Battery state of health determination with impedance measurement

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
what can we say about online and offline battery monitoring ? only that battery is discharged by a load in online and in offline battery is at rest ?
 

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
at 1OKHz i got the inductance value , L and phase angle to be positive .....Now in this case I also directly noted the Z of( battery n capacitor combination ) here the calculations for real and imag shall remain the same (Z*cos) and (Z*sin) or shall it be different ........
While doing alone with the capacitor (1000µF) i did not go upto 10KHz , as now i went above 10KHz (with battery and capacitor) i got this L and i m not sure as to take XL and make the calculations ?
 

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You do the same calculations at each frequency even if the phase angle becomes positive. You must measure the capacitor alone at the same frequencies where you measure the capacitor + battery.

However, I'm not sure whether you can draw any conclusions about the battery health at such high frequencies. Your tutor may have an opinion about this.
 

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
ya such high frequencies cannot properly draw the conclusion for battery health , the freq range of interest is between upto 1KHz .....i have kept the battery to charge it is really taking too long ......thus the delay in characterizing the fully charged battery
 

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
All batteries exhibit predominantly resistive behaviour in freq ranges 10Hz to 1KHz , how can it be concluded ?
As in from the results of Z (the real part that )
what implies this behavior? can you help ?


Float voltage conditions? does it mean a specific termianl voltage after battery is charged ?
 
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After the battery is charged, the applied voltage should be reduced to the "float" voltage. This will keep the battery fully charged, but not overcharge it.

The battery properties you ask about are probably explained in the battery manufacturers literature.
 

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
After the battery is charged, the applied voltage should be reduced to the "float" voltage. This will keep the battery fully charged, but not overcharge it.

The battery properties you ask about are probably explained in the battery manufacturers literature.





Need to include few things about the capacitor selection ?
The reason behind choosing the capacitor with low ESR and how shall it affect the internal R of the battery which we want to characterize ...The one what you explained about the Fc as when it will be 0.707 times that of what it was at high frequency range , shall it be includedto determine the fc , ?
About this series capacitor please can you tell me the exact reasoning behind it .....
 
The reasoning behind the series capacitor is to remove the DC voltage from the battery from the measurement. The battery voltage might damage the LCR meter if it is applied to the terminals of the LCR meter. The capacitor blocks the DC battery voltage but does not block the AC voltage from the LCR meter which is used to measure the battery impedance.

The capacitor needs to have a low ESR because that ESR appears in series with the battery internal R during the measurement. If the ESR is large it degrades the accuracy of the measurement.

I don't understand the need for the Fc measurement anyway. It was supposed to be used to determine the capacitance of the capacitor. Since the LCR meter can measure that directly, there is no need for the Fc measurement. You might ask your tutor what the purpose of the Fc measurement is.
 

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
the project is done , and i no longer have to go to the lab for the measurements as the battery i used even after charging and discharging the terminal voltage does not remain above 9.6V , and after discussing with the tutor it is clear that the batteries are seriously damaged....

Now i have to properly document my work in this week and wait for the presentation date .....
 
the project is done , and i no longer have to go to the lab for the measurements as the battery i used even after charging and discharging the terminal voltage does not remain above 9.6V , and after discussing with the tutor it is clear that the batteries are seriously damaged....

Now i have to properly document my work in this week and wait for the presentation date .....
Good luck. :)
 

Thread Starter

Bhargav Jani

Joined May 20, 2016
114
for high value of capacitance 1000µF, do




ew one and throw away the one that got hot.


Can you suggest a reason for suggesting 1000µF with 50V rating , in the LCR meter website there is a pdf in which they mentioned using Voltage rating of cap 3 times higher than that of the battery rate voltage ??
 
It has been noticed by other people on this forum and on other forums that if you examine manufacturers data such as this:
http://www.cde.com/resources/catalogs/300-301.pdf

that the ESR of electrolytic capacitors seems to be the smallest for a given capacitance when the voltage rating is in the range of 50 to 100 volts. Since you would like the smallest possible ESR for measuring your batteries, a voltage in that range would be best.
 
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