• Battery (SLA) modeling

    From Don Y@21:1/5 to All on Thu Dec 12 23:57:54 2024
    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)

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  • From Martin Brown@21:1/5 to Don Y on Fri Dec 13 10:59:33 2024
    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.

    --
    Martin Brown

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  • From Bill Sloman@21:1/5 to Don Y on Fri Dec 13 22:17:03 2024
    On 13/12/2024 5:57 pm, 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?

    The current carrying elements in a battery are ions moving through a
    soluvent, and they do look capacitative, but they are Warburg impedances
    and the capacitance varies with frequency.

    https://pubs.rsc.org/en/content/articlehtml/2024/cp/d4cp00975d

    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).

    Probably not that much if the battery isn't getting close to full charge
    or total discharge.

    Fully charged nickel cadmium batteries generate molecular oxygen at one electrode which diffuses back to the other electrode and oxidises metal
    there (which is why you can trickle charge Ni/Cd cells for ever if you
    keep the trickle charge current low enough). That might mess up the
    impedances a bit.

    --
    Bill Sloman, Sydney

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  • From Don Y@21:1/5 to Martin Brown on Fri Dec 13 06:31:27 2024
    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.

    I.e., I suspect having to "wait" a bit (hence the RC in my proposed model)
    as I alter observation conditions -- but don't want to have to let the battery come to some particular state before adjusting my assessment of it's SoC.

    I want to use them to bridge brief "brownouts" for a ~3KW load (supplemented with ~500W from the mains)

    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.

    The value they have (for a large energy store) is they are not as likely
    to be seen as "dangerous" (e.g., lithium) by customers. And, are
    available cheaply and locally -- as well as legally disposable without
    special measures.

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  • From Don Y@21:1/5 to John R Walliker on Fri Dec 13 07:05:36 2024
    On 12/13/2024 6:39 AM, John R Walliker wrote:
    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.

    <frown> That was what I feared.

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  • From Liz Tuddenham@21:1/5 to Don Y on Fri Dec 13 15:54:44 2024
    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.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

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  • From Martin Brown@21:1/5 to Liz Tuddenham on Fri Dec 13 16:43:15 2024
    On 13/12/2024 15:54, Liz Tuddenham wrote:
    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!")

    I've seen kit intended to be powered by lead acid accumulators that has
    three diodes in series with the supply for when the battery is fresh off
    the charger and nearer to 14v than 12 with a switch to short them out
    when the battery starts to get low. It avoid the annoyance you had.

    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 think most regular users of SLA's are aware of their weaknesses.

    I love the way they swell up spectacularly inside certain brands of UPS
    making them almost impossible to remove. Cruel environment for any SLA.

    --
    Martin Brown

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  • From Don Y@21:1/5 to Liz Tuddenham on Fri Dec 13 10:05:38 2024
    On 12/13/2024 8:54 AM, Liz Tuddenham wrote:
    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!")

    I'm primarily looking at ways to determine SoC while charging and/or
    powering loads. In the first case, to guard against overcharging.
    In the second, to guard against too deep of discharge.

    In the second case, I obviously can't "disconnect" the battery to take
    a peek at the open circuit voltage (which could be an option in the
    first case).

    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.

    The batteries are just acting like "super caps". I am more concerned
    that they can manage a particular load (for a predictable time -- even
    if that time is determined on-the-fly) than how LONG they can supply power.

    SLAs are preferable because of cost, reputation (lack of association
    with spectacular fires), availability of replacements (want more
    capacity? buy larger replacement batteries!) and ease of disposal
    (you can drop them off at many businesses to be recycled -- hazardous
    waste -- and even select "recycling facilities" if you want to
    recover some of their monetary value)

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  • From Don Y@21:1/5 to Martin Brown on Fri Dec 13 10:10:53 2024
    On 12/13/2024 9:43 AM, Martin Brown wrote:
    I love the way they swell up spectacularly inside certain brands of UPS making
    them almost impossible to remove. Cruel environment for any SLA.

    I'm of two minds on that.

    One, you can argue that you want the battery to be returned to a full
    SoC as quickly as possible as a second "outage" could follow a
    previous one and the UPS would then fail to provide much carryover time.

    Two, the UPS vendors want to sell more batteries!

    OTOH, UPSs seem to be treated as consumables; folks seem to just
    discard the whole unit when the battery needs replacing (because they
    likely contact the vendor for the replacement battery and cringe
    at the price!).

