connecting batteries in parallel or series, myth and theory

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Aug 14, 5:21 pm, [email protected] wrote:
|> In alt.engineering.electrical [email protected] wrote:
|>
|> | On Aug 14, 2:52 am, [email protected] wrote:
|> |> In alt.engineering.electrical [email protected] wrote:
|> |>
|> |> | Batteries are the very heart of your system. That should tell you
|> |> | something about the choice of battery/ cell used. You sound like a guy
|> |> | looking for an excuse to use golf cart batteries.
|> |>
|> |> You sound like a guy wanting to tell everyone to do things exactly the
|> |> same way you do things, without being willing to tell them why, whether
|> |> you actually know why or not.
|> |
|> | I have told you why, parallel strings do not charge/discharge in a
|> | uniform manner. That is the truth.
|>
|> I'm not doubting the truth of this. I'm wanting to understand the means
|> by which this happens, and the degree to which it happens. I want to
|> understand this enough to know how well it may be mitigated. For example
|> the non-uniform charging may be dealt with by smaller chargers isolated
|> on each string (not one big charger trying charge the strings in parallel).
|
| It happens because every cell has a different internal resistance. You
| may see nothing wrong with spending the rest of your life trying to
| get several strings of batteries to a balanced state of charge but
| most peopls have lives beyong the battery room

This argument can also be applied to limit the number of cells in series, too.
Are you limiting your thinking about charging to one which only involves one
single charger system and charging all batteries together?


| Starting small and adding to a system is another false economy.

And you suggestion is to start out as big as you will ever need all at once
at the start, even though you don't need anywhere near that capacity now,
and may not for years?


|> I want to explore means to manage the load balancing before deciding.
|> Maybe it will be the case that those methods are not worthwhile. I
|> cannot say today. Today is the learning time. The decision is later.
|> The conditions will be known then.
|
| Start with your energy audit. Size a system to suit and play what if
| on paper for a while.

This does little good until _after_ one has all the scientific information
about batteries.


|> No. I want to know all the reasons for all the choices.
|
| Until you know what goes into system design you will fail to
| understand the relationship of the parts.

Until you are offering this level of information, what good is your advise?


|> What happens if you have ONE string of several very large cells/batteries
|> and one dies? Are you saying you don't have to replace the whole bank in
|> this case?
|
| That is absolutely right, one dead cell in a bank of batteries more
| than a year old, you replace the lot.
|
| Parallel strings are more prone to cell failure due to unequal
| charging.

But _you_ don't really know why that happens, and as a result of that, _you_
are not able to envision ways around it. But the important thing is, _you_
can't offer real scientific information because you simply don't have it.
All you have is specific "do what I (would) do" advice, and nothing more.


|> That is a work in progress. Much of it will be done when I start going
|> with some battery power. More will be done later. This is not a one big
|> step all the way project.
|
| You will find that is incorrect. You size a system to your need and
| build it.

Such an idealist. Maybe you should work in the _commercial_ UPS market or
something.


|> Quite a lot of it is unsupported "what to do" advice.
|
| Yep. that's often the case. You might try Swinbourne University and
| see if they will sell you the notes and work book for the
| "Introduction to Renewable Energy" course.

Is that a course on the science of how batteries work, or just a technician class
on how to install batteries using common "still thinking in the box" approaches?


|> Rectifiers are made of diodes (or other things).
|
| Yes that's right. They are used to change AC to DC.

That's not the only thing they can do. Do not assume that because there is more
need for one thing (converting AC to DC) that no other need (isolating DC directions)
is valid to consider.


|> |> |> I'm exploring all options. I'm not interested in specific advice on what
|> |> |> I should do (at least not without well explained why) ... I'm interested in
|> |> |> the information to make the best decision in the circumstances that will be
|> |> |> present at the time the decision is to be made.
|> |> |
|> |> | You still sound like a guy looking for an excuse to use golf cart
|> |> | batteries.
|> |>
|> |> I am someone looking for the technical information that would be a valid basis
|> |> for deciding what circumstances that golf cart batteries can be used in, and
|> |> what circumstances they cannot be used in, where "circumstances" involves a lot
|> |> of things that I don't even know, yet.
|> |
|> | You can use golf cart batteries, they can be wired in series, parallel
|> | and series/parallel in as many strings as you feel are required. Most
|> | people only ever do this once. Their second battery bank is usually a
|> | single string of cells with the correct Ah rating.
|>
|> And maybe I will migrate to that. One possible path is that I would start with
|> a small bank and migrate to a larger bank. I may parallel things in the interim.
|> I will also be looking at possible circuits to manage the load balancing between
|> parallel strings. Maybe that won't be practical. I'm sure you'll say it won't
|> but I want to know why, if that's the case.
|
| The reason why is that all cells have different internal resistance,
| so they all charge/discharge at different rates. As a battery a single
| series string has the aggregate of all the cells resistances and is
| basically balanced. Parallel strings must be constantly monitored to
| keep them in a balanced state of charge.

If the resistances in _series_ are different, that can result in an imbalance
as well. It's just more easily hidden becuase the single string still has a
behaviour like a single string. It charges up at whatever rate it can and it
discharges at whatever rate is demanded up to what it can. All this while one
cell is forced to go along until it dies. But you won't see it coming unless
you are monitoring each cell separately by some other means. And then you are
into the same amount of work to manage the system, anyway.


| And when it comes to using a hydrometer, a single string is a lot
| nicer to do than a number parallel strings.

