How to measure the amount of energy stored in a battery ?

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the measurement
?

 

[KLR]

On Fri, 21 Jan 2005 01:44:30 +1100, <E> wrote:

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the measurement
?


as far as Im concerned - a battery should be tested under load to get

its true remaining energy level. Preferably the load under which its
expected to operate under most of the time in normal use.

Unfortunately - this will use some of its energy

even applying a voltmeter to a battery has to use some energy from the
battery in the process.
>

 

[Ed [:-)>]

assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

 

[Rod Speed]

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...

assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

 

[Phil Allison]

<E>

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the
measurement ?

** That depends entirely of what sort of cell - common "dry" cells can be
tested with a volt meter and a load resistor or just measured while in use.





................... Phil

 

[Roger Lascelles]

<E> wrote in message news:41efc397$0$20754$afc38c87@news.optusnet.com.au...

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the
measurement
?

Put a resistor in parallel with your voltmeter. Choose the resistor to draw
the same current as your appliance will draw. Connect to battery for a
second or so while you read the voltage. Select the end of life point as a
voltage - say 1.3V - below which your application will not work - and at
which point remaining cell life and reliability is poor.

This test is realistic, because it duplicates the conditions of service for
the battery.

In strict terms, it is very hard to estimate the actual *energy* stored in a
battery.

If you go to Radio Shack and buy a *battery tester* you will get a voltmeter
with a load resistor wired across it - just like I suggest.

Roger

 

[Mike Harding]

On Fri, 21 Jan 2005 09:44:37 +1100, "Rod Speed" <rod_speed@yahoo.com>
wrote:

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...
assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

So tell us the rest...? If you know?

Mike Harding

 

[hadda hadda]

NO

<E> wrote in message news:41efc397$0$20754$afc38c87@news.optusnet.com.au...

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the
measurement
?

 

[Rod Speed]

"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:urq0v09vuq4urf9ttpfoiik9djnst8178j@4ax.com...

On Fri, 21 Jan 2005 09:44:37 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...
assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

So tell us the rest...? If you know?

Measuring the electrolyte is only part of the story
on remaining capacity with a lead acid battery, stupid.

 

[Mike Harding]

On Sat, 22 Jan 2005 09:58:51 +1100, "Rod Speed" <rod_speed@yahoo.com>
wrote:

"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:urq0v09vuq4urf9ttpfoiik9djnst8178j@4ax.com...
On Fri, 21 Jan 2005 09:44:37 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...
assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

So tell us the rest...? If you know?

Measuring the electrolyte is only part of the story
on remaining capacity with a lead acid battery, stupid.

So tell us the rest...? If you know?

Mike Harding

 

[Franc Zabkar]

On Fri, 21 Jan 2005 01:44:30 +1100, <E> put finger to keyboard and
composed:

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the measurement

An alkaline battery has a fairly linear discharge characteristic
whereas NiCd and NiMH rechargeable batteries maintain close to 1.2V
full voltage up to 80-90% of usage. They tend to go flat very
abruptly. I can see how one could reasonably estimate the remaining
capacity of an alkaline battery by measuring its terminal voltage at a
certain discharge rate, but a rechargeable battery would be more
difficult. That said, mobile phones can assess their battery's state
of charge, probably by pulsing it with a predetermined load. My own
phone doesn't do a very good job of this, though. The battery meter
can be at 50%, but the "attention: battery low" warning still appears.
<shrug>


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar"

An alkaline battery has a fairly linear discharge characteristic
whereas NiCd and NiMH rechargeable batteries maintain close to 1.2V
full voltage up to 80-90% of usage. They tend to go flat very
abruptly. I can see how one could reasonably estimate the remaining
capacity of an alkaline battery by measuring its terminal voltage at a
certain discharge rate, but a rechargeable battery would be more
difficult.

** Impossible is the word.

That said, mobile phones can assess their battery's state
of charge, probably by pulsing it with a predetermined load.

** With devices like mobile phones or lap tops there is often a micro
dedicated to monitoring the internal battery - the time duration and the
rates of charge or usage are constantly measured, the data is processed and
a **model** of the battery's likely condition held in memory and also
displayed as a "fuel gauge".

Sometimes the calculated **model** and the battery get right out of whack
and the micro has to be reset while the battery is fully cycled -
likewise if the battery becomes defective or dies of old age the model will
be wrong.



............... Phil.

 

[Rod Speed]

"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:al43v0ta3kfibqvg6fj0beta51oreelhl2@4ax.com...

On Sat, 22 Jan 2005 09:58:51 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:


"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:urq0v09vuq4urf9ttpfoiik9djnst8178j@4ax.com...
On Fri, 21 Jan 2005 09:44:37 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...
assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

So tell us the rest...? If you know?

Measuring the electrolyte is only part of the story
on remaining capacity with a lead acid battery, stupid.

So tell us the rest...? If you know?

Wota terminal fuckwit you have always been, Harding.

 

[Ross Herbert]

On Fri, 21 Jan 2005 01:44:30 +1100, <E> wrote:

When I measure an old battery with a voltmeter I can read almost full
voltage of the battery. But when I connect it to a load voltage drops. Is
there a way of measuring the amount energy stored in a battery WITHOUT
wasting its energy (without drawing to much current) during the measurement
?

