Back to RETRO2

– RETRO 2 - Run Times –

The table below lists estimated lamp run times for various battery packs. Light output is in Lumens (lm), power rating of bulbs / LED's is in Watts (W).

Back to RETRO2

RETRO 2 - 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 5Ah is used to power the RETRO 2, then the total input voltage is 3.6V, this corresponds to a input current of 0.80A at 2.0W, 0.50A at 1.5W, 0.35A at 1.0W and 0.11A at 0.3W, dividing the battery pack capacity by the input current will give an estimation of the run time for a particular setting - 2.0W = 5 / 0.8 = 6.25 hours run time, 1.5W = 5 / 0.5 = 10 hours run time, 1.0W = 5 / 0.35 = 14.3 hours run time and 0.3W = 5 / 0.11 = 45.5 hours.

Back to RETRO2

RETRO 2 - 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 7.1V). 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 (0.3 - 2.0W) for different cell combinations are: 2 cell battery pack (2.4V) 74 - 80% efficiency, 3 cell battery (3.6V) pack 82 - 85% efficiency, 4 cell battery (4.8V) pack 85 - 88% and a 5 cell battery (6.0V) pack 86 - 90% efficiency.

Back to RETRO2

RETRO 2 - 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 2 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.

It is also possible to make the unit work from 1V (it will work down to 1V normally, but only start from 1.3V because of the reverse battery protection) by using the shorting jumper provided once correct battery polarity and connection has been established.

Back to RETRO2