For a moment there, I thought you might say that BIG MONSTER CELLS are easier
to measure than dozens of little batteries because the latter means taking a
measurement dozens of more times.


|> If it is the case that cost is why I would replace one cell/battery at a
|> time, then cost would clearly prohibit the monster cells.
|
| A single series string of the correct Ah rating will, with proper
| care, out last parallel strings. Good quality batteries will have a
| longer warranty that cheaper batteries.

But your advice is to not have any strings of batteries at all until such time
as one can have the biggest baadest string bought all at once. No economic
planning involved.


|> Apparently we have a different understand of this term. I don't know
|> what yours is, then. So it's pointless to proceed on this.
|
| Days of autonomy is how long your batteries will supply your daily
| load with no input.

I can't tell you what the future might hold in terms of the longest period
that might be when dealing with solar and wind sources. But I guess you are
the one with the crystal ball.



|> | Oh, I know what it is you want to know alright. But to understand you
|> | need to listen.
|> | You want some one to tell you what you want to hear.
|>
|> You want some one to do what you tell them to.
|
| No, I have given you information. What you decide is your choice.

You have not giving me the information I seek. All you have given is advice
of what you think I should do, and simplistic reasoning (like "parallel will
charge unevenly" without considering mitigating methods).


|> I can see I'm not going to get anything useful from you.
|
| You got an awful lot if you listened. You are fishing for an answer
| that fulfills your idea of solar power. Reality may be different.

I don't have the idea, yet. I'm seeking scientific information (NOT The end
results like "batteries will charge unevenly") that explains what is going on
and what methods might exist to deal with it and manage it.


| Learn to size a system, play what if with the numbers, cost your
| sizings. Parallel strings are second best choice for home power
| systems and should be avoided wherever possible.

Learn the reality that size needs change, finances are not all at once, etc.
Lots of that might work in commercial UPS systems for companies that need a
short ride through an outage to maintain "five nines" uptime. My goal does
not include any "five nines" uptime for my home.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

|>So, a basic rule for GC batteries is, if you put them in any system that
|>doesn't have at least 5 days of autonomy, then you are going to kill them.
|
| Baloney. Batteries can be well-maintained and last the maximum with
| zero days autonomy. It's done all the time with grid-connected setups
| that only have storage enough to last through short outages.

What about off-grid setups?


|>That is because the charging , and discharging rates are going to kill them.
|>As for as GC batteries go, it's mainly the charging rates that get them.
|
| Nonsense. The #1 cause of premature failure of home-power batteries is
| chronic undercharging.

Sounds like a design problem.


|>If you keep the charge/discharge rate in line with design specs then they
|>will last for decades.
|
| No. Batteries have a finite life-rating usually stated as a number of
| cycles at a particular discharge level.

Which is only a simplistic view of the usage patterns of batteries.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Aug 14, 5:32 pm, [email protected] wrote:
|> In alt.engineering.electrical [email protected] wrote:
|>
|> | Now you can take that as an insult if you like. But, Golf cart
|> | batteries only last for decades if they are used as door stops. Most
|> | people who are capable of learning only ever buy one set of GC
|> | batteries for their house system. Those that have bought two sets have
|> | a learning disability.
|>
|> The real question is, who knows the science behind why this is so? Maybe you
|> do or maybe you don't. I'm not expecting you to write papers for me. But if
|> your knowledge is limited to hearing people say things like "I had GC batteries
|> and I will never do that again", that isn't ruling out to me that someone just
|> didn't build it right. If you know of the science behind this, please point
|> it out (e.g. PDFs of papers with graphs and charts and basis in physics, etc).
|> Otherwise, its doubtful I'd ever get anything useful from you.
|
| I have never sold GC batteries, but I sure have replaced lots of them
| with single series strings of 2V cells of the correct Ah rating for
| people who thought that they were saving money buying GC batteries. I
| have also swapped out parallel strings of batteries, not just GC
| batteries, for single series cells.

So you are a dealer of very large cells/batteries.


| I can only repeat what I learned getting my accreditation. That was
| many years ago and I am sorry that I no longer have the notes to show
| you.
|
| The science says that parallel strings do not charge and discharge
| equally. Parallel strings should be avoided where ever possible and GC
| batteries belong in a golf cart.

That's not science. Science would tell you why and how that happens.
Further, science would tell you how they behave under various methods
of connecting charging and discharging circuits.

You're taking the training you've been giving regarding certain finite
methods to install battery systems, and calling it "science". Real
science comes from research laboratories and investigative processes
that explore all options and find out why things really happen and how
control methods may or may not work.


| If you want to use them, fine. But in the long run you will say, "That
| bastard was right".
|
| The tests were done at Royal Melbourne Institute of Technology in
| Melbourne. The test was done on a rig of six parallel strings of six
| two volt cells. They tried all the tricks like isolating the strings
| with diodes and fancy interconnecting of cells. The results were
| always much the same. Unbalanced charging across the array.

What kinds of chargers did they use? Did they have separate chargers for
each string?

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Aug 14, 5:27 pm, [email protected] wrote:
|>
|> | [email protected] wrote:
|>
|> |
|> |> You sound like a guy
|> |> looking for an excuse to use golf cart batteries.
|> |
|> | I take that as a personal insult. There is nothing wrong with golf cart
|> | batteries if his storage needs are modest. If the discharge is kept at
|> | some respectable level, they will last decades. Most batteries don't
|> | die, they're murdered.
|> |
|> | Not everyone needing a car needs a limousine.
|>
|> I think he's upset that I haven't ruled out golf cart batteries long before
|> the time to make the decision(s). Who knows, maybe I will rule them out at
|> that time. Or maybe I will find an effective way to manage a dozen strings
|> of them.
|
| Not at all. Many people use GC batteries. Most only once.

