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  #42   Report Post  
Gould 0738
 
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This is the point I was trying to politely make to Gould. If you listen to
his story half the newbie boaters will be filing into West Marine to buy new
batteries when the ones they have are likely to be perfectly fine.

Eisboch


Your point is accurate, merely incomplete and also misleading if considered
without
taking important variables into account.

If that "newbie" owns a battery that cannot be charged to a point above 12.6
volts on a functional charger he darn well just might be in need of a new one.

Do most boaters disconnect the battery from the boat, and set it on the dock
overnight, before evaluating the state of battery charge? If we are going to
discuss
testing a battery and the results that should be expected, it makes sense to
frame that discussion around actual boating conditions.

What happens when the "surface charge"
bleeds off a battery that can only absorb 1.1 volts per cell? Probably drops
down close to 12 volts in fairly short order- a marginal level that all of us
will agree is getting rather weak.

There's also a difference in the voltage one can expect if checking the
batteries on a trailer boat sitting in the backyard under a tarp vs a boat that
is connected to shorepower. But in either case, at the moment when the battery
has absorbed a full and healthy charge or recharge it will
read 2.2 volts per cell. I don't disagree with a statement that later on it may
read less.

  #43   Report Post  
Eisboch
 
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"Gould 0738" wrote in message
...


But in either case, at the moment when the battery
has absorbed a full and healthy charge or recharge it will
read 2.2 volts per cell. I don't disagree with a statement that later on

it may
read less.


Awesome! We agree.

Thanks

Eisboch

  #44   Report Post  
Rod McInnis
 
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"Gould 0738" wrote in message
...

Do most boaters disconnect the battery from the boat, and set it on the

dock
overnight, before evaluating the state of battery charge?


If you want to establish state of charge based on voltage alone then that is
what you should do. It doesn't have to be overnight, but an hour would be a
good idea.

If the battery is not at rest then you have to consider the current along
with the voltage, which makes things a lot harder. A battery at rest will
NOT be at 13.2 volts. A battery charger will "float" a battery at around
13.2 volts, and IF the battery is fully charged there will be little or no
current flow into the battery. If you measure the battery voltage when it
is connected to a charger then you need to verify that the current is near
zero before you can say that the battery is fully charged.

Rod


  #45   Report Post  
Jeff Morris
 
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"Gould 0738" wrote in message
...
This is the point I was trying to politely make to Gould. If you listen to
his story half the newbie boaters will be filing into West Marine to buy new
batteries when the ones they have are likely to be perfectly fine.

Eisboch


Your point is accurate, merely incomplete and also misleading if considered
without
taking important variables into account.

If that "newbie" owns a battery that cannot be charged to a point above 12.6
volts on a functional charger he darn well just might be in need of a new one.


A bad battery or a depleted battery may still read a high voltage when connected
to a charger, and even for a while after being removed. All your reading of
13.2 tells you is that your charger decided to go into float mode. This may be
a strong hint that the battery is fully charged, but it doesn't necessarily mean
that.


Do most boaters disconnect the battery from the boat, and set it on the dock
overnight, before evaluating the state of battery charge?


If you read the information I presented, you would know that a flooded battery
will settle most of the way rather quickly, and that the surface charge can be
removed by applying a load for a few minutes. Every boater should learn these
simple facts, it isn't rocket science.

If we are going to discuss
testing a battery and the results that should be expected, it makes sense to
frame that discussion around actual boating conditions.


What could be more of an "actual condition" than checking the state of charge
when you wake up after a night on the hook? Your scenario seems to be connected
to shore power. Further, if someone is interested in getting a reliable State
of Charge, they should use the methods described by all of the experts. It only
takes a few minutes to remove a surface charge; failure to do so gives a
meaningless answer.



What happens when the "surface charge"
bleeds off a battery that can only absorb 1.1 volts per cell? Probably drops
down close to 12 volts in fairly short order- a marginal level that all of us
will agree is getting rather weak.


I'm not sure what you mean by "absorb 1.1 volts" - batteries absorb Amps, not
Volts. But yes, if a battery is reading 12 Volts with no load, it is probably
either discharged or in poor health.


There's also a difference in the voltage one can expect if checking the
batteries on a trailer boat sitting in the backyard under a tarp vs a boat

that
is connected to shorepower. But in either case, at the moment when the battery
has absorbed a full and healthy charge or recharge it will
read 2.2 volts per cell. I don't disagree with a statement that later on it

may
read less.


This may be true with a given charge protocol, but it is not true in all cases.
Further, the opposite is not true at all: if you get a reading of 13.2 without
having any knowledge of the history, you can't say anything about the charge
state or the general health of the battery. This is the essential point in this
discussion. If a battery is discharged to 80%, and then you put it on a float
charger at 13.2, you won't add much (if anything) to the charge state, but
because of the surface charge you will get a reading of 13.2.

