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High-powered LED based headlamps, batteries and rechargers

Detailed description of 2x3 watt homemade LED headlamps for caving and outdoor activities


As a caver (speleologist) it has always been essential to have a reliable, high powered headlamp.
Since the professional headlamps were extremely expensive in the '80s, I created a homemade one, then based on my experience, I improved them. These acetylene lamps were double burner and equipped with piezo lighter. In places where it is wet or you need to crawl a lot, the acetylene lamp is not practical, therefore, I started to create electric lamps. Among these were 5, 10 and 20 watt halogen bulbs, however the weight of the battery awkward. The 5 Watt fluorescent light tube is promising but fragile.
Fortunately, high-powered white LED and lithium-ion batteries became available (in 2006) and made it possible to put together a revolutionary, powerful and lightweight lamp.
The headlamp I designed has more than enough light even for caving (it produces stonger light than the Petzl MYO XP lamp in boost mode). It is durable, efficient, lightweight and cheap.

Detailed description of 2x3 watt homemade LED headlamps for caving and outdoor activities (bicycle lamp) - DOLA K2

Last modified: 17th September 2010 (first version: 20th September 2006)

A few years ago, I took up caving again so I designed and made several high-powered LED headlamps and because I was using the latest technology, my lamps were better in several parameters than the ones available in the shops, and significantly cheaper too.
I would like to share my experience. I have made a step by step precise description how to create a high-powered LED lamp at home.
Based on the instructions below, you can make your own headlamp at home. All you need is a little technical background.

Pictures of the twin LED head lamp
(2x3 Watt)
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In order to get a bigger picture,
click on the photos
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Pictures of the 3 Watt LED headlamp Click for large image...  
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In order to get a bigger picture,
click on the photos
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1. Pros and cons of my headlamp

    Click for large image...
  • It produces brighter light than the Petzl MYO XP lamp in boost mode!
  • Controlable light intensity
  • It last for approx. 25 hours with a small Li-Ion battery (1 led, in eco mode)
  • It has homogeneous light
  • The optical system can be set for narrow to wide beam (10, 30, 50 degrees)
  • Water resistant
  • Durable, ideal for caving
  • Low battery is indicated by a small red LED
  • When the battery is getting low, it will not switch off suddenly, it will continue to have a faint light. So it is safe.
  • It can be modified to serve your specific needs
  • Small and lightweight (~90 gram plus the battery 50, 100 or 150 gram)
  • Simlpe design
  • DIY at home (Do it yourself at home)
  • Much cheaper than the similar lamps available in shops (e.g. Stenlight S7, Radon, Scurion, Petzl MYO XP, Petzl DUO LED 5)
  • Two LEDs give light to fix directions (but can made to be adjustable)
  • Intensity of the light changes as the battery gets flatter (in case of using resistance / multifuse)
  • Battery and the connector are not water proof (but can made to be)
  • Battery has no electric protection, so you can deep discharge it which should be avoided (in caves it is for safety...)
  • It was not designed for its beauty -:)