Most probably didn't install them, or use them, correctly. Then they come
crying to someone to fix it for them, and since their existing batteries are
dead (or worse), they will take anything that comes along with a promise,
especially if it is a design used for commercial ride-through emergency
systems that have nothing to do with home power.

You sound like a battery salesman.

 

[[email protected]]

|> And yet, somehow, we EVers manage to get thousands of miles out of golf
|> cart
|> batteries, discharging them daily to 50-80% at amp draws up to about 500
|> amps.
|>
|> I had about two years on my last pack when I sold the car. That's 2 years
|> worth of daily driving. You can count the cycles. I had my controller's
|> battery amps programmed to 400 amps max, a limit that I hit fairly often.
|> No
|> significant loss of capacity or range.
|
| Yes, but how fast do you charge them? Amperes over what time period?
| I would say that it isn't close to the rate at which you charge them.
| The key isn't how fast or how much you discharge them, it's how fast you
| charge them.

Charging a battery is similar to electroplating. While they do try to find
ways to speed up electroplating, doing it well is something done slowly.
Slow charging is something I've always done, with a few exceptions in urgent
cases.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

|>So, a basic rule for GC batteries is, if you put them in any system that
|>doesn't have at least 5 days of autonomy, then you are going to kill them.
|
| Baloney. Batteries can be well-maintained and last the maximum with
| zero days autonomy. It's done all the time with grid-connected setups
| that only have storage enough to last through short outages.

What about off-grid setups?

Same difference. Whether it's 1 day or 10, ignore the need to get
batteries fully charged regularly and it won't matter whether they're
5 or 20 year batteries, whether they're wired in series or parallel,
charged fast or slow, etc.

|>That is because the charging , and discharging rates are going to kill them.
|>As for as GC batteries go, it's mainly the charging rates that get them.
|
| Nonsense. The #1 cause of premature failure of home-power batteries is
| chronic undercharging.

Sounds like a design problem.

It can be, but it's more often just life. For example, a setup can be
well designed for say, 2 hours use of TV per day. But if the user buys
a larger model and/or watches it longer then he's likely to have a
problem. The key IMO is a proper battery monitor. That provides the
user with a routine method of knowing his battery's true SOC, which
gives him a chance to adjust habits or hardware if needed. DJ, a solar
dealer who used to post here, once wrote that he wouldn't sell a setup
anymore unless it included a battery monitor. Either the customer
would pay for it or he'd include it free if necessary. I'll add that
I'd question the business sense of any dealer who installs a
whole-house setup without a proper battery monitor. Besides doing the
customer a disservice, he's inviting call-backs that will eat up his
profit margin. In my own experience with strongly encouraging friends
and acquaintances to buy and use battery monitors for their home power
installations, I've yet to have anyone regret their purchase. Most
rave that they should have had one from the beginning, and some blame
their dealer for not including it. The necessary $50 shunts are
installed in the popular Outback power panels, so many owners need add
little more than the meter itself, which only costs about $150.

|>If you keep the charge/discharge rate in line with design specs then they
|>will last for decades.
|
| No. Batteries have a finite life-rating usually stated as a number of
| cycles at a particular discharge level.

Which is only a simplistic view of the usage patterns of batteries.

Batteries are rated to supply a specific number of amp-hrs. The amount
will vary with the number and depth of discharge cycles, and can
certainly be less than spec if subjected to poor maintenance or bad
habits. But it can't be more unless you've discovered something that's
escaped everyone else.

Of course, that's the prevailing wisdom, and this being Usenet, there
are certainly alternative theeries. For example: "A lead acid battery
stores a chemical reaction. Therefor every time you charge/ discharge
the battery you use up some of the chemicals involved. Also the
greater the depth of discharge the more chemical used = fewer cycles.
When the chemical is gone the battery is dead."
http://groups.google.com/group/alt.solar.photovoltaic/msg/3142a005266414bd

According to the learned discussion in that thread, the leading
candidate for the depleted chemical is "orgone". So you could try
adding some of that and perhaps extend your battery's life
indefinitely.

Wayne

 

[[email protected]]

Open mouth, insert foot.

You've been making a habit of it, such as the other day for example
when you wrote that narrow-minded baloney about off-grid AC lighting
being "stupid".

You undercut your own argument with your own statements.
Example.

http://www.cdstandbypower.com/product/battery/vrla/dcs75bt.html

Here is the specs for the C&D 75AH battery.
They recommend a MAXIMUM of C/5

So what? Home power batteries tend to be discharged a fraction of
their capacity per day, and (ideally) recharged at a rate that will
get them fully recharged most days. The charge rates tends to rise
during the morning, and fall in the afternoon or anytime with
concurrent loads. Batteries that are discharged over several days tend
to take days to reach full charge again, and owners who suffer that
scenario frequently, probably wish they had some overcharging to
limit. In the case of grid-connected setups with batteries designed to
be discharged in a shorter time, the charger is programmed to recharge
at the ideal rate.

Any faster than that, then the amount of damage far outweighs any benefit of
reduced charging time.

Nobody has said that exceeding recommended charge rates is good
practice, and you're the only one who's claimed it's necessary. You're
arguing with yourself.

