How to Replace a Flashlight Bulb with an LED

This arrangement allows halving consumption of the flashlight and to quadruple its lighting! As there is no electronic circuit assembly is not sensitive to moisture. Indeed we may face this situation: having light outside in the pouring rain, so we have here a mounting “all terrains.”

Mounting is done simply with a 1 watt LED and a series resistance of 4.7 ohm or 5.6 ohm ¼ watt. With this resistance have been a rate of 200 mA at 4 volts which means in the LED power 3.5x 0.2 A 0.7 watt.

Intensities measured with the LED at different voltages of the battery:

250 to 280 mA at 4.5 volts
200 mA at 4 volts
150 mA at 3.5 volts
intensity measured with the original ampoule:
The intensity measured at 4 volts is 450 mA. The bulb is given to: 3.5 V – 500 mA. Indeed the flat battery flashlights, battery gives approximately 4 volts which counting a slight drop due to the internal resistance of the battery, and the expectation that the performance of the bulb increases if the “Boosts” slightly, leads to the choice of this tension.

Comparative results. The lighting of the LED is wider, whiter, better distributed.

Determining the best intensity

We may regret that there is no control in this arrangement with series resistance, however this type of flat lamp generally works with non-rechargeable batteries, or the batteries have a more stable operating voltage of the rechargeable, they give to 4.5 volts when new, then stabilize for most of their lifetime to 4 volts, and the voltage drops gradually end of life.

The lighting when the battery is discharged.

With an exhausted battery which gives only 3.5 volts with a conventional bulb is no longer a reddish glow while with 50 mA of LED intensity and we still have a significant brightness. The lack of regulation has another advantage: the end of life if one has no spare battery consumption down and prolongs the many cell operation while maintaining brightness remains higher than long that gave the same bulb at full speed. This is a good point for safety in case we would absolutely need an emergency light that only “loose” not immediately when the battery discharges.

The welding

The power LED has a small tab on it that serves sink but this plate is undersized, it must be welded to another surface to improve heat transfer.
The lean this wide leg of the LED is the most difficult part. Depending on the option chosen that it will weld the tab is in the tongue inside the housing is the body of the ampoule.

Direct mounting in the lamp

This is the simplest installation: just weld the biggest leg (+) on the tab of the contact of the lamp (see photo) for the tongue makes cooler office. The other side of the LED (-) is welded to the resistance, and the resistance is welded to the second tab.
It is necessary to heat the leg with a soldering iron and then bring the tin wire (small diameter, 1 mm for example) in contact with the tab that covers the tin. Do the same with the other party, then we put the two parties in contact and heated again, this welding on both surfaces will make a “bridge” and take the set. We need a clean and operate in a very short iron (seconds) to avoid overheating the LED.

Note on the LED power dissipation

The LED is cooled by the original tab which is on its positive pole, which represents a small area of 4mm x 5mm 0.2 square centimeter.
The dissipation of a copper surface is about 250 degrees per watt per square centimeter of surface area, so to dissipate 1 watt requires a minimum area of 2 square centimeters if we consider that the limit temperature is 150 degrees. For use as a coolant for example a flat battery tab that has a width of 6 mm to a power of 1 watt, it would use the full length of the tab of negative pole is 3 cm x 6 = 1.8 mm square centimeter. In our mounting tab is used which ensured contact with the bulb, which is the same.
It must also take account of this calculation if used Led other conditions. It is better because surdimentionner cooling performance decreases with temperature, and the life: the long one LED overheating deteriorates.

Mounting the LED in the body of a bulb

To change the bulbs: to remove the glass must be the copper part with pliers in one hand, grasp the glass bulb with a wire stripper in your other hand, gently pull and the part glass must take off; at worst it may break, take precautions (goggles, gloves, etc.) then just cut the son and clean the cement inside by rotating the hand a lock of 8 mm for example. It is good to clean the inside because a good air passage promote cooling.
There are two types of bulbs 3.5 volts to 4.5 volts flat battery, one has a thread the other not. Note that the bulb without thread is best for our achievement because it has a collar which adds a bit to the surface and thus improves the power dissipation.
Weld ¼ watt resistor in the LED by putting it very close. Surround the base of the weld a tack to avoid a short circuit with the mass of the bulb when fitting.
Press the soldering iron on the bottom of the bulb and push from the top all-led resistance is going down. When the button LED based off the iron. Make exceed béquillon of the led of the recessed portion of the bulb. Then weld it béquillon on the body of the cartridge, this is what will enable the heat transfer.
This works well in the case of a light bulb without screws; for a bulb with screw can not put a lot of welding otherwise interfere with the complete screwing the other hand there is no vacuum at the top to let one of the electrodes of the LED exceed, so the weld is less reliable; to see if we could not solder a wire electrode on the big LED and also weld the top of the thread, it would consolidate the weld.

