I'm making an led light for video shoot purpose. It's an array of 20, 5w led in parallel. The problem I'm encountering is, current drops when I'm connecting them in parallel. My power supply is adequate, it's a 12v 10amp power supply. When I connect a single led directly to 12v supply, the current I get comes to be .8 amps. So .8amps X 12v ~ 10w, which is higher than the led's output rating, but when I connect 20 of them in parallel, the current flowing through is 4.12 amps. So 4.12amps X 12v ~ 50w. When logically the current flowing should at least be 8.2 amps. What is happening here? Kindly help.
It is hard to figure out just what you're doing. Is it possible that your LEDs have built-in current limiting resistors, and are intended for 12 volt operation? That would explain why connecting one to 12 volts doesn't kill the LED. Plus, if the LED takes 5 watts, that would leave 5 watts to be dissipated in the resistor, which seems about right. However, this would make the LED get very (very!) hot, and it's hard to see how this could happen. But let's say that this is the case. Then, when 20 LEDs are connected in parallel, the total current draw is 20 x 0.8, or 16 amps, and this would cause your power supply to limit. Are you sure this isn't happening? When you get 4.12 amps, what is the power supply output voltage?