And if you do charge at the C/5 level to the 14.7V.

http://www.mil.ufl.edu/projects/koolio/Koolio/offline_webpages/battery_charger_info.htm

You will have a battery that is only 85% full at the end of the day
(considering that you have a panel just big enough to supply the total load
demand.
If you take 60% out of the battery then you have a 25% SOC battery at the
start of the next charge level. Then recharge it to 85% then to 25% Repeat
infanitem

So you've invented an unlikely scenario to support your case. I'm not
impressed.

It never gets close to 100% charge.

So it sulfates and dies.

That's the first thing you've written that relates to a common problem
with home power batteries.

If you up the panel size so you get C/3 charging, you end up with 75 when
you go into float. And with the added float time you get with the change in
charging level, you won't get much over 87% charge level. So you won't gain
anything by just increasing the size of your solar array.

For EV people, the general consensus is that C/10 is about the fastest you
will want to try to charge your battery system. But slower than C/10 is
preferable because it increases charge efficiency.

On the solar front here is what other people have to say.
http://www.solarquest.com/Schoolhouse/Task.asp?id=1623

"The best overall charging rate for deep cycle lead-acid batteries is the
C/20 rate."

And if you take a C/20 rate, it will give you about 95% full batteries when
you go into float. With if far better than 85%.

So you can step up your final charge level from 85% to 95% by just
increasing the size of your battery bank by 4X, That reduces sulfating from
chronic undercharging, and you reduce the charging stress on each battery at
the same time, so the lifetime improvement is in orders of magnitude. A win
win situation.

So basically you're saying that if you start with a strawman-battery
sized to prove that overcharging is a big issue in home power
applications, and then enlarge that size to about what most people
actually have, the problem goes away. IOW, it only exists in a
tortuous Usenet post.

And when you are not at the house using a bunch of stuff, then it will give
the system time to push it up to close to 100% SOC with a few hours of float
charge every day..

It just makes logical sense to me.

The key to high peak charge level is by reducing total charge current.

That's done automatically by modern multi-stage chargers. They supply
full available current (which is highly unlikely to exceed the
recommended rate in my experience) until bulk voltage is reached,
tapered current as needed to maintain bulk voltage for a set time,
then further reduced current to maintain a lower float voltage. PV is
generally too expensive to size for overcharging, but generators are
sometimes capable of it, so AC chargers are programmable and are
normally set to the proper rate, then shut down after absorption.
Finish charging is optionally delayed until PV is available again in
order to prevent extended generator run times.

Which
reduces battery charging damage

But this "damage" only exists in your strawman scenario. In normal
home power applications, it's *low* charge rates that tend to be
symptomatic of bad design or operation. The closest I've seen to an
overcharging problem is where people who are chronically short on
supply raise their bulk and float voltage settings to limit
throttling. Which isn't too terrible unless there are days when the
batteries are charged early, which wouldn't be often considering the
shortage of supply that prompted the fiddling. My own setup suffers
from that overcharging scenario but for a different reason - I have a
single stage turbine charge controller in parallel with an MX60. The
turbine charging voltage is set a little higher than the MXs bulk
setting, which means that when the batteries are full but the wind is
still blowing and loads are minimal, the batteries are being floated
at above normal bulk voltage. That only happens occasionally and
doesn't tend to last long, so it hasn't been a factor in my battery
life which is 13 years and counting.

and increases total final charge level. As I
said, a win win situation.

<sigh>

Wayne

 

[[email protected]]

Explain to me this... How do you go from sub 50% State Of Charge to 100% SOC
in one solar day?
Explain how that is suppose to work in a real life system.

Why? It's *your* contention that SOC routinely goes from sub 50% to
100% in one day, which makes it *your* job to show some examples of
such systems.

Wayne

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

|>Sounds like a design problem.
|
| It can be, but it's more often just life. For example, a setup can be
| well designed for say, 2 hours use of TV per day. But if the user buys
| a larger model and/or watches it longer then he's likely to have a
| problem. The key IMO is a proper battery monitor. That provides the
| user with a routine method of knowing his battery's true SOC, which
| gives him a chance to adjust habits or hardware if needed. DJ, a solar
| dealer who used to post here, once wrote that he wouldn't sell a setup
| anymore unless it included a battery monitor. Either the customer
| would pay for it or he'd include it free if necessary. I'll add that
| I'd question the business sense of any dealer who installs a
| whole-house setup without a proper battery monitor. Besides doing the
| customer a disservice, he's inviting call-backs that will eat up his
| profit margin. In my own experience with strongly encouraging friends
| and acquaintances to buy and use battery monitors for their home power
| installations, I've yet to have anyone regret their purchase. Most
| rave that they should have had one from the beginning, and some blame
| their dealer for not including it. The necessary $50 shunts are
| installed in the popular Outback power panels, so many owners need add
| little more than the meter itself, which only costs about $150.

Based on the description of there being just one monitor wired in at the
inverter, it would seem this monitor only checks the health of the whole
string, not each individual battery/cell.

Exactly what parameter(s) does this monitor check?


|>| No. Batteries have a finite life-rating usually stated as a number of
|>| cycles at a particular discharge level.
|>
|>Which is only a simplistic view of the usage patterns of batteries.
|
| Batteries are rated to supply a specific number of amp-hrs. The amount
| will vary with the number and depth of discharge cycles, and can
| certainly be less than spec if subjected to poor maintenance or bad
| habits. But it can't be more unless you've discovered something that's
| escaped everyone else.