2. Parts and materials for the double LED headlamp

Click for large image... - alkatrészek, Luxeon LED, home made,
  • 2 Luxeon K2 LED: LXK2-PWC4-0180 5W (or LXK2-PWN4-0180, LXK2-PWW4-0160) [~1600Ft each]
  • 1 10 and 1 50 degree lens (for surface use 10 and 30 degree) [500Ft each]
  • 2 lens holder [150Ft each]
  • 2 22 mm diameter, 1.2 mm thickness policarbonat plate to protect lens (e.g. blank CD - which is tranparent)
  • 2 three-stage switch, with three pins (3A, 8x13x33mm M6x0,5mm) [150Ft each]
  • 4 22 mm diameter copper pipeend for heating systems (e.g.: RYW-KIWA, ENDEX) [170Ft each]
  • 1 5x5 cm, 1.5 mm thickness, yellow brass plate (for one LED lamp you need 2x6 cm, 1 mm thickness plate)
  • 2 db current limiting electronics: multifuse and/or resistances or Integrated Circuit [100-15000Ft each]
  • 38+16 cm 2x0.75 mm black double isolated wire
  • 10 cm 0.5 mm thin wire (the best is teflon covered with 1 mm diameter)
  • 1 RCA "male" connector
  • 1 RCA "female" connector for battery
  • 1 mm /0.5 mm heat shrink tube for soldering of LED and wires
  • 4 mm /2 mm heat shrink tube for switch and wires
  • 6.5 mm /3 mm heat shrink tube to make switch waterresistant, and for the Multifuse
  • 35 mm /12 mm heat shrink tube for the double-cell battery
  • 1 red LED (3mm, 1.8V 2mA), 1 1kOhm resistor and 1 KIA7033P (3.3V TO-92) IC to indicate low baterry
  • Black insulating tape
  • Good quality transparent silicon glue (e.g. Wacker Elastosil E-41 is the best)
  • Rubber glue (e.g. BISON Contact adhesive gel)
  • PVC glue (e.g. BISON Rigid PVC adhesive)
  • 4 screws M2.5x20 or M3x20 (copper or stainless steel)
  • 3 2.5 mm cable ties for cables and switches
  • 9 cm, 30 mm wide, black elastic band or 16 cm long, 3 mm diameter rubber cord to hold battery. (If you want to use the lamp without a helmet, then you need 62 cm long 30 mm wide and 45 cm long 20 mm wide elastic band. Plus a buckle and a plastic holder for the lamp: 2 mm thick plate 62x38 mm and 25x61 mm)
  • Two-component glue to glue the elastic band (e.g. UHU Plus Endfest 300 Binder + Harter is the best epoxy glue), or you can sew them together
That is, the total cost of double-LED lamp is approx. 30 EUR plus the time it takes to make which is approx. two-three days.

Where to bay the parts:
Flashlights and parts (DIY): www.dealextreme.com (LEDs, Circuit boards/LED driver for LEDs, Cree flashlights, free shipping: 30 days)
If you are located in Hungary please refer to the following websites:
  Luxeon LED: www.ledaruhaz.hu
  (Cree LED: www.chipcad.hu or www.arrowce.com)
  Copper pipeend: any heating engineer shop (select the nice pieces...)
  Electronic parts: www.lomex.hu/ KIA7033P IC: www.hqelektronik.hu

Tools to make the lamp

Click for large image...
  • digital multimeter (voltage, current and to measuring the resitance)
  • soldering iron (thin)
  • pincers (thin, self-locking)
  • tolómérő, ruler, metal needle, thin alkoholic felt pen
  • screwdrivers, pliers, pen knife
  • drill with 1; 2; 2.5; 3 and 6 mm diameter drill stem
  • M2.5 or M3 -as screw tap
  • hack saw with fine finom teeth
  • fine metal file (rasp)
  • fine sandpaper
  • lighter for heat shrink tube
  • alcohol (izopropil alcohol) to remove grease
If you have all the parts and tools ready, let's start assembling the lamp.
If you create the lamp with special care, it will be reliable and last for decades.

3. Step by step instructions to create the headlamp

Fejlámpa négy fő részből áll:
1. LED container
2. Switch and electronic part
3. Holder plate
4. Battery

