Good day together
Has anyone of you
how can i Calculate the internal resistance of the battery depending on the temperature using the Arrhenius equation.
Thanks and many greetings
Potentially you cannot:
This "Arrhenius equation" seems to be related to the internal chemical reaction.
But a battery has an intrinsic resistance (Ohm resistance, e.g. due to wires, contact resistance) which might matter more.
And you can "measure" the resistance on the outside, e.g. how much current, was is the voltage
take into your circuit board. But it does not tell you anything about the "chemical resistance" (speed of chemical reaction).
For sure, the current you can draw depends on the battery temperature. But most of the time the battery is "oversized", provides always the current you need for all conditions.
And you have another effect: when you draw current - the battery heats up (internally) and will increase the resistance. So, you have a differential equation at the end.
And why it would be important? if you have a battery which provides the current for your board, for all temperature regimes you need, even the battery gets hot when drawing current: what you want to achieve is a current needed for your board running, never mind how hot the
battery is (as long as it remains in the spec. range).
Nobody (as electronic circuit designer) would raise such a question: instead they assume they have a "perfect" voltage (power) source (a minimal internal resistance for avoiding voltage drops by current drawn). What happens inside the chemical - "we" do not care: we would go with a better (larger) battery.
Without a great deal more information, you can't.
And to add insult to injury, every time you use the battery and then measure the internal resistance, it will have increased because there are now fewer active molecules in the chemical reaction. This continues with each use, or with age, until there are no more useful chemical reactions and the battery is considered "dead".
Hi,
What is the application?
Thanks.. Tom.. 
The "beta" value is an experimentally determined property of the battery.
i had to Google is and found this: " In physical chemistry, the Arrhenius equation is *a formula for the temperature dependence of reaction rates".
That has NOTHING to do with internal resistance, but ONLY the rate that electrical current can be produced by the chemical reaction.
Yes, and one comment:
If you check the schematics: the battery is connected via PMIC chip: when you measure from MCU - you see what is the VBAT on MCU input, not the real battery voltage (going though PMIC).
What I see: even no battery connected - there is a voltage (approx. 3.2V) (potentially the PMIC provides VBAT even no battery connected).
So, when you want to "track" really the battery: you might need the PMIC (where the battery is connected). But I have not found that PMIC can "measure" battery. It seems to provide just thresholds (voltage levels to set for charging and reading the status (if charging or not)).
Yes: if you use the battery (you drain current) the parameters change a lot: temperature, internal resistance, constant vs. peak current able to provide. And any peak current (MCU draws a bit more current due to heavy actions) - will affect you measurements (for a stationary situation).
BTW: many LiPo batteries have a temperature sensor integrated (3 pin). But you cannot read temperature from MCU: even the third pin (middle pin) is there on Portenta H7 battery connector - it does not look like as wired, never used (e.g. by PMIC).
BTW:
You can calculate the resistance of the battery: you just need to measure voltage in "without load" mode and "with load". And measure the current (in "with load").
You will get the ENTIRE battery resistance.
But it does not tell you anything about the chemicals really: the resistance depends also on the internal wires, the resistance of the wires due to temperature. And a small voltage drop on connectors give you a wrong result.
You might need to think about to create a dedicated battery tester: not with an MCU also connected on the same battery. Your battery is the DUT (Device Under Test) and should not be
part of the test system.
It has to do with the internal resistance...
The internal resistance is the sum of al real resistivity in the circuit (connectors, wires) plus an 'experienced' resistivity that is dependent on the reaction rate (and also diffusion rate of electrolytes). This reaction rate as a func of temperature will be described by Arrhenius equation.
The higher T, the faster the reaction, the higher the current at a certain voltage or the higher the voltage at a given current. In real life it is best to stay out of the region where current is so high that you get a serious voltage drop (as it reduces battery efficiency and also may damage the battery).
But in a car battery, during starting the motor, it is quite common to run into this chemical limit. At 100 amps a 12V car battery may deliver only 6V. In cold conditions it may be not at all able to deliver 100 amps and your car will not start.
So, as said by others, the beta is not really a constant. It changes over time due to aging of the battery.
But if you maintain the current temperature for the instant you check the internal resistance, the equation result is zero because there is no temperature change.
Aren't you supposed to measure the battery temperature and use that temperature in the equation? After calibrating beta at a known temperature...
Edit:
You need to measure R twice. Once at ambient T (Rref) and once at a higher T. Then you can calculate beta.
I think I can explain that to you better
First I simulated the battery with the Shpherd model and now I want to simulate the battery with the same model but this one with the temperature effect
I think I can explain that to you better
First I simulated the battery with the Shpherd model and now I want to simulate the battery with the same model but this one with the temperature effect
I think I can explain that to you better
First I simulated the battery with the Shpherd model and now I want to simulate the battery with the same model but with the temperature effect
I think I can explain that to you better
First I simulated the battery with the Shpherd model and now I want to simulate the battery with the same model but with the temperature effect
Hi,
You don't have to repost your post 4 times, just the once will do.
When you reply to someone, we and they can still see all the replies.
Tom..