If the manufacturer rates the battery for its most ideal circumstance, then
sure, you can't get the battery to do better than the rating. And most of
the manufacturers are interested in diverting all sales to their products, so
of course they will rate as high as they can. If there is some independent
source of battery rating information that rates batteries based on how well
they do in real life scenarios, then I'd be more inclined to use those kinds
of ratings, which are likely to be less where the real life scenarios are not
what is ideal for the battery.


| Of course, that's the prevailing wisdom, and this being Usenet, there
| are certainly alternative theeries. For example: "A lead acid battery
| stores a chemical reaction. Therefor every time you charge/ discharge
| the battery you use up some of the chemicals involved. Also the
| greater the depth of discharge the more chemical used = fewer cycles.

A theoretically perfect battery will perfectly reverse the discharged chemical
reactions during the charging cycle. Even if real life gets very close to that
one big issue is that the reaction doesn't reverse in the same way (for example
the lead that redeposits on the plates does not form the plates in the same way
as they were formed in manufacturing). And of course, as soon as any gassing
occurs and the gas bubbles move someone else, that's rather hard to reverse
without some means to move the gas back. The best we can do for loss of water
is to add some pure water back.

 

[[email protected]]

|
| |> On 14 Aug 2008 17:01:28 GMT, [email protected] wrote:
|>
|>>In alt.engineering.electrical [email protected] wrote:
|>>
|>>|>So, a basic rule for GC batteries is, if you put them in any system that
|>>|>doesn't have at least 5 days of autonomy, then you are going to kill
|>>them.
|>>|
|>>| Baloney. Batteries can be well-maintained and last the maximum with
|>>| zero days autonomy. It's done all the time with grid-connected setups
|>>| that only have storage enough to last through short outages.
|>>
|>>What about off-grid setups?
|>
|> Same difference. Whether it's 1 day or 10, ignore the need to get
|> batteries fully charged regularly and it won't matter whether they're
|> 5 or 20 year batteries, whether they're wired in series or parallel,
|> charged fast or slow, etc.
|
| Explain to me this... How do you go from sub 50% State Of Charge to 100% SOC
| in one solar day?

With a very fast charge?


| Explain how that is suppose to work in a real life system.

If I'm aiming to charge at a C/20 rate, I wouldn't expect to get a full charge
back within, say, 6 hours of good sunlight in the winter. So it would seem to
be a good idea to rate the system so that if it takes 4 days to recharge from
an XX level of discharge, you need to rate the system capacity and manage your
usage so you would discharge it to no more than XX level of discharge during
both the unlit times of those 4 days PLUS the number of days between those days
of light (e.g. the cloudy/snowy days). So we need a new ratio: rate of usual
discharge divided by rate of usual charge. And since we want to charge slowly
while also avoiding a deep discharge, the rate of discharge needs to be quite
small, such as C/100. That means a BIG system, possibly larger than practical
to do with a single string of single monster cells.

I wonder where those replaced submarine batteries end up

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

|> So you are a dealer of very large cells/batteries.
|
| No longer. Today the only solar work I do is helping people fix the
| problems caused by poor design.
|>
|> | I can only repeat what I learned getting my accreditation. That was
|> | many years ago and I am sorry that I no longer have the notes to show
|> | you.
|> |
|> | The science says that parallel strings do not charge and discharge
|> | equally. Parallel strings should be avoided where ever possible and GC
|> | batteries belong in a golf cart.
|>
|> That's not science. Science would tell you why and how that happens.
|> Further, science would tell you how they behave under various methods
|> of connecting charging and discharging circuits.
|
| The science is that cells all have different internal resistances.

I guess you don't have an EE degree.

Not that I have one, either. But I respect the knowledge AND understanding
real engineers need to have. The information I seek is what would be
learned in an Electrical Engineering, Power Elective, curriculum (not all
of it, of course ... just the parts I'm interested in right now).


|> You're taking the training you've been giving regarding certain finite
|> methods to install battery systems, and calling it "science". Real
|> science comes from research laboratories and investigative processes
|> that explore all options and find out why things really happen and how
|> control methods may or may not work.
|
| As you wish, but, all the systems I designed using my training have
| worked to spec.

Are you talking about true design, or just mere deployment configuration?

Bob needs twice the capacity as Carl, so you install a system for Bob
that has a string of cells twice as big as those you installed for Carl,
that's NOT "design". That's "configuration". You select a design (one
single string) and you select a capacity based on available models.

Configuration is when you select from existing known designs. Have you
ever installed a system which was wired different than _any_ example you
ever saw before?


|> | If you want to use them, fine. But in the long run you will say, "That
|> | bastard was right".
|> |
|> | The tests were done at Royal Melbourne Institute of Technology in
|> | Melbourne. The test was done on a rig of six parallel strings of six
|> | two volt cells. They tried all the tricks like isolating the strings
|> | with diodes and fancy interconnecting of cells. The results were
|> | always much the same. Unbalanced charging across the array.
|>
|> What kinds of chargers did they use? Did they have separate chargers for
|> each string?
|
| Shit, that was close to twenty years ago. Battery technology has not
| changed much since.

But you didn't want to answer my question. Don't worry, you are under no
obligation to answer it. And, besides, this is Usenet. Most questions go
unanswered, anyway.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Aug 15, 1:21 pm, [email protected] (Floyd L. Davidson) wrote:
|> [email protected] wrote:
|> >> They can do things like ensuring that one bank does not cross change another.
|> >> They can allow separate chargers for each bank.
|>
|> >A diode is not a rectifier.
|>
|> Why is anyone bothering to talk to you?
|>
|> And I'll point out that the above is just the worst
|> example, not the only one.
|>
|> --
|> Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
|> Ukpeagvik (Barrow, Alaska) [email protected]
|
| Gee Floyd, looks like you have been taking lessons from Tweedledum. I
| never said;
|
|> >> They can do things like ensuring that one bank does not cross change another.
|> >> They can allow separate chargers for each bank.

