Lithium ion battery

Thread Starter

Kayukayu

Joined May 24, 2021
10
I don’t know who to ask so I am posting this question here. I am conducting pulse discharge testing on a lithium ion battery. Sometimes I get a waveform that looks like the one below. It’s not supposed to have a dip in the beginning but it does. The duration of the pulse discharge is 10 seconds
 

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Alec_t

Joined Sep 17, 2013
12,321
? I'm confused. If the horizontal scale is seconds then the dip is at 40 sec, not 'the beginning'. Also, the dip duration is 20 sec, not 10 sec.
All batteries and test leads have resistance, which drops the measured voltage when current flows. The graph appears to show cell voltage dropping from ~4.2V with no load current, down to ~ 3.7V with an unknown load current. Looks like what one should expect.
 

Thread Starter

Kayukayu

Joined May 24, 2021
10
What are you describing as a "dip" ?
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This is what I mean by the dip. Right after the discharge pulse begins, there’s this instantaneous voltage sag and then the voltage rises back up a bit and decays which is Normal but why is this instantaneous voltage dip/sag happening? It happens sometimes and sometimes it doesn’t
 

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LowQCab

Joined Nov 6, 2012
1,372
Every component has Inductance, Capacitance, and Resistance ..... Including Batteries.
Also including Test-Leads.
Everything .........

What you are seeing is generally called "over-shoot", and is completely normal.

You could probably get rid of it with the right sized Capacitor in parallel with the Battery.
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Thread Starter

Kayukayu

Joined May 24, 2021
10
Every component has Inductance, Capacitance, and Resistance ..... Including Batteries.
Also including Test-Leads.
Everything .........

What you are seeing is generally called "over-shoot", and is completely normal.

You could probably get rid of it with the right sized Capacitor in parallel with the Battery.
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Thank you. Do you know what might be the cause of this overshoot? And why does it happen only sometimes?
 

LowQCab

Joined Nov 6, 2012
1,372
When you "hit" and Inductance, or a Capacitance,
with a very fast change of Voltage/Current,
it will "Ring" like a Bell.

If you increase the Load on the Battery more gradually
there will be very little, or even almost zero, "Ringing".

It happens every single time,
but sometimes it may be at a higher amplitude than others,
or at various different Frequencies of Oscillation.
It could also be that,
sometimes it happens too fast for your Scope to "see it".
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Thread Starter

Kayukayu

Joined May 24, 2021
10
When you "hit" and Inductance, or a Capacitance,
with a very fast change of Voltage/Current,
it will "Ring" like a Bell.

If you increase the Load on the Battery more gradually
there will be very little, or even almost zero, "Ringing".

It happens every single time,
but sometimes it may be at a higher amplitude than others,
or at various different Frequencies of Oscillation.
It could also be that,
sometimes it happens too fast for your Scope to "see it".
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Thanks a lot for your replies Sir! I can’t seem to find any related study material so that I can read up on this ringing effect. For context: I am doing the pulse discharge testing for battery parameter extraction.
 

LowQCab

Joined Nov 6, 2012
1,372
For your purposes, You can completely ignore the Ringing.
If you want to "suppress it" so that your Scope-Trace looks cleaner
just add a 1-Microfarad-Ceramic-Capacitor where your Test-Leads attach.

One is not guaranteed to work,
You may need to stack-up 5 or 10 of them to get a perfect Trace every time.
This is to counter the cumulative Inductance in the Battery, Wiring, and your Load,
and we don't have a clue how much Inductance there actually is,
because most of it is incidental/accidental/circumstantial.

Something like this .......
DigiKey p/n 565-4710-1-ND ~$2.28 each
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Ceramic Cap 1 .PNG
 
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