Why have 3 AAA batteries not one AA and raise voltage (how expensive is it to raise voltage from 1.5 to 5v)?

Question

I have led headlight with 3 AAA batteries. I will rather have similar device use 1 AA battery, even if it will be more expensive. But seems there are no such devices. Why?

I've got the question after watching https://www.youtube.com/watch?v=4alV5LzHLE4 and later I've found Least expensive way to boost DC voltage where charge pump is also mentioned.

How expensive can converter from 1.5 to ~5V be if mass produced? How small by volume and weight? TIA

TL;DR

As I've understood from mentioned QA there are limitations to charge pump. Namely only 2x raise and some issues "under load". How much load is LED? I've just tried to use my headlight with only 2 AAA and light is much dimmer (I recall there is optimal voltage to LED); ok, producer may insert bigger LEDs to compensate for that (I don't recall efficiency drop is voltage is reduced, or is it? *). Or maybe solutions to raise from 1.5 to 5 are also cheap is mass produced?

* When searching for efficiency of LEDs found How can I efficiently drive an LED? where graphs are mostly vertical.

Now found https://www.candlepowerforums.com/threads/why-3x-aaa-batteries-in-stead-of-1x-aa-battery.364897/:

The 50 cents for a boost circuit might seem like nothing, but on a $3 flashlight that would wipe out any profit.

If true I will gladly pay $1 higher price knowing I'll save much more on batteries. Really almost nobody else will?

Answer 1

White LEDs run at around 3V. the current will depend on the size of the LED. For example, 0.33A for a 1W LED, or 1A for a 3W LED.

It's certainly possible to boost the voltage from a 1.5V cell to 3V to run an LED, and some small torches do that. They tend to use a small LED that draws perhaps 20mA (0.02A). But if you want to double the voltage, then you'll also draw double the current from the battery. So 0.33A at 3V requires 0.66A at 1.5V, even if the boost converter is 100% efficient (and it won't be).

So not only would the headlight require a boost converter capable of delivering a reasonably large current, but it would run the AA cell flat rather too quickly.

Answer 2

I offer an alternative solution here, which worked for me.

I have a head torch that I use on the bike, designed to run off 3xAA cells. It works just as well with 1.2V NiMH cells as it does with 1.5V alkaline cells, i.e. the input voltage can be taken to be 3.6--4.5V.

This has a battery box on the back of the headband, and I wanted to mount a rear light in that box.

So what I did was to use a single 14500 rechargeable lithium cell (3.7V), which has the same dimensions as an AA. I already had a suitable charger for lithium cells. Rewiring the battery box to work off a single cells was easy (just bypass some contacts) and the space saved by removing 2 AA cells gave me plenty of room for the PCB of a rear bike light, with holes drilled for the LEDs and a switch.

The energy density of lithium cells is better than of alkalines, so runtimes were more than adequate for my use case.