How _not_ saying those 2 things somehow making your other statement more
correct?

Have you even considered how to wire rectifiers in series with each battery
string to ensure the current only flows in one direction with respect to where
that rectifier is connected? Wired one way, the rectifier allows the string
to discharge into a load at the other end of the connection (but it cannot be
charged from that point). Wired the other way, the rectifier allows the string
to be charged from a source at the other end of the connection (but it cannot
discharge into a load at that point).

But your posts do seem to indicate you are limited to only doing things you
have seen done before.

 

[[email protected]]

Why should I?

I can think of one good reason... the knowledge might have prevented
your writing endlessly quackish posts, and readers of yet another
newsgroup from finding out about them. Like the 150A/200A/150 ohm/8.5
ohm rheostat that you use for controlling field current on a 400W
alternator
http://groups.google.com/group/alt.solar.photovoltaic/msg/280d1994dfda27b7.
Or the "300 kOhms" wire that you recommend for a substitute
http://groups.google.com/group/alt.energy.renewable/msg/99bcc1d3c8cfc9f8.
Or the 300mm nichrome wire that's 25 ohms
http://groups.google.com/group/alt.energy.homepower/msg/782f4bb5531ca70d?dmode=source.
Not to mention all the other hilarious quotes at
http://www.citlink.net/~wmbjk/tbfduwisdumb.htm

Wayne

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

|>Sounds like a design problem.
|
| It can be, but it's more often just life. For example, a setup can be
| well designed for say, 2 hours use of TV per day. But if the user buys
| a larger model and/or watches it longer then he's likely to have a
| problem. The key IMO is a proper battery monitor. That provides the
| user with a routine method of knowing his battery's true SOC, which
| gives him a chance to adjust habits or hardware if needed. DJ, a solar
| dealer who used to post here, once wrote that he wouldn't sell a setup
| anymore unless it included a battery monitor. Either the customer
| would pay for it or he'd include it free if necessary. I'll add that
| I'd question the business sense of any dealer who installs a
| whole-house setup without a proper battery monitor. Besides doing the
| customer a disservice, he's inviting call-backs that will eat up his
| profit margin. In my own experience with strongly encouraging friends
| and acquaintances to buy and use battery monitors for their home power
| installations, I've yet to have anyone regret their purchase. Most
| rave that they should have had one from the beginning, and some blame
| their dealer for not including it. The necessary $50 shunts are
| installed in the popular Outback power panels, so many owners need add
| little more than the meter itself, which only costs about $150.

Based on the description of there being just one monitor wired in at the
inverter,

Battery monitor shunts are wired in series at the negative battery
cable so that they count all battery current. For example, in my case
that's routine PV and wind charging, occasional DC backup charging,
rare AC backup charging, routine AC loads from 3 inverters and a tiny
DC load.

it would seem this monitor only checks the health of the whole
string, not each individual battery/cell.

Yes. One still needs to use a hydrometer occasionally to check for the
need to equalize, and to verify that the monitor is synched.

Exactly what parameter(s) does this monitor check?

Monitor features vary, but for a Link 10: Volts, amps, watts. Applies
charge efficiency factor and Peukert to establish Ahrs below full,
also displayed as SOC percentage, along with a 4 segment bar graph
that can be set to display useable storage (usually the top 50%). With
some juggling of breakers etc, the device can be used occasionally to
compute individual sources and loads. The Link10 manual is a useful
read. http://www.xantrex.com/web/id/72/docserve.aspx

|>| No. Batteries have a finite life-rating usually stated as a number of
|>| cycles at a particular discharge level.
|>
|>Which is only a simplistic view of the usage patterns of batteries.
|
| Batteries are rated to supply a specific number of amp-hrs. The amount
| will vary with the number and depth of discharge cycles, and can
| certainly be less than spec if subjected to poor maintenance or bad
| habits. But it can't be more unless you've discovered something that's
| escaped everyone else.

If the manufacturer rates the battery for its most ideal circumstance, then
sure, you can't get the battery to do better than the rating.

Most batteries are rated at multiple discharge levels, one can make
reasonable extrapolations as needed.

And most of
the manufacturers are interested in diverting all sales to their products, so
of course they will rate as high as they can. If there is some independent
source of battery rating information that rates batteries based on how well
they do in real life scenarios, then I'd be more inclined to use those kinds
of ratings, which are likely to be less where the real life scenarios are not
what is ideal for the battery.

You're over-thinking the issue IMO, and you're unlikely to find
independant testing results. But if you don't trust the maker then you
might ask for clarification about exactly what some specs and warranty
terms mean.

| Of course, that's the prevailing wisdom, and this being Usenet, there
| are certainly alternative theeries. For example: "A lead acid battery
| stores a chemical reaction. Therefor every time you charge/ discharge
| the battery you use up some of the chemicals involved. Also the
| greater the depth of discharge the more chemical used = fewer cycles.

A theoretically perfect battery will perfectly reverse the discharged chemical
reactions during the charging cycle. Even if real life gets very close to that
one big issue is that the reaction doesn't reverse in the same way (for example
the lead that redeposits on the plates does not form the plates in the same way
as they were formed in manufacturing). And of course, as soon as any gassing
occurs and the gas bubbles move someone else, that's rather hard to reverse
without some means to move the gas back. The best we can do for loss of water
is to add some pure water back.

