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Old 02-08-2012, 05:26 PM   #31
hcker2000
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I'm glad I ran across this post. I have been looking at a 50 Watt LED for my 29 gallon tank and after seeing this I think that might be a bit extreme for that size of tank. The worst part is that two 10 Watts are almost as expensive as the single 50 Watt.
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Old 02-09-2012, 01:07 AM   #32
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Originally Posted by Chlorophile View Post
And so does your algae!
doe.. yeah cuz i was going too much light..

at one point this entire fixture was over that tiny 10gallon..


i got greedy in a bad way... and bam... paid for it hardcore.

im only running 2 x 10W on it now... not so much algae problems, however i have green dust algae that broke out.... and i need to do the 3 week wait time to kill it...
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Old 02-09-2012, 02:52 AM   #33
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Quote:
Originally Posted by hcker2000 View Post
I'm glad I ran across this post. I have been looking at a 50 Watt LED for my 29 gallon tank and after seeing this I think that might be a bit extreme for that size of tank. The worst part is that two 10 Watts are almost as expensive as the single 50 Watt.
If you restrict your eBay search, you can find 10W LEDs for less than $5. I bought four of them for $20 (shipped).

Also, I was looking through some specs, and I think it might make more sense (for me at least) to get the BridgeLux. The test power on some of them are at 7W (which is where I want to run them) and the cost per LED is the same EXCEPT the spec/datasheet is available and you can drive some of them with currents to bring them reliably to a higher current.

Oh, and instead of buying from China and waiting 3-4 weeks, you can get them from an online electronics store within a week.
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Old 02-10-2012, 05:40 PM   #34
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You would think some one would be importing the 10 Watts and selling/shipping them from in the USA. I have not heard much about the bridgelux's got any seller links here in the USA?
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Old 02-10-2012, 06:13 PM   #35
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For someone who is new at this, mind if I ask some stupid questions?

Is this what one would need to buy to get this working:
- LED
- Driver
- Heat sync (required?)

Then you just solder the LED to the driver wires, and run the AC into your nearest wall receptacle? Anything else required?

If doing multiple LED's, instead of running 1 x 10W driver per LED, could you just wire them in series (or parallel) and run them back to a single larger driver. So, say 2 10w LED's to 1 20W driver?
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Old 02-10-2012, 08:24 PM   #36
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That is correct just pay attention to the driver.

In my case I want to run three 10 watt leds off a single driver. Each led is rated at 10-11v so three in series would be 30-33v. So I need a 30watt driver that outputs 30-33v.

Heatsinks of some sort are required. Keep in mind the cooler you keep them the longer they last.
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Old 02-12-2012, 07:18 AM   #37
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Thanks so much.
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Old 02-12-2012, 04:36 PM   #38
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Quote:
Originally Posted by RandomMan View Post
For someone who is new at this, mind if I ask some stupid questions?

Is this what one would need to buy to get this working:
- LED
- Driver
- Heat sync (required?)

Then you just solder the LED to the driver wires, and run the AC into your nearest wall receptacle? Anything else required?

If doing multiple LED's, instead of running 1 x 10W driver per LED, could you just wire them in series (or parallel) and run them back to a single larger driver. So, say 2 10w LED's to 1 20W driver?
depends on the driver...

if its a constant current driver, you wire them up in a series.
if its a constant voltage driver, you wire them up in paralell.

Constant current will tend to have a variable voltage which changes on fly but holds current constant.

Constant voltage psu's, the good regulated ones will hold voltage steady, but can change current on the fly... nature of led's
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Old 02-12-2012, 05:16 PM   #39
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Originally Posted by hcker2000 View Post
You would think some one would be importing the 10 Watts and selling/shipping them from in the USA. I have not heard much about the bridgelux's got any seller links here in the USA?
On eBay, there is one guy selling them for about $10.

You can get the Bridgelux at Digikey.com

Quote:
Originally Posted by Naekuh View Post

if its a constant current driver, you wire them up in a series.

if its a constant voltage driver, you wire them up in paralell.

