LED Schematics

You can use them in series if you have a constant current source power supply. It will need to be rated at 350 mA or 700mA, or both. It will also have a maximum power rating, to match the combined wattage of your led's. These power supplies must be used with the leds in series. Or use a normal power supply and work out the resistance needed to limit current.
Led drivers here:
http://www.rapidonline.com/Electronic-Components/Optoelectronics/LED-Drivers

They do standard power supplies as well, or you could make your own.
To work out current limiting resistor (resistor also needs to be in series and able to withstand the power)
Resistance R= (V-Vf)/I
I=Current required for optimum light output.(within device spec).
V=Voltage
Vf=Forward voltage drop of device. (led)

You can more or less ignore the Vf you will just end up with slightly higher resistor value.
So, A power supply of sufficient power supplying 12V/.35mA (eg)= 35ohms more or less.
This is just an example though, Constant cuurent sources are easier, but more expensive. And you will need a lot of power. Maybe more than one led driver.
Alternatively you can run them from ac, as long as you use a suitable transformer, and use a reverse Diode to protect the led. Cheaper still!
These power Led's get very hot though and need lots of heatsink or they go dim, and fail.

To sum up either way will work but depends what power source you are using, No1 for constant current, No2 for standard power supply with current limiting resistor.

Ok, i'll try to answer your questions as best I can.
I have to say though that, I personally found the initiall start up costs of a diy Led setup too high to make it viable.

If you have ordered drivers, they should be wired in mains at one end and give you a DC power source at the other.

Disclaimer: Check first! that thet are 240vAC to DC switch mode power supplies meant for mains voltage use.

The DC power source end of your kit will be of known maximum power output, And will state a value for its current output.
The difference with these to a normal power supply is, that they provide a constant current regardless of the load on them up to their operating limit. It is the voltage that changes to suit the power consumption of the led.
A normal power supply will give you a constant voltage up to its operating loadlimit. Hence it needs current regulating with a series resistor.

Regarding the first diagram.
Your 3W Leds, will probably be 350mA units. Taking each string seperately you will need 3 x 350mA Drivers rated at min 21W. One driver may not work. Led drivers in excess of 36W are harder to get hold of. So I presume you have multiple drivers.
A seperate supply for each series set rather than 3 series sets in parrallel seems more appropriate.
Of course you can use pc power supplies, But these would be fixed voltage sources rather than current sources.

Let us know what exactly you have ordered I might be able to be more specific.

Im being a bit vague cos I dont know exactly what you have brought and dont want to lead you up the garden path, with irelevant info.

About underdriving them and spectrum etc, I cant say, A 7W led at 700ma is too bright to gaze at. The same led driven off a 350mA power source looks very similar. But does run a lot cooler. (this is from my own experiment) They are very intense, I wouldnt worryabout thatjustdont try to put 700 up a 350 or it will fail. Like wise dont run 4 3W leds from a 9W powersource it will also fail.

A nice piece of Aluminium with your heatsinks attached to that sounds ok as long they are ventillated. (Still air may be ok). Forced ventillation may not be needed. But keep an eye on it. Each led can operate normally with temperatures up to 80 degC. But this power heat loss is very local, you can not feel much irradiated heat. But touching may leave you with burnt fingers.

Good luck, Ive seen some good DIY led lighting here, I just dont think its as cheap and practical as fluorescant. Dont let me put you off though. My attempts with it failed honestly, which is why the small knowledge. Too hot, too power hungry, too expensive. The benefits are there but it does take a bit of experimentation.
You can pm me if you have more details or need specific values.

From what I gather reading online, you'll need a DC power supply that is at least equal to the total voltage drop across the LEDs in one series. You can get the voltage drop from the LED's datasheet. Assuming a 3.7V drop across one LED, for a string of 7, you will need a DC power supply with 25.9V. Laptop power supplies don't go up that high unfortunately. The largest commonly available one is an Apple Powerbook type supply with 24V 65W output. Something like this: http://cgi.ebay.com/AC-Adapter-Charger- ... 947wt_1141.

I thought of using a PC's ATX power supply, using the +12V and -12V to create a 24V voltage difference, but I don't know if it'll work.

You'll also need to check if your LED drivers can handle 7 3W LEDs in series and the input DC voltage of 25.9V. I'm planning on using these, which can handle 6 of them in series. http://ledsupply.com/03023-d-e-1000.php

About altering the current to change the wavelength, I'm not sure if its possible. A check of the datasheets doesn't show a chart for current vs wavelength. Most reefers use a combination of white and blue LEDs, then control the intensity of each to get the colour rendition they require.