There is (as yet) no method of accurately measuring the state of
charge of a battery. All of the suggested methods will provide an
approximation of SOC and even then there may be some reliance on
interpretation of the results of any test.

Cadex are probably one of the most innovative companies specialising
in battery testing equipment and the history timeline
http://www.cadex.com/about_history.asp will give some idea of how long
they have been trying to solve this problem. Most of their equipment
is concerned with batteries for portable quipment but their latest
Spectro CA-12 may yet provide the closest approximation to the true
SOC of a lead-acid battery http://www.cadex.com/prod_testers_ca12.asp

This page http://www.cadex.com/prod_testers.asp has links to some
articles which detail the issues related to determinining the SOC (or
reserve capacity) of batteries.

 

[Mike Harding]

On Sat, 22 Jan 2005 15:56:34 +1100, "Rod Speed" <rod_speed@yahoo.com>
wrote:

"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:al43v0ta3kfibqvg6fj0beta51oreelhl2@4ax.com...
On Sat, 22 Jan 2005 09:58:51 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:


"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:urq0v09vuq4urf9ttpfoiik9djnst8178j@4ax.com...
On Fri, 21 Jan 2005 09:44:37 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...
assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

So tell us the rest...? If you know?

Measuring the electrolyte is only part of the story
on remaining capacity with a lead acid battery, stupid.

So tell us the rest...? If you know?

Wota terminal fuckwit you have always been, Harding.

So you don't actually know then, I'm not surprised.

Mike Harding

 

[Rod Speed]

"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:ucq4v0pr2csc2sv7eoi3apq92o9331upff@4ax.com...

On Sat, 22 Jan 2005 15:56:34 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:

"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:al43v0ta3kfibqvg6fj0beta51oreelhl2@4ax.com...
On Sat, 22 Jan 2005 09:58:51 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:


"Mike Harding" <mike_harding@nixspam.fastmail.fm> wrote in message
news:urq0v09vuq4urf9ttpfoiik9djnst8178j@4ax.com...
On Fri, 21 Jan 2005 09:44:37 +1100, "Rod Speed" <rod_speed@yahoo.com
wrote:

"Ed [>" <eddie_bounce@optusnet.com> wrote in message
news:41efeda2$0$803$afc38c87@news.optusnet.com.au...
assume the internal ris increases with reduced remaining capacity and
you can work the rest out yourself
the test discharge current pulse can be short if using some smarts.

if it is a lead acid cell then the SG of the electrolyte can be measured

Thats only part of the story tho, particularly with sulphated plates.

So tell us the rest...? If you know?

Measuring the electrolyte is only part of the story
on remaining capacity with a lead acid battery, stupid.

So tell us the rest...? If you know?

Wota terminal fuckwit you have always been, Harding.

So you don't actually know then, I'm not surprised.

Wota terminal fuckwit you have always been, Harding.

 

[Franc Zabkar]

On Sat, 22 Jan 2005 14:09:54 +1100, "Phil Allison"
<philallison@tpg.com.au> put finger to keyboard and composed:

"Franc Zabkar"

An alkaline battery has a fairly linear discharge characteristic
whereas NiCd and NiMH rechargeable batteries maintain close to 1.2V
full voltage up to 80-90% of usage. They tend to go flat very
abruptly. I can see how one could reasonably estimate the remaining
capacity of an alkaline battery by measuring its terminal voltage at a
certain discharge rate, but a rechargeable battery would be more
difficult.


** Impossible is the word.


That said, mobile phones can assess their battery's state
of charge, probably by pulsing it with a predetermined load.


** With devices like mobile phones or lap tops there is often a micro
dedicated to monitoring the internal battery - the time duration and the
rates of charge or usage are constantly measured, the data is processed and
a **model** of the battery's likely condition held in memory and also
displayed as a "fuel gauge".

That's the prevailing technology for expensive lithium laptop
batteries, but I don't believe my mobile phone battery works that way.

Sometimes the calculated **model** and the battery get right out of whack
and the micro has to be reset while the battery is fully cycled -
likewise if the battery becomes defective or dies of old age the model will
be wrong.

If your model were to apply to my phone, then why would it display a
50% battery meter while warning that the battery was low?

With an old battery, I have observed the battery meter drop to about
25% over a couple of days and then mysteriously increase. No calls
were made or received during this time.

I have two identical phones with identical, genuine Ericsson NiMH
batteries. If I swap batteries between phones, one fully charged, the
other at about 25%, then the phones correctly assess the state of
charge of the replacement batteries ... almost. The fully charged
battery from phone A shows only about 90% in phone B.

My conclusions are that there is no intelligent IC within the battery
pack, otherwise the SOC info would be communicated to the new phone.
Secondly, the phone itself senses the SOC in some way, probably by
measuring the terminal voltage at a certain discharge rate. That's why
the battery meter is often updated during a call, especially when the
SOC is low.

