Headtorch / Flashlight Booster

The Headtorch is modified using circuitry from a solar garden light. It will enable you to use only 2 batteries instead of 3.

This is useful when buying batteries. Often they are only sold in packs of 2 or 4 but not three. It may also allow 'dead batteries' to be re-used a little longer.

My story:
I noticed there was some corrosion on one of my headtorch's battery terminals. In the process of removing it, the terminal broke off.

I was about to throw it out, then I had 'a think'. 'The main problem to overcome was the headtorch uses 3 AAA batteries (4.5 volts), with the broken terminal now only 2 sets remain. Somehow 2 batteries need to provide the same voltage as 3. A voltage booster was required!' As it happens these are used in inexpensive solar garden lights. The plan was to use the circuitry from one in the headtorch. This is how it was done:

Headtorch
Solar garden light
Thin copper sheet (available from art stores)
Soldier
Wire
Wire from coat hanger

Tools:
Soldier iron
Wire cutters
Screw driver
Pliers

Disassemble solar garden light;
* Remove screws.
* Cut off connections to solar panel, close to circuit board.
* Cut off connections to battery, close to batteries as the wires attached to the circuit board will be used. Leave enough wire next to battery so you know which colour is positive and which is negative.

Test light by connecting it to a 1.5 volt battery. The 3 volt LED lights up from a 1.5 volt battery! Obviously, some sort of electric-trickery is at work.

How it works:
IC (integrated Circuit) pulses the inductor, this boosts the battery voltage output by rapidly creating and collapsing a magnetic field.

No free lunch:
Voltage Is boosted but at the expense of reduced mWh (battery used up faster).

Unsoldier the LED (Light Emitting Diode), pliers may be required to pull it off. Be carefully not to burn yourself with the hot soldier iron.
Mark on the circuit board which side of the LED was positive.

Solder on the positive output wire to positive side of where the LED was. Check you have soldiered it to the positive side.

* Cut 3 small connection tabs from thin copper sheet. (I got some from an Arts supplies store).
* Check they will fit into the battieries slots.
* Sand the tabs to make soldiering easier.
* 'Tin' tabs by heating with soldiering iron and applying soldier.
* Soldier to the output leed and the 2 input leeds.

These tabs will allow the booster to be easily removed when not in use. It also saves having to soldier directly onto the headtorch. When I fixed my headtorch with the broken connector, I soldier one directly to the battery terminal, then when attempting to soldier to the second connector, the heat melted the surrounding plastic. This lead to the idea of using tabs instead of soldiering directly. I had also directly soldiered the output lead to the light on the headtorch as it had been broken off. This had the advantage of not requiring a 'battery spacer' but meant the booster couldn't be removed.

In these instructions, no soldiering to headtorch is required and the booster can easily be removed.

This circuit will take the voltage from the batteries, boost it. And sends the boosted voltage to the headtorch via the positive output wire. This output needs to power the light at the same battery connector as the input connector. The 2 positive tabs need to be separated by an insulator. A small piece of plastic from packaging is ideal.

* Cut a piece of plastic from some packaging, slightly larger than the tabs.
* Glue one side to the positive output tab.
* Glue the positive input tab to the other side of the plastic.
* Trim so it fits into the battery holder. The 2 positive tabs can not touch each other.

The booster is now ready to be used in the headtorch.
As one of the batteries will be removed, a spacer which conducts electricity is required. I used a piece of wire from a coat hanger. Cut the wire to fit and insert into the battery holder.

* Identify the positive output from the battery.
* Place the positive tabs (previously glued together separated by plastic) into the positive connector position.
* The positive output wire/tab needs to go closest to the outside of the headtorch. The positive input goes next to the battery.
*Instert the positive end of a battery, once the battery is clicked in, the tab is secure.
* Secure the negative wire and tab with the next battery, with the negative end.

Attempt to close the back cover, I managed to close it on the previous headtorch with the broken connector. But on this one it wouldn't click into place This shouldn't be surprising as a booster has been placed in the back.
* Secure the cover with sticky tape.

An App was downloaded to measure the light output with and without the booster. It showed, with 2 batteries the output was doubled. (See above).

When it was added to a headtouch with 3 batteries, surprisingly, the output was less. This is probably due to 4.5 volts being too high an input, outside its operating range.

When the booster is installed it is always on, even if the headtorch is turned off. So it needs to be removed when not in use. Or at least a tab disconnected.

The booster does use more power than without, as it is putting out more light. This may be a consideration if you want the the headtorch to be operational for maximum time.

A test was done to see how long the 3 battery headtorch would last vs the 2 battery headtorch with booster.

3 batteries: 20 hours
2 batteries with booster: 9 hours

Both were still working at these times but only dimmly.

After the headtorch with 3 batteries had been running for more than 20 hours the main white light would no longer shine (the red still could).
The booster was connected and the white light shone some more, though not at full strength for another 4 hours.