3.1 LED container

For the LED container we need a 22 mm diameter copper pipeend (for heating systems) for each LED. This is small and durable, and the best for heat reduction.
Step by step instructions:
Round the ends of the copper caps (inside and outside).
Click for large image... Mark the positions of the holes (2 1 mm holes for the wires, 2 2.0 mm holes for the M2.5 screws. (if you use M3 screws, you need 2.4mm holes). Then drill them precisely.
Make the thread with a screw-tap. .
ARaound the edges of the holes of the wires on both sides. If the edges of the holes remain sharp, they may cut the wires which may lead to short-circuit!
Clean the copper caps with alcohol.
Next is to adjust the lense holder. Put the lense into the lense holder then put the LED inside. The back of the LED should be in line with the edge of the holder. Be careful with the lense and the LED since they get scratched easely!
Put the LED and holder into the cap. There should be enough space for the protector plate and to glue it with silicon.
The original lense holder does not press the back of the LED (cooling area) to the copper (cap); it is necessary for the adequate cooling. So we have to modify it: measure the distance between the LED cooling surface and the edge of the LED holder (approx. 0.4mm) then remove it with sandpapper (do it without the LED inside). To ensure accuracy do it in several steps. Click for large image... Then to make sure the holder fits tightly into the cap, you must sandpaper the parameter of the lower part of the LED holder (at an approx. angle of 45 degrees and 0.75mm) otherwise the edge of the holder will sit on rounded inner part of the cap, so the LED will not be able cool.
What type of lense do we need? For caving use 50 and 10 degree lenses. For hiking use 30 and 10 degree lenses.
Click for large image...
Lens protector plate: 1.2mm transparent policarbonate plate (e.g. cut 22mm diameter disc from completly transparent (empty!) CD) To make sure you do not scratch the surface, stick transparent tape on both sides. To mark the size you can use a sutable coin (5 HUF -:) ) and alcoholic felt tip pen. To cut the disc use a fine saw then use fine file to fit it to the cap.

Soldering the LED: use two 5cm long thin wires (with teflon isolation), remove 2mm of isolation from both ends. Melt tin solder onto both ends, then cut the wire so that the remaining part is 1mm.
Do not use any acid for soldering because it will corrode the wire within a few years.
Click for large image... Hold the pin of the LED with tweezers tweezers (needle headed) at the bend (as in the picture). It will hold the LED for the soldering and will remove the heat too. Solder fast with fresh soldering tin. Do it for both pins. Mark the positive wire with an alcoholic pen.
Isolate the soldering with 2.5mm long heat shrink tubes. Be careful not to overheat the LED, and do not damage the lens either!
Bend the wires as in the picture and put it in the LED container.
Click for large image...
After putting the LED and lens into the LED container, we can test it. Try putting the lens protector in, too.
The lens holder moves freely so put insulating-tape around it.
Clean all parts (with alcohol) then with a drop of silicon rubber glue the LED into the cap. Push the LED to the bottom of the cap then isolate the wires with a drop of silicon rubber inside and out.
Push the lens with the holder into the cap (be careful not to damage the lens).
Test the light, it should be homogenious, if not move/adjust the LED and try again. Then push them together and hold them for approx. 12 hours (use a sponge on the side of the lens). After that air it.

Gluing in the lens protector: Clean the disc with alcohol, remove the dust and put the disc into the cap, push it in and adjust it, finally glue it with silicon rubber (use a sharp tooth pick to apply the glue). Be careful not to smudge the glue on the inner part of the disc. It is easy to remove the excess glue from the metal but not from the disc.

For the double LED lamp two of these should be made.

3.2 Switch part

The switch and current limiter will be placed in a 22mm copper cap.
Click for large image... Current limiter:
Preparation: measure the LEDs and determine the current limiters, then test them before placing them into the cap.
We have to limit the maximum current of the LED, the value given by the manufactorer should not be exceeded, because it will overheat the LED and it will be damaged.

For the current limiter we can use a complicated electronic with IC or a simple and cheap one made of a multifuse and resistor.
Advantage of the IC version is that the light will be steady while in use. However, it is expensive and difficult to create.
Advantage of the serial resistor is that it is very simple and very cheap and lasts forever (if the value and the size (power dissipation) are good). Disadvantage is that the light will be weaker with time as the battery gets flatter.
Multifuse a kapcsolóval Multifuse is the best choice since it works like a piece of wire until the current reaches the predefined level, then it becomes a resistor. If the current exceeds twice the predefined level, the value of the resistance will be huge (it will almost switch off the current.
I recommend using the multifuse + resistor solution because of the advantages.
All three methods have 70-95% efficiency.
It is important to determine the current limiter for each individual LED and of course for the battery type!