Check out nanoreef.com, I think they're really at the forefront of LED retrofits. http://www.nano-reef.com/forums/index.p ... owforum=25.

Also check out these 2 projects on TPT, lots of information to be learned from these two pros.
http://www.plantedtank.net/forums/diy/8 ... t-2-a.html
http://www.plantedtank.net/forums/diy/8 ... xture.html

By the way, I'm currently only planning my LED retrofit. I've ordered some parts and should get to building them in the coming weeks. All that I've written are the results of my research online, I don't have practical experience yet. So you're most welcomed to dismiss my post as blasphemy

Here is a very basic idea of something similar to what you may want to make your led's automatically dim.

To understand this you need to research transistors.
The idea is for the microcontroller to send voltage to the middle (base) pin of the transistor. The amount to voltage sent determines the amount of voltage which is send from the top pin (collector) to the bottom pin (emitter)
which ends up powering your led's.

I havent played around with Led drivers so I don't know how they would fit into this.
I think the idea would be to get your led setup running and then place the microcontroller and transistors inbetween your positive and negative.

As for adding AC to this I wouldnt have clue. Hope his helps somewhat LOL

When I was looking into the LEDs I found this company, who sell the R5s for a slightly cheaper price than the R4s (not sure what the difference is really, the technical specs seem to be fairly similar, though there are a few differences such as the k temperature). I've not used LED Rise yet, as they're currently awaiting more stock of their 700ma LED drivers, but once they've got them I shall be placing an order hopefully.

However the postage is more expensive, but it might work out to be a saving if you're spending enough.

They also stock PCB squares for the Cree XP-G series, which you could attach them onto if you got them without the stars, but they do stock them with the stars. (It seems to be cheaper to buy them separately and then attach them yourself)

I also found another LED, the Seoul Z-Power P4 which is quite a bit cheaper than the Cree LEDs. It appears to be pretty bright (but not quite as bright as the Cree XP-G R4, and reviews on the internet seem to be pretty positive about them. I'm planning to use this though I'm still making my mind up.

If you're still looking for a driver, they have a good range available too.

After some research it appears that the R5s are 7% brighter than the R4s, so it would make sense to get them, especially as they are cheaper!

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I'm not sure what size tank you're going to be using these one, so can't suggest any numbers!

However I seem to remember that Supercoley found that he needed about 1W of LED per 2W of T5s (might not be the right numbers). However as the LEDs are over twice as bright compared to the ones he was using, this figure has probably gone down a bit.

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This article makes interesting reading. It's pretty recent so mentions many of the LEDs that have been discussed in this thread (such as the XP-G, which TMC are apparently using in the new AquaBeam 1500XG so they should be suitable). It suggests that 12W of LED can replace at least 100W of MH, so you probably won't need very many LEDs!

The photo that they show, comparing a grass like plant grown with hydroponics makes a very encouraging image!

I do realise that this could not have been a fair test, but it still looks good.

It suggests that 12W of LED can replace at least 100W of MH, so you probably won't need very many LEDs!

Click to expand...

A little exaggerated but not too far wrong.

Basically the 75W Solaris was giving out nearly 90% of the PAR a 250MH was when tested. That means 1W LED is equal to 2.83W MH in terms of PAR.

The same test showed that the 75W Solaris was giving out 110% of the PUR of the 250W MH which now means 1W LED is equal to 3.67W MH in terms of PUR.

Already we are at 27W LED = 100W MH. Halfway there nearly 😉

Now comes the unscientific part that nobody seems to consider and always dismiss my theory on the forums (except for this one 😉 ). lol:

Think of flouro lights. If you get 1 tube then directly below will be a 'hotspot' with higher PAR/PUR than the front or rear substrate. Ther is also something else happening in this situation. Taller plants can block light from anything else that is in a direct line. We also have to add more PAR than we want to get the PAR we do want at the front and back.

To correct this we now use 2 tubes. Instantly we have improved the possibility of shading as there are now 2 angles for the light to come in from. This also means we now have 2 hotspots though. However we can now use less to reach the PAR we want in areas that aren't directly under the tubes.

So it goes to say if we add 3 or 4 tubes we can reduce the actual total amount we use. Say we used (not possible I know) a 100W tube on its own. With 2 we could (example not a calculation) go for 90, with 3 85 etc. Each addition would mean to get an equal spread we could use less total to achieve it.

It is for that reason the trendy slimline luminaires are not a great idea. Especially if you are after saving power etc. Yes they use 2,3,4 tubes but they then negate the advantage by packing them all into an area over the centre again.

So for flouros I am now suggesting that 4 x 18W T8 will be far superior for growth than 2 x 40W T5HO. This of course is dependent on spacing them properly.

