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Old 07-21-2010, 10:39 AM   #21
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Thanks! It think it might have been in your thread, but what I believe was discussed was leds just in parallel (like 3.7v ps with high amperage, and running 1 led in each string.) I'm not familiar with the meanwell, but I have taken E & M in college, but applying it to real life like this is just funky :P as it should be.

I'm curious to know what would stop you from running a parallel series on a meanwell. It might be something inherent in the design, but from my E&M knowledge, splitting the string should double the amount of current and halve the amount of voltage. Like I said, I'm not sure if there's something inherent in the meanwell that will prevent me from doing this, but I thought what I learned could be applied to any power supply.

Also, I probably won't be running more than 6 for this project, but I'd like to be able to use the same design, and maybe the same meanwell when I upgrade to 29 and 40B, which is why I'm trying to future-proof the design now.

Since I'm using a driver, wouldn't that prevent most fluctuations within each string, since current within a string is the same for all "resistors"? I'm trying to find out what instability is there when using a parallel (or parallel series) circuit


Thanks so much guys, sorry for the essay I wrote :P. I've found that with the delay of forums, it's not like iming, where it's best to get as much information out as possible

Thanks again
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Old 07-21-2010, 11:03 AM   #22
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The problem with parallel strings is that you cannot get the rated current through both strings. With two parallel strings, you will get half. This is because the meanwell will keep the current drawn at 1A (for a 1A model).

So if we have a 1A current source, and two parallel strings then we will have 0.5A go through each string. The current will divide at the node connecting the two strings to the positive terminal of the meanwell.

There is also the method by which the meanwell senses the current draw and adjusts itself. Many common constant current sources have a way to detect, in real time, the current drawn. They then adjust to maintain the predetermined current. This usually is a resistor that they measure the voltage across and via ohms law (v=IR) they know the current being drawn. I built drivers that would output 75v and control 60A. These used and op-amp and current sense resistor for each channel. The channels could be put in parallel for more current, but still had a way to detect the current through each channel to keep it constant. Id check with meanwell to see what they say.

0.5A + 0.5A = 1.0A

If you add a third string, that will then be 1/3 the rated current.

This might not be what you want, but its what you want the meanwell to do. (Keep the current constant regardless of what you or the line power does).

This may benefit you if your lights are already too intense. (A way of dimming them).

I suggested 16 simply to avoid spot lighting. Optics would increase spot lighting as well. My light has the leds spaced 2in apart and the strings spaced 3in apart. It covers my 12in^2 area nicely, but just so.

I tried it over my 20g reef and was very dissapointed. Its much larger, but the spread was terrible. My 20g is 13in by 24in. It looked like it would need three of my lights AND optics.8-O

Deffinately will leave the t5 over the 20g.

We dont add leds for the watts/gallon thing, but for even spread. We dim the leds for the watts/gallon. (usually dim them because they are too intense). This is why the led lights are costly. They need a lot of leds to cover the tank well.

I wouldnt concentrate so much on the idea of total power for two reasons:
1-LEDs are inefficient. They draw 48w but they sure dont put out 48w of light. Same with t5 and MH. Youll have to look up your led efficiency.
2-Nothing in the tank will see the total combined light output. The sun is a great example. I forget how much power 1m^2 of sunlight has, but 1in^2 within that 1m^2 certainly isnt equal.

Matt
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Old 07-21-2010, 11:08 AM   #23
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Real quick for a visualization. 3x4 pattern, lights 8" off the tank. You had said 14" but that seemed really super high to me. Any reason in particular you are going with 14"?

White is 90 degrees viewing angle, Blue is my estimated range of max power, 60 degrees.
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Old 07-21-2010, 11:12 AM   #24
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Originally Posted by mrg02d View Post

I wouldnt concentrate so much on the idea of total power for two reasons:
1-LEDs are inefficient. They draw 48w but they sure dont put out 48w of light. Same with t5 and MH. Youll have to look up your led efficiency.

Matt
What do you mean by this?
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Old 07-21-2010, 11:14 AM   #25
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Originally Posted by krap101 View Post
Thanks! It think it might have been in your thread, but what I believe was discussed was leds just in parallel (like 3.7v ps with high amperage, and running 1 led in each string.) I'm not familiar with the meanwell, but I have taken E & M in college, but applying it to real life like this is just funky :P as it should be.

I'm curious to know what would stop you from running a parallel series on a meanwell. It might be something inherent in the design, but from my E&M knowledge, splitting the string should double the amount of current and halve the amount of voltage. Like I said, I'm not sure if there's something inherent in the meanwell that will prevent me from doing this, but I thought what I learned could be applied to any power supply.

Also, I probably won't be running more than 6 for this project, but I'd like to be able to use the same design, and maybe the same meanwell when I upgrade to 29 and 40B, which is why I'm trying to future-proof the design now.

Since I'm using a driver, wouldn't that prevent most fluctuations within each string, since current within a string is the same for all "resistors"? I'm trying to find out what instability is there when using a parallel (or parallel series) circuit


Thanks so much guys, sorry for the essay I wrote :P. I've found that with the delay of forums, it's not like iming, where it's best to get as much information out as possible

Thanks again
Not sure what you mean by splitting the string, but...

