DIY LEDs - The write-up

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Another dummy question for the EE types in this thread, since I still don't have a total grasp of how some of these components work together.

Would it be reasonable to use one "large" power supply (say, 32VDC and 4amps) to power several buckpucks, if you wired the pucks in parallel?

Given that this arrangement would work, could you put relays in series with each puck to allow for turning each puck's LEDs on and off individually? Would the power supply be OK with this? I realize it's probably a foolish question but I just don't know if a power supply would typically be OK with the load on it getting switched on and off - typically it seems like people switch the AC going *to* the power supply on and off, not the load downstream of the supply.

I'm planning an LED rig for a nano tank, partly as "proof of concept" while I'm awaiting my next big tank project, which is a few years off at best. I'd like to have 8 - 10 LEDs above the display tank (half blue and half white, on separate buckpucks), and 3 or 4 on a refugium. For the sake of simplicity, I was thinking about running all three strands off a single power supply, but I'd like to figure out how to be able to turn them on and off individually, too.

MPJA has 24v power supplies at 4 or 6 amps for $15 - $20. It would be nice to use one of those, and one timer, to control everything. Besides saving money, this approach would be easiest to fit in a tiny stand without taking up a lot of room. The timer could trigger relay(s) to turn the DT lights on and the 'fuge lights off in the morning, then turn the 'fuge on and the DT off in the evening. Is this a reasonable approach?
 
<a href=showthread.php?s=&postid=15037821#post15037821 target=_blank>Originally posted</a> by der_wille_zur_macht
Another dummy question for the EE types in this thread, since I still don't have a total grasp of how some of these components work together.

Would it be reasonable to use one "large" power supply (say, 32VDC and 4amps) to power several buckpucks, if you wired the pucks in parallel?
Click to expand...

Yes, you are going to have the buckpucks wired in parallel off of the power supply. The larger voltage power supply means you can have more LEDs in series. 24v ~ 6 LED's in series... 32v ~ 8 LEDs in series.

Given that this arrangement would work, could you put relays in series with each puck to allow for turning each puck's LEDs on and off individually? Would the power supply be OK with this? I realize it's probably a foolish question but I just don't know if a power supply would typically be OK with the load on it getting switched on and off - typically it seems like people switch the AC going *to* the power supply on and off, not the load downstream of the supply.
Click to expand...

By adding relays to the DC side of the power supply you would be able to control each parallel branch (buckpuck). This would be just like adding a controller. Turinging off/on the AC side of the power supply with a timer seems to be what everyone has done so far.

I'm planning an LED rig for a nano tank, partly as "proof of concept" while I'm awaiting my next big tank project, which is a few years off at best. I'd like to have 8 - 10 LEDs above the display tank (half blue and half white, on separate buckpucks), and 3 or 4 on a refugium. For the sake of simplicity, I was thinking about running all three strands off a single power supply, but I'd like to figure out how to be able to turn them on and off individually, too.
Click to expand...

Controller of some kind...... Timers modified to switch DC power instead of AC?

MPJA has 24v power supplies at 4 or 6 amps for $15 - $20. It would be nice to use one of those, and one timer, to control everything. Besides saving money, this approach would be easiest to fit in a tiny stand without taking up a lot of room. The timer could trigger relay(s) to turn the DT lights on and the 'fuge lights off in the morning, then turn the 'fuge on and the DT off in the evening. Is this a reasonable approach?
Click to expand...

A 24v PS @ 6 Amps should be enough for 3 or 4 strings with 1000mA buck pucks. 4 strings @ 1000mA = 4 Amps.


SBC
 
Thanks. I'll only have three strings, and probably only 4 LEDs in each string, so the 4 Amp PS should be enough.

For controlling each buckpuck, I was thinking an AC-coil relay in series with each puck, with the coil controlled by a conventional plug-in appliance timer. I could use normally open relays on the display tank lights, and a normally closed relay on the sump lights. This way, one timer would switch all three buckpucks on and off appropriately. I would set the timer to be "on" when I wanted the DT lights on.

This raises another question. I will have three relays, and I want to control them with one appliance timer. So, I should wire the coils of all three relays to the output of the timer, correct? Should the coils on the relays be in series or parallel?

