noise voltage on DC lines, we have always used a mix of components to minimize the ESR over a wide range of frequencies due to SRF of different sizes. Thus 100uF, 1uF and 0.01 to 0.1uF are put in parallel. For Microwave the DC decoupling caps are usually less than 50pF as SRF drops with rising sizes and values.

One only has to look at the proliferation of capacitance families over the decades, with many being dropped and replaced with new materials and processes to understand that capacitor designs is not so simple and are still being improved today.

Fortunately for most applications, we can simply use the value ratings and tolerance and try not to push the limits for longer life and get expect results.

 

[Tony Stewart]

grand

Throwing out a good 12,000uF capacitor is a criminal offence.

spec

That 12 mF cap is worth >$20 if you buy by the hundred. To buy one would be unthinkable price, if you had to as they are not kept in stock.

 

[granddad]

OK guys. I will hide it somewhere ...
May have to bin this...

 

[spec]

OK guys. I will hide it somewhere ...
May have to bin this...
View attachment 98817

Not sure what that is- looks like a beefy diode.

spec

 

[granddad]

looks like a beefy diode.

My guess but no forward voltage ? in any direction ...could be an ex-diode.

 

[Nigel Goodwin]

Not sure what that is- looks like a beefy diode.

Three connections, more like a thyristor?.

 

[dr pepper]

Mercury tilt switch?

Thats a cool tx/rx board Nige, I'll have to get me one of those, 5 is a bit much though.

 

[Nigel Goodwin]

Mercury tilt switch?

Thats a cool tx/rx board Nige, I'll have to get me one of those, 5 is a bit much though.

Well you need at least two in order to use them

They do sell them in ones, but I ordered five - as you never know when you might want some, and they take a long time to arrive from China.

 

[spec]

Three connections, more like a thyristor?.

I'll put my glasses on next time.

spec

 

[granddad]

but I ordered five - as you never know when you might want some,

I orderd 2 HC12 from Banggood , 2 weeks ago give or take , packet only arrived with 1 ! , 4 emails to sort out !

 

[Tony Stewart]

That 12 mF cap is worth >$20 if you buy by the hundred. To buy one would be unthinkable price, if you had to as they are not kept in stock.

For a reservoir cap from a full wave rectified transformer, and get 10% ripple voltage, one needs an RC time constant of about 5T which for 50Hz x2 is 50ms. The 12 mF cap is suitable for a load of R=50ms/12mF = 4 Ohms. Which for LEDs is only 1/4Ω or 250mW. Thus you can see the advantage of SMPS for high F caps can be quite small, making this dinasaur, somewhat limited in use. But at the end of along wire inductance at your load, very useful to provide the initial current needed for starting DC motors. But still tiny in Comparison with a 100 Farad SLA battery.

With 10% ripple current the cap peak current will be about 10x average current and higher for startup.