The following table will help to calculate the serial resistor (multifuse), it also contains the main parameters of most commonly used batteries: LED_lampahoz_soros_ellenallas_akkuk_elemek.xls (40KB - MS Excel)

Which ever type of current limiter you choose, you should check the configuration for the worst case, e.g. fully charged battery with cool and hot LED.
The following table will help to check the configuration (to measure and calculate the parameters): LED_lampa_meresek_szamolasok.xls (40KB - MS Excel)
1W Luxeon LED, Multifuse
The diagram on the right clearly shows the effect of the multifuse. When the power reaches the 1 W (0.3 A), the multifuse starts to open (gets higher resistance) so the power stabilizes. (Multifuse: 0.25A, LED: Luxeon XK2-PW14-U00 U: 3.0-4.2V)

The graph below shows the changes of the strength of the light. It is clear that the strength of the light does not only depend on the power (volts) but also it strongly depends on the temperature of the LED. When the LED is cool, it provides more light and the whole system is more efficient. (Multifuse: 0.25A, LED: Luxeon LXK2-PWN4-U00 U: 4.2-3.3V) Thanks to H. Balázs for the graph.

Wiring diagram when the current limitor is MULTIFUSE:
LEDes_fejlampa_kapcsrajz_multifuse_v2.dch (15KB, DipTrace 2.00) and as a picture:
Click for large image...

Wiring diagram when the current limitor is MULTIFUSE and resistor:
LEDes_fejlampa_kapcsrajz_multi_v1.dch (15KB, DipTrace 1.50) and as a picture:
Click for large image...

Wiring diagram when the current limitor is resistor:
LEDes_fejlampa_kapcsrajz_ell_v1.dch (15KB, DipTrace 1.50) and as a picture:
Click for large image...

The low battery indicator: a red LED
When the Li-Ion battery is low (below 3.3V), the voltage will decrease fast so we can use it to signal the low battery status.
With the following very simple wiring, a red LED will be on when the voltage goes below 3.3V, so we have a few minutes to replace the battery.
Parts: 1 red LED (3mm, 1.8V 2mA), 1 1kOhm resistor and 1 KIA7033P (3.3V TO-92) IC to indicate low baterry.
Wiring diagram, pictures: coming soon XXXX
It is recommended to place the red LED into the second cap, which has only thin wires in it (therefore there is more free space inside).
Solder the three parts close together and leave only two thin wires (3 cm long) for the connection then put the whole in a heat shrink tube.
Bore a 2.9 mm diameter hole into the copper cap. Do it with the next step "Switch part - copper cap". LED should face downwards to light your nose -:). Put the LED into the hole and glue it inside with silicon.

Switch part - copper cap
File the inside edge of the cap, it should fit well onto the cap of the LED.
Mark the holes of the switch, screws, wires and red LED then drill them precisely.
The hole of the switch should probably be filed to an oval shape for easier assembly.
The holes of the wires should be as small as possible to fit the cables tightly.
Click for large image...
For quick testing assemble the whole switch part, check that everything has enough space (switch, screws, wires, multifuses) and place the cap of the switch together with the cap of the LED.
- Remove 25 mm of the external isolator of the power cord then coat both wires with tin (5mm).
- Pull the power cable into the cap then put and fasten a 2.5 mm wide cable tie on the power cable (see the picture) to protect the power cable from accidently being pulled out.
- If you are creating a double LED lamp, install the power cable for the switch cap of the second LED too.
- Glue the inner part of the power cable with silicon then pull it out until the cable ties are in contact with the inner side of the cap.
- Switch: this is the most vulnerable part of the lamp. I recommend you shrink the length of the rod of the switch by 4 mm (remove it with a fine saw).
Hint: While you are sawing, filing, etc. cover the base of the rod of the switch with isolating tape to protect the inside of the switch from dust / metal filings.
- Solder the multifuses to the pins of the switch. If you are using resistors or electronics (IC) for current limiting, put it near the power cord and use thin wires for connections.
Be careful with the electrical insulation!
- Mount the switch. Glue the base of the male thread then screw the female screw and fasten it.
- Solder the LED (and switch), Check the polarity before soldering!
- To test assemble the whole lamp, screw loosely. Try the lamp...
- If everything is OK, open it and leave it open for the glue to dry (for 10 hours).
insulation of the RCA connector - The length of the power cable: suggested length of the cable is 38 cm if you put the battery pack on the back of the helmet.
- Binding the RCA connector: The middle pin is the positive (+) and the outer ring is the negative (-).