Sound reasonable? Or am I off my rocker?
 
You will have to get a different size power supply if you are going to only have 4 LEDs per string.

The typical voltage drop for each LED is 3.3v - 3.7v with a max of 3.9v. If you have a 24v powersupply with 6 LEDs on a string...each LED will drop 4 volts (which is just a bit higher than the spec sheet calls out). If you have a 24v power supply with 4 LEDs on a string...each LED will drop 6 volts.

Here is the spec sheet for the cree-xre LEDs....look on page 4 for forward voltage specifications
http://ledsupply.com/docs/cree-xre.pdf

As for the timers..... yes, you would have to have a plug-in timer driving an AC relay for each buckpuck. You could cycle your lights on/off at any time you wanted. If you went this route, you would not need another timer on the power supply.

SBC
 
Ok, once again I am showing my lack of LED knowledge. I had thought that the buckpuck would "take care" of things as long as the max output (voltage and current) of the power supply was not exceeded.

So if I use a 24v power supply, I HAVE to put 6 of these LEDs on each branch of the circuit? And, if I want 4 of these LEDs on each branch, should I use an 16 or 18v supply? MPJA has a 4.2 Amp 18v supply for cheap, and it's small. . .

Reading back through the thread, it seems like the trend is to add up the forward voltages for the number of LEDs you want, then allow a few v on top of that. For instance, ReefEnabler is using a 32v supply and he claims each branch has ~28v drop. This would lead me to believe that if I wanted 4 LEDs per string, the 18v supply would work, even though by spec, the total drop would be 14v.
 
Has anyone built LED spotlights with these LEDs and drivers for T5 shimmer supplementation? I'm thinking 4 or 5 of the 1 amp LEDs clustered together might be bright enough to overcome 4 or 6 54w T5s and provide a nice shimmer, but that's a complete guess. On my 48" long 90g, I'm thinking a spotlight on each side might be sufficient.

Has anyone tried this yet?
 
It might have been stated earlier but I can't find a decisive statement so here goes.
I see that Soundwave runs his Blues at 700mA but is that necessaery.

If I just get one buckpuck for my whites and blues would the 1000mA be too much for the blue?
 
It might have been stated earlier but I can't find a decisive statement so here goes.
I see that Soundwave runs his Blues at 700mA but is that necessary.

If I just get one buckpuck for my whites and blues would the 1000mA be too much for the blue?
 
I am running both white and blue with the 1000ma, I have read other posts about people doing the same including one where they started with white at 1000 and blue 700 but decided the blue was not strong enough so they bought the 1000 to replace.

Jerome
 
<a href=showthread.php?s=&postid=15038402#post15038402 target=_blank>Originally posted</a> by shouldabenacowboy
The buckpuck is used to keep a constant current to the LEDs...it doesn't do anything with voltage.
Click to expand...


AHHHHhhhhhhh shouldabenacowboy. You were doing so well up until you went off the rails here, (and only here).

der_wille_zur_macht; The BuckPuck does take care of the excess voltage! It does it by screwing with the voltage. A current controller like the BP controls current by varying its voltage by varying its own resistance or switching. It shaves off whatever voltage it needs too to keep the current where it's supposed to be.

Yes you could use a 24V supply to run 4 LEDs. It would however mean that the system efficiency would be lower than it would otherwise be. More of your power will be lost as heat. Depending on how the BP works would result in more or less loss in efficiency.

As shouldabenacowboy was trying to flesh out, you ideally want your power supply to be 2V, (as required by the BP), higher than your series string of LEDs needs.


BTW der_wille_zur_macht; That is one cute little Crocodilia there. It doesn't look like a Camin nor is it acting like a Camin, (latched onto the nearest finger!). Is that a North American Alligator?
 
kcress, thanks for the additional information. I'm still trying to piece ideas together in my head, as I (clearly) don't understand the "unified theory" of LED and am basing my plans mostly on observation of others (isn't this the way most new development ends up working in this hobby?)

If we were to write a one-sentence rule for picking a power supply for LED, assuming use of a buckpuck, would this be correct?

