As u said the ESR of the capacitor then , if i use 1Khz my capacitor which is 670pf is showing the reading of C and R in the picture , in that scenario what shall be done then ? How would the calculations look like if need to choose the Fc for the calculations?

 

If you do the calculation of the corner frequency of a resistance of .0226 ohms and a capacitor of 1000 uF, you will find that it is about 7042 Hz.

The way to find the corner frequency with the LCR meter is to measure the Z of the series combination at the highest frequency of the meter (200 kHz), and then make measurements at successively lower frequencies until you find the frequency where the impedance Z is .707 times its maximum value at 200 kHz. From this you can then calculate the value of the capacitor assuming it has zero ESR.

However, this assumes that the battery internal R is exactly .0226 ohms, which is not likely. I thought the whole point of this exercise is to measure the internal R of the battery, not to assume it is some value specified on a data sheet.

 

Notice that this capacitor has an internal resistance (ESR) of 1221 ohms. This is 53 thousand times greater than the assumed .0226 ohms internal resistance of the battery. This is not a good choice of capacitor for your measurements.

You should use a capacitor of about 1000 uF. This will be an electrolytic capacitor. I think you said you had such a capacitor available. Measure it with the LCR meter and see what its ESR is.

 

the batteries internal resistance might have some increased definately, not exactly 22.6miliohms. My end results must obviously show increase in internal impedance when i plot the graphs (Re vs Img)......i can show some considerations from that graph ?
I am not clear about how to find corner frequency ?
Do you mean i set 200Khz on the meter and see the value of Z and then by decreasing the frequency on the meter i see the change in the value of Z ? Will this help me to get the correct value of C?

 

Ok i shall measure the ESR of 1000µF and post the results .........ASAP

 

For a 1000µF capacitor at the lowest possible frequency see the results the ESR is 0.3827Ohms

 

the batteries internal resistance might have some increased definately, not exactly 22.6miliohms. My end results must obviously show increase in internal impedance when i plot the graphs (Re vs Img)......i can show some considerations from that graph ?
I am not clear about how to find corner frequency ?
Do you mean i set 200Khz on the meter and see the value of Z and then by decreasing the frequency on the meter i see the change in the value of Z ? Will this help me to get the correct value of C?

Consider the circuit you showed in post #58. The capacitor and battery are in series, and if you use the LCR meter to measure Z of that combination, you will find that at high frequencies it will reach a maximum as the graph in that image shows. As the measurement is lowered, Z will at some frequency begin to decrease. Continuing to decrease the measurement frequency, finally you will reach a frequency where Z is .707 times its high frequency maximum. That will be the corner frequency (Fc). However, this assumes that the capacitor has zero internal resistance; this a big assumption which is not likely to be true.

The true behavior of the circuit would need to include the resistance (ESR) of the capacitor.

I don't understand what the tutor's purpose in doing this would be. Why would you try to determine the value of the capacitor this way when you can just measure it with the LCR meter?

 

For a 4700µF capacitor (its too much i guess) i got ESR of 0.0487Ohms (but this value will be too big for the characterization)
I guess 1000µF is appropriate and by the time i just explain this to my tutor, so we agree on selecting a 1000µF capacitor for the calculations

 

For a 1000µF capacitor at the lowest possible frequency see the results the ESR is 0.3827Ohms

Please also make a measurement at 1 kHz and at 10 kHz. The ESR of this capacitor (at 12 Hz) is an order of magnitude larger than the expected internal resistance of the battery. This fact makes it difficult to get a good measurement of the battery's internal resistance.

The ESR of electrolytic capacitors usually varies quite a bit with frequency. Maybe it will be low enough at 1 kHz to be useful.

 

For a 4700µF capacitor (its too much i guess) i got ESR of 0.0487Ohms (but this value will be too big for the characterization)
I guess 1000µF is appropriate and by the time i just explain this to my tutor, so we agree on selecting a 1000µF capacitor for the calculations

Why would an ESR of .0487 be too large? What you would like is an ESR of zero, but since this is not possible, the lowest ESR is the best.

 

I'm going to have to be away so I won't respond for a while. I understand you must turn in your report tomorrow. I hope it goes well.

I don't understand why your tutor wants you to do the high pass filter measurement.

I think you should use the largest possible series capacitor. Measure it with the meter in Z/theta mode, then you can get the real and imaginary parts of the impedance like this: Real part = Z * cos(theta) and imaginary part = Z * sin(theta)

Next you can do this: make a measurement of the real and imaginary parts of the capacitor alone, then the series combination of capacitor and battery. Subtract the real and imaginary parts of the capacitor alone from the real and imaginary parts of the capacitor plus battery combination. That should give you the real and imaginary parts of the battery alone.

Good luck with your project.

 

Thank you so much for your support ....
Thanks a ton


I hope all goes well .....


Take care

 

Hi, Bhargav,

I'm back home now. Have you had any luck with your project?

 

Hi, Bhargav,

I'm back home now. Have you had any luck with your project?

I have started with the documentation work now , i will see if the method you suggested goes well , will use the series capacitor 1000µF and will check for the calculations tomorrow in the lab.....

The book on impedance spectroscopy by J ross macdonald, has a lot of infromation but is too complex and invloves lot of anode , cathode , prous layer and lot of stuff related to impedance .but i will keep it simple using the capacitor and hope i get a week extension as the lab was not available last week .........


just started with some basic intro and aging effects

Fingers crossed

 

hello with alone capacitor 1000µF the results of Z and theta are ok
but as i placed this capacitor in series with the meter and the battery , the display readings started fluctuating like crazy , there is no constant value


What can be the case ? or using tthe series capacitor can be problem ?
But this was not the case when i used 670pF last week in series with the battery and the meter

 

when used the capacitor it got hot , i used then a series resistor of 100Ohms with that capacitor ......

when using the series capacitor , is there any need to see any parameter apart from C with R (ie ESR C\R) and Z and theta ........????

