If anyone has seen one of these off the top of their head I'd be grateful. I'm looking to power a 1w LED with a 9vdc battery, but I am looking for a board with these specs:
Input: 0.9v to 9vdc
Output: 3.3 to 5vdc.
I've been searching Ebay and Amazon for these and haven't found what I want. I've found other step-up convertors that have an input from 0.9-5vdc but don't handle input up to 9vdc. An input of 0.9v-9vdc would also allow me to use other battery configurations with this flashlight, like 2AA, 3AA, a 3.7vdc lithium battery, etc.
I've found small power supplies but they are too big for a flashlight, even in a box case, or the input voltage required is too high, 10-30vdc.
Thanks for your help! I'm sort of new to the world of step-up convertors.
You mean a 9v has less watt-hours? How is that when it has 6 AAAA batteries?
As far as the drivers go, will any typical end cap, latching, clicky switch work? As this light will not likely be in a tubular flashlight housing. It will be in a box for a prototype. Will a normal latching switch work? Or do I need a momentary switch to work with these boards?
The problem with 9V batteries is that they waste a lot of volume on inert structural material that contributes no energy storage.
The 6xAAAA type is the worst, because the AAAA cells are cylindrical, so there's no way to pack them together without wasting some space between the cylinders. In addition to that, they're surrounded by an external shell and a top section with the PP3 snap contacts on it. The actual volume of electrochemically active material is remarkably small.
There's another type of 9V battery that uses 6 prismatic cells in a cuboid form. Those don't leave any space between them, which eliminates the cylinder packing problem, but they still have a high ratio of inert structure to electrochemically active material, simply because they're so small*. Of course, this type of battery also pays the penalty of having an external shell and PP3 contact section.
* On a related note: larger cells tend to achieve a higher percentage of electrochemically active material per unit volume, because much of the structural part scales by surface area, whereas the electrochemically active part scales by volume. Volume scales proportionately faster than surface area.
For example, scaling a cell to be 1.25 times larger in every dimension requires 1.56 times the surface area, but gives it 1.95 times the volume. This effect is one of the main reasons an 18650 cell has such a drastically better energy density than a 14500 cell.
On the other hand, a AAAA cell or a 9V-type prismatic cell is so small that there's hardly any space left for the electrochemically active material after you've accounted for the volume consumed by the casing. They get absolutely hammered by the volumetric scaling effect.
Of course the volume vs surface area is not really relevant when the cell development is not equal. 18650 beats 26650/36650 etc for energy density as does AA to C/D in NiMh.
The common and cheap MT3608 boost converter from eBay can achieve most of your specs if you convert it to SEPIC. Here’s a page where I originally found info on doing the conversion, and I have since done it myself and confirmed it works well: Пара Step-Up конвертеров и их небольшой апгрейд до SEPIC
Oh, it’s still relevant, it’s just not the only factor.
If I compare like with like, using AAA 750 mAh and AA 2000 mAh Eneloops, the dimensions are:
Cell
Height
Diameter
Surface Area
Volume
AAA
44mm
10mm
1539mm²
3454mm³
AA
50mm
14mm
2506mm²
7693mm³
Scaling Factor
1.14
1.4
1.63
2.23
On that basis, you’d expect the AA to have 2.23 times the capacity of the AAA, or about 1670 mAh. The 330 mAh difference is what you gain from losing a smaller proportion of the cell volume to inert structural material in the larger cell.