At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance).
On 13/12/2024 06:57, Don Y wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally, >> a parallel RC to cover transients?
Depends what you want to do to the battery for any non-trivial charging or discharging rate you ought to take its temperature into consideration too. I^2R
heating with a fudge factor probably a good enough proxy.
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
It might at least near fully charged states or about to be damaged by deep discharge. Manufacturers datasheets are usually helpful.
Not all SLA's are as good as each other for every usage. The ones used in UPS's
and invalid buggies seem to be particularly bad & overpriced.
On 13/12/2024 13:31, Don Y wrote:
On 12/13/2024 3:59 AM, Martin Brown wrote:
On 13/12/2024 06:57, Don Y wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally, >>>> a parallel RC to cover transients?
Depends what you want to do to the battery for any non-trivial charging or >>> discharging rate you ought to take its temperature into consideration too. >>> I^2R heating with a fudge factor probably a good enough proxy.
Yes. I'm just interested in taking a peek at it at a point in time.
E.g., look at it while under charge (knowing voltage at terminals
and charge current) and then briefly under DIScharge (same observations).
If series resistance is the same, I can infer the potential of the voltage >> source from a set of linear equations UNDER THESE CONDITIONS.
Except for a few special cases, electrode-electrolyte interfaces are
very non-linear and you may find that the potential of the inferred
voltage source is different for charge and discharge conditions.
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
Don Y <blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
Design for the worst possible series resistance and then some. I have
been caught out by that a couple of times. Screaming and apparently untraceable audio instability in the middle of doing the P.A. for a
public event is highly embarassing. ("Yes, we put in a new battery - oh
no, someone must have put the old one back in the box with the others - terribly sorry!")
Also, whatever the manufacturers clain for the battery capacity, designI think most regular users of SLA's are aware of their weaknesses.
for half that amount. Batteries don't last forever but your customers
will assume they do and won't want to change them until they are well
below half capacity.
Don Y <blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
Design for the worst possible series resistance and then some. I have
been caught out by that a couple of times. Screaming and apparently untraceable audio instability in the middle of doing the P.A. for a
public event is highly embarassing. ("Yes, we put in a new battery - oh
no, someone must have put the old one back in the box with the others - terribly sorry!")
Also, whatever the manufacturers clain for the battery capacity, design
for half that amount. Batteries don't last forever but your customers
will assume they do and won't want to change them until they are well
below half capacity.
I love the way they swell up spectacularly inside certain brands of UPS making
them almost impossible to remove. Cruel environment for any SLA.
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
On Thu, 12 Dec 2024 23:57:54 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
I've wondered about electro-chemical time lags, ions drifting around
in liquids, as in what would the Spice model of some battery be? And
on a slower time scale, the morphology of a battery changes with time.
Nearly discharged batteries sure go Hi-Z.
What we need here is a good physical chemistry guy.
On 12/13/2024 1:57 AM, Don Y wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally, >> a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
For what value of "safe"?
Probably better, in general, to use manufacturer's
discharge curve, at least as a starting point. If
your application differs appreciably from the test
conditions in the manufacturers specs, you need to
test it yourself, again depending on what you have
in mind by "safe".
It's better to design the system to accommodate the
battery at its best and worst SOC/capacity levels.
Also the age of the battery and how it has been
treated over that age is a factor, so take that
into account too.
On Thu, 12 Dec 2024 23:57:54 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
I've wondered about electro-chemical time lags, ions drifting around
in liquids, as in what would the Spice model of some battery be?
And
on a slower time scale, the morphology of a battery changes with time.
Nearly discharged batteries sure go Hi-Z.
What we need here is a good physical chemistry guy.
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
On Thu, 12 Dec 2024 23:57:54 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
I've wondered about electro-chemical time lags, ions drifting around
in liquids, as in what would the Spice model of some battery be? And
on a slower time scale, the morphology of a battery changes with time.
Nearly discharged batteries sure go Hi-Z.
What we need here is a good physical chemistry guy.
On 12/13/2024 4:20 PM, ehsjr wrote:
On 12/13/2024 1:57 AM, Don Y wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly,
additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
For what value of "safe"?
Probably better, in general, to use manufacturer's
discharge curve, at least as a starting point. If
your application differs appreciably from the test
conditions in the manufacturers specs, you need to
test it yourself, again depending on what you have
in mind by "safe".
Discharge curve depends on knowing the starting point SoC.
For a battery in continuous, cyclic use, you need to
*determine* the SoC at any given time. I.e., when to
STOP charging, when to stop DIScharging, how much charge
you can expect to have available, how long until you
are likely going to reach "full" charge, etc.
It's better to design the system to accommodate the
battery at its best and worst SOC/capacity levels.
Also the age of the battery and how it has been
treated over that age is a factor, so take that
into account too.
The hope is that by continuously updating the (albeit
simple) model, you can reflect the effects of age IN
the model and, potentially, indicate when replacement
is required (which largely depends on the service it
has seen)
On 12/13/2024 7:06 PM, Don Y wrote:
On 12/13/2024 4:20 PM, ehsjr wrote:
On 12/13/2024 1:57 AM, Don Y wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly, additionally, >>>> a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
For what value of "safe"?
