Calling all EE's please

[DarinSchmidt]

If you ahvent seen my LED unit yet, its in my 280+ gal build thread.

What i have is a 48v 5A psu, 28 CREE LEDs, 14 running at 900mA the others at 800mA. What i want to do is design a PWM that can handle up to 1-5A (preferably 3-5A). I havent messed with a 555 timer before so i dont want to screw anything up.

Can anyone help me do this?

[DarinSchmidt]

anyone?

[cyberwollf]

Run 555s through MOSFETS

[DarinSchmidt]

easier said than done. i have never messed with either and my extent of electrical doesnt go too deep into chips. just your basic beginner stuff. Though, it shouldnt be hard to figure out.

I was hoping for more of a "You noob, you hook the 555 to a flux capacitor, then use some invisaline to clip to the retractor beam trigger, then yell "Beam me up scotty"" type answer.

[cyberwollf]

to get a basis, just do some googleing on PWM circuits.  They are all going to run the 555 through some sort of transistor.  The only thing specific to your application is going to be sizing the MOSFETs to handle your amperage.  I'd also bet there were some already fully designed ones on nanoreefs.com.  Those guys are huge into DIY leds.

here's a random site i googeled that looks good. http://www.elecircuit.com/lighting/2010/0823339.html

[lazylivin]

That is an interesting alternative to dimming to consume less energy but have same perceived intensity. Do you think the strobe could have an unnatural or negative affect on the corals, or is that just silly?

[DarinSchmidt]

That's what I'm wondering. I was wanting to put this on one unit I made for testing. I don't think that it does anything. Orphek has 60 leds on one unit and it consumes little over 100watts if I remember correctly,  so I'm thinking that's what they use.

[cyberwollf]

PWM is extremely common for light dimming... Because its easy.  If you actually want to vary the current, it gets more involved.  I have made a simple variable current supply, but it was only good for about 1.5 amps I think, using a LM317.  Thats pretty easy, but you would have to manually turn pots for each string lol.

[DarinSchmidt]

Isnt the main benefit to a PWM the power savings because of the on/off wave it produces?

[DarinSchmidt]

I dont think that i can do what i was thinking i could. Running the LED's off of a PWM (from what i have read) will reduce the brightness precieved to the human eye even if each cycle runat max. Running a very tight frequency of on/off will still reduce the brightness of the LEDs. Which isnt what i was wanting to acheive. I was moreso hopeing that they would be turned on/off so fast that you wouldnt tell, the led's wouldnt be dimmed, and overall meant that they would use 1/2 power as they are technically only on for 1/2 the time.

But i think my 360PAR @ 24" deep water is good for being only 105-107w and only running at 80% max power.

I guess I'll just get back to finishing my tank and then mess with the color of the LEDs some to get the right combo I'm looking for.

[Wall_Tank]

A PWM will affect the brightness of the LED.  I thought you were just trying to build a dimmer yourself.

On a side note, did you see the guy on Reefcentral building his LED with a ThompsonResearch 295volt 700ma power supply.....   That is kind of nuts.  I'll stick with my 24 or 48 volters.

[DarinSchmidt]

Lol. Yeah. I saw that. Mitzi but prob nice to have only 1 psu. But that leaves only one point of failure. Not a good idea.

[cyberwollf]

I dont think that i can do what i was thinking i could. Running the LED's off of a PWM (from what i have read) will reduce the brightness precieved to the human eye even if each cycle runat max. Running a very tight frequency of on/off will still reduce the brightness of the LEDs. Which isnt what i was wanting to acheive. I was moreso hopeing that they would be turned on/off so fast that you wouldnt tell, the led's wouldnt be dimmed, and overall meant that they would use 1/2 power as they are technically only on for 1/2 the time.

But i think my 360PAR @ 24" deep water is good for being only 105-107w and only running at 80% max power.

I guess I'll just get back to finishing my tank and then mess with the color of the LEDs some to get the right combo I'm looking for.

Not sure i understand what you are wanting to do. PWM is done by duty cycle.  a 50% duty cycle is half on and half off. Half the photons in a giventime will look half as bright.  99% duty cycle is on 99% of the time and only off1%.  I bet you couldnt tell a differnce in brightness.  You set the frequency high enough so your eyes cant detect the flickers. >30 htz is good.  PWM is a form of dimming, which uses less power. 

[cyberwollf]

295volt 700ma power supply.....   That is kind of nuts.  I'll stick with my 24 or 48 volters.

Yea... i dont think i'd be playing with 300VDC.  Im too carless.  thats why i never built a tesla coil lol

[DarinSchmidt]

That's what I'm wanting to do. Set the duty cycle to 50% as long as it doesn't similar it and up the frequency so its not detectable.

[DarinSchmidt]

As long as it doesn't dim it*

[Wall_Tank]

Meanwell drivers accept a PWM input as a function of dimming.  100hz to 3khz.     I'm not certain if they are passing the duty cycle of the PWM directly to the switching power supply or not.

I don't think the LED will get to peak brightness when switched on an off.    But it maybe worth a small scale test.

[DarinSchmidt]

yeah, i'm thinking i might have to make a small test unit to see how it goes once i get a PWM built. Might not get to that for a couple months as i have a ton of other stuff to pay for in the mean time.

[cyberwollf]

I still dont understand the point of this??? You want to run them at 50% duty cycle to only use 50% of the power, but want them to remain at 100% Brightness??

[DarinSchmidt]

Maybe I'm still not completely understanding a pwm. Lets say you are supplying 700mA to the LEDs. When the on sign wave hits, its delivering 700mA correct? Basically striving the light but so fast you donelt see it turn off or does it make it appear at 1/2 the brightness.

[Wall_Tank]

If found some information that claims LED's are supposed to be very fast response to full brightness....... but while the LED's are turning on and off to full brightness, your eyes will "interpret" this as a dimmer light source.     

[DarinSchmidt]

That's what I was afraid of.

[cyberwollf]

50% duty cycle will be around 50% darker... Its simple physics, Photons per second.  Half the time its off, half the photons over time, half the PAR output.

[DarinSchmidt]

50% duty cycle will be around 50% darker... Its simple physics, Photons per second.  Half the time its off, half the photons over time, half the PAR output.

Yeah but what doesn't make sense is that its not photons spread out over time but bursts within a given amount of time.

[cyberwollf]

Yeah but what doesn't make sense is that its not photons spread out over time but bursts within a given amount of time.

your eyes aren't instant.  Otherwise you'd see your TV flicker.  what you see is average over some tiny timeframe.  PWM just varies what % of that timeframe the LEDs are on.  If you could really use PWM to maintain brightness and only use 50% of the power, Dont you think consumer electronics would be ALL over that?  Half your laptop's battery drain from a backlight, etc.