Goals

What we wanted to achieve developing our lamp:

• Weight - the headlamp / battery combination has a reasonable weight
• Cold - the whole must function at extreme cold weather conditions
• Light - the set should provide enough light (at full capacity) for training a larger team (also in a dark forest without snow!)
• Uptime - optimise long-term burning time

Some general facts about lamps and batteries

How long does my headlamp continu burning?

Below the method (eplained with some example figures) to calculate burning time:

• V = Voltage, you can find this value in the specifications of the battery and bulb
• Ah = Ampère/hour, you can find this value in the specification of the battery
• Wh = Watt/hour, the power that the battery can deliver. So (VxAh)=Wh (f.i. 7.2 Volt times 6.5Ah = 47 Wh)
• W = Watt, this is what your bulb consumes, therefore (VxA)=W (f.i. 4.9 Watt)
• Burning time = Wh / W (thus 47 Wh / 4.9 W = 9.6 hours)


This time is always an approximate figure. In practice the burning time is shortened by losses, surroundings temperature, age of the batteries etc. You can to obtain a realistic value by reducing the calculated value with at least 10% (in our example 9.6 * 0.9 = 8.5 hours).

Which type of battery?

Ni-Cd battery - Nickel-cadmium batteries

• 1.2 voltage per cell therefore can be used for 7.2 volts as 6 volts applications
• Ni-Cd batteries cause environmental pollution due to the cadmium in the battery
• Memory effect: a Ni-Cd rechargeable battery used over a regular period while consuming only a small part of it's capacity cannot give it's full energy any longer. This happens when parts of the rechargeable battery material mass are excluded from the loading- and discharging procedure. The unused material-mass "clumps" together and is not becomes unfit for a chemical reaction. The unused capacity space becomes slow-acting, losing its voltage, as if the rechargeable battery is already empty, even though enough energy is still stored
• Nickel-cadmium batteries can be reloaded at least 700 times. The battery loses something less than 1% of its power per day. This could mean losing 70% of the initial capacity under unfavourable conditions

Ni-Mh battery - Nickel-metal-hydride batteries

• Voltage 1.2 per cell
• The energy density is higher compared with other good quality Ni-CD cells
• They can be loaded at least 700 times and can be used until -20 degrees Celcius
• Self-discharge of 15% in the first week following upon fully loading the cell
• Memory effect Ni-Mh: being stored longer than 6 months, this type of rechargeable battery will build-up a memory-effect by losing up to 15% of its initial capacity

Li-ion battery - Lithium-ion batteries

• Voltage 3.6 per cell, therefore it cannot be used for 6 volt applications
• An extremely low self-discharge of maximum 15% over the period of a full year
• Better voltage conditions under high strain and cold weather conditions up to -40° Celcius


The Li-ion battery is the best battery for our project.

Advantages

• Can be used under extreme cold circumstances
• Low in weight with a energy density at least 40% higher compared to Ni-MH cells
• No memory effect


Disadvantages: (price)

• Li-ion batteries are more expensive
• Li-ion battery sets require a cost-intensive sealing as they must be absolutely waterproof

The headlamp

CSF Headlamp:

The original CSF headlamp is light in weight and is suiteable for exterme cold conditions (UHMW frame).

• Features: vacuum sealed mercury coating on reflector, designed to withstand heat from the brightest bulbs and provide excellent reflective qualities
• The CSF is a 6 volt application and can be used with 4 D-Cell batteries or 2 D-Cell 3 volt Lithium batteries
• These 3 Volt Saft Lithium batteries can be used in exterme cold but are very expensive (17.00 US$ each)

The adaptations

Adaptations made by us:

Replaced the light bulb

• We replaced the standard CSF bulb by a Xenon Star lamp (4.8 Watt) which can be used with 7.2 volt application (IMPORTANT note: never look directly at a Xenon Star Lamp when it's illuminated!)

Added power-controlled switch

• The switch comes with 4 default software programs, which can be adapted by the user. The chosen program corresponds with the number of times the switch button is pressed:
1: On/off switch
2: 100% and 40% power (the user can put the dimmed setting between 40% en 75%)
3: 100%, 60% or 30% power respectively
4: variable (by holding the button) between 10 en 100%
• The switch has an automatic S.O.S function (lamp flashes 3-short, 3-long, 3-short for an indefinite period of time)
• To increase the life span of the lamp the voltage increases to the maximium level in 1 second

Used Artic-Wire

• We fitted the Li-ion battery with Artic-Wire. This wire is still flexible in extreme conditions (up to -40 Celsius)

The results

Our project resulted in a rather spectacular headlamp, which we named Polarstar:

• With the 6.5Ah battery the burning time is about 8.5 hours (with 4.5Ah this is 6 hours and with a 9Ah batteryup to 12 hours)
• The lifetime of the Xenon Star bulb is about 25 hours at 100% power

The pictures below are taken around 22:15 hours with a clear sky on August 27, 2005.
Lowlandstrail Polarstar at 100% power. The pile left in the turning to the right is 49 meters away.


Lowlandstrail Polarstar at 40% power. The pile left in the turning to the right is 49 meters away.