Dang, there goes my idea to market orgone to Usenetters.

Wayne

 

[[email protected]]

All right. You stated "Whether it's 1 day or 10(days of autonomy)".

You're quoting out of context. Read it again in full, I was referring
to the need for regular complete charges.

Lets look at one day of autonomy for the winter months. 5 hours sunshine.
You have 19 hours between charging periods.

Says you. My own charging period is 24 hours per day. Perhaps you
meant your hypothetical to be limited to fixed PV without any
supplemental sources.

To have exactly 1 day autonomy
would mean that you have to ride through two dark periods and one cloudy
charging period. Given an average power usage spread (lights at night and
other stuff in the day) that will give you about 44% capacity usage between
charging periods. So each charging day, you are starting from 56% SOC.
(close to my original guess)

Even using your worst tortured example, the user is likely to compare
extending charging time with a supplemental source against enlarging
storage 5X.

So I will refine that question.

How do you get from 56% SOC to 100% SOC in one charging period.

If it can't happen then it does mater if the system has 1 or 10 days of
autonomy.

I do see what you're getting at with these hypotheticals. The thing
is, they're not practical issues for anybody that I've ever heard of.
I for damned sure have never heard anybody say "my charging rate is
too high, I'm going to enlarge my storage to cure it", and I bet
you've never heard that or anything like it either. If you really
believe it's an issue, then I suggest you post some examples of where
folks are asking for help with the problem.

Wayne

 

[[email protected]]

|> Why? It's *your* contention that SOC routinely goes from sub 50% to
|> 100% in one day, which makes it *your* job to show some examples of
|> such systems.
|
| All right. You stated "Whether it's 1 day or 10(days of autonomy)".
|
| Lets look at one day of autonomy for the winter months. 5 hours sunshine.
| You have 19 hours between charging periods. To have exactly 1 day autonomy
| would mean that you have to ride through two dark periods and one cloudy
| charging period. Given an average power usage spread (lights at night and
| other stuff in the day) that will give you about 44% capacity usage between
| charging periods. So each charging day, you are starting from 56% SOC.
| (close to my original guess)
|
| So I will refine that question.
|
| How do you get from 56% SOC to 100% SOC in one charging period.
|
| If it can't happen then it does mater if the system has 1 or 10 days of
| autonomy.

After a few days of no available solar/wind energy, I would expect the SOC
of a battery bank to be lower than usual (if less than a few days of no
available solar/wind energy is usual). And I would expect that when the
energy becomes available, again, it can take at least a few days to get
back to 100% SOC.

So is the issue a matter of how _long_ the bank sits at below 100% SOC, even
if it doesn't go below 50% SOC?

 

[[email protected]]

|> |> That's not science. Science would tell you why and how that happens.
|> |> Further, science would tell you how they behave under various methods
|> |> of connecting charging and discharging circuits.
|> |
|> | The science is that cells all have different internal resistances.
|>
|> I guess you don't have an EE degree.
|>
|> Not that I have one, either. But I respect the knowledge AND
|> understanding
|> real engineers need to have. The information I seek is what would be
|> learned in an Electrical Engineering, Power Elective, curriculum (not all
|> of it, of course ... just the parts I'm interested in right now).
|
| This paper may be what you are looking for.
|
| http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf
|
| Bealiba may have an aneurysm if he reads it though.

I saw that from an earlier reference. Good paper. But I guess we need to
keep it secret to protect the health of other people.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Aug 15, 12:58 pm, [email protected] wrote:
|> In alt.engineering.electrical [email protected] wrote:
|>
|> |> So you are a dealer of very large cells/batteries.
|> |
|> | No longer. Today the only solar work I do is helping people fix the
|> | problems caused by poor design.
|> |>
|> |> | I can only repeat what I learned getting my accreditation. That was
|> |> | many years ago and I am sorry that I no longer have the notes to show
|> |> | you.
|> |> |
|> |> | The science says that parallel strings do not charge and discharge
|> |> | equally. Parallel strings should be avoided where ever possible and GC
|> |> | batteries belong in a golf cart.
|> |>
|> |> That's not science. Science would tell you why and how that happens.
|> |> Further, science would tell you how they behave under various methods
|> |> of connecting charging and discharging circuits.
|> |
|> | The science is that cells all have different internal resistances.
|>
|> I guess you don't have an EE degree.
|
| Why should I?

It would make you recognizable as a _possible_ expert in the field. But
it is the learning process behind the degree (even if you skip out in the
last semester and don't actually get the sheepskin) that matters.


|> Not that I have one, either. But I respect the knowledge AND understanding
|> real engineers need to have. The information I seek is what would be
|> learned in an Electrical Engineering, Power Elective, curriculum (not all
|> of it, of course ... just the parts I'm interested in right now).
|
| Perhaps you should get a degree.

If I had the time to go through all that, I would, actually.


|> |> You're taking the training you've been giving regarding certain finite
|> |> methods to install battery systems, and calling it "science". Real
|> |> science comes from research laboratories and investigative processes
|> |> that explore all options and find out why things really happen and how
|> |> control methods may or may not work.
|> |
|> | As you wish, but, all the systems I designed using my training have
|> | worked to spec.
|>
|> Are you talking about true design, or just mere deployment configuration?
|
| Sorry, it doesn't work that way. Every design is different. There is
| no such thing as one size fits all.

