AVR Freaks

It's almost impossible to know a battery's "state of health" simply from a single instantaneous reading. I suppose if the battery chemistry has a very well defined discharge profile then by reading the terminal voltage very accurately you might be able to gauge where on the curve you were. But this is why mobile phones and similar have constant monitoring systems so they know how much energy has been put into the battery and the rate at which it was consumed so they know where in the "life" the thing is.

sounds like a fuse tester ... !!

 

       

I mean your test shows how much energy was stored - by the end of that test, there is nothing left!

 

I think the OP is asking for a way to know how much energy is currently left ... ?

Ah - you may be right.

 

But that test may not be representative of how the battery performs in "Real Life" ...

 

There is a BIG problem with all batteries to estimate charge state.

 

It depends hugely on LOAD! I'm not just talking about discharge rate. Internal battery resistance means that the terminal voltage will be lower, at a given battery charge state, when the load current is higher. This gives an apparent state estimate that is lower than it really is.

 

Further, this internal electrical resistance is, in part, electro-chemical. This means that the apparent battery state does not return, instantly, when the load is removed. It can take minutes, or longer. 

 

The short take-away from this is that your goal of measuring thousands of batteries per day is somewhat of a fantasy. 

 

Here is a snap-shot of what I am currently doing. I make a battery powered device. It SHOULD last a long time with a pair of C cells. When it is screwed up (software), the life can be 5-10 days. When it operates correctly, it can be 45 to 90 days. Now, with just one battery (they are in parallel), I get half life, so 45 day life turns into 23 days with a single cell. I can tell, pretty well, what the life will be at the 50% discharge point. That is 12 days. BUT, I can usually tell if it is going to be good or not in 2-3 days; by that time, I can see if it is AFU or if it is (relatively) good, but not how bad or how good. That is how I have been doing it. Though, I should be clear, my interest is in how the instrument behaves, not how good any particular battery is. I should also add that this device has highly irregular battery energy consumption patterns, which come from WHEN a microSD memory card is written (device  sleep current is microAmps, write current is 100+ mA).  

 

What I am now doing is starting with a software build with known good battery life, and another software build with known poor battery life. I have a test fixture using super-capacitors that will run the instrument. By measuring the super-cap  discharge rate over some time interval, I can determine the average current for the known good unit and the known bad unit. Then, in the future, I can compare new software builds against the known cases, and do this in a few minutes.  

 

Not sure this will help but maybe it will?

 

Cheers

Jim

That's a big pile of AA's!!!!

I think I have one of these laying around somewhere, I can send the OP.

You know it gotta be good, it came from RadioShack

This just landed in my inbox:

 

https://www.electronicdesign.com/technologies/test-measurement/article/21128843/measuring-dcir-of-lithiumion-cells

 

I would like to go back and ask Moe a question which I do not think has been directly asked:

 

What do you mean by "state-of-health, quality, etc."? I ask because the question might refer to a variety of things that have been alluded to, but not really stated. For example?

 

A. Does this refer to the current present state of charge of the battery?

 

B. Does this refer to the ability of a battery to hold charge?

 

C. Does this refer to the ability of a battery to deliver charge (e.g. energy)?

 

D. Does this refer to the fraction of remaining useful battery life?

 

Each of these means something different (though are often related in a variety of sometimes obtuse ways). Each of these is measured differently (and not always consistent across battery chemistries). Each takes different amounts of time to determine. 

 

A little clarity here would help all of us, and probably, also the OP.

 

Jim

 

edited, hopefully with your agreement Jim, in the interests of avoiding any ambiguity because of language difference. Ross.

 

<add> Good catch - jim </add>

This just popped up on my FB:

 

Wow!...that is pretty impressive piece of gear.  They really went to town in the measurement dept:

 

Next, the voltage across the battery is measured. The voltage drop across each component is very small in the range of microvolts (μV) ....

Using the discrete Fourier transform (DFT) hardware accelerator, a DFT is performed on the ADC data where the real and imaginary numbers are calculated and stored in the data FIFO for both the R_CAL voltage measurement and the battery voltage. 

 

Someone spent a lot of lab time (years) developing this battery of knowledge and this test hardware....of course battery tech forms entire industries, with many researchers and $$$ at stake, especially nowadays.

 

It's a bit amusing, that in the end they still say open the comm port & get the terminal going to see the results.  Simplicity never goes outta style.

Neil,

 

This is when we need Carl, "MicroCarl", to jump in with some firsthand engineering knowledge.

 

 

Model S has a 100 kWh battery, with a pack voltage of 400V, and a few different charging options, but the supercharger has the highest power at 150-200 kW at 480V DC, so over 400A.

 

More than 60 kW worth, apparently.