LED driver help

[flamer]

Hi all, been researching but ended up with more questions than answers

I bought outdoor string lights online, it's 25 LED bulbs, 24VDC. The bulbs have no markings whatsoever but it said online somewhere they are 1 watt. Where im getting confused is the power supply it came with says Prated 6 watts, there is no mention of amp output. I should mention they run perfectly fine on this supply. Just can't understand how 6 watts can drive 25x1watt bulbs.

Due to other factors I can't use this power supply, I need to buy another one, so I think I need to buy a constant current driver, I believe a 12-40VDC, 250mA will work does that sound right? And what if I got went higher ie 320mA will that burn the LEDs out?

Thanks for any help!

 

[danadak]

The leds a series parallel combo ? The 24 all in series, depending on color, >> 24 Vdc :



Constant current is prefered for leds in series, helps in brightness matching.

LEDs can be run at less than their ratings and produce usable lkight, depends on application
and goals for design.

A 1 W LED, if its Vdrop = 2V we have P = I x V, or I = P / V = 1 / 2 = .5 A

Regards, Dana.

 

[kellys_eye]

Just can't understand how 6 watts can drive 25x1watt bulbs.

Clearly it can't. Without making actual measurements we can only make assumptions. Assuming the PSU is rated correctly then the LEDs are, individually, rated at 0.25W, not the 1 watt stated elsewhere. This 0.25W figure is still rather high for a standard LED where 50mA (at any voltage between 2V i.e. red and 4V i.e. white) gives a power dissipation of 0.1W and 0.2W respectively.

Most standard LEDs are run at 20mA which gives an even lower power dissipation.

You would have to make some voltage or current measurements to determine the reality.

Most (Chinese) manufacturers overstate the ratings of such devices anyway. Pinch of salt moment.

 

[flamer]

Thanks both for your replies. I measured the supply, with load its 21.7V and without load load it was 23.7v. Not sure anyway I can test power draw with a multimeter. But

However I had a bright idea last night, the reason why I couldn't use this power supply is because its a plugin (wall wart) type supply and I need to hard wire it in, so what I did instead of getting a new one, I have cut the plastic open and extracted the circuit board, I will mount that into a junction box and solder the wires onto it.