Techie question

[Simon]

I'm no electronics expert, thats where you all come into this.............

If I have a electrical device that runs a 2500 mah battery down in 30 mins
say. If i was to put 4 batteries together and place a resistor inline to
reduce it back to 1.25v. Would the item run for 2 hours or considerably more
than 30 mins anyway? If not how could I do this?

 

[Alexander]

"Pippa Reeves" <send_pdreeves_no_spam@bigpond.net.au> schreef in bericht
newsan.2005.12.12.04.12.45.53629@bigpond.net.au...

On Sun, 11 Dec 2005 11:50:58 +0000, Simon wrote:

I'm no electronics expert, thats where you all come into
this.............

If I have a electrical device that runs a 2500 mah battery down in 30
mins
say. If i was to put 4 batteries together and place a resistor inline to
reduce it back to 1.25v. Would the item run for 2 hours or considerably
more
than 30 mins anyway? If not how could I do this?

If you connect 4 identical batteries, with all their Negative terminals
connected to each other, and all their Positive terminals connected, you
will still have the same voltage, but the ability to pull the same current
from the battery for 4 times the length of time.

The load is shared between all the batteries by connecting them in this
fashion, so effectively you end up with a 1.25 volt, 10,000 mAh battery,
(10 Amp Hour battery).

In real life you will probably find that using 4 batteries in parralell to
increase the capacity will make the device run for more than 4 times the
previous time period, as the load sharing between the batteries will have
the effect of slightly reducing the losses in the battery.




Pip



There will always be some current between the batteries.

To prevent this place a schotky diode in series with each battery

 

[Pippa Reeves]

On Sun, 11 Dec 2005 12:08:48 +0000, Simon wrote:

"Simon" <lw004v6382@blueyonder.co.uk> wrote in message
news:CoUmf.6571$iz3.5938@text.news.blueyonder.co.uk...
I'm no electronics expert, thats where you all come into this.............

If I have a electrical device that runs a 2500 mah battery down in 30 mins
say. If i was to put 4 batteries together and place a resistor inline to
reduce it back to 1.25v. Would the item run for 2 hours or considerably
more
than 30 mins anyway? If not how could I do this?


p.s If that would work, what value resistor would I need to reduce 4.8v to
1.2?

Hi again Simon,

I just thought of a good way of explaining the difference between
parralell connection and series.


Think of 4 water tanks.....

In parralell they are all sitting at the same height, but have their
outlet pipes connected together, as you use water, you are using it
equally from all 4 tanks at once...... but the pressure (voltage) is the
same as if you had only 1 tank. You have the ability to use water at the
same rate as you were from the single tank, only you get to do so for 4
times longer before the supply runs out.



In series, you are stacking the tanks on top of each other, so the top of
the water level is 4 times the height.... giving you a much higher
pressure (voltage)...... Because this voltage is higher than you need you
have to waste pressure to stop the supply from exploding your plumbing
(the electric thing you are running)... so you waste 3/4 of the water to
keep the pressure from being too high.



I hope this makes it a bit clearer.....

Pip

 

[Simon]

"Pippa Reeves" <send_pdreeves_no_spam@bigpond.net.au> wrote in message
newsan.2005.12.12.04.17.04.839887@bigpond.net.au...

On Sun, 11 Dec 2005 12:08:48 +0000, Simon wrote:


"Simon" <lw004v6382@blueyonder.co.uk> wrote in message
news:CoUmf.6571$iz3.5938@text.news.blueyonder.co.uk...
I'm no electronics expert, thats where you all come into
this.............

If I have a electrical device that runs a 2500 mah battery down in 30
mins
say. If i was to put 4 batteries together and place a resistor inline
to
reduce it back to 1.25v. Would the item run for 2 hours or considerably
more
than 30 mins anyway? If not how could I do this?


p.s If that would work, what value resistor would I need to reduce 4.8v
to
1.2?


The value of the resistor would need to be damn low..... but it would be
wasting 3/4 of the power stored in the battery if you connect them in
series. So there would be no benefit in using 4 batteries connected in
series.... in fact it would be a waste of energy, waste of 3 batteries,
and a waste of a very high power, low ohms resistor.

Connect the batteries in parralell as suggested in my other reply. There
would be no dropping resistor required by doing it that way.

Pip
Thats a big help thanks. Your water analogy was very helpful too

 

[Simon]

"Alexander" <electricdummy@hotmail.com> wrote in message
news:dnh57e$mgh$1@news3.zwoll1.ov.home.nl...