Anyone interested in learning about this should read the links I've provided, or
google on: "surface charge" battery








  #46   Report Post  
Eisboch
 
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"Jeff Morris" wrote in message
...

A bad battery or a depleted battery may still read a high voltage when

connected
to a charger, and even for a while after being removed. All your reading

of
13.2 tells you is that your charger decided to go into float mode. This

may be
a strong hint that the battery is fully charged, but it doesn't

necessarily mean
that.


Exactly. The best way to tell (other than checking specific gravity of the
cells) is to also monitor the charger current delivered to the battery. If
it is at it's float voltage (13.2v - 13.5v) and is still indicating a small
current flow, then the battery voltage - which is a reflection of it's
apparent internal resistance - is less than the float voltage. A difference
of potential must exist in order for current to flow. If the battery charge
potential were the same as the charger float potential, the current meter
would read zero.

With due respect, I think this is where Gould's understanding is flawed.
The battery behaves like a variable resistance as it is charged, much like a
large capacitor. For a given charge voltage delivered by the charger, the
current will vary (decrease) as it is charged).

Not to start this debate all over again, but I think Gould might be
surprised that while his voltage meter is reading the float potential of the
charger, it is almost a certainty that there is still a small amount of
current flow - probably an amp or 2. This can only mean that the battery
has not come up to 13.2 volts.

Eisboch


  #47   Report Post  
Phil
 
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Just to maybe add more fuel to the fire, when I measure the current into the
battery (flooded lead acid) from my fixed voltage (13.3 volts) float
charger, and the float charger has been floating the battery for days on
end, the continuous unchanging current is around 20ma. I guess my battery
is fully charged. The current is not going up or down and the voltage is
not changing. I can then conclude the internal leakage current of the
battery (while on float charge for days) is 20ma.

Also, when I remove the float charger and wait 24 hours for the battery
voltage to settle, it measures around 12.65 - 12.72 volts (depending on
which battery I measure) This is as measured with a DVM.

Have a nice day.....

"Eisboch" wrote in message
. ..

"Jeff Morris" wrote in message
...

A bad battery or a depleted battery may still read a high voltage when

connected
to a charger, and even for a while after being removed. All your

reading
of
13.2 tells you is that your charger decided to go into float mode. This

may be
a strong hint that the battery is fully charged, but it doesn't

necessarily mean
that.


Exactly. The best way to tell (other than checking specific gravity of

the
cells) is to also monitor the charger current delivered to the battery.

If
it is at it's float voltage (13.2v - 13.5v) and is still indicating a

small
current flow, then the battery voltage - which is a reflection of it's
apparent internal resistance - is less than the float voltage. A

difference
of potential must exist in order for current to flow. If the battery

charge
potential were the same as the charger float potential, the current meter
would read zero.

With due respect, I think this is where Gould's understanding is flawed.
The battery behaves like a variable resistance as it is charged, much like

a
large capacitor. For a given charge voltage delivered by the charger, the
current will vary (decrease) as it is charged).

Not to start this debate all over again, but I think Gould might be
surprised that while his voltage meter is reading the float potential of

the
charger, it is almost a certainty that there is still a small amount of
current flow - probably an amp or 2. This can only mean that the battery
has not come up to 13.2 volts.

Eisboch




  #48   Report Post  
Gould 0738
 
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If a battery is discharged to 80%, and then you put it on a float
charger at 13.2, you won't add much (if anything) to the charge state, but
because of the surface charge you will get a reading of 13.2.


If a battery has discharged to 80% and
you put it on a charger that brings it up to
13.2, nothing really happened. OK. Whatever you say. Guess one has to wait for
the battery gods to bless the charger before there's any "real" change in the
voltage.

I should have been buying lotto tickets all these years. With frequent checks
of battery electrolyte level, quarterly checks of specific gravity with a
hydrometer, and periodic terminal cleaning I thought I could trust my
voltmeter. Come to discover that my track record of never being stuck without
battery power is nothing but dumb luck.






  #49   Report Post  
Gould 0738
 
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Default Battery Meter

Just to maybe add more fuel to the fire,


Here's yet another reference stating that
a battery cell has a capacity of 2.2 volts, not the 2.1 being trotted through
the NG by those on the other side of this question:

Illustrations to the text are available at:

http://www.allaboutcircuits.com/vol_1/chpt_11/2.html



Battery construction


All About Circuits Volume I - DC Chapter 11: BATTERIES AND POWER SYSTEMS
Battery construction

--------------------------------------------------------------------------
------

Battery construction
The word battery simply means a group of similar components. In military
vocabulary, a "battery" refers to a cluster of guns. In electricity, a
"battery" is a set of voltaic cells designed to provide greater voltage and/or
current than is possible with one cell alone.

