LED heat question

[zikac]

Hi!
Im planning mounting some 3W power LEDs in my grow cab, can i mount the LED stars directly to the wall on the cab that is made of MDF (wood), or would it produce too much heat? Also, do i have to protect the leaves from being able to touch the LEDs?

Also I'm unsure about the wiring... Can i take 4pcs 700mA 3.0V (3W) LEDs and connect them in serial to a 12V source (3.0V * 4 = 12V)? Also if I'd like to put more series in parallel, how do i calculate the power draw?

 

[rives]

Hi!
Im planning mounting some 3W power LEDs in my grow cab, can i mount the LED stars directly to the wall on the cab that is made of MDF (wood), or would it produce too much heat? Also, do i have to protect the leaves from being able to touch the LEDs?

Also I'm unsure about the wiring... Can i take 4pcs 700mA 3.0V (3W) LEDs and connect them in serial to a 12V source (3.0V * 4 = 12V)? Also if I'd like to put more series in parallel, how do i calculate the power draw?

Those stars are not intended to take the place of a heat sink - they are to be used in conjunction with one.

Yes, you can run (4) 3v leds in series on a 12v supply. You do realize that there needs to be something to limit the current, whether it be a current-limiting resistor or a constant-current driver? Series circuits are additive as far as voltage (3v x 4 = 12v), but they all use the same current. When you run a parallel string, the voltage remains the same (12v supplied to it), but the current that the driver sees is additive (700ma x 2 strings = 1.4 amps). Parallel strings are very difficult to match up, and tend to run away from each other if not perfectly balanced. Also, if one string opens, the other will get the full current from the supply and burn up.

 

[stratmandu]

Good info from Rives. At least try to find some scrap aluminum channel or bars or strips, nice and thick, to polish smooth on one side and thermal glue the stars on there for cheap-but-good heatsinks. The more metal the better.

PS heatsinks on the cheap? Go by your local recycling center, check the metal bin, and take anything that looks useful OUT lol. I do it almost every week and the old guy just rolls his eyes. Its recycling, right?

 

[zikac]

thanks for the info guys!
and thanks for clearing the electronics up for me, rives. i've ordered a "driver" from ebay.

 

[T_B_M]

You don't want thickness per say. You want the most surface area possible. This is why heat sinks have fins. More surface area gives more thermal dissipation.

 

[zikac]

so wood doesn't work as heat sink at all?
i'm going to put leds over the walls in my speaker-grow, so they will be spread over i wide area. i don't know how much heat these leds produce nor how well wood works as heatsink, but is it really necessary with aluminium heatsink in this case?

 

[rives]

so wood doesn't work as heat sink at all?
i'm going to put leds over the walls in my speaker-grow, so they will be spread over i wide area. i don't know how much heat these leds produce nor how well wood works as heatsink, but is it really necessary with aluminium heatsink in this case?

Wood is a far better insulator than conductor. If it was saturated with water, it might be fractionally better, but still totally worthless as a heat sink. Think of things that are electrically conductive and typically they are thermally conductive - copper, aluminum, etc. Steel would be a far better heat sink than wood, but still very poor compared to aluminum or copper.

As far as the heat that the leds are producing, depending on the led they are probably somewhere from 20-35% efficient, so the balance of the consumed wattage is going to heat. Yes, you will need a heat sink.

 

[zikac]

thanks for the advice!