We all have at home any torch using conventional lamps incandescent filament lamps, which consume an enormous amount of batteries and also provide little light.
While filament bulbs produce around 14 lumens per watt, LED technology now produces 100 lumens per watt (and up to 160 lumens in the best Cree LEDs, improving year on year), as well as having a much longer estimated life.
Although torches with the much more efficient LED lighting are already on sale, we can modify an old lantern and have fun and learn along the way, by replacing your incandescent lamp with one or more LEDs.
In this entry we will look at how to retrofit a Cegasa lantern which uses 4.5 Volt batteries to save on batteries and provide more light.
Materials and tools
- Old lanterns that don't work, any one will do, but each one will need a different adaptation.
- Dremel o small rotary cutter for cutting small materials with the necessary Personal Protective Equipment (goggles, gloves, etc.).
- Tin soldering iron 20W minimum
- LEDs of the power we needIn this case, it uses 1W, which is more than enough, and we can get them in LED shops, Dealextreme or Aliexpress very cheaply. If it does not support the voltage delivered by the battery, we will see how to regulate it with a resistor.
- Resistance (optional if the battery supplies a slightly lower voltage than the LED works). It is necessary to calculate the value of the same according to the voltage and intensity that the LED needs, we have automatic calculators on the internet. If we can avoid its use, we will save battery power as it dissipates energy in the form of heat to regulate the current.
- Suitable heatsink for the LED; we can get it by cutting an old one from a computer or power supply to the required size (the more watts of LED, the bigger it needs to be).
- Epoxy glue two-component or similar, withstanding temperatures between 40 and 90°C and good tensile strength.
- Optional rectifier diodeWe can find it in many electronic circuits such as transformers, power supplies, CCFL and LED bulbs. Any one will do, but we should try to use one that works at 6V maximum (as it will have little internal resistance to the passage of current, which we can check with any tester; if we put the tester polarised, it will give us a resistance between 100 and 1500 ohms, but in the cut-off direction it will give us a very high resistance).
Keep in mind that LEDs are like microprocessors in computers; they are semiconductors and if they get too hot, their life is dramatically shortened. We will have to find a way to transfer the excess heat to the LED we install to avoid this. To make room for the aluminium heatsink, we measure the height we need for the LED holder and We cut with a dremel or a cutter the plastic that held the old bulb in place, what is left over..
There we will place, glued with epoxy glue (any type of glue that is rigid enough and not affected by temperatures of 80º Celsius) a piece of heatsink from a computer (cutting it with a dremel) or a piece of metal that helps to cool the LED diode.
After hardening of the epoxy on the aluminium/metal part we can glue the LED diode with another drop of epoxy. (very little, what is needed is that the diode is as close as possible to the metal so that the heat from the LED is transferred to the metal) and press it tightly against the metal.
To identify the positive and negative side In this type of LED, we can see on the negative side a small cut (in the shape of a -) in the middle of one of the metal pins:
Before gluing the LED make sure it is centred and coincides with the mouth of the reflector. plastic cover:
We will continue soldering the resistor; the LED in place works at 3.2 volts and 250 mA (milliAmperes), so according to the calculation we need a 3.7 ohm resistor which we solder to one of the poles of the LED and to the closest sheet metal.
Note: Voltage (voltage) is not the same as current or intensity. (measured in amperes). To give you a simile, the passage of electrons through a wire is like the passage of water droplets through a pipe. The voltage is like the width of the pipe, and the amperes is the amount of electrons (or drops) flowing through the pipe.
Power(W) = Voltage(v) x Current (A)
Or if we turn the formula on its head; Current (A) = Power(W) / Voltage(v)
To prevent damage to the LED when the battery is turned upside downWe can place a rectifier diode (the black one in the image); these only allow electricity to pass in one direction and generally have a grey band on the negative side; we solder this side to the positive side of the LED to keep the direction of the current (we are soldering in series, so the positive side of one element must go with the negative side of the next). The rectifier diode is optional if we are careful with the poles of the battery.
You can see that the LED is perfectly tucked inside the reflector. If necessary we could trim part of the reflector so that the heatsink does not stick to the LED. With the use of LEDs there is no need for a reflector as their light comes out at a very narrow angle.The range is between 60 and 120º depending on the type of LED.
And this is the result; a powerful, energy-saving light for life:
- Get an LED that works at battery voltage. to avoid unnecessary energy expenditure with the resistor.
- Check that it does not get too hot when switched on for 5 minutes. If you can't touch it with your hand, then either it doesn't have an adequate heatsink for the power of the LED or you are pushing it too hard, shortening its life.
- Do not supply the LED with more voltage than recommended. by the manufacturer, you will greatly shorten the life of the LED.
- This LEDs in the lantern does not have adequate ventilation, avoid turning it on for prolonged periods of time, or else to improve the lantern, find a way for the heat from the LED to communicate with the lantern housing. (e.g. by cutting a hole in the plastic); this will make cooling much more efficient.
- Do not look directly at the LED when switched on; high-powered ones can damage eyesight as much as when looking at the sun.
More information - How an LED works, How to build your own high-powered homemade LED torch