Loads in parallel will have the same voltage across them, and will attempt to draw more current. You can reason it in that more parallel paths means more routes for current to go. The more parallel strings you add, the more places for current to go. The voltage stays the same across each parallel string.

ANother way to view things is peer pressure. The voltage is the peer pressure, and the parallel paths are more things the peer pressure wants you to try. (Smoke this dope, kill this bottle of vodka, and then snort this stuff). Three no-nos and peer pressure mean three chances to get in trouble. The more bad things to try, the more chance to get into trouble. You may resist well under the current peer pressure, but once it goes up (voltage rise) you may crack and give in. Unless you have a constant current controller.

Not sure what E and M is, but this comes from Kirchoffs current and voltage laws via nodal analysis and loop analysis.
That would be from my EE classes.

Matt
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Old 07-21-2010, 11:16 AM   #26
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What do you mean by this?
The led will draw 3.7v at 1A (or so) and that is 3.7W. It will NOT put out 3.7W as that violates the laws of physics. It will put out: power in times efficiency. So if we had a 50% conversion efficiency, 3.7W in would mean 3.7/2W out of light. So a light consuming 48W will only produce 24W of light. (Under ideal circumstances).

Well, off to my class...

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Old 07-21-2010, 11:43 AM   #27
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But how many watts of light it puts out isn't as important i thought. What matters is the lumens and PAR for our uses.
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Old 07-21-2010, 12:15 PM   #28
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Aside from the light issues I'm thinking about discussing your CO2 method. Unless you can control the temperature of the thermoelectric plate there's no controlling your co2 output throughout the day. The Sodium Bicarbonate will decay at a rate non-linear to temperature due to the fact that rate of reaction will be dependent on the mass not only temperature of the substance. Your rate of reaction constant K in NaHCO3---> NaO2 + CO2 would be constantly changing. Furthermore your CO2 output is minuscule in comparison the amount of NaHCO3 you need.

Let's do this:
1mole NaHCO3 decommposes to 1 mole Co2
While accounting for experimental loss it's close enough to 84 grams of NaHCO3 to 22.4 litres of gas at STP. At 50C [temperature of decomposition of sodium bicarb] or 323.15K.
Using the charle's laws: V/t=v/t. 22.4 litres will become a whopping!:...26 litres of gas.
Now 26 litres of gas may seem like a lot, especially out of only 84 grams (about palmful) of NaHCO3 but imagine the difficulty of controlling the gas. Once it hits the temperature of reaction, it's not going to slow down, instead speed up then slow down when only a minuscule amount of bicarb remains. I can't find the rate constant to show you the exact rate of reaction but considering it only took a few extra seconds for me to turn a perfectly good anhydrous sample of CuSo4 to copper and sulfur, it's not very long.

Stick with a traditional diy co2 and also a traditional aluminum heat sink. If you really want the ultimate in cooling pick up some Arctic Cool Silver Thermal CPU compound and buy a Zalman all copper heat sink.


All in all, bad idea.
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Old 07-21-2010, 03:32 PM   #29
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Well, baking powder (sodium bicarbonate with a acid in solid form) releases its co2 when it touches water (water dissolves whatever is keeping the acid from reacting, so you get sodium bicarbonate + acid=co2 + something else. I was thinking you could use something akin to an iv bag and drip water in at a consistent rate. I'm worried about the used up baking powder compacting, and eventually stopping the water from reaching the rest of the unused baking powder. I'm not that familiar with baking powder, so it may not act this way.

I know that watts are a bad form of measurement, but it is hard to measure par (expensive or rare maybe)

I mean splitting the string as in rather than putting all the leds on one string, add a second string. You'll need half the voltage and twice the current in this case.

An led either uses more than the rated wattage to put out the rated amount of light, or it uses that much energy and puts out less light. Yes they're not 100% efficient (they do put off a decent amount of heat when at these specs) but compared to fluorescent metal halide incandescents, it is a drastic increase. I think the last time I checked were at around 70-75% and were getting closer to 80%?

For the parallel strings, you're saying that I can do it, just it has a greater chance of risk? If I get the 24V, I'll have around 2.5A of current I can play with, which is around 3 strings running the leds at 800ma. I'm unsure of what'll happen to the extra .1A. will it just not get drawn through, or will I have to dissipate it somehow?

My 10 gallon is 12" high, so with no gravel or anything, the bottom of my plants will be around 14" below my lights (2 inches above frame/water)
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Old 07-21-2010, 03:56 PM   #30
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You need a tiny amount of baking soda solution to reach 30ppm and even then adding excess Na+ ions from bicarb is bad for both plants and fish. 30ppm co2 makes 30ppm Na. You should never have that high of sodium in a fw tank. And this doesn't account for the fact you have to add a continuous supply of bicarb to maintain 30ppm. That 30ppm sodium is just the initial dose. After a day you may have a few hundred ppm na.
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