Just remember though, even with LEDs from the same manufacturer with the same exact specs aren't PEFERCTLY matched. If it's a constant voltage driver and you wire in parallel, each branch can still have different currents. So there's a chance that if you're running 2A through the entire setup and you need 1A to each branch, that it's possible that 1A++ can go through one branch and the rest goes to the other. So one might be slightly overdriven and one slightly underdriven. This probably won't be an issue, but with operational stresses and temperature changes, it could effect it.

Running a series resistor PER branch helps.

The plus side to running them in parallel though is that if one branch breaks, it doesn't kill your entire light.

I'm currently going to run two 10W LEDs in series for my 10G setup, but when I build my 75G setup, I am going to run my white and reds off two different drivers. Each set will use constant current mirrors (basically, it maintains the same current in each LED given a reference - so I can set it for 500 mA and they'll ALL have 500 mA going through them).
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Old 02-12-2012, 11:43 PM   #40
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Originally Posted by sendthis View Post
Just remember though, even with LEDs from the same manufacturer with the same exact specs aren't PEFERCTLY matched. If it's a constant voltage driver and you wire in parallel, each branch can still have different currents. So there's a chance that if you're running 2A through the entire setup and you need 1A to each branch, that it's possible that 1A++ can go through one branch and the rest goes to the other. So one might be slightly overdriven and one slightly underdriven. This probably won't be an issue, but with operational stresses and temperature changes, it could effect it. .
sorry but this doesn't apply with DC and constant voltage.

DC circuits only draw the amps it requires if you match voltage.

Saying u cant tie up 1 parallel 3V LED with a 12V led, unless u serial 4x3V = 12V.
You need to keep the voltage on each parallel array the same...

If you have 2 different arrays strung up in parallel.. one array draws 3A... and the other draws 2A... the psu will output a total of 5A, where 3A will go to the 3A portion and 2A will goto the 2A portion.
Again this is looking at constant Voltage.

constant current doesnt work like that, because of the nature of LED's themselves.... LED's can variate Voltage yet the driver forces constant current though them.

Hence why Constant current does run a tad bit cooler then constant voltage.
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Old 02-13-2012, 05:37 AM   #41
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sorry but this doesn't apply with DC and constant voltage.

DC circuits only draw the amps it requires if you match voltage.

Saying u cant tie up 1 parallel 3V LED with a 12V led, unless u serial 4x3V = 12V.
You need to keep the voltage on each parallel array the same...

If you have 2 different arrays strung up in parallel.. one array draws 3A... and the other draws 2A... the psu will output a total of 5A, where 3A will go to the 3A portion and 2A will goto the 2A portion.
Again this is looking at constant Voltage.

constant current doesnt work like that, because of the nature of LED's themselves.... LED's can variate Voltage yet the driver forces constant current though them.

Hence why Constant current does run a tad bit cooler then constant voltage.
I'm about to go to bed... but I wanted to answer this real quick and I'll come back to it just in case I'm misunderstanding what you're saying...

The reason you want to limit the current even with a regulated DC voltage source is because as your device heats up, it causes a shift in the nominal foward voltage. So while you maintain the voltage, there is a disproportionate shift in the current. So nominally, at 25C, a Vf=3.5V may have 350mA, as it heats up it will begin to draw more current without changing Vf. As it pulls more current, it'll generate more heat, until finally it reaches breakdown (device failure).

The key here is that diodes are current driven devices. If you take a look at the ideal diode equation, you will notice there is a thermal voltage term. This parameter is in the exponential --- small variation can lead to large current change.

So, why would one be overdriven and one underdriven?

In the above situation, let's say you have a 10W 10V regulated constant voltage source. That means it can supply 1A and let's say it is a limited power supply / driver.

Let's say your LED devices operate at 10V, but needs 500 mA.

In the above situation, if one of your devices is slightly mismatched (via manufacturing or operation), it's possible that one will be driven with a larger current, exceeding the value for your driver is designed to handle as well as your device.

But this goes back to parallel being safer b/c only one branch breaks.

