12v supply from a 24v system

Ok I've risen to the provocation.

You guys have given Neal the validation he seeks by arguing with him and
you've turned a perfectly innocent query into a battleground. As a result he
has managed a troll into uk.rec.sailing which uptill now commonsence has
denied him.

To answer the original query - and all the attempts to explain electrical
theory

Let's make this simple, a battery resists the flow of electricity through
it. Most things resist the flow of electricity, this resistance is
demonstrated by dissipating some of the energy as light (the light bulb), or
heat (the radiant heater) or work (the electric motor). In humans this
resistance is demonstrated by burning (the electric chair). In a battery
this resistance is demonstrated by a chemical reaction that builds up a
charge on one side of the cell, when the capacity of the battery to sustain
that chemical reaction is satiated then the battery dissipates the energy in
heat. In a circuit the battery absorbs energy and shows a high resistance.
What is more a battery isn't really that efficient a lot of the work put in
is wasted as a by-product of the chemical reaction (heat, hydrogen given off
etc)

Resistance is often regarded as as wrong thing, because of the english
connation of the word resistence as somehow negative, it isn't it merely
means the more resistance the more work that has been achieved.

At the start of battery technology you had the basic lead acid cell powering
your radio, and once a week little johnny would go to the chemist who would
top up the acid and recharge the battery cell. At this stage the cell was a
simple device that held a few volts charge, and anyway we could see it
bubbling nicely so it must be magic.

Then along can applications that needed more of the magical oomph (had a
greater resistance) so some clever people put a whole sucession of these
strange devices together. In each one they connected the positive (oomph
end) with the -ve (oomphless end). They put Exide on the outside and retired
rich because they had created the modern battery. One can assume mistresses
and debauchery at this point.
The positive result is that if you put 2 oomphs together (one after the
other) you got 2 oomphs (bit like doubling up the number of horses) (but if
you put the oomphs side by side you only got one oomph for twice as long -
analogy is a bugger).

The battery isn't a magical concept, the word walmart on the outside hasn't
somehow made it sacred, it's a number of little cells connected together,
each one reacting to what's passed through it. Each little cell contributing
ther own bit bof oomph to the party.

Now say you've 24 oomphs harnessed together (a 24 Volt circuit) and you only
need 12 oomphs to move your wagon train. Well you can split the two in half
and take the 12 oomphs away, but they will become tired compared to the 12
oomphs you've left unharnessed.

If the world was fair the 12 unused oomphs would share energy with 12 used
oomphs, but they can't (at least for more than a moment) because to put the
energy back into the 12 used oomphs they'd need both the energy to drive the
chemical reation (+heat, hydtogen etc) plus the energy to provide the
replacement oomphs. They haven't got that extra energy so they see the 12
depleted oomphs as a wall they can't climb.

Then along you come with the charger (and the charger wont take no for an
answer it's got an 'effing great diesel engine diesel engine behind it) ,
because all these little cells are in sucession, you are pushing the same
amount of charge through each. The 12 depleted cells take the charge (+waste
a lot of it on heat and hydrogen), the 12 full cells waste all of the
charge (heat,hydrogen) because they can't store anymore oomph. Because the
world is unfair the charger has put a lot more oomph into the circuit (to
provide the energy for the heat, the hydrogen given off, the basic chemical
reaction, plus the energy for the charge that is stored) than you ever get
out of the battery.

A battery only has so much electrolyte (the thing that is reacted upon to
provide the oomph), if that electrolyte is wasted in generating hydogen and
heat then it ain't being used to provide electricity (oomph). So the battery
effectively dies sooner.

In an ideal world where a battery was 100% efficient then it wouldn't matter
if you were taking off 12 volts from a 24 volt cell. But in the real world
that does matter ('cos in that ideal where there was no resistance a battery
couldn't exist, try imagining a battery at absolete zero - where there is no
resistance to drive the reaction to store energy).

Batteries are a bit like Tax, you put in lots more than you get back.

OK

So to answer the original question
- yes your radio will work fine
- no because the battery is inefficient the charge will not fully equalise
- depending on how you charge your batteries, how often you use your 12 volt
circuit you might find yourself having to replace your batteries sooner
-In other words it ain't a proper job, it'll work, at sometime it'll give
someone a problem.

Lets now go back to ignoring Neal, like Alice he can live in his own fantasy
land where only the simplest rules of physics apply.