    "Hell, we haven't really NEEDED it much for the past few years...
    why don't we just try living without it?"

    I wonder what the replacement interval is for the flooded cells they
    use (used?) in emergency lighting? (modern versions seem to have
    taken a different -- replaceable? -- route)

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  • From john larkin@21:1/5 to blockedofcourse@foo.invalid on Fri Dec 13 09:23:26 2024
    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.

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  • From ehsjr@21:1/5 to Don Y on Fri Dec 13 18:20:22 2024
    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.

    Ed

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  • From piglet@21:1/5 to john larkin on Fri Dec 13 23:15:35 2024
    john larkin <JL@gct.com> 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? 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.



    Yes I have noticed SLA can exhibit an initial voltage sag far longer than
    can be explained just by internal resistance- I assumed some kind of
    stagnant electrolyte layering effect?


    --
    piglet

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  • From Don Y@21:1/5 to ehsjr on Fri Dec 13 17:06:40 2024
    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)

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  • From Bill Sloman@21:1/5 to john larkin on Sat Dec 14 12:57:04 2024
    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.

    --
    Bill Sloman, Sydney

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  • From Don Y@21:1/5 to Don Y on Sat Dec 14 02:14:53 2024
    On 12/12/2024 11:57 PM, 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)

    I've found papers proposing models that do, and don't. Wunnerful.

    If I can access their raw data, maybe I can evaluate the benefits
    (or not) of each approach.

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  • From Martin Brown@21:1/5 to john larkin on Sat Dec 14 17:23:02 2024
    On 13/12/2024 17:23, 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? 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.

    You can usually model them (voltage across real chemical battery
    systems) adequately with 2 or 3 different exponential decay time
    constants and amplitudes if you must.

    The first is for transient behaviour ions already close to electrodes,
    the next for reactions already in progress in bulk and the very slowest
    for diffusion limited chemistry as the thing equilibrates into its new
    state. The latter can be quite long but usually only a small correction.

    --
    Martin Brown

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  • From ehsjr@21:1/5 to Don Y on Mon Dec 16 15:16:22 2024
    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

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  • From Don Y@21:1/5 to ehsjr on Mon Dec 16 16:20:43 2024
    On 12/16/2024 1:16 PM, ehsjr wrote:
    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.

    Isn't that what I said? Knowing the shape of the curve and points
    on it doesn't help me unless I can map my battery's current
    state (SoC and age) to that.

    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.

    There are two (three?) issues here, each addressable (?)
    with an appropriate model.

    The first is to be able to ascertain the SoC of the battery
    to determine how much charge it needs to accept to be returned
    to "full" charge and the best way of delivering that charge
    to meet a given timeframe, etc.

    The second is to be able to ascertain the SoC of the battery
    to determine how much longer it can support the *current*
    load and how that load may want to NOW be shaped to meet a
    given support time.

    The third is to be able to notice how the model has changed,
    over time, to reflect aging in the battery. Determining
    when/if replacement is necessary will depend on the SoH
    of the battery as well as its load and charging history;
    a battery *might* appear to be "shit" yet can still be
    suitable for certain smaller loads or shorter support
    intervals.

    When would the analysis be "safe"?  I dunno. After enough

    I'm not concerned with the "safety" of the analysis but,
    rather, the safety of the *model* -- the two are distinctly
    different. I.e., one can have a perfect model and use it
    poorly.

    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.

    It will never be that cut and dry. Rather, it will be
    "YOUR usage patterns suggest the battery should be replaced
    soon. Failure to do so can result in loss".

    Or,

    "Based on your usage patterns, you might consider changing the
    battery to something larger (or smaller)"

    [No reason to force people to buy more than THEY need]

    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

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  • From bitrex@21:1/5 to Bill Sloman on Tue Dec 17 00:25:21 2024
    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 PhD in non-physical chemistry
    these days. :(

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to bitrex on Tue Dec 17 22:22:57 2024
    On 17/12/2024 4:25 pm, bitrex wrote:
    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. :(

    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.

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From bitrex@21:1/5 to Bill Sloman on Wed Dec 18 11:56:50 2024
    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...

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to bitrex on Wed Dec 18 13:58:55 2024
    On Wed, 18 Dec 2024 11:56:50 -0500, bitrex <user@example.net> wrote:

    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...

    I don't know about Biomedical Engineering, but in Biology, the working
    level is PhD; anything less is a technician.

    I'd troll through listings of available positions and see what the
    require, or at least desire.

    Joe Gwinn

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)