Possible improvements: intensity control bulb Led

An integrated control circuit can be used in this case have a low loop “dropout” because the battery will give between 3.5 and 4.5 volts depending on its charge level, we see that the end of life of the battery only gives 3.5 volts or the LED also need 3.5 volts to give all its power. Can not use a regulator that “eat” 1 volt as the standard controllers. The AMC7135 circuit could suit as it is announced with a dropout of 0.12 volts which is great, on the other hand it regulates the current to 350 mA which corresponds to a power of 1 watt, but is a little high for our lED that accepts 300 mA. You can see the characteristics of the circuit here:
Our site.
This circuit requires no external components for operation. It does not work in switching, so that the power dissipated is not insignificant, better weld a little cooler: a piece of tongue of an old flat battery should. Please note also in this case very well cool the LED because it will operate at its full potential so welded to his leg a piece of copper or a tongue recovered on another flat battery at least 3 cm long is appropriate as explained previously. Please note also in this type of arrangement can not afford to connect the battery upside down or we can destroy the regulator, the flat battery casings are often not provided with keying because the original incandescent bulbs n ‘no special meaning for current.
A test of this circuit I see my 400 delivers 350 mA and not it’s true that it is given to a margin of error of 10 percent, which in this case amounts to 15 percent of hit the intensity is too important to our lED, we made a new installation with a 1 watt lED that accepts 350 mA; (sold under the name 1W High Power Warm White LED Lamp Bead 80 90 Lm) this type of LED is much smaller so that we weld it onto a clip formed of a stack of tongue that will serve him cooler, and it is clipped into the reflector instead of the bulb. Warning tabs are some batteries in a material that does not soda, test before; can also be used a copper plate piece.
The quality of light is different, we have a better concentration in the center because the broadcasts led to 180 degrees and better exploits the reflector, by cons we had led a “warm white” whose quality of light is not very nice and pulls a little yellow. We should try with a cool white LED that have more performance and another model, mine was announced for 80 lumen (must be 50); others are announced 100 lumen should see if they actually do.
Flashlight with regulator and 350mA 1w LED welded on a clip.

Use with button cell

This lamp is well suited for use with a Li-ion battery 3.6 volt type 18650. You must use a battery “protected” ie containing a circuit that cuts its operation when the voltage drops below d a certain threshold for these batteries do not tolerate deep discharge. With Li-ion battery 3-amp-hour running time of over 10 hours. We added a pod under the battery side with a piece of curved tongue to spring, welded to a black (see photo) which brings the contact to the second tab. A Li-ion battery size 18650 costs about 7 Euros; attention auction sites there are many fakes. Another alternative is to use a LiFePO4 battery called Lithium phosphate again. Compared to the lithium ion capacity of 18650 will be lower at 1400 mAH, and somewhat lower brightness, it should reduce the resistance because the average voltage of 3.2 volts is LiFePO4 against 3.6 for Li -ion. As against it is a truly environmentally friendly battery with the following advantages: Very long life, supports up to 2000 discharge cycles, with no risk of explosion in case of overload, and does not lose its qualities with the weather. In both cases you have to buy a special charger to recharge. Currently found in the home seller at a price of about 3 Euros room.

Flashlight with limitation resistance and led 1w 10 mm welded to the contact of the lamp tab.

this lamp can also be run using a single 1.5 volt battery, or two 1.5 volt batteries, in this case you have to use an IC cutting “step-up” that will transform the voltage 1.5 volts or 3 volts 3.5 volts. In this case the series resistance with the LED should be removed.

If the assembly does not work or works poorly?

If the LED does not light: Check the side of the LED that has the pin goes to the + battery (short tongue) otherwise change the direction of the pile. Check that there are no false contact on the light switch.
If the brightness of the LED decreases rapidly: It could be bad cold, or the resistance is not connected or absent and the LED dissipates too much power, stop the fast current.

A flat flashlight mount with a 3 watt LED

If we want more lighting one can use a 3 watt LED, we used here a rather large LED sold in the shop Our site as “3W White Round COB LED SMD Light 280LM Lamp 6pcs clips “It belongs to the COB technology (chip on board) that allows for fairly wide areas. We used a voltage converter circuit named Solar DC boost converter 9v (see our article Led 10 watts.) Now this converter provides maximum 9 volts and needed 10 volts to achieve the power of 3 watts; 9 volts there was a watt. I soldered in parallel with the resistance that is next to the green LED (it is a LED that lights when the power is below 2.7 volts) a resistance 15Kilo Ohms. Thus, the voltage can go up to 10 volts. Welding resistance on a CMS is quite delicate, not try that if you are qualified for this job and confident.

Mounting in a flat flashlight housing. The various elements have just been stuck in the casing with a glue gun.