Why am I talking about flouros?

Remeber we are at 27W LED = 100W MH. I went through the last part to lead into this next aspect. multiple point sources 🙂

Her is the 'hidden' advantage of LED. Rather than have 'fixed' positioning as we do with other lighting where all the light has to come from a length of tube or a bulb of MH LEDs can be spaced out equally.

That means we can now reduce the hotspots and it also means we can reduce the difference in PAR/PUR between the area below the light and the are further away.

What this means is we now don't have to supply more PAR than we want just to get that figure in the areas that are not directly under the light. We can therefore use less power to get the baseline figure all over the substrate.

This is just theory. No calcs. What we are saying is yes 27W is equal PUR to 100W MH but for an larger area rather than just a single plant under a single LED we can use less power to have a good spread.

Will be a smaller reduction thatn the 12W is suggesting but it will be a reduction. So maybe we are now talking 20W LED = 100W PAR 🙂

So there you go. Yes LED provides more PAR/PUR per watt than the other options but it also enables you to use less power inthe first place to achieve the baseline PAR/PUR all over the are below 🙂

I didn't make my LED because of this. I was stumbling over 'overlapping light years ago on flourescents but didn't really understand what I was theorising. I made my LED setup because it would look cool and use less watts and suddenly the years old theory made itself clear (love the pun) and I saw the light (oops another one) instantly.

For the chap above who said it wasn't financially viable. I would suggest if a complete flouro DIY job cost £50 for say a 50W setup then thats great and the only maintenance would be to replace the tubes every 2-3 years. If the DIY LED setup costs £110 it doesn't look financially viable however:

You now can use 20-30W to achieve the same result. That means a year of 20-30W less power consumption. The LEDs will last 5-10 years so that means you can reduce the cost of 2-4 replacement tubes (per tube position.) It also means less scrap, when they are done for. Oh and it looks much cooler.

Someone else can do the calculation as I have no idea how much electricity costs but over 5-10 years life of the LED you will have saved money at the end and helped the environment with less power consumption plus less material wastage for disposals 🙂

Garuf - I'll post the result of that 7 string test tomorrow. Those ebay drivers are the newer version of mine. dimmable too 🙂

AC

Garuf said:

Good link and neat little read, the only issue I can spot is that the growth form seems indicative of lower light levels,

Click to expand...

I agree. The authors seem to be missing that point, and on other plants would most likely lead to spindly growth rather than bushy growth.

Garuf said:

I've laid my hands on a CPU which my mums dog decided it would like to chew, am I right in thinking I open the case, chop off all the wires I don't need that go to 3v and 5v, add all the wires together onto one output and use the -12v and the +12v to create 24v out put, then it's a matter of adding a switch between the green and the grey wire and I'm done, that does however leave me without a ground, where would that fit in the whole scheme of things, I understand they're vital after all?

Click to expand...

I did think about this, but was afraid that the -12V may not be able to sink all that current. Also, using -12V as a reference in this case may not be as stable as using GND, but if you use 6 LEDs or less per series string, I think it should be alright.

You'll need it under load, since different loading draws differing amounts of current. And using a multi-meter may not be accurate enough, since the spikes and dips maybe happen on a millisecond timescale. How that affects your drivers and LEDs is hard to predict though. I suppose if the multi-meter shows big variations then its very possibly a no-go.

Well I started testing the LEDs on the same drivers I have used for 3. but encountered a problem. Not a mjor one, just one my non-electrical knowledge could counter.

I was attempting to use 2 x 12V adaptors wired into the same connector to supply 24V and then test 6 and 7 LEDs on the current controller.

Problem was when I plugged one in the other one was receiving power without being plugged in!!! I know this because these adaptors have an LED on them and it lights up only when I complete the series. If 1 wire isn't connecting within the series the LED doesn't come on.

Well I plugged the first one in and lo and behold the LED on both adaptors lit up!!!

So I got up to 5. 12V was lighting up all 5 but only at a brightness I could look at (anywhere near full you can't look directly at these LEDs for more than a slight glimpse without having a sever headache afterwards.)

So there the test ends as I have no 24V power source.

I can't see a problem though. 3 on a series powered by 12V - 1.5V for the controller = 10.5V/3 = 3.5V eaxh. 7 on a series powered by 24V - 1.5V for the controller = 22.5/7 = 3.2V each.

Like I said above with 5 powered by 12V (10.5V after controller) they were lighting up but not too bright to look at. With 4 they WERE too bright to look at and that would be 2.625V each. Much less than 7 on a 24V supply would be.

The drivers are stated as being 7V minimum to 24V maximum.

Sorry for failing the test 😉

AC