The symbol for a cell is very simple, consisting of one long line and one short
line, parallel to each other, with connecting wires:



The symbol for a battery is nothing more than a couple of cell symbols stacked
in series:



As was stated before, the voltage produced by any particular kind of cell is
determined strictly by the chemistry of that cell type. The size of the cell is
irrelevant to its voltage. To obtain greater voltage than the output of a
single cell, multiple cells must be connected in series. The total voltage of a
battery is the sum of all cell voltages. A typical automotive lead-acid battery
has six cells, for a nominal voltage output of 6 x 2.2 or 13.2 volts:



The cells in an automotive battery are contained within the same hard rubber
housing, connected together with thick, lead bars instead of wires. The
electrodes and electrolyte solutions for each cell are contained in separate,
partitioned sections of the battery case. In large batteries, the electrodes
commonly take the shape of thin metal grids or plates, and are often referred
to as plates instead of electrodes.

For the sake of convenience, battery symbols are usually limited to four lines,
alternating long/short, although the real battery it represents may have many
more cells than that. On occasion, however, you might come across a symbol for
a battery with unusually high voltage, intentionally drawn with extra lines.
The lines, of course, are representative of the individual cell plates:



If the physical size of a cell has no impact on its voltage, then what does it
affect? The answer is resistance, which in turn affects the maximum amount of
current that a cell can provide. Every voltaic cell contains some amount of
internal resistance due to the electrodes and the electrolyte. The larger a
cell is constructed, the greater the electrode contact area with the
electrolyte, and thus the less internal resistance it will have.

Although we generally consider a cell or battery in a circuit to be a perfect
source of voltage (absolutely constant), the current through it dictated solely
by the external resistance of the circuit to which it is attached, this is not
entirely true in real life. Since every cell or battery contains some internal
resistance, that resistance must affect the current in any given circuit:



The real battery shown above within the dotted lines has an internal resistance
of 0.2 O, which affects its ability to supply current to the load resistance of
1 O. The ideal battery on the left has no internal resistance, and so our Ohm's
Law calculations for current (I=E/R) give us a perfect value of 10 amps for
current with the 1 ohm load and 10 volt supply. The real battery, with its
built-in resistance further impeding the flow of electrons, can only supply
8.333 amps to the same resistance load.

The ideal battery, in a short circuit with 0 O resistance, would be able to
supply an infinite amount of current. The real battery, on the other hand, can
only supply 50 amps (10 volts / 0.2 O) to a short circuit of 0 O resistance,
due to its internal resistance. The chemical reaction inside the cell may still
be providing exactly 10 volts, but voltage is dropped across that internal
resistance as electrons flow through the battery, which reduces the amount of
voltage available at the battery terminals to the load.

Since we live in an imperfect world, with imperfect batteries, we need to
understand the implications of factors such as internal resistance. Typically,
batteries are placed in applications where their internal resistance is
negligible compared to that of the circuit load (where their short-circuit
current far exceeds their usual load current), and so the performance is very
close to that of an ideal voltage source.

If we need to construct a battery with lower resistance than what one cell can
provide (for greater current capacity), we will have to connect the cells
together in parallel:



Essentially, what we have done here is determine the Thevenin equivalent of the
five cells in parallel (an equivalent network of one voltage source and one
series resistance). The equivalent network has the same source voltage but a
fraction of the resistance of any individual cell in the original network. The
overall effect of connecting cells in parallel is to decrease the equivalent
internal resistance, just as resistors in parallel diminish in total
resistance. The equivalent internal resistance of this battery of 5 cells is
1/5 that of each individual cell. The overall voltage stays the same: 2.2
volts. If this battery of cells were powering a circuit, the current through
each cell would be 1/5 of the total circuit current, due to the equal split of
current through equal-resistance parallel branches.

REVIEW:
A battery is a cluster of cells connected together for greater voltage and/or
current capacity.
Cells connected together in series (polarities aiding) results in greater total
voltage.
Physical cell size impacts cell resistance, which in turn impacts the ability
for the cell to supply current to a circuit. Generally, the larger the cell,
the less its internal resistance.
Cells connected together in parallel results in less total resistance, and
potentially greater total current.
Back
Forward


  #50   Report Post  
Jeff Morris
 
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Yet another irrelevant link. Why do you keep posting links to high school
physics experiments, rather than acknowledging the information from the leading
manufacturers and experts? The issue is not the voltage from an "ideal" cell
on a lab bench, it's how to measure the State of Charge for a real life battery,
which has a different chemistry.

The bottom line is that the method you're recommending is considered by all the
experts to be flawed.