3.3 Holder plate

A yellow brass plate holds the lamp together and this fixes it to the helmet too. To attach it to the helmet you can use the 20 mm wide holder of the miner's lamp or just screw it on.
The thickness of the yellow brass plate should be 1.5 mm for the double LED lamp and 1 mm for the single LED lamp.
When you draw the shape on the plate, be careful to have the flatten (mill) direction parallel with the handle (perpendicular with the line of the bending).
Cut/saw and file the shape of the holder plate then drill the holes. The position of the holes of the screws must be accurate! It should fit precisely to the copper caps.
I recommend that the left side LED should give the closer light (with 50-degree lens) for right-handed people.
Bend the plate and test the angles with your helmet!
Click for large image

Final assembly

Click for large image... Before the final assembly make sure the lamp works fine see the " Test section"

Steps of the final assembly:
- Glue together the LED and the switch parts with silicon. Fasten the screws but do not glue the screws. Let it dry.
- Glue together the holder plate and the cap(s), use silicon for the screws too and fasten the screws. Let it dry.
- Fix the power cord with a cable tie to the holder plate (see the pictures).
Accurate gluing is very important. It is not just for the water isolation but for the strength too (the two small crew are weak).

How to make the switch water-resistant Click for larger image
If you can not buy a rubber cap for the switch, do not worry, you can make it yourself from heat shrink tube.
Just overheat the end of the 6.3/3 mm heat shrink tube then press it flat with pliers (be fast and strong). The tube should melt together.
Cut the edge of the melted end to a curve then cut a 20 mm long piece from the tube.
Push the rod of the switch into the middle position, put the tube on it and cut the length if it is too long (leave 1 mm plus). Use a new switch, not the one you have fitted into the cap.
Use a narrow flame to shrink the tube onto the thread of the screw - see the pictures.
Do not give up if the first one is not a show-piece, the third attempt should be fine. -:)

Finally, glue the tube onto the thread of the switch:
Clean the inner side of the tube and the thread with alcohol then glue them together with rubber glue. Make sure the rod of the switch can move freely.
Use a 2 mm wide cable tie to secure the tube.

Headband without the use of a helmet

If you made a superb lamp, you may want to use it without the helmet too.
So let's make a headband or you can use a headband of a cheap Chinese headlamp.
How to make a headband for your lamp
First, a plastic holder plate is required. Based on the drawing below, cut the shape from a 2 mm thick PVC plate, glue the holder parts with "PVC glue".
Cut the elastic bands then put them into the buckle and the holder plate then sew or glue them together. (I prefer epoxy glue.)
Click for large image... Click for large image... Click for large image... Click for large image...

4. Battery

Click for large image... Before you can design the current limiter, the battery type should be defined.
The most common type of batteries are: Li-Ion, Ni-Mh or Ni-Cd and Alkali-Mangan.
The Lithium-Ion battery is the best choice for headlamps.
The capacity / weight ration of the Li-Ion is the best, the voltage is just perfect for high power LEDs and it is not too expensive. It is even free if you take the good cells from a dead battery pack of notebook.
Because of the great advantages of it, I have chosen the Li-Ion battery.
For the headlamp one or two-three (parallel connected) Li-Ion cells are required.
The most common type of Li-Ion battery cells are 18650. (18650 means that the diameter is 18 mm and the length is 65 mm.) The capacity of one 18650 Li-Ion cell is 1600-2200mAh, the nominal voltage is 3.7 V. The usable range of voltage is between 4.2 and 3.0 V.
So, one 18650 Li-Ion cell could provide power for a 1 watt LED for 4.5-6.5 hours, in eco mode (0.3 W) it could give light for 10 hours. It is implicit, 2 or 3 cells will provide power for 10 / 20 hours and in eco mode 20 / 30 hours!

