300-pc. LED Dimmer

[grandmasteralok]

Hi guys,

It's been a while...

I have been trying to build a 300-pc. LED lighting unit... It's a simple project consisting of 300 pieces of 5mm superbright white LED's... I was able to make them light up using 4 pcs. of AA NiMH batteries, which then I switched to an 8-pc. AA power source for prolonged sustained output... What put me to a halt is the question of how to make them dim altogether... I heard about potentiometers but I don't know how to use them, I mean would I still need the resistor for each LED??? One more thing... Since the potentiometer has 3 pins, which one will I connect to either + or - leg of the LED???
It would be best if you could provide me a diagram and parts listing, especially the potentiometer or any dimming piece...
By the way, I don't have access to any chip-programming device so basically I am doing an non-programming project...
I plan to use 8-10 pcs. of AA NiMH batteries as power source or a 12v AC-DC converter...

Your help is very much appreciated...

 

[grandmasteralok]

One more thing, I would also want to do a 150-pc. LED dimmer...

 

[audioguru]

A few hundred LEDs use a fairly high current. But a potentiometer is designed to control a very low current like a volume control at the input of an amplifier.

A modern led dimmer does not dim by making itself heat up, instead the potentiometer controls the very low current at the input of the pulse-width-modulation dimmer circuit where an output power transistor or Mosfet turns on and off at a high frequency and the pulse width controls the brightness of the LEDs. The transistor or Mosfet does not waste power by making heat because it fully turns on with very low waste and it turns off with very low waste.

A simple 555 timer IC can be the PWM controller that drives the power transistor or Mosfet.

 

[grandmasteralok]

If that's the case, how could I control the intensity of the lights???

 

[alec_t]

In post #1 you want a 300 LED dimmer and in post #2 it's a 150 one?
Should all LEDs be at the same brightness at any point in time?
Can you connect them in series? For example, 3 LEDs could probably be connected in a series string if you have a 12V supply. Then you would need 100 (or 50?) strings.

how could I control the intensity of the lights??

You switch them on-off-on-off..... very rapidly. To the eye they seem to be on continuously with a brightness which depends on the ratio of the 'on' time to the 'off' time. This is called Pulse Width Modulation (PWM).

 

[grandmasteralok]

Sorry, I meant that there will be to projects... One is consisted of 300 LED's and the other, 150...
I can't switch them on-off because it will serve as a light source for my photography hobby, hence, I need a dimmer so I could adjust the brightness...

 

[alec_t]

I can't switch them on-off because it will serve as a light source for my photography hobby

That's a complication. In that case you will need a respective controllable current source for each LED or LED string (probably not practical), or else a single controllable voltage source for all of them.
What is the spec of the LEDs you are using? Brand, forward voltage, max current...?

 

[grandmasteralok]

Yeah, quite complicated (for me, at least)... The reason I thought of using a potentiometer but I have no idea which one to use or even how to use it...
I don't know the brand of the LED since the seller does not know as well... As for the forward voltage and max current, also no idea... But for the other projects that I did, I powered them using a 9v battery with a 220 ohm 1/4 watt resistor on each LED of up to 30 LED's which lasts for up to 3-4 hours (NiMh) and 5-6 hours (alkaline)...

 

[be80be]

A 12 amp wire wound potentiometer but it would sure be hard on batteries that can burn off 108 watts

this would work for the easiest way to dim them View attachment 68003

I would go a different route

Brings back the days when motor controllers used these to slow down sewing motors

But you know Cars use wire wound resistor to slow the heater fan down. Don't burn off a 100 watts but a good 50 LOL

here a link to it **broken link removed**

But If you want and are not in a big hurry you could make something better

You camera shutter speed would maybe pick up PWM but you could make a filter that would make the power look like you just lowered the voltage.

Or make a constant current supply and just lower the output of power.

 

[grandmasteralok]

Thanks for the suggestion...
I really do prefer the potentiometer approach or a step-down / step-up button (- or +) because there are times that I take pictures of my nieces (new born) so I can't use max output on them...
Max output plus filter on my lens would do good for the grown ups but not for the new born...
The current supply is a good alternative but will require power outlets all the time... I need this project to be portable and DC powered...

Thanks for the suggestions... More suggestions are welcome...

 

[ronv]

You could try a pwm dimmer like this. The frequency is high enough I don't think the phosphors in the led will have time to fade.

 

[be80be]

You may not need one that big im just going by what you said 30 leds at nine volts and 220 ohm resistors
so I figured your using 300 leds 300 resistors which is and your giving each led about 40 mA thats 108 watts

 

[grandmasteralok]

Thanks, ronv... I could try this one with just one or two LEDs... If this does the trick, how many LEDs could I fit in??? By the way, how could I dim the LEDs out??? I mean increase or decrease the intensity of the LEDs??? Could you please provide the parts used together with the labeling in the diagram??? Thanks...

@be80be - I'll do the 150-LED first... If all go well, will do the 300 next...

 

[grandmasteralok]

@ronv - Is the potentiometer the one labeled as U2???

 

[ronv]

Yes. U2 is the potentiometer with a value of 10K ohms.
D3, 4 are your leds.
M1 is an N channel FET with at least a 10 or 20 amp rating. (If you use a high enough rating you won't need a heat sink)
The capacitors are in Ufds.
It will work with 2 to 300 LEDs. For each additional set of two use the 220 ohm and 2 leds in parallel with the ones already there.

We should check what type of leds you are using. (a link would be nice)
Also, 300 leds will make some heat. Depending on how close together they are you may not be able to run them at full power.

 

[grandmasteralok]

I looked for another supplier and found this:
**broken link removed**

 

[ronv]

Make the 220 ohm resistor 270 ohms instead.