Probably better, in general, to use manufacturer's
discharge curve, at least as a starting point. If
your application differs appreciably from the test
conditions in the manufacturers specs, you need to
test it yourself, again depending on what you have
in mind by "safe".
Discharge curve depends on knowing the starting point SoC.
No. The state of charge indicates the location on the curve.
That location tells you how much time remains to reach the
terminal charge or discharge points, under the conditions
that were used to produce the discharge curve. The curve is
a design tool, not something you produce dynamically with
each charge/discharge cycle in actual use.
For a battery in continuous, cyclic use, you need to
*determine* the SoC at any given time. I.e., when to
STOP charging, when to stop DIScharging, how much charge
you can expect to have available, how long until you
are likely going to reach "full" charge, etc.
Exactly.
It's better to design the system to accommodate the
battery at its best and worst SOC/capacity levels.
Also the age of the battery and how it has been
treated over that age is a factor, so take that
into account too.
The hope is that by continuously updating the (albeit
simple) model, you can reflect the effects of age IN
the model and, potentially, indicate when replacement
is required (which largely depends on the service it
has seen)
From your last paragraph, it seems that you do want to
model dynamically, using the dynamically updated model
as (put simply) the yes/no decider for replacement.
Certainly you could gather data from charge/discharge
voltage and current during same and idle time and write
code to do the analysis.
When would the analysis be "safe"? I dunno. After enough
total cycles of replacing batteries you could arrive at a
better figure than something like "replace after 500
charge/discharge cycles whether it needs it or not", or
"replace every 5 years whether it needs it or not", etc.
But that's using much more than fixed time and temperature
and voltage data to arrive at whatever you have in mind by
"safe".
Ed
On 14/12/2024 4:23 am, john larkin wrote:
On Thu, 12 Dec 2024 23:57:54 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly,
additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
I've wondered about electro-chemical time lags, ions drifting around
in liquids, as in what would the Spice model of some battery be?
That's what Warburg impedances are about.
And
on a slower time scale, the morphology of a battery changes with time.
Nearly discharged batteries sure go Hi-Z.
What we need here is a good physical chemistry guy.
I've got a Ph.D. in physical chemistry, but batteries are
electrochemistry - I know a guy who has just completed a Ph.D. with a
thesis on a particular lithium ion battery chemistry. It's a specialised subject.
On 12/13/2024 8:57 PM, Bill Sloman wrote:
On 14/12/2024 4:23 am, john larkin wrote:
On Thu, 12 Dec 2024 23:57:54 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
At a fixed time and temperature, is it safe to model a battery as a
fixed voltage source behind a series resistance? Possibly,
additionally,
a parallel RC to cover transients?
In particular, does the model need to change based on whether the
battery is being charged or discharged? (i.e., to estimate that
series resistance)
I've wondered about electro-chemical time lags, ions drifting around
in liquids, as in what would the Spice model of some battery be?
That's what Warburg impedances are about.
And
on a slower time scale, the morphology of a battery changes with time.
Nearly discharged batteries sure go Hi-Z.
What we need here is a good physical chemistry guy.
I've got a Ph.D. in physical chemistry, but batteries are
electrochemistry - I know a guy who has just completed a Ph.D. with a
thesis on a particular lithium ion battery chemistry. It's a
specialised subject.
I guess not many universities offer a Ph.D. in non-physical chemistry
these days. :(
I guess not many universities offer a Ph.D. in non-physical chemistry
these days. :(
The choices in my day at Melbourne University in Australia were Organic Chemistry, Inorganic Chemistry and Physical Chemistry. Win Hill started
a Ph.D. in Chemical Physics at MIT at much the same time. It's more a theological distinction than anything with any real world significance,
but John Larkin never paid much attention to his undergraduate chemistry lectures. I completed a master's degree in Inorganic Chemistry on the
way to getting my Ph.D.
The clever thing to have done at the time would have been physical
organic chemistry, and the Melbourne professor of Physical Organic
Chemistry moved to America while I was getting my Ph.D, and took a
couple of his graduate students with him.
On 12/17/2024 6:22 AM, Bill Sloman wrote:
I guess not many universities offer a Ph.D. in non-physical chemistry
these days. :(
The choices in my day at Melbourne University in Australia were Organic
Chemistry, Inorganic Chemistry and Physical Chemistry. Win Hill started
a Ph.D. in Chemical Physics at MIT at much the same time. It's more a
theological distinction than anything with any real world significance,
but John Larkin never paid much attention to his undergraduate chemistry
lectures. I completed a master's degree in Inorganic Chemistry on the
way to getting my Ph.D.
The clever thing to have done at the time would have been physical
organic chemistry, and the Melbourne professor of Physical Organic
Chemistry moved to America while I was getting my Ph.D, and took a
couple of his graduate students with him.
I've been thinking about doing a mid-life master's degree, though some
of my buddies in comp sci tell me there's not much point to a "terminal >master's degree" these days and should just go for a PhD if one's going
to bother putting the money down. Biomedical engineering is my interest
at this time. I hear there are some great programs at Canadian schools,
never been a better time to see the world I think...
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