Preparation of the Li-Ion cells

The cheapest and easiest way to obtain Li-Ion cells (type 18650) is to extract them from a battery pack made for notebooks. It could be either a new or dead pack. The most common problems of the battery packs of notebooks are the failure of the electronics or one cell has short-circuited.
If you obtain the Li-Ion cells from used battery pack (for notebooks), first the cover and the electronic part should be removed. Then measure the voltage of the cells. If the voltage is close to 0, the cell is dead. Mark the dead cells and later dispose of them in a recycling bin. Usually 2-3 cells are connected parallel. If one fails, the ones connected parallel will also fail. Leave the cells connected parallel together. Do not connect cells parallel which were not originally parallel.

Charge the good cells then measure the capacity of them. Mark the capacity onto the cells.
Connector of the cells: for fast and easy replacement use RCA male connector.
Power cable of the cells: 16 cm long 2x0.75mm double isolated PVC cable.

Preparation of the new battery pack:
First remove 3-3 cm from the external isolator. Be careful not to damage the inner isolators!
Remove 4-4 mm from the inner isolator then coat the wires with tin.
Then solder the RCA connector, use 9 mm long (3/1.5 mm) heat shrink tube for insulation. See the pictures for more details.
Click for large image... Push the external isolator until it reaches the heat shrink tubes at the RCA connector.
Then screw on the external cover of the RCA connector. Glue it with PVC glue.
Now solder the cables to the pins of the battery cells. Check the polarity! The inner pin of the RCA is positive (+). Use heat shrink tube for the insulation of the positive wire (30 mm long 3/1.5 mm).
Then use double sided adhesive (used for mirrors) to attach the power cable (8x20 mm).
Finally, use an 80 mm long heat shrink tube (type 35/12 mm for a single cell, type xxx/xxx mm for double cells and type xxx/xxx mm for three cells) for the new battery case.
Glue both ends with silicon or PVC glue to make it water-resistant.

Click for large image... Click for large image... Battery indicator: If you use several battery packs, it is useful to mark the flat batteries.
This is the cheapest solution: place a red 7x12-mm insulating tape outside of the battery pack then cover it with a black insulating tape: cut a 21 mm long one and fold back 5 mm. See the pictures.
If the battery is discharged, simply move the black cover next to the red mark.
Important: This type of battery pack does not have an electronic protection circuit, so you have to take care not to discharge the Li-Ion cell under 3.0 Volts - the red LED (with KIA7033P) is designed for that purpose.

4.1 Recharging the Li-Ion battery

It is easy to recharge a single Li-Ion cell or cells connected parallel. It is required to limit the voltage and current.
The maximum voltage is 4.20 Volt and the maximum charging current is 1 to 3 Amperes (it depends on the type of the cells), but the 1 Ampere is adequate and it will be easier to design the charger.
You can buy a charger for a single Li-Ion cell or cells connected parallel, or based on the following guide you can create one yourself: Wiring diagram and a guide how-to make a Li-Ion battery charger (Sorry, it is in Hungarian at the moment.)

Notes: The lamp should be prepared very carefully. If the water gets into it, the lamp will break down rapidly. Or if the lamp has a contact failure, you will not be able to enjoy using it.
The electric insulation is very important! The battery contains such huge amount of energy, in case of a short circuit it can cause a fire or an explosion!
Make and use the lamp at your own risk.

5. Testing

Before you make the final assembly and following that too, you are advised to test the lamp thoroughly.
With a fully charged battery switch on the lamp and after 10 minutes the temperature of the lamp should be under 50 C (at cool room temperature with slight air draft). Test both LEDs at both power stages.
During the test, shake and knock the lamp to notice any contact failure. Check the battery connector and the switches too.

