5W power LED in series to 220V mains for aquarium, How can I do that ?

#12

Joined Nov 30, 2010
18,224
It looks like you need about 7.5 ohms, 8 watts for each resistor. One resistor for each LED.
It isn't exactly 7.5 ohms, but that's a standard size.
With 5 volts to use up, you might build a current driver from an LM317 but it's been difficult enough to come up with enough information to name one resistor!
 

Dodgydave

Joined Jun 22, 2012
11,285
if your going to run it with all the leds in series,

then ten leds is 70V , twenty leds is 140V, thirty leds is 210V.

i would use a pc power supply and put a 7 ohms resistor in series with each led, and put them all in parallel across the 12V supply,

ten leds should take 7.5Amp,
twenty leds is 15Amp approx.
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
It looks like you need about 7.5 ohms, 8 watts for each resistor. One resistor for each LED.
It isn't exactly 7.5 ohms, but that's a standard size.
With 5 volts to use up, you might build a current driver from an LM317 but it's been difficult enough to come up with enough information to name one resistor!
Ok the capacitor in series with each LED on positive side, and each LED will go in parallel , and plug it into 5 v dc ? is that what you mean sir ?
and to connect the LM317 in what configuration ?
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
if your going to run it with all the leds in series,

then ten leds is 70V , twenty leds is 140V, thirty leds is 210V.

i would use a pc power supply and put a 7 ohms resistor in series with each led, and put them all in parallel across the 12V supply,

ten leds should take 7.5Amp,
twenty leds is 15Amp approx.
Wow, thank you so much sir, and no other part is needed to be added on to this , and also, what is the maximum no. of LEDs I can put into this parallel circuit, with PC power supply of 12v, and also can I mix Parallel and series so as to get maximum, use of the spare amps from the power supply ?
 

#12

Joined Nov 30, 2010
18,224
Ok the capacitor in series with each LED on positive side, and each LED will go in parallel , and plug it into 5 v dc ? is that what you mean sir ?
and to connect the LM317 in what configuration ?
What?
Where did 5 volts come from?
How does, "You need a resistor" turn into a capacitor?
How does, "You need a resistor" turn into, "Use an LM317"?
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
What?
Where did 5 volts come from?
How does, "You need a resistor" turn into a capacitor?
How does, "You need a resistor" turn into, "Use an LM317"?
Sorry I confused it with something else, now am clear with the thing, thanks so much for the support :)
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
Well thank you everyone for all the support, after much mind boggling quest, you people helped me figure it out (I am a biology student, and this is the first time am getting into tweaking with electronics) So I hope it will work out for me, I'll get it done, and PM you all with photographs that how it worked out, till then Take care everyone, and bless you all. again thanks so much :)
 

Alec_t

Joined Sep 17, 2013
14,280
.... but if your 12V transformer can provide only 5A then the maximum number of LEDs it will power is 6. The LEDs must each have a series resistor as stated above. The LEDs cannot be connected in series.
 

wayneh

Joined Sep 9, 2010
17,496
It's remotely possible the LED would run off the 5V rail of the PSU and you might get away with no resistor. It's also possible that two LEDs in series might run off the 12V rail.

Neither of these cases is ideal and neither is likely to use the full power capability of the LEDs, but could work in a pinch. As you've learned, one LED cannot take the full 12V.

Your transformer may put out 12V AC RMS, but that means it is putting out peaks at 16V.
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
It looks like you need about 7.5 ohms, 8 watts for each resistor. One resistor for each LED.
It isn't exactly 7.5 ohms, but that's a standard size.
With 5 volts to use up, you might build a current driver from an LM317 but it's been difficult enough to come up with enough information to name one resistor!
Ok so I plugged in my LEDs with 7 Ohm resistor to the 12v dc, with resistor on the positive side of the led, plugged it on and then after 50 seconds., the resistor smokes up, What did i do wrong ? checked with 10 ohm resistor same it is.
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
It's remotely possible the LED would run off the 5V rail of the PSU and you might get away with no resistor. It's also possible that two LEDs in series might run off the 12V rail.

Neither of these cases is ideal and neither is likely to use the full power capability of the LEDs, but could work in a pinch. As you've learned, one LED cannot take the full 12V.

Your transformer may put out 12V AC RMS, but that means it is putting out peaks at 16V.
You mean to say that the transformer is putting out 12v AC, and not 12v dc ? and the transformer is made into 12v by connecting a 4700uF condenser and two diodes, is it AC or DC ? I got confused with this .
 

Thread Starter

Ronald Saraswat

Joined Apr 2, 2015
41
I told you you need a 5Watt resistor, otherwise it will burn out.
But I guess, that wouldn't be energy efficient ? would it be ? using a 5W resistor.

Would you rather advice., on using some other circuit then resistor, cause., the LEDs take more then a few hundreds of amps and I researched that resistors are not a energy efficient way to tackle with LEDs with such high ma consumption
 

Dodgydave

Joined Jun 22, 2012
11,285
your better off using different low current leds , or if you insist on using these high power leds its either resistors or a constant current regulator,or dedicated led driver.
 
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