Using Pulse Width Modulation to enable INCREASED intensity and efficiency. Cost savings? Chk it out!

[Gigaahxl]

Well Its ..yet again been a VERY long time since I've visted you guys.I'm thrilled to see the V2 scrubber released.

In my travels as I venture further and further into electronics and micro controllers. I found something I guess I knew(from lasers) but never connected the dots. I immediately thought of you guys so I wanted to pass this bit of information on. Because i've not heard mention of it in relation to algae scrubbers..or aquarium tank lighting with LED but it may be a boon to both. I havn't done the math on costs or looked at how the standard Pulse Width modulation(PWM) dimmers apply to LEDs. They may be suitable directly or the circuits may have to be made. ANYWAY..sorry.. Here it is Two links follow the information.

Say an LED is rated at 350mA and 100 lumens.(this is rough but close according to the data provided--->Take the LED and run 3.5amps to it but using PWM of 1ms on 24ms off(5% duty cycle).This flashes the LED on and off 50 times per second. The chart goes higher. But extrapolation indicates that your light intensity would reach 4x more than you get at 350mA. So basicly for "Free" you get 4x intense light. Did that make sense? If not some one more adept maybe can clear it up.

I know this would mean you would now need a 3.5A CC LED driver. But with the right design. You could run not one but 25 LED from the same driver. Since you only switch the LED on for 1ms out of 25ms. The 24ms of dead time can be used to light up to an additional 24 LED at 5% duty for 1ms. So this may as well wind up saving money.

Don't quote me on cost savings..I havn't even attempted to run the math on cost of the Equipment(LED and driver) or cost of the PWM/multi LED circuit. I doubt I will..Unless there is a sizable interest in me designing the "PWM LED overdriver driver".

I just wanted to put this out there for fellow enthusiasts. Peace.
Arick

http://www.gardasoft.com/uploads/APP930%20Overdriving%20LEDs.pdf
http://budgetlightforum.com/node/1273

[kerry]

They already have these PWM drivers. Texas Instruments makes a nice one, 12 bit and 24 channel. Resistance based values and I imagine it would do a nice job. Buy here: http://www.newark.com/texas-instruments/tlc5947dap/ic-12bit-led-drvr-tssop-32/dp/03P5011?CMP=AFC-JY6146109556
You could control it with simple CMOS and Mosfet logic circuit.

[SantaMonica]

Although higher intensity is always good up until algae burn, the total amount of algae growth is proportional to the total number of photons hitting it. So a 50% duty cycle might appear to be the same as 100%, but would only grow 50% as much algae.

[kerry]

If you had the LED's fire one after another this affect might be canceled if you could tune it this way. You would need some truly sophisticated measuring device to tune the channels. An oscilloscope would not even be close!!! You would also need a ton of really nice J/K flip flops to pull this off, plus a timing circuit that I could not even begin to build. You could do it but it would require an array of LED's. I think I will stick to my CC drivers and call it scrubbed LOL.
I never thought about the photons striking the algae at a rate that would be the same as constant light. Doing this would be a huge chore if not impossible without a huge amount of money.

[patbob]

Unless there is a sizable interest in me designing the "PWM LED overdriver driver".


StevesLEDs has PWM-capable drivers that run at a high frequency.. just the thing you'd need for this. Just buy one for a larger current LED :).. or replace the current sense resistor and inductor to make a custom current. You won't get 2.5A out, but you probably can't overdrive them that far before the junction cooks, even at the brief duration.

[Gigaahxl]

I figured a microcontroller(Atmel/Arduino) would probably be pretty cheap and easy to set up the PWM timing required for it all. With an arduino, some quick digital write instructions should do it. Then 5v gate mosfets to handle the power switching. Depending on the chip you could have 14-50+ channels. I'm a bit over tired but I think just that and a CC driver would do it. the microcontroller can handle well under 100 microsecond timing.

[Lloydxmas]

From what I understand, increasing the amps gives you progressively worse lumens per watt. Even leds rated at 3amps are alot better energy wise at 700ma, going to be alot of wasted energy running a 350ma led at 3 amps