I have build an LED array consisting of 75leds, 5 connected in series with a 39ohm-1/4watt resistor and 15 such series connected in parallel to the rectifier circuit having 2-IN5408 diodes and 1- 25V_4700µF capacitor. The transformer is 12-0-12v_3A. The leds forward voltage is 3.3v-3.4v and forward current is 60mA. As the whole fixture is for an aquarium i have to run it continously for 6 hrs and the transformer gets quite hot (cannot touch it for more than 5 secs)? Is the rectifier circuit and the transformer not adequate for running the leds?
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1\$\begingroup\$ Please draw a schematic! \$\endgroup\$– winnyCommented May 18, 2018 at 9:19
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2 Answers
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It should be adequate.
Measure the voltage across the 39-ohm resistors and you should get ~2.34V. If it is significantly more then you should increase the resistor values to get ~60mA.
answered May 18, 2018 at 4:05
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That is not too hot. You may be able to reduce the heat with an improved rectifier, by reducing current, or using a more efficient number of LEDs in the strings.
Efficiency is mostly a function of how close the supply voltage is to the LED string's forward voltage.
You measure the DC forward voltage of the LED strings and the supply voltage.
Then select a current that gives you the desired LED intensity.
This online calculator will give you the efficiency based on the measured values.
answered May 21, 2018 at 4:07