LED Lantern With Joule Thief

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Introduction: LED Lantern With Joule Thief

This is a small LED lantern to be installed inside the farm storage house.

As the size of the storage house is less than 10 square meters, the brightness of the LED lantern is not necessarily high and strong.

This lantern shall be hanging under the ceiling of the storage house to shine 2 to 3 meters in radius.

As no wall outlet is available inside the storage house, the lantern should be powered with a battery.

But 1.5V batteries (AA or AAA size) are the kind of luxury in the rural area where I live, a cheap and affordable solution is necessary for making the LED lantern.

Although buying a brand new battery is difficult, still I can get many used batteries from neighbors.

Therefore, I made this LED lantern by utilizing the Joule thief circuit.

As I mentioned in other instructable below, the Joule thief is a very useful and interesting circuit.

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https://www.instructables.com/Bicycle-Headlight-With-Joule-Thief-LED-Circuit/

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Overall LED lantern circuit structure is the same as the one shown in the instructable above.

But more white LEDs are used for this new project to support the adequate brightness that is necessary to shine the area inside the storage house.

Let's look at more details of the LED lantern.

Step 1: Schematics and Parts

As shown in the schematics of other instructable above, the overall circuit structure is the same as the LED lantern.

For overall LED flasher circuit consists of the following five major components.

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- Lamp part includes 8~12 white LEDs (including female IC pin header, universal PCB)

- Joule thief circuit board (Troidal transformer, TIP41 transistor, 1K VR)

- AAx2 battery and battery holder

- Toggle switch and cable wires

- Plastic box, acrylic top cover, bolts, and nuts

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As relatively many (8~12EA) white LEDs are used, the TO-220 type of TIP41 NPN transistor is used.

Also to supply adequate current to many LEDs, up to two 1.5V batteries are supposedly utilized.

Two batteries are connected as a parallel for limiting the overall voltage to less than 2V.

Let’s look at the details of the LED lantern circuit.

Step 2: White LED Driving Circuit

The white LED board is import part as it produces light to brighten dark storage house areas.

I'm using a female IC pin header socket for conveniently plugging or unplugging white LEDs on PCB.

When more brightness is required, additional LEDs can be plugged into the pin header socket without soldering anything.

Step 3: Joule Thief Circuit

As the Joule thief circuit requires only several parts, the small size of universal PCB can house all circuit components.

Although I used a heat sink for mounting the TIP41 transistor, it is not necessary as the overall current flow in the circuit is less than 100mA.

The battery holder is mounted together with the Joule thief circuit board using a small acrylic board.

Although 8 LEDs are plugged into the board originally, two more white LEDs are plugged into the board to get more brightness.

Step 4: Operating LED Lantern With 8 White LEDs

The Joule thief circuit operation can be seen in the picture above with one AA size 1.5V battery and 8 white LEDs.

When looking closely at the ampere meter, about 80mA is flowing into the Joule thief circuit.

The brightness is just fine for illuminating 10 square meters of storage house.

The output voltage of the used AA battery is about 1.2V and it is discarded from the TV remote controller after it complains low battery.

But as you can see, Joule thief can draw untapped current from the near flatten the battery.

Step 5: Operating LED Lantern With 10 White LEDs and Two AA Batteries

This time LED lantern is operating with 10 white LEDs and two AA 1.5V batteries.

The additional battery is also salvaged from the electronic lock after a low battery is announced by the lock controller.

The overall brightness is slightly increased as two more LEDs are added.

But there is no change of current flowing into the circuit with two AA batteries is connected as parallel.

As the overall output voltage is the same (with a single battery), a similar amount of current (about 80mA) is flowing into the circuit.

But operational hours shall be increased as two batteries are storing more electrical energy.

Step 6: Plastic Enclosure

As the lantern is supposedly hanging under the ceiling of the storage house, a suitable enclosure is necessary for housing all circuit components.

The plastic box is bought from a bowl shop and it is used for storing sugar or salt in a kitchen.

Anyway, the overall shape is just right to be used as a lantern and the size is also spacious enough to house all circuit boards.

To prevent dust or water enter inside the plastic box, an acrylic board cover is used on the top side of the plastic box.

Step 7: Finalizing

This is the finishing appearance of the LED lantern after assembling is completed.

When adjusting VR, brightness can be controlled.

As I don't have knob type potentiometer that can support 1K resistance, changing resistance value requires a small size screwdriver.

Normally it can continually operate for about 24 hours with a single AA battery.

With two AA batteries, about more than 30 hours of operation is possible.

The brightness is eventually decreased with a continuous turn on the lantern.

But in the actual, it shall be turned on for short time (3 ~ 10 minutes) and less than 10 times in a day.

Therefore, I'm expecting a month of usage can be possible with a single AA battery at my storage house in the province.

Thank you for reading....

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