Great anology....i think 'oooph' should become a new lab
standard.
I think CN had one good point...engineers regard batteries as
a two-terminal device with a certain transfer function...chemists
working in the battery industry would see them totally differently.
Norm B

On Tue, 19 Apr 2005 03:39:02 +0100, "Nick Temple-Fry" wrote:

>Ok I've risen to the provocation.
>
>You guys have given Neal the validation he seeks by arguing with him and
>you've turned a perfectly innocent query into a battleground. As a result he
>has managed a troll into uk.rec.sailing which uptill now commonsence has
>denied him.
>
>To answer the original query - and all the attempts to explain electrical
>theory
>
>Let's make this simple, a battery resists the flow of electricity through
>it. Most things resist the flow of electricity, this resistance is
>demonstrated by dissipating some of the energy as light (the light bulb), or
>heat (the radiant heater) or work (the electric motor). In humans this
>resistance is demonstrated by burning (the electric chair). In a battery
>this resistance is demonstrated by a chemical reaction that builds up a
>charge on one side of the cell, when the capacity of the battery to sustain
>that chemical reaction is satiated then the battery dissipates the energy in
>heat. In a circuit the battery absorbs energy and shows a high resistance.
>What is more a battery isn't really that efficient a lot of the work put in
>is wasted as a by-product of the chemical reaction (heat, hydrogen given off
>etc)
>
>Resistance is often regarded as as wrong thing, because of the english
>connation of the word resistence as somehow negative, it isn't it merely
>means the more resistance the more work that has been achieved.
>
>At the start of battery technology you had the basic lead acid cell powering
>your radio, and once a week little johnny would go to the chemist who would
>top up the acid and recharge the battery cell. At this stage the cell was a
>simple device that held a few volts charge, and anyway we could see it
>bubbling nicely so it must be magic.
>
>Then along can applications that needed more of the magical oomph (had a
>greater resistance) so some clever people put a whole sucession of these
>strange devices together. In each one they connected the positive (oomph
>end) with the -ve (oomphless end). They put Exide on the outside and retired
>rich because they had created the modern battery. One can assume mistresses
>and debauchery at this point.
>The positive result is that if you put 2 oomphs together (one after the
>other) you got 2 oomphs (bit like doubling up the number of horses) (but if
>you put the oomphs side by side you only got one oomph for twice as long -
>analogy is a bugger).
>
>The battery isn't a magical concept, the word walmart on the outside hasn't
>somehow made it sacred, it's a number of little cells connected together,
>each one reacting to what's passed through it. Each little cell contributing
>ther own bit bof oomph to the party.
>
>Now say you've 24 oomphs harnessed together (a 24 Volt circuit) and you only
>need 12 oomphs to move your wagon train. Well you can split the two in half
>and take the 12 oomphs away, but they will become tired compared to the 12
>oomphs you've left unharnessed.
>
>If the world was fair the 12 unused oomphs would share energy with 12 used
>oomphs, but they can't (at least for more than a moment) because to put the
>energy back into the 12 used oomphs they'd need both the energy to drive the
>chemical reation (+heat, hydtogen etc) plus the energy to provide the
>replacement oomphs. They haven't got that extra energy so they see the 12
>depleted oomphs as a wall they can't climb.
>
>Then along you come with the charger (and the charger wont take no for an
>answer it's got an 'effing great diesel engine diesel engine behind it) ,
>because all these little cells are in sucession, you are pushing the same
>amount of charge through each. The 12 depleted cells take the charge (+waste
>a lot of it on heat and hydrogen), the 12 full cells waste all of the
>charge (heat,hydrogen) because they can't store anymore oomph. Because the
>world is unfair the charger has put a lot more oomph into the circuit (to
>provide the energy for the heat, the hydrogen given off, the basic chemical
>reaction, plus the energy for the charge that is stored) than you ever get
>out of the battery.
>
>A battery only has so much electrolyte (the thing that is reacted upon to
>provide the oomph), if that electrolyte is wasted in generating hydogen and
>heat then it ain't being used to provide electricity (oomph). So the battery
>effectively dies sooner.
>
>In an ideal world where a battery was 100% efficient then it wouldn't matter
>if you were taking off 12 volts from a 24 volt cell. But in the real world
>that does matter ('cos in that ideal where there was no resistance a battery
>couldn't exist, try imagining a battery at absolete zero - where there is no
>resistance to drive the reaction to store energy).
>
>Batteries are a bit like Tax, you put in lots more than you get back.
>
>OK
>
>So to answer the original question
>- yes your radio will work fine
>- no because the battery is inefficient the charge will not fully equalise
>- depending on how you charge your batteries, how often you use your 12 volt
>circuit you might find yourself having to replace your batteries sooner
>-In other words it ain't a proper job, it'll work, at sometime it'll give
>someone a problem.
>
>Lets now go back to ignoring Neal, like Alice he can live in his own fantasy
>land where only the simplest rules of physics apply.
>