"Watson A.Name - "Watt Sun, the Dark Remover"" wrote
in message ...

"Tim Martin" wrote in message
...

"Joerg" wrote in message
...

Yes. But it requires that engineers learn to design down to
transistor
level again. With opamps it usually isn't going to work without the
cost
going through the roof.

By the way, while many op-amp circuits published specify a supply
coltage of
+- 15 volts, or +- 9 volts, many circuit designs will work with +- 3
volts,
which is easily achieved with two pairs of AA cells.

Also, many circuits will take more power from one side of the power
supply
than the other; so if you're using batteries to provide a +- power
supply,
it's worth testing them to see if only half need replacing.

Tim

I just had to bash the hell out of a mini Maglite to get the innermost
AA cell out of it. It had started to leak and the corrosion on the end
was just enough to prevent it from coming out. I had to smakc it
against a concrete floor, with a few layers of paper towel on it to give
just a small amount of give.

Reason for saying this is that it'e really poor advice to give to reuse
half spent batteries. Works really great if the equipment takes a
single cell. But if you put a half spent battery in series with a new
one, it's likely that the half spent one will be discharged to zero and
beyond, leaking in the process. I think if I had two of four cells run
down faster than the other two, I would swap the sets halfway thru their
life. Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

Measuring and matching used batteries is not that difficult, if you need to
use them in pairs. Also, some sources for used batteries are applications
where they were originally used in pairs. I collect and cull AA's from RF
mics all the time with little ill-effect. Sometimes I come in from a gig
with my pockets literally bulging with AA's. I usually just match them by
open-circuit voltage and put them in different piles matched within a 0.1 or
..05 volts of one another. Anything below 1.4 volts, I usually either
relegate to the kids' CD/Mp3 players or discard.

It saves me hundred$ a year, at least.

jak

"Watson A.Name - "Watt Sun, the Dark Remover""

Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

OK. Suppose we have a circuit that draws 20 milliamps at -3v, and 220
milliamps at +3 volts. And suppose our power supply is four 1.5v 2200mAh
batteries, wired so one pair provides +3v, and the other pair provides -3v.

Is it possible to redesign the power supply to do better than replace the
+3v pair of batteries every 10 hours, and the -3v pair of batteries every
110 hours? (So for 110 hours of operation, we'd need to replace 12 pairs of
batteries.)

Tim

Tim Martin wrote:
"Watson A.Name - "Watt Sun, the Dark Remover""
Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

OK. Suppose we have a circuit that draws 20 milliamps at -3v, and 220
milliamps at +3 volts. And suppose our power supply is four 1.5v 2200mAh
batteries, wired so one pair provides +3v, and the other pair provides -3v.

Is it possible to redesign the power supply to do better than replace the
+3v pair of batteries every 10 hours, and the -3v pair of batteries every
110 hours? (So for 110 hours of operation, we'd need to replace 12 pairs of
batteries.)

Make a switching powersupply using 6V input and outputing
two 3V voltages?

Use a latching relay to switch the batteries (3V -3V)
every once and a while?

"Kristian Ukkonen" wrote in message
...

Tim Martin wrote:
"Watson A.Name - "Watt Sun, the Dark Remover""
Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

OK. Suppose we have a circuit that draws 20 milliamps at -3v, and 220
milliamps at +3 volts. And suppose our power supply is four 1.5v
2200mAh
batteries, wired so one pair provides +3v, and the other pair
provides -3v.

Is it possible to redesign the power supply to do better than replace
the
+3v pair of batteries every 10 hours, and the -3v pair of batteries
every
110 hours? (So for 110 hours of operation, we'd need to replace 12
pairs of
batteries.)

Make a switching powersupply using 6V input and outputing
two 3V voltages?

Use a latching relay to switch the batteries (3V -3V)
every once and a while?

Seems like a lot of extra effort and expense for no net benefit.
If you improve the circuit by converting the 6V to +/- 15V instead,
(assuming that does provide some benefit for the circuit involved) at least
there may be some point to it all.
Otherwise it would probably be easier to provide a battery low indicator for
each pair of cells.

MrT.

"Tim Martin" wrote in message
...

"Watson A.Name - "Watt Sun, the Dark Remover""

Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

OK. Suppose we have a circuit that draws 20 milliamps at -3v, and 220
milliamps at +3 volts. And suppose our power supply is four 1.5v
2200mAh
batteries, wired so one pair provides +3v, and the other pair
provides -3v.

Is it possible to redesign the power supply to do better than replace
the
+3v pair of batteries every 10 hours, and the -3v pair of batteries
every
110 hours? (So for 110 hours of operation, we'd need to replace 12
pairs of
batteries.)

Tim

I would use a DC-DC converter to get the minus 3V, at 20mA. SHould take
just a 555 and a cap and a couple rectifiers. A V doubler with a zener
seems like it would do the trick.

http://ourworld.compuserve.com/homep...0.htm#5volts.g
if
But use a CMOS 555 if the supply is less than 5V. But the CMOS 555 may
not source enough current, I'm not sure how much it can handle.

http://www.mpja.com/productview.asp?product=2308+PS This one is already
assembled.

http://www.build-it-electronics.com/page4.htm It doesn't have to be this
fancy.

http://www.national.com/ms/LB/LB-18.pdf