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Learning the difference - Page 12

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Posted by Todd on June 18, 2007, 1:43 am
 



Identical batteries will never happen either. My batteries were
identical when I bought them. Discharging one and leaving a second
fully charged makes them non-identical.


Wrong. It "always" happens.


Well duh!


Well duh!


Perhaps ... but while they're charging, the voltage across each
battery will be different. You can't just put 3 12-V batteries in
series and put 39V across the them and expect 13V across each battery.
One will leave the pack and get over 15V across it. You must then
lower the total voltage or you'll ruin that battery as you bring the
other two up to charge.


Putting 2 12 volt batteries in series makes two batteries. There's a
voltage across each (nominally but not exactly 12V) and there's a
voltage across the pair (nominally and maybe exactly 24V. One could be
11.8V and the other 12.2 and there's nothing to force them to become
the same. This is exactly why you have to equalize the 6 cells in a
single 12V battery ... because over time and because the cells are in
series, some cells have a higher voltage than others. Equalizing
brings them all up to the same voltage.).

Putting 2 12 volt batteries in parallel makes two batteries. The only
way you can consider them one battery is to put their cells and
electrolyte together (and of course you don't do that). Putting 2 12V
batteries in parallel forces both batteries to be at the same
potential (nominally 12V). You then have 2 strings of 6 2V batteries
where the strings are in parallel.



Posted by George Ghio on June 17, 2007, 12:23 am
 


Todd wrote:

find a set of batteries

batteries to a series string

six 12V - 100Ah batteries in series will be 100Ah at 12V

twelve 12V - 100Ah batteries in series will be 100Ah at 24V

not be available so the

and double your battery

More care is required to maintain correct charge in parallel sets of batteries
  It is a geometric progression

2 Parallel strings - twice the maint.

3 parallel strings _ four times the maint.

Several hours later they should all read the same (well as near as) if they
don't then you have a
problem. Look at your connections to start with.

Many charge controllers have come and gone. The best charge controller is
between your ears.
Unfortunately the user manual was lost in the mail.

system. Funny thing, he

was doing with his

ones that exploded in use.

If you remember, eh did not say what he was doing with his batteries.

It would depend on the application.

reality these loads

Cost and efficiency. What you want and what's true are not the same thing.

If it was cost effective for the job then it is practical.

capacity. Changing the

and adding batteries to

No you still have only 70Ah capacity.

do know of a system, 23

undercharged. The owner is saving

learn the difference

Equalizing batteries is part and parcel with owning and using them, A good reg
will do the job on a
regular basis.

the bank for the new

question is a nonsense as far

would be used. The charging

be replaced as often

off on the taxes anyway.

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Posted by Todd on June 18, 2007, 2:06 am
 


find a set of batteries

batteries to a series string

So far so good, George.


not be available so the

and double your battery

I asked what was the nature of the maintenance. If more care is
required, what is that care doing?


Doing what?


Doing what? And why is it climbing geometrically.


don't then you have a

If that's the case, then why doesn't the voltage across each cell
remain the same when fully charged? Why do I have to go through a
monthly equilization exercise if not to coax each cell back to being
the same?


between your ears.

If you're going to be insulting, you shouldn't be stupid at the same
time George.


system. Funny thing, he

he was doing with his

ones that exploded in use.

I didn't ask what he was doing with his batteries. I asked what he was
using to charge them. I then asked what he was using to tap that
charge (i.e. to invert from DC to AC). If you're going to be glib
George, at least pay attention.


Oh really? Name an application where you have a new custom inverter
built to suit as the demands change.


In reality these loads

George. You completely evade my question. I asked "what's the
principle behind that rule of thumb". And your answer just hangs out
in air. It neither addresses my question nor my statement. What are
you doing George?


And if it's not, you don't. And if it never is cost effective you
don't. Name a case where it's cost effective.


capacity. Changing the

and adding batteries to

That's current capacity. But real battery capacity (or bank capacity)
is it's ability to store and deliver energy (power). And that power is
volts x current or watts. It stores charge. When that charge moves
over time it's called current. And when that move is caused by a
voltage differential it's called power. And battery capacity is both a
function of the charge it can deliver and voltage under which it
delivers it. Are you really this stupid George?


I do know of a system, 23

undercharged. The owner is saving

to learn the difference

will do the job on a

But equalization is complicated with a series string. You must assure
that no cell in the string gets too much voltage while the other cells
catch up. With batteries in parallel you never have more than 6 cells
in a string. With batteries in series (say 4 12V batteries), you now
have 24 cells in the string. It's more likely that some cells can be
overvoltaged when charging batteries in series than when charging them
in parallel.



Posted by George Ghio on June 18, 2007, 1:20 pm
 

Todd wrote:

find a set of batteries

batteries to a series string

not be available so the

and double your battery

Largely checking connections and charge levels with a hydrometer.

See above

See above

It is a dirty, tedious, job. Try it some time with a large series/parallel
battery bank

don't then you have a

Because every battery is an individual. A good charge regulator will do the job
just fine with a
single series string of batteries and well enough for two parallel strings with
a proper maintenance
  program.

More parallel strings and you get more variation requiring longer equalization.

between your ears.

Neither insulting nor stupid, everyone got a brain and no one got a manual. You
either learn to use
the tool or not, as the case may be.

I monitor my system all the time and make adjustments to the reg for summer and
winter.

system. Funny thing, he

he was doing with his

ones that exploded in use.

And I said he did not offer further information, at least pay attention.

Oh really! Most people in the position of needing such a service will not follow
the tried and true
wankery followed by those who feel that a system should be sized to the bare
minimum as determined
by measuring loads at what they think they will run the load at.



In reality these loads

Cost and efficiency. How many times do you have to be told something?

Large grid feed. 240VDC in 240VAC out.

capacity. Changing the

and adding batteries to

No but you seem to be.

Battery capacity is measured in Amp Hours. Sorry but that is the way it is.

If you need 1000Ah of batteries at twelve volts then you would use 500Ah of
batteries at 24 volts.
Your watts stay the same, and the actual capacity in hours of use is the same.

You see, this is the reason for using a higher voltage battery bank. It's called
system sizing and
determines the capacity of the battery required. It is usually worked out on
days of autonomy.


I do know of a system, 23

undercharged. The owner is saving

to learn the difference

reg will do the job on a

Oh yeah, real complicated. It happens every month, automatically.

It would appear that you really are stupid. Your last statement is as worthless
as the rest of your
post.


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Posted by merlin-7 on June 18, 2007, 10:59 pm
 


 Ok now I am confused with this one....

 A 12 volt battery is 6 2.2volt cells (depending on battery type, it may
vary a bit)

 I do not think it matters if their equilized in a string or in parallel, it
would stand to reason that the results would be the same. Besides, you are
over chargeing the battery bank during equilization anyway. Thats how you
bring up a weak cell in a battery bank, unless you have all 2 volt cells and
can charge each one, by itself when needed.

 Correct me if I am wrong here...



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