It is worth trying how long the lamp/battery lasts. With a fully charged battery switch a LED to "1 Eco" position. Note the time (start a timer) and leave it until the voltage of the battery falls under 3.2 V. This time will be the longest illumination time with that battery pack. Repeat the same procedure with "2 Max power" stage too.

Finally, there is only one thing left to do and that is to mount the lamp onto the helmet and head for caves! -:)

6. How to use the lamp in extreme conditions

Cold weather (below 0 degrees)
When the lamp is cold, the efficiency of the lamp is high, therefore, it is better to use it in "1 Economy" mode.
Under -10 degrees the capacity of the Li-Ion battery fails rapidly, so keep the battery warm, for example keep it in your inner pocket of your coat (use a power cord extension if necessary).
Under -20 degrees the Li-Ion battery is unusable.
Recharging the Li-Ion battery is only possible above 5 degrees.

Hot weather (over +30 degrees)
When the lamp is hot the efficiency of the lamp is low, and the battery could get hot too, therefore, it should be used in "1 Economy" mode.
The LED is protected against overheating by the multifuse, but as the temperature rises the efficiency gets lower and lower.
Over 30 degrees the Li-Ion batteries must be charged with strong ventilation, and deep discharge should be avoided!
Over +50 degrees the Li-Ion battery is unusable.

Clayey and muddy environment If the lamp gets muddy, rinse it with water. The clay should not be cleaned with your finger or a cloth from the lens protector because it could scratch it.
If you know that a lot of water, clay or mud will reach the lamp, you may want to protect the connector of the battery with insulating tape. This also prevents the power connector from accidental disconnection.
Hint: For easier removal, make a flap by folding back about 1 cm of the insulating tape.

Under water The lamp is water resistant but it is not suitable for diving.
If it is taken under water, cool the lamp before immersing as follows: the cap of the LED should be kept in cold water for a minute.
The insulation of the switch is the weakest point of the lamp. If a hot lamp is taken under water, as the lamp gets cooler it will suck in the water, so it is better to cool the lamp beforehand.

Damage, rough environment
The carefully constructed lamp is quite robust, but always prepare for the worst!
Make sure your lamp is attached to the helmet securely. If you do not use a screw to attach it, always tie the power cord to the helmet with a string.
If the protector of the switch is damaged, bandage it with insulating tape until you replace it. (Before the replacement dry the switch thoroughly.)
If the power cord is damaged, disconnect the battery and only reconnect it if you are sure there will not be a short circuit.
If the holder plate is damaged, gently bend it back in such a way that the insulation is not affected between the cap and the holder plate. If you are not sure, unscrew the plate and after repairing it, glue it again with silicon.

Finally, no matter how reliable your headlamp is, always take a spare lamp with you for caving!

7. Front lamp for bicycle

Based on the description given above, it is easy to create front lamps for bicycles.
I chose Li-Ion batteries for my bike, but a dynamo could also be used.
I suggest you use two 5 Watt LEDs, one with 10 and the other with 30 or 10/50-degree lens.
If you prefer the dynamo, you can use a simple but very precise circuit.
Solder a resistor between the OUT and ADJ pin of an LM350T IC. For example, use a 3.67 Ohm (1 W) resistor for 340 mA, or 1.8 Ohm (2W) for 690 mA...
The LM350 should be mounted to the frame of the bike or onto a heatsink (4x4cm).
Wiring diagram: Coming soon XXXX
Datasheet of LM350 IC
Click for large image...
Bicycle lamp for city use
Click for large image...
Light with a 30 degree lens

8. Internet links

Do It Yourself LED Bike Light Guide on bikeled.org
Information about factory made LED based lamps, about components, etc.
Other useful links are displayed here.

All comments and ideas you may have are welcome. info@dola.huE-mail
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© The description above is free for non-commercial use. For commercial / business use, please contact me.