On the flip side, a constant current source running through a series of LEDs is 'safer' because it will never allow more current (when well deisgned) than the diodes can handle. The problem with this is that your LED in the string may break for other reasons and you have to replace it or bypass it to get the other LEDs to work. This is probably less likely than the above situation, but still possible.

Hopefully I answered that and it was coherent, but I'll come back to it tomorrow when I'm more awake.
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Old 02-13-2012, 05:34 PM   #42
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Oh, I should add that functionally a constant voltage source is just a constant current source with a resistor in parallel. Also, functionally, a constant current source is just a constant voltage source with a resistor in series.

So basically, by putting a resistor in series with a constant voltage power supply and the LED, you're basically converting your source into constant current.

The reason you need to put a resistor in each branch is that since your LEDs drop a different forward voltage, your resistor takes up the slack and maintains the ideal current in each respective branch. If you only put one resistor in series before the LEDs, then you're going to limit the total current but not control the current in each loop.

Ideally, even if you had tightly binned LEDs, their characteristics will vary over time. Also, I believe manufacturers bin their devices with current and not voltage (as LEDs are current driven devices).
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Old 02-13-2012, 05:47 PM   #43
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Quote:
Originally Posted by Naekuh View Post

If you have 2 different arrays strung up in parallel.. one array draws 3A... and the other draws 2A... the psu will output a total of 5A, where 3A will go to the 3A portion and 2A will goto the 2A portion.
Again this is looking at constant Voltage.
Okay, now that I'm awake and full of coffee...

That's correct. The problem is (as mentioned in previous post) is that the branch that the circuit WILL maintain voltage IRRESPECTIVE of current. So when your device heats up, it's possible that it will start to draw more current. So one loop will put 2A and the other will put 7A and then your PS is supplying 9A assuming that your device can handle the additional 4A. Since this works as a feedback system (device gets hot, pulls more current, gets hotter, pulls more current.. etc) then you will overdrive the device. It may not be immediately noticeable but it will eventually happen especially if you run them for the durations required for planted aquariums.

The problem with a slight mismatch in LEDs is that even with a constant voltage, even without thermal runaway is that it will drive the devices with different currents to maintain that voltage. One will always see more current while the other will see a different current. So in the case of slight mismatch, you will always have one either overdriven or underdriven if not both in any combination of those states. It's highly unlikely they will ever be perfectly matched. Even if they are, you run back into the thermal voltage issue.

Note: Don't take numbers literally. As the operating characteristics are just for illustration and actual performance specifications will vary between manufacturers and products. The numbers were just pulled out of my "hat" to show what -could- happen.

Assuming you're lucky and with perfectly matched LEDs in the full range of operational environments, then it's just poor design. It may work in one case, but fail when you reproduce it in another case. If it works now, it may shorten the lifetime and not work later. As far as I know, it's pretty difficult to predict long-term operation and most manufacturers do not know. Current devices haven't been in the market long and they're soon to be replaced by other devices with different material technologies in the years to come.

I've bought a few LED bulbs from different manufacturers. After they burn out and I take them apart to look at them, they were obviously poorly designed. With the chinese bulbs, one of the problems is putting the devices in parallel and not limiting the devices. My guess, especially for eBay purchases is that the vendor is gambling that the product lasts long enough to get a positive rating. If it dies in a week or more, as long as they have positive feedback, they don't care any more.

I'm highly hesitant to buy any new bulbs on eBay any more but I'm more adventurous in working with individual components (since I believe most are made in Asia anyway). The reason for failure is less with the quality of the components, but in the cost-saving reductions in proper design.

In any event, even if you disagree and think that it's safe to run each "string" of LEDs without a resistor, isn't it worth the $0.50 per branch to improve reliability of your fixture? In fact, buying the resistors off... eBay, you will probably pay much less per resistor anyway.
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Old 02-13-2012, 08:46 PM   #44
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It really seems the way to go with these are to run them off a current regulated power. I think now rather than using one 30 watt current regulated power supply I will use three 10 watt regulated power supplies as the cost difference is about $5 and its worth $5 to over come the issue with running LEDs in a series.
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Old 02-15-2012, 09:15 PM   #45
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Looks great. I would like to try it!
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