How low can ya go???

Another thread got me thinking. How low can a 1.5 volt alkaline be pulled down to with the right led and circuit.

I seem to accumulate batteries and refuse to mix batteries. I have been thinking about various lighting applications that can use up those loose batteries. I feel that the D-cell body is best for this as you can get those adapters to put a single C, AA, or AAA battery were a D once was. A light like this would not be a bright light but would be a nice addition to an arsenal of lights. One that can use what was waste batteries. Perhaps at least two lights for this purpose. One light that is fairly bright for a single Cell 1.5 volt light to drain the batteries down some, and a Second light to pull the last bit of juice from them. I do like my bright flashlight but there are times when the brightest is not called for and even not desired. So what do you think? What circuit led combo to get a fair amount of light from a 1.5 volt light and one circuit led combo to rip the last bit of life out of the battery?

If you don't want too high brightness, a modified Sacture unit plus a good LS should give reasonable amount of light and let you drain the battery to less than 0.3V before you are left with total darkness.

a madmax works very well on a single 1.5volt battery. i've been running a madmax+ with a single aa battery as my edc for sometime. if you look through the sandwhich shop forum, you will find runtime graphs.
the runtime isn't the greatest, but it's suffiecient for me.

Like most 'great ideas' someone has been here before. Lucky for us, he put up a web site.....

Warm up your favorite browser and point it toward 'Joule Thief', it leads to a Brit who describes just such a beast, able to drain the last two electrons from a cell (runs down under half a volt as I recall).

Sounds like just what you're looking for?

Doug Owen

That joule thief circuit looks similar to the SatCure circuit. Is it basically the same? I couldn't get to the original website and only saw a crude drawing on another guy's website.

Finally got in. Yep, based on the Z. Karparnik circuit featured in Everday Practical Electronics (or some magazine of similar name). Similar to the SatCure in that the capacitors have been taken out.

I think how much juice you can suck out from the cell is highly dependant on your transistor. I usually use 2N2222A (it's generic, cheap and easily available) and that has a cut off voltage of 0.7V.

A PT-40 can serve well with
three used cells, a dummy
and a 2 cell D bulb. This
combination is really pretty
bright. Or of course you can
use 4 used cells with a KPR 103
bulb.
I keep all my used
cells to use for testing
various voltage combinations.
With all my various bulbs, dummys
and used & new cells I could
probably have light for several
months. When it comes down to it,
it's about having the right bulb
for cells (voltage) you have on hand.
-Rebus

Rebus>buy arent you not supposed to mix cells

[ QUOTE ]
Steelwolf said:
I think how much juice you can suck out from the cell is highly dependant on your transistor. I usually use 2N2222A (it's generic, cheap and easily available) and that has a cut off voltage of 0.7V.

[/ QUOTE ]

Er, yeah, but that's not what happens. While it's true that Vbe of all silicon bipolars (and since there are 'no' Ge parts anymore, we might as well say 'all transistors') is .7 Volts more or less, such circuits will not start at such low voltages. If, however, they are already running, they can easily be made to run lower than that (that is 'drain all the power out'). The key is that base drive doesn't come directly from the source, but rather from the base winding of the 'transformer'.

The one the author built as well as the several I have all run down to under half a Volt. I too have used an assortment of NPNs for this, 2N2222, 2N3904 and MPS6417 come to mind. Efficiency falls off, but there's still light and nobody can deny that you're getting a little more power from the 'dead' cell.

Doug Owen

[ QUOTE ]
JonSidneyB said:
Rebus>buy arent you not supposed to mix cells


[/ QUOTE ]

Are you talking about mixing brands? As long as they
are the same kind (alkaline) mixing brands won't
matter. I would not let them lie around for long
periods of time (2 months) without checking them however.
The main reason being that a cell is most likely to
leak when it is older and discharged somewhat.

-Rebus

Rebus: I think JonSidneyB is talking about not mixing cells which have been discharged to different levels. This is because you can wind up with one cell that is weaker than the rest, then the other cells in the battery will end up reverse-charging the weaker cell. Your light could then die very quickly, or the reverse-charged cell might leak, or... well, there are quite a few scenarios, none of them good.

Doug: I figured that might be the case, but I wasn't sure.

[ QUOTE ]
Steelwolf said:
Rebus: I think JonSidneyB is talking about not mixing cells which have been discharged to different levels. This is because you can wind up with one cell that is weaker than the rest, then the other cells in the battery will end up reverse-charging the weaker cell. Your light could then die very quickly, or the reverse-charged cell might leak, or... well, there are quite a few scenarios, none of them good.

Doug: I figured that might be the case, but I wasn't sure.

[/ QUOTE ]

Yes I try to keep the the voltage in all cells
as close as possible. I have not had a problem
yet.

-Rebus

so .7 is the lowest for an IC circuit. does anyone have a stepup available that will go down to .7 and will drive at least 200mau or better using a single 1.5 volt battery as the power source?

I am trying to get the best education I can to better know how to recycle batteries down in single cell 1.5 volt applications. Maybe I can learn alot from any follow up posts.

[ QUOTE ]
JonSidneyB said:
so .7 is the lowest for an IC circuit. does anyone have a stepup available that will go down to .7 and will drive at least 200mau or better using a single 1.5 volt battery as the power source?

[/ QUOTE ]

I am guessing that you mean 200mA at a voltage that a white luxeon would need at 200mA [around 3.3V typ]. A circuit based on a Max1674 or Max1675 will do it at 1.5V and will continue to operate below 0.7V but will not still be delivering 200mA at the lower input voltages. Due to the power limitations of a single cell, I would prefer using the Max1675 in this application due to its lower current limit [it will be more efficient].

Thanks Doug S.

keep the education comming please.

[ QUOTE ]
JonSidneyB said:
Thanks Doug S.

keep the education comming please.

[/ QUOTE ]
As Roth suggested above, dat2zip's MM modules work. They use the Max1674. If you want the highest efficiency, check with Wayne and see if he has any made with the Max1675. I know that he made at least a few. Alternately, you could buy a MM module with a Max1674 and swap out the IC with a Max1675. This requires a bit of skill but you could likely find someone here on the forum to help you out with this.

0.7 volts is the bandgap voltage for a silicon PN junction. For germanium it's more like 0.3 volts. I think there's still such a thing as germanium power devices, but I don't know any part numbers offhand.