hi all,-im converting my marine fish tank from flourescent compact tubes to leds, ive ordered and recieved the leds but ive dropped a boo boo on the drivers there will be 3 strings of leds but output of the one im interested in altering (a meanwell clg-60-24,60w watt 24volt)is a constant current device pumping out 2.5amps at upto 24volt-the leds it will be powering are 7 off 3 amp cree xmls white in series(£6 each),so they will take the current ok,the thing is they are going to be bright and im worried they will be too bright-i wanted dimmable drivers(ELNs) but they are rare in the uk and of course i leapt in and bought the cheaper none dimmable ones,anyhow at work we use low ohmn high wattage resistors and i started thinking if i put one or more in parallel to the led string it would shunt some of the current thro that(i have LARGE heatsinks for this project btw)i could of course add another string in parallel but then you have to start 'balancing' the current thro the strings and its another £42 and may well end putting out just as much light but spread out
ok my problem id like to alter this shunted current with a timer so more pass's thro the leds and adjusts the brightness up or down,i thought timer controlled relays on a string of resistors but the supplier of my leds thinks that might 'shock' them and either blow them or shorten their life so my thoughts turned to a power transistor controlling the current thro the resistor/bank-is this possible ?
im thinking something like a 24 ohmn resistor/s passing 1 amp (disappating 24 watts ?) at switch on, passing thro a 2n3055 which gradually switchs off forcing more current thro the leds and vice versa(dawn/dusk effect)
Soooooooooooo am i talking rubbish ? if not can someone point me to a circuit please
thanks howie

 

just incase someone might wonder why i dont put a dimmer switch on the input -i presume id have to drop below 90 volts before it had an effect ?

Input Voltage 90 ~ 264VAC 127 ~ 370VDC Input Frequency 47 ~ 63Hz Power Factor PF0.9 at 75 ~ 100% load, 115VAC / 230VAC AC Current 0.8A/115Vac 0.4A/230Vac Inrush Current 10A/230Vac Leakage Current <0.75mA/240VAC Current Adjustment Range Fixed. Can be modified between 3% ~ -25% rated output voltage

 

Just remember that, if you shunt 24W, (50%) ? 50% power is not giving a brightness that looks halved. You probably wan't less light than this. Nah, I don't think this is the way to go.

The wide input range of the psu allows it to be used on both 110VAC and 230VAC systems. A VAC lower than the operating voltage can make the psu operate unpredictably.

 

I know of some very good techniques for dimming LEDs, how complicated are you willing to go. If you do it yourself (as with a soldering iron) it is cheap, if you buy the parts not so much.

 

im interested in any advice,i can use a soldering iron but if its cheaper and quicker to buy then im all ears

 

Do you have it with u know, the soldering iron and solder too...

 

return the clg...buy an eln