One other observation about my phone is that it will refuse to charge
a battery pack that it considers to be dead flat. To get around this,
I trickle charge the pack using a DC supply and series resistor until
the voltage is at a reasonable level. I then install it in the phone
and allow the phone to complete the process.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar"
"Phil Allison"

An alkaline battery has a fairly linear discharge characteristic
whereas NiCd and NiMH rechargeable batteries maintain close to 1.2V
full voltage up to 80-90% of usage. They tend to go flat very
abruptly. I can see how one could reasonably estimate the remaining
capacity of an alkaline battery by measuring its terminal voltage at a
certain discharge rate, but a rechargeable battery would be more
difficult.


** Impossible is the word.


That said, mobile phones can assess their battery's state
of charge, probably by pulsing it with a predetermined load.


** With devices like mobile phones or lap tops there is often a micro
dedicated to monitoring the internal battery - the time duration and the
rates of charge or usage are constantly measured, the data is processed
and
a **model** of the battery's likely condition held in memory and also
displayed as a "fuel gauge".


That's the prevailing technology for expensive lithium laptop
batteries, but I don't believe my mobile phone battery works that way.

Sometimes the calculated **model** and the battery get right out of whack
and the micro has to be reset while the battery is fully cycled -
likewise if the battery becomes defective or dies of old age the model
will
be wrong.

If your model were to apply to my phone, then why would it display a
50% battery meter while warning that the battery was low?

** Frank - can you fucking read at all ???

What does the very first line of my post say ???

My conclusions are that there is no intelligent IC within the battery
pack, otherwise the SOC info would be communicated to the new phone.
Secondly, the phone itself senses the SOC in some way, probably by
measuring the terminal voltage at a certain discharge rate. That's why
the battery meter is often updated during a call, especially when the
SOC is low.

** Your particular phone is your problem.





.................... Phil

 

[Franc Zabkar]

On Sun, 23 Jan 2005 09:18:42 +1100, "Phil Allison"
<philallison@tpg.com.au> put finger to keyboard and composed:

"Franc Zabkar"
"Phil Allison"


An alkaline battery has a fairly linear discharge characteristic
whereas NiCd and NiMH rechargeable batteries maintain close to 1.2V
full voltage up to 80-90% of usage. They tend to go flat very
abruptly. I can see how one could reasonably estimate the remaining
capacity of an alkaline battery by measuring its terminal voltage at a
certain discharge rate, but a rechargeable battery would be more
difficult.


** Impossible is the word.


That said, mobile phones can assess their battery's state
of charge, probably by pulsing it with a predetermined load.


** With devices like mobile phones or lap tops there is often a micro
dedicated to monitoring the internal battery - the time duration and the
rates of charge or usage are constantly measured, the data is processed
and
a **model** of the battery's likely condition held in memory and also
displayed as a "fuel gauge".


That's the prevailing technology for expensive lithium laptop
batteries, but I don't believe my mobile phone battery works that way.

Sometimes the calculated **model** and the battery get right out of whack
and the micro has to be reset while the battery is fully cycled -
likewise if the battery becomes defective or dies of old age the model
will
be wrong.

If your model were to apply to my phone, then why would it display a
50% battery meter while warning that the battery was low?



** Frank - can you fucking read at all ???

What does the very first line of my post say ???

Ummm, the very first line says "Impossible is the word."

impossible
ADJECTIVE: Not capable of being accomplished.

Sure, nothing beats counting the coulombs into and out of a cell, but
clearly it *is* possible to estimate the SOC without any dedicated
monitoring chips. The accuracy may not always be great, but it is good
enough for most practical purposes. Mobile phone manufacturers have
been doing it this way for years.

In fact, here is an innovative, accurate, 100% analogue circuit tuned
for a particular battery that relies solely on ESR to predict SOC:
http://www.hagtech.com/pdf/fuel.pdf

It has no ICs, smart or otherwise, just 6 transistors and a zener. It
also shows the SOC while the battery is being charged.

AFAICT, smart monitoring is generally reserved for lithium-ion
batteries because they are less resistant to abuse. These chips do a
lot more than just report the SOC.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar"
"Phil Allison"

** Frank - can you fucking read at all ???

What does the very first line of my post say ???

Ummm, the very first line says "Impossible is the word."

** " With devices like mobile phones or lap tops there is often a micro
....... "

Your bloody phone is not the subject !!!

In fact, here is an innovative, accurate, 100% analogue circuit tuned
for a particular battery that relies solely on ESR to predict SOC:
http://www.hagtech.com/pdf/fuel.pdf

** What BULLSHIT - you have ZERO idea if that design works accurately in
practice.


The "impossible" question is to determine, with a brief test, the SOC of a
NiCd or NIMH battery that is presented for such test. The continuous
discharge curve is of **no use** as a predictor when a battery is used
intermittently - as is usually the case.

Cells recover when at rest for some time, voltages rise and ESRs fall -
this * voids* the accuracy of tests that rely on those two parameters. The
temperature and age of the cells also has a major effect on those same
parameters.

The upshot is that a NiCd or NiMH battery placed on a brief test will show
an ESR and voltage reading consistent with near full charge when in fact the
true SOC is as little as 10 % of capacity.




............. Phil