And I suspect not every situation best fits a solitary string, either.
It might look to be the best fit if you limit the parameters to only
certain ones. Engineering does not limit itself that way. Engineering
does not determine what is the technically best design and try to fit
that into every scenario.


|> Bob needs twice the capacity as Carl, so you install a system for Bob
|> that has a string of cells twice as big as those you installed for Carl,
|> that's NOT "design". That's "configuration". You select a design (one
|> single string) and you select a capacity based on available models.
|>
|> Configuration is when you select from existing known designs. Have you
|> ever installed a system which was wired different than _any_ example you
|> ever saw before?
|
| Yes.

So it wasn't just a solitary string of batteries every time? You designed
somthing different than that for at least one customer?


|> |> | If you want to use them, fine. But in the long run you will say, "That
|> |> | bastard was right".
|> |> |
|> |> | The tests were done at Royal Melbourne Institute of Technology in
|> |> | Melbourne. The test was done on a rig of six parallel strings of six
|> |> | two volt cells. They tried all the tricks like isolating the strings
|> |> | with diodes and fancy interconnecting of cells. The results were
|> |> | always much the same. Unbalanced charging across the array.
|> |>
|> |> What kinds of chargers did they use? Did they have separate chargers for
|> |> each string?
|> |
|> | Shit, that was close to twenty years ago. Battery technology has not
|> | changed much since.
|>
|> But you didn't want to answer my question. Don't worry, you are under no
|> obligation to answer it. And, besides, this is Usenet. Most questions go
|> unanswered, anyway.
|
| The answer was quite clear.

I'm not looking for the one way you would do things. Among the things I do
want to know is the "how you would do things" across a wide range of people.
But I'd also like to know _why_ for each, if it is not the case that 100%
would do things exactly the same way. And I have found that it is true that
not everyone would do the same. Some people have explained some science
behind what they do, or referenced papers or articles that explain that.
So far I've not yet seen such a thing from anyone who is adamant that no
battery system should be designed with parallel strings.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:

| Battery monitor shunts are wired in series at the negative battery
| cable so that they count all battery current. For example, in my case
| that's routine PV and wind charging, occasional DC backup charging,
| rare AC backup charging, routine AC loads from 3 inverters and a tiny
| DC load.

Current alone (which, BTW, is a single value for the whole string) is
going to tell you what about the condition of each cell in the string?

You don't measure the voltage anywhere?


|>it would seem this monitor only checks the health of the whole
|>string, not each individual battery/cell.
|
| Yes. One still needs to use a hydrometer occasionally to check for the
| need to equalize, and to verify that the monitor is synched.

I'd like to figure out a means to have the check automated. That might
mean a built-in factory-calibrated hydrometer interfacing to an optical
sensor that can be attached over the window that accesses the hydrometer.

Then if the science tells me that for certain conditions, a different
level of charge or discharge should be applied to that cell, then either
that would be done if the design has the means, or the operator would be
warned if it can't.


|>Exactly what parameter(s) does this monitor check?
|
| Monitor features vary, but for a Link 10: Volts, amps, watts. Applies
| charge efficiency factor and Peukert to establish Ahrs below full,
| also displayed as SOC percentage, along with a 4 segment bar graph
| that can be set to display useable storage (usually the top 50%). With
| some juggling of breakers etc, the device can be used occasionally to
| compute individual sources and loads. The Link10 manual is a useful
| read. http://www.xantrex.com/web/id/72/docserve.aspx

Volts of each cell?


|>|>| No. Batteries have a finite life-rating usually stated as a number of
|>|>| cycles at a particular discharge level.
|>|>
|>|>Which is only a simplistic view of the usage patterns of batteries.
|>|
|>| Batteries are rated to supply a specific number of amp-hrs. The amount
|>| will vary with the number and depth of discharge cycles, and can
|>| certainly be less than spec if subjected to poor maintenance or bad
|>| habits. But it can't be more unless you've discovered something that's
|>| escaped everyone else.
|>
|>If the manufacturer rates the battery for its most ideal circumstance, then
|>sure, you can't get the battery to do better than the rating.
|
| Most batteries are rated at multiple discharge levels, one can make
| reasonable extrapolations as needed.

The biggie 2V Surrette cell (shown in the PDF file) had a lot of them listed.

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:
| On Fri, 15 Aug 2008 06:20:32 -0700 (PDT), [email protected] wrote:
|
|>On Aug 15, 12:58 pm, [email protected] wrote:
|>> In alt.engineering.electrical [email protected] wrote:
|
|>> I guess you don't have an EE degree.
|>
|>Why should I?
|
| I can think of one good reason... the knowledge might have prevented
| your writing endlessly quackish posts, and readers of yet another
| newsgroup from finding out about them. Like the 150A/200A/150 ohm/8.5
| ohm rheostat that you use for controlling field current on a 400W
| alternator
| http://groups.google.com/group/alt.solar.photovoltaic/msg/280d1994dfda27b7.
| Or the "300 kOhms" wire that you recommend for a substitute
| http://groups.google.com/group/alt.energy.renewable/msg/99bcc1d3c8cfc9f8.
| Or the 300mm nichrome wire that's 25 ohms
| http://groups.google.com/group/alt.energy.homepower/msg/782f4bb5531ca70d?dmode=source.
| Not to mention all the other hilarious quotes at
| http://www.citlink.net/~wmbjk/tbfduwisdumb.htm
|
| Wayne

A good laugh, especially that last one. I was wondering why it seemed that
almost everyone else was ignoring him, or at least not responding to him.