Using a 3xAAA pack to create high voltage

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MoreGooder

Newly Enlightened
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Jan 1, 2010
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Suppose one took the battery pack of this:

http://www.dealextreme.com/details.dx/sku.18697

and instead of populating it with 3 AAA's as intended, one instead put one of these:
http://www.onlybatteries.com/showitem.asp?ItemID=15741.25&cat1=&uid

and one of these:

http://www.onlybatteries.com/showitem.asp?ItemID=11733.25

in place of each AAA. That would provide 6x1.2=7.2V. Or, how 'bout 9 of the 1/3'rd AAA's....10.8V! Crazy, I know.....

Oh, just think of the combinations!

These little guys don't appear to have very much capacity individually though. However, with a buck circuit the capacity might still be significant enough to warrant a trial.

Interesting, no?

Imagine driving a P5 in that little flashlight with a buck circuit... hee hee....
 
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That would not work, all cells has to be the same capacity or you will reverse charge the small cells.

The capacity will be less than half of AAA batteries. 3*120mAh is only 360mAh, an eneloop AAA has 800mAh.
 
Nope... cell capacities need to be identical for cells in series.

Someone else may come along and justify its feasibility so long as the lowest capacity cell is not excessively depleted. But that is a very unsafe practice, in the event that the lowest capacity cell is performing under spec, or the user neglects to terminate pack discharge.

3x10440 cells would be your best bet, assuming the cell carrier can handle the discharge. Some of those 3AAA carriers do not have much by way of power output capacity.
 
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6x10180 and spacers!

25.2 volts hot off the charger :drool:... with a maximum drain of 180mA. :sigh:

I guess if you wanted to drive Nixie tubes or EL wire, that might make it easier.
 
kramer5150 said:
3x10440 cells would be your best bet, assuming the cell carrier can handle the discharge. Some of those 3AAA carriers do not have much by way of current capacity.
Click to expand...

OT but wouldn't the current be less when using higher voltage cells with a buck converter?
 
Very good points! And, I wasn't aware that matching battery capacities mattered all that much.

Also, I did find some interesting things about those buck drivers. Ideally, you don't want the Vin to be terribly much higher than the Vf of the LED, otherwise there is considerable waste of power as the buck circuit trims down the voltage producing waste heat (I'm referring to the 7135 linear regulator versions here). Highest efficiency is when their just about matched, with the Vin a bit higher than Vf.

Guess what..... 3xAAA NiMH's @ 1.2V each = 3.6Vin. XP-G Vf @ 1Amp is 3.3V. Nearly perfect match for a linear regulator using three 7135's.

I assume that bit of info is new knowledge to only me in this forum. Thanks for listening to my rambling.
 
Another option is to modify the AAA carrier to 3P (3 parallel) cells and use the Li-Ion 10440s to get longer time in regulation and longer runtime overall.
1 amp on 3xAAA NiMH's in series is almost 3C whereas it would only be about 1C on the 10440s.
 
Morelite said:
Another option is to modify the AAA carrier to 3P (3 parallel) cells and use the Li-Ion 10440s to get longer time in regulation and longer runtime overall.
1 amp on 3xAAA NiMH's in series is almost 3C whereas it would only be about 1C on the 10440s.
Click to expand...

Wow! Brilliant! Just.... Brilliant!
 
MoreGooder said:
Very good points! And, I wasn't aware that matching battery capacities mattered all that much.

Also, I did find some interesting things about those buck drivers. Ideally, you don't want the Vin to be terribly much higher than the Vf of the LED, otherwise there is considerable waste of power as the buck circuit trims down the voltage producing waste heat (I'm referring to the 7135 linear regulator versions here). Highest efficiency is when their just about matched, with the Vin a bit higher than Vf.

Guess what..... 3xAAA NiMH's @ 1.2V each = 3.6Vin. XP-G Vf @ 1Amp is 3.3V. Nearly perfect match for a linear regulator using three 7135's.

I assume that bit of info is new knowledge to only me in this forum. Thanks for listening to my rambling.
Click to expand...

... FWIW, freshly charged eneloop AAA cells top off at 1.45V. So for a while you will be about half a volt higher than Vf.

Another alternative to 3AAA is a single 18500 cell, and some 3AAA lights have room for an 18650.
 
MoreGooder said:
Also, I did find some interesting things about those buck drivers. Ideally, you don't want the Vin to be terribly much higher than the Vf of the LED, otherwise there is considerable waste of power as the buck circuit trims down the voltage producing waste heat (I'm referring to the 7135 linear regulator versions here). Highest efficiency is when their just about matched, with the Vin a bit higher than Vf.
Click to expand...
Linear regulators are not the same as buck drivers, and buck drivers can be very efficient when stepping down big voltage differences, for example 96% for a single LED driven from 12 V. If you used a driver like that, using 3x 10440 Li-ion cells in your battery holder instead of 3x AAA NiMH cells would work quite nicely. You'd have 10.5-12.6 V depending on the state of charge of the cells.

:welcome:
 
TorchBoy said:
Linear regulators are not the same as buck drivers, and buck drivers can be very efficient when stepping down big voltage differences, for example 96% for a single LED driven from 12 V. If you used a driver like that, using 3x 10440 Li-ion cells in your battery holder instead of 3x AAA NiMH cells would work quite nicely. You'd have 10.5-12.6 V depending on the state of charge of the cells.

:welcome:
Click to expand...

Fantastic!
I think you may be referring to Kenneman (spelling?) drivers. What I was originally thinking, thow was about using 7135's. I read here: http://www.candlepowerforums.com/vb/showthread.php?t=192925 about the 7135 drivers. They can step down the voltage but efficiency drops and they get quite hot. So hot that some claim to have desoldered 7135's.

I already have one of these: http://www.dealextreme.com/details.dx/sku.26111~r.85749907 on order, but unfortunately it won't handle that high of a Vin according to the specs. So, I'd have to shunt one of the battery positions to keep my input between 7 to 8.4V using some nice wire and a good solder job. Of course, with a higher voltage in this means that there will be less current draw. I'm not all that concerned about exceeding the current rating of my 3AAA adapter.

And, thanks for the welcome!
 
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Oh phooey.

I can't find a protect 10440 cell that can deliver the amps I need in the US. They all come from Asia, and I have a fealing that given Hong Kongs clamp down on shipping lithium batteries via air mail will make for a very frustrating experience indeed.

*sigh*
 
for this 3xaaa flashlights, I use 1x18500 or 14500 with homemade adaptor
 
Hey MG,
Your enthusiasm is enjoyable. And those little 1/3 aaa batteries are mostly harmless but with-out some background knowledge you may easily start getting into unsafe combinations.
try batteryuniversity.com. Very helpful site. It'll take a while to get through it all but you'll start seeing rewards very quickly.
 
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