Author Topic: Calling all EE's please (Read 3762 times)

DarinSchmidt · « **on:** April 24, 2011, 13:36:23 »

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 · « **Reply #1 on:** April 24, 2011, 20:48:50 »

anyone?

cyberwollf · « **Reply #2 on:** April 24, 2011, 20:57:39 »

Run 555s through MOSFETS

DarinSchmidt · « **Reply #3 on:** April 24, 2011, 21:03:50 »

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 · « **Reply #4 on:** April 25, 2011, 16:29:03 »

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 · « **Reply #5 on:** April 25, 2011, 23:57:40 »

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 · « **Reply #6 on:** April 26, 2011, 05:55:02 »

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 · « **Reply #7 on:** April 26, 2011, 07:52:24 »

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 · « **Reply #8 on:** April 26, 2011, 08:48:07 »

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

DarinSchmidt · « **Reply #9 on:** April 26, 2011, 11:20:32 »

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 · « **Reply #10 on:** April 26, 2011, 20:24:55 »

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 · « **Reply #11 on:** April 26, 2011, 20:27:28 »

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 · « **Reply #12 on:** April 26, 2011, 20:32:38 »

Quote from: DarinSchmidt on April 26, 2011, 11:20:32

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 · « **Reply #13 on:** April 26, 2011, 20:34:15 »

Quote from: Wall_Tank on April 26, 2011, 20:24:55

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 · « **Reply #14 on:** April 26, 2011, 23:31:46 »

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 · « **Reply #15 on:** April 26, 2011, 23:32:56 »

As long as it doesn't dim it*

Wall_Tank · « **Reply #16 on:** April 27, 2011, 19:27:27 »

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 · « **Reply #17 on:** April 28, 2011, 09:17:10 »

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 · « **Reply #18 on:** April 29, 2011, 19:55:06 »

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 · « **Reply #19 on:** April 29, 2011, 20:36:42 »

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 · « **Reply #20 on:** April 29, 2011, 20:57:44 »

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 · « **Reply #21 on:** April 29, 2011, 21:01:04 »

That's what I was afraid of.

cyberwollf · « **Reply #22 on:** April 29, 2011, 22:06:05 »

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 · « **Reply #23 on:** April 29, 2011, 22:31:16 »

Quote from: cyberwollf on April 29, 2011, 22:06:05

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 · « **Reply #24 on:** May 02, 2011, 17:20:11 »

Quote from: DarinSchmidt on April 29, 2011, 22:31:16

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.

DarinSchmidt · « **Reply #25 on:** May 02, 2011, 17:22:49 »

lol, makes sense, i never thought of it that way. Thanks cyber

DarinSchmidt · « **Reply #26 on:** May 18, 2011, 03:42:22 »

Ok, i'm going to scratch the PWM for now as i dont feel like messing with it at the moment and will be wanting to incorporate an Andruino for that. So for now i just want to do some manual adjusting with some POTs.

I was looking up a LM317A and I'm assuming that this will do the trick to limit the current. Just dont know how i would connect it though. I connect the 48vdc to the in, out to the negative of the psu and the POT to the ADJ peg??? If thats correct, how exactly does this work? as in, do i connect the 48vdc + to the POT then to the ADJ peg or what? Its kind of late and my brain is ready for bed...

Trying to make a cheap manual control constant current device to hold me over till i am ready to dive into an Andruino later this summer.

cyberwollf · « **Reply #27 on:** May 18, 2011, 18:18:54 »

http://diyaudioprojects.com/Technical/Voltage-Regulator/
2nd project down shows you how to connect and calculate the R values.

Whats max Vin on 317?

cyberwollf · « **Reply #28 on:** May 18, 2011, 18:23:00 »

even better

http://www.reuk.co.uk/Using-The-LM317T-With-LED-Lighting.htm

And you'll want a big heatsink. Also, whats the max Watt draw. 48V at 700mA is 33 watts.

DarinSchmidt · « **Reply #29 on:** May 18, 2011, 21:35:22 »

not sure what the Vin is, i dont see it on here. but here is the datasheet for it http://www.national.com/ds/LM/LM117.pdf I'd like tfor the max draw to be 48 watts just to be on the safe side if i want to run them at 1A, but i doubt that i want to.

DarinSchmidt · « **Reply #30 on:** May 19, 2011, 14:43:58 »

well it seems that chip can only handle 40v, i may need to go with something a little more powerful since it also cant provide me the 50w needed.

this looks suitable, but is it saying that it can only handle an 80v input or up to an 80v input? http://www.national.com/ds/LM/LM4732.pdf

DarinSchmidt · « **Reply #31 on:** May 19, 2011, 20:43:38 »

nm, overlooked where it said supply voltage is 20-80v. I think this is the chip that i'm going to use so that i can still keep the amount of LEDs per array that i have since i only have 5A to work with.

2024 Ohio Reef Frag Swap

Author Topic: Calling all EE's please (Read 3762 times)