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– RETRO XP - Technical Details –

RETRO XP - Light Level Usage

When you are on a multi-day trip Mode 1 - still provides a perfectly adequate amount of light, so you can now consider dumping the carbide or spare batteries as you can easily achieve +100 hours (for mixed power mode usage with predominately Mode 1 output) lamp run time from a standard Oldham battery.

For normal activities Mode 2 is perfect and more than enough at 150 lumens! This is 3 times the light output of a standard Oldham 3W bulb, however due to the light output being closer to 'day light' and having a wider flood angle the perception of brightness is enhanced.

If you require an extra amount of light then Mode 3 or 4 gives that extra illumination.

RETRO XP - Run Times

If you have a battery pack or cell combination that is not listed below it is possible to calculate the estimated battery run time, see: RETRO XP - Input Voltage / Current Curves.

The table below lists estimated lamp run times for various battery packs. Light output is in Lumens (lm), power in Watts (W):

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RETRO XP - Input Voltage / Current Curves

The switch mode power supply keeps a constant power level to the LED's over a varying input voltage. As the input voltage falls the input current rises. From the curves below it is possible see the current that will be drawn for a particular input voltage. This can be used to estimate the lamp run time on a particular battery pack.

If a 3 cell NiCAD battery pack with a capacity of 6.5Ah is used to power the RETRO XP, then the total input voltage is 3.6V, this corresponds to a input current of 0.802A at 2.4W, 0.567A at 1.7W, 0.351A at 1.1W and 0.109A at 0.33W, dividing the battery pack capacity by the input current and multiplying the result by 0.9 will give an estimation of the run time for a particular setting - 2.4W = (6.5 / 0.802) x 0.9 = 7.3 hours run time, 1.7W = (6.5 / 0.567) x 0.9 = 10.3 hours run time, 1.1W = (6.5 / 0.351) x 0.9 = 16.7 hours run time and 0.33W = (6.5 / 0.109) x 0.9 = 53.7 hours.

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RETRO XP - Efficiency Curves

Using a switch mode power supply to drive LED's is more efficient than limiting the current with a resistor especially at higher powers (a resistor can only be used if the forward voltage of the LED's is lower than the batteries - in this case with two 1W LED's the forward voltage is around 6V). Where possible it is better to use a higher number of cells (higher input voltage) to keep efficiencies high and power loss to the minimum. Efficiencies over the whole power range (0.4 - 2.4W) for different cell combinations are: 2 cell battery pack (2.4V) 73 - 82% efficiency, 3 cell battery (3.6V) pack 83 - 86% efficiency, Li-Ion battery (3.7V) pack 83 - 86% efficiency, 4 cell battery (4.8V) pack 85 - 88% and a 5 cell battery (6.0V) pack 90 - 92% efficiency.

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RETRO XP - Light Output

Due to the power supply light output remains constant as the battery pack drains. The LED's will still give out light when a normal bulb would not even glow. The optimal input voltage range is 1.3 to 6V, however the RETRO XP will also work with input voltages as high as 7V (absolute maximum), if the input voltage is above 6V then the lower settings will actually give more output than stated - this is because the switch mode power supply cannot regulate when the input voltage goes above the LED forward voltage - this will not damage the unit. If you look at the curves below this can be seen above 6V.

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