Help on power source for simple LED array

[chugadie]

I'm trying to wire together some red and blue LEDs into a grow light. I'm thinking of 8 parallel rows of 5 350ma LEDs in series. Each series row might need one LED of a different voltage, 3.3v

The only power supply I can find on mouser that plugs into a (US) wall outlet is 16v DC 2.4A @47W.

Is this wall wart powerful enough to comfortably supply 40 LEDs?

each series:
2.4v * 4 + 3.3 * 1 = 12.9 v

each parallel:
.350 A * 8 = 2.8A

This would result in the LEDs only being slightly dimmer than their top rating if the 2.4A power supply is trying to deliver 2.8A to the whole thing, right?

I can't seem to find the right kind of power supply, so I'm wondering what values are fungible or if my math is wrong.

 

[ronsimpson]

LEDs are not voltage devices they are current devices. You should never place 3.3 volts across a "3.3 volt" LED. It is a 350mA LED that just happens to need approximately 3.3 volts to work.

"2.4v * 4 + 3.3 * 1 = 12.9 v" I don't have a problem mixing LEDs in series. Some people do. The 12.9 volts is very approximate. You need to either drive it with a constant current source or add a resistor!

You are paralleling 8 strings of LEDs. This is not good without a resistor in each string.
One string might turn on at 12.9V and another string will light at 11 volts and blowup at 12.9. A third string might need 14V.
This is why when paralleling LEDs you need to have resistor for each string and probably use a 15V supply. (or more)

If you are very lucky and have LEDs all made on the same day, same minute, their voltage will be almost the same.
There is much talk on this forum about paralleling LEDs and using LEDs with out resistors. Search!

 

[alec_t]

If a LED is rated 350mA, the slightest excess current is likely to destroy it. It is not good practice to run LEDs at their maximum current. Always allow a good safety margin.

 

[ronsimpson]

1 watt LEDs need a heat sink, or at least wide PCB traces to take away heat.