"Gould 0738" wrote in message
...
Just to maybe add more fuel to the fire,



Here's yet another reference stating that
a battery cell has a capacity of 2.2 volts, not the 2.1 being trotted through
the NG by those on the other side of this question:

Illustrations to the text are available at:

http://www.allaboutcircuits.com/vol_1/chpt_11/2.html



Battery construction


All About Circuits Volume I - DC Chapter 11: BATTERIES AND POWER SYSTEMS
Battery construction

--------------------------------------------------------------------------
------

Battery construction
The word battery simply means a group of similar components. In military
vocabulary, a "battery" refers to a cluster of guns. In electricity, a
"battery" is a set of voltaic cells designed to provide greater voltage and/or
current than is possible with one cell alone.

The symbol for a cell is very simple, consisting of one long line and one

short
line, parallel to each other, with connecting wires:



The symbol for a battery is nothing more than a couple of cell symbols stacked
in series:



As was stated before, the voltage produced by any particular kind of cell is
determined strictly by the chemistry of that cell type. The size of the cell

is
irrelevant to its voltage. To obtain greater voltage than the output of a
single cell, multiple cells must be connected in series. The total voltage of

a
battery is the sum of all cell voltages. A typical automotive lead-acid

battery
has six cells, for a nominal voltage output of 6 x 2.2 or 13.2 volts:



The cells in an automotive battery are contained within the same hard rubber
housing, connected together with thick, lead bars instead of wires. The
electrodes and electrolyte solutions for each cell are contained in separate,
partitioned sections of the battery case. In large batteries, the electrodes
commonly take the shape of thin metal grids or plates, and are often referred
to as plates instead of electrodes.

For the sake of convenience, battery symbols are usually limited to four

lines,
alternating long/short, although the real battery it represents may have many
more cells than that. On occasion, however, you might come across a symbol for
a battery with unusually high voltage, intentionally drawn with extra lines.
The lines, of course, are representative of the individual cell plates:



If the physical size of a cell has no impact on its voltage, then what does it
affect? The answer is resistance, which in turn affects the maximum amount of
current that a cell can provide. Every voltaic cell contains some amount of
internal resistance due to the electrodes and the electrolyte. The larger a
cell is constructed, the greater the electrode contact area with the
electrolyte, and thus the less internal resistance it will have.

Although we generally consider a cell or battery in a circuit to be a perfect
source of voltage (absolutely constant), the current through it dictated

solely
by the external resistance of the circuit to which it is attached, this is not
entirely true in real life. Since every cell or battery contains some internal
resistance, that resistance must affect the current in any given circuit:



The real battery shown above within the dotted lines has an internal

resistance
of 0.2 O, which affects its ability to supply current to the load resistance

of
1 O. The ideal battery on the left has no internal resistance, and so our

Ohm's
Law calculations for current (I=E/R) give us a perfect value of 10 amps for
current with the 1 ohm load and 10 volt supply. The real battery, with its
built-in resistance further impeding the flow of electrons, can only supply
8.333 amps to the same resistance load.

The ideal battery, in a short circuit with 0 O resistance, would be able to
supply an infinite amount of current. The real battery, on the other hand, can
only supply 50 amps (10 volts / 0.2 O) to a short circuit of 0 O resistance,
due to its internal resistance. The chemical reaction inside the cell may

still
be providing exactly 10 volts, but voltage is dropped across that internal
resistance as electrons flow through the battery, which reduces the amount of
voltage available at the battery terminals to the load.

Since we live in an imperfect world, with imperfect batteries, we need to
understand the implications of factors such as internal resistance. Typically,
batteries are placed in applications where their internal resistance is
negligible compared to that of the circuit load (where their short-circuit
current far exceeds their usual load current), and so the performance is very
close to that of an ideal voltage source.

If we need to construct a battery with lower resistance than what one cell can
provide (for greater current capacity), we will have to connect the cells
together in parallel:



Essentially, what we have done here is determine the Thevenin equivalent of

the
five cells in parallel (an equivalent network of one voltage source and one
series resistance). The equivalent network has the same source voltage but a
fraction of the resistance of any individual cell in the original network. The
overall effect of connecting cells in parallel is to decrease the equivalent
internal resistance, just as resistors in parallel diminish in total
resistance. The equivalent internal resistance of this battery of 5 cells is
1/5 that of each individual cell. The overall voltage stays the same: 2.2
volts. If this battery of cells were powering a circuit, the current through
each cell would be 1/5 of the total circuit current, due to the equal split of
current through equal-resistance parallel branches.

REVIEW:
A battery is a cluster of cells connected together for greater voltage and/or
current capacity.
Cells connected together in series (polarities aiding) results in greater

total
voltage.
Physical cell size impacts cell resistance, which in turn impacts the ability
for the cell to supply current to a circuit. Generally, the larger the cell,
the less its internal resistance.
Cells connected together in parallel results in less total resistance, and
potentially greater total current.
Back
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