No need to see the L , and separate R ????


In series connections after 1000Hz battery showed L behaviour , ie as THETA turned positive angles and the values of L were in milihenries.......

Now does that mean , while taking the method of subtracting the Z (of combination of battery and capa) and only cap this freq where L is effective dont need to be considered????

 

when used the capacitor it got hot , i used then a series resistor of 100Ohms with that capacitor ......

The capacitor should never get hot when used with an LCR meter, unless it was connected with the wrong polarity. Electrolytic capacitors have the unfortunate property that if you apply a voltage to them with the reverse polarity, they will not act like a capacitor but rather they will conduct DC current instead of blocking it. This will make them get hot, and probably damage them. Double check how you are connecting the capacitor. Is there any possibility that it was connected with reverse polarity? If it got hot you should probably get a new one and throw away the one that got hot.

when using the series capacitor , is there any need to see any parameter apart from C with R (ie ESR C\R) and Z and theta ........????

No need to see the L , and separate R ????

All of the parameters that are displayed in the various modes of the LCR meter can be derived from the real and imaginary parts. In fact, what the meter actually measures are the real and imaginary parts and then it calculates the parameters in the other modes using appropriate mathematical formulas.

In series connections after 1000Hz battery showed L behaviour , ie as THETA turned positive angles and the values of L were in milihenries.......

Now does that mean , while taking the method of subtracting the Z (of combination of battery and capa) and only cap this freq where L is effective dont need to be considered????

All real electronic devices such as batteries, capacitors, inductors and resistors are imperfect and they each have some parasitic components of impedance. In other words, capacitors have mostly capacitance but they also have some parasitic resistance (ESR) and also some parasitic inductance. Resistors have some parasitic capacitance and inductance. Inductors have some parasitic resistance and capacitance.

These parasitic components tend to have larger effect at higher frequencies. For example, if you measure a 1000 uF capacitor using the Z/theta mode, you will find that at 20 Hz it will have a negative phase angle, which means that it looks like a capacitor. But if you make successive measurements at higher and higher frequencies, eventually it will have a positive phase angle which means it looks inductive. This is caused by the parasitic inductance of the capacitor forming a series resonant circuit in combination with the capacitance of the capacitor.

The battery itself also has this property of becoming inductive at higher frequencies. For this reason you probably shouldn't make your measurements at excessively high frequencies. Ask your tutor about this.

 

hello

i have attached the excel in which in one case i used the capacitor to see the Z and (re an Im) values , in the other case with the battery 1000µF capacitor , i highlighted a 100Hz freq part .


In this case for the calculation you said ,to get only the battery impedance Shall i directly subtract the Z (of only Cap) which is1.5906, from that of the batteries Z (at the specific freq range )

Is this behaviour correct ? and ya i replaced that hot capacitor i was wrong in the polarity in hurry?

 

If I am reading your Excel charts correctly, it appears that the capacitor ESR at 100 Hz is about .045 ohms, and the combination of battery + capacitor is about .535 ohms. This means that the battery impedance is about .535-.045 = .49 ohms. This is much higher than the .0226 ohms that the fully charged battery should exhibit. Are you measuring a good, fully charged battery?

Strictly, you should measure the capacitor Z at each frequency where you wish to make a measurement and then follow the procedure I outlined above:

"make a measurement of the real and imaginary parts of the capacitor alone (at each frequency), then the series combination of capacitor and battery. Subtract the real and imaginary parts of the capacitor alone from the real and imaginary parts of the capacitor plus battery combination. That should give you the real and imaginary parts of the battery alone."

Also, be aware that the ESR of the capacitor changes with temperature so you should measure the capacitor just before you measure the battery + capacitor.

 

If I am reading your Excel charts correctly, it appears that the capacitor ESR at 100 Hz is about .045 ohms, and the combination of battery + capacitor is about .535 ohms. This means that the battery impedance is about .535-.045 = .49 ohms. This is much higher than the .0226 ohms that the fully charged battery should exhibit. Are you measuring a good, fully charged battery?

Strictly, you should measure the capacitor Z at each frequency where you wish to make a measurement and then follow the procedure I outlined above:

"make a measurement of the real and imaginary parts of the capacitor alone (at each frequency), then the series combination of capacitor and battery. Subtract the real and imaginary parts of the capacitor alone from the real and imaginary parts of the capacitor plus battery combination. That should give you the real and imaginary parts of the battery alone."

Also, be aware that the ESR of the capacitor changes with temperature so you should measure the capacitor just before you measure the battery + capacitor.

yes , i took a measurement of the capacitor before putting it in series with the battery and the meter.......
And you are right the battery was not fully charged , or else it would have shown terminal voltage of (14.2V as marked on the battery)
Tomorrow what shall i do is put the battery to complete charge and check again if the ESR is approx to battery IR
And then discharge the battery to some extent (and take the readings again)

So , as you said about the Z (of capacitor alone direct subtracting from the Z of the series )
if i get a negative value ? (i can take absolute one )
Not a problem??
I will continue with the documentation
Just one question is In the Introduction part of my report at the end of Introduction shall i shortly mention what i am doing in the project or just general Intro is enóugh?


Thank You