"Pippa Reeves" <send_pdreeves_no_spam@bigpond.net.au> schreef in bericht
newsan.2005.12.12.04.12.45.53629@bigpond.net.au...
On Sun, 11 Dec 2005 11:50:58 +0000, Simon wrote:

I'm no electronics expert, thats where you all come into
this.............

If I have a electrical device that runs a 2500 mah battery down in 30
mins
say. If i was to put 4 batteries together and place a resistor inline
to
reduce it back to 1.25v. Would the item run for 2 hours or considerably
more
than 30 mins anyway? If not how could I do this?

If you connect 4 identical batteries, with all their Negative terminals
connected to each other, and all their Positive terminals connected, you
will still have the same voltage, but the ability to pull the same
current
from the battery for 4 times the length of time.

The load is shared between all the batteries by connecting them in this
fashion, so effectively you end up with a 1.25 volt, 10,000 mAh battery,
(10 Amp Hour battery).

In real life you will probably find that using 4 batteries in parralell
to
increase the capacity will make the device run for more than 4 times the
previous time period, as the load sharing between the batteries will
have
the effect of slightly reducing the losses in the battery.




Pip



There will always be some current between the batteries.
To prevent this place a schotky diode in series with each battery

schotky diode? Just looked on www.maplin.co.uk. couldn't find one. There

again I wouldn't really know what I was looking for!

 

[Alexander]

"Simon" <lw004v6382@blueyonder.co.uk> schreef in bericht
news:1%Umf.6611$iz3.1133@text.news.blueyonder.co.uk...

"Alexander" <electricdummy@hotmail.com> wrote in message
news:dnh57e$mgh$1@news3.zwoll1.ov.home.nl...

"Pippa Reeves" <send_pdreeves_no_spam@bigpond.net.au> schreef in bericht
newsan.2005.12.12.04.12.45.53629@bigpond.net.au...
On Sun, 11 Dec 2005 11:50:58 +0000, Simon wrote:

I'm no electronics expert, thats where you all come into
this.............

If I have a electrical device that runs a 2500 mah battery down in 30
mins
say. If i was to put 4 batteries together and place a resistor inline
to
reduce it back to 1.25v. Would the item run for 2 hours or
considerably
more
than 30 mins anyway? If not how could I do this?

If you connect 4 identical batteries, with all their Negative terminals
connected to each other, and all their Positive terminals connected,
you
will still have the same voltage, but the ability to pull the same
current
from the battery for 4 times the length of time.

The load is shared between all the batteries by connecting them in this
fashion, so effectively you end up with a 1.25 volt, 10,000 mAh
battery,
(10 Amp Hour battery).

In real life you will probably find that using 4 batteries in parralell
to
increase the capacity will make the device run for more than 4 times
the
previous time period, as the load sharing between the batteries will
have
the effect of slightly reducing the losses in the battery.




Pip



There will always be some current between the batteries.
To prevent this place a schotky diode in series with each battery

schotky diode? Just looked on www.maplin.co.uk. couldn't find one. There
again I wouldn't really know what I was looking for!

Whoops, try Schottky diode

 

[Jasen Betts]

On 2005-12-11, Simon <lw004v6382@blueyonder.co.uk> wrote:

I'm no electronics expert, thats where you all come into this.............

If I have a electrical device that runs a 2500 mah battery down in 30 mins
say. If i was to put 4 batteries together and place a resistor inline to
reduce it back to 1.25v. Would the item run for 2 hours or considerably more
than 30 mins anyway? If not how could I do this?

connect the cells in parallel
(that is: put the batteres side-by side and connect all the pointy ends
together and all the blunt ends together )

or better get a size-D Cell. - no cancel that 4 AA cells are cheaper.

--

Bye.
Jasen

 

[Simon]

"Jasen Betts" <jasen@free.net.nospam.nz> wrote in message
news:3a3b.439d1b6f.b684e@clunker.homenet...

On 2005-12-11, Simon <lw004v6382@blueyonder.co.uk> wrote:
I'm no electronics expert, thats where you all come into
this.............


Thanks for everyones help

 

[Rich Grise]

On Sun, 11 Dec 2005 11:50:58 +0000, Simon wrote:

I'm no electronics expert, thats where you all come into this.............

If I have a electrical device that runs a 2500 mah battery down in 30 mins
say. If i was to put 4 batteries together and place a resistor inline to
reduce it back to 1.25v. Would the item run for 2 hours or considerably more
than 30 mins anyway? If not how could I do this?

No, you've got it wrong. You wire the batteries in parallel. This will
increase the mAH capacity times the number of batteries, i.e., your
device will run for two hours. There is no resistor involved.

And putting batteries in series will smoke your equipment.

Remember, parallel = equal voltage.

Good Luck!
Rich