"The power supply must supply 2v more than the sum of the forward voltages of the LEDs at the buckpuck's design current."

In other words:

1) If I want to run 4 XR-E on a 700mah buckpuck, I need (3.5 * 4) + 2 volts, aka 16 v.

2) If I want to run 6 XR-E on a 1000mah buckpuck, I need (3.7 * 6) + 2 volts, aka 24.2 volts.

3) If I want to run 2 XR-E on a 350mah buckpuck, I need (3.3 * 2) + 2 volts, aka 8.6 volts.

I have no idea what my avatar image really is. Several years ago there was a joke in The Lounge that since I am not a moderator, I am a modelgator - hence, the avatar image is supposed to be a "model" (i.e. scale reprodution of a) gator.
 
Just to add to the below:

How does the # of STRINGS of buckpuck affect the voltage?

der_wille_zur_macht is only assuming ONE string per 4, 6, 2 leds

Does it make a difference if I have 4 string of 4 (700ma) LEDS? Is that still 16V? When does the # strings come into the calculation? Technically, I have 16 LEDS (4x4) in that scenario.

Thanks.


<a href=showthread.php?s=&postid=15040076#post15040076 target=_blank>Originally posted</a> by der_wille_zur_macht
kcress, thanks for the additional information. I'm still trying to piece ideas together in my head, as I (clearly) don't understand the "unified theory" of LED and am basing my plans mostly on observation of others (isn't this the way most new development ends up working in this hobby?)

If we were to write a one-sentence rule for picking a power supply for LED, assuming use of a buckpuck, would this be correct?

"The power supply must supply 2v more than the sum of the forward voltages of the LEDs at the buckpuck's design current."

In other words:

1) If I want to run 4 XR-E on a 700mah buckpuck, I need (3.5 * 4) + 2 volts, aka 16 v.

2) If I want to run 6 XR-E on a 1000mah buckpuck, I need (3.7 * 6) + 2 volts, aka 24.2 volts.

3) If I want to run 2 XR-E on a 350mah buckpuck, I need (3.3 * 2) + 2 volts, aka 8.6 volts.

I have no idea what my avatar image really is. Several years ago there was a joke in The Lounge that since I am not a moderator, I am a modelgator - hence, the avatar image is supposed to be a "model" (i.e. scale reprodution of a) gator.
Click to expand...
 
LOL OK.

Whatever your past understanding of the unified theroy you now have it well in hand.

I would add that once you have your 'number' try to get the next higher voltage power supply to run the system. e.g. 16V -> 24VDC supply.

24.2.... Yer screwed. :)

Options. A lot of supplies allow fin adjustment of the output voltage. This allows the user to dial it in to exactly 24.0V This would also allow you to dial it up a bit. probably to 24.2V. I would look for 24V "with adjustment".

Alternative 1. Try it yo might get lucky and find that the LEDs add up to less than 3.7V each, perhaps 3.6?

Alternative 2; I think the BPs work on less than the 2V head they spec. However instead of 1000mA they can fall out of regulation and only provide something less like 900ma for instance. Just live with that.

Alternative 3; Find a 28V supply, (somewhat common).
 
Ill try a response to fernandokng
Lets put up some saftey barriers

***********SPECULATION****************

I think you hit the max capacity of LED strings when you run up against the watt output of the power supply.

***********SPECULATION****************

Thank you.
 
Well I have been lurking around this site for a little over a year now without ever even creating a user name just reading and looking at the posting. Anyway, I made a user name to tell you guys what a great job you did with the LEDs. I made a set over the past few weeks and I guess I should post some pictures and get your input.
 
Welcome to the Reef Central melee webbrage! We await your pics.


fernandokng; Sorry the site was doing the chicken and after about 20 tries my previous reply came after your question. I never noticed it.

Tron87's response is basically correct. It is easier though to just add up the string currents.

All strings are just hooked across the power supply terminals with their own current controllers(LED drivers)(Buckpucks). NOT in series!

So each string will have its LED driver current. 350mA, 500mA, 700mA, 1000mA, whatever, etc., etc.

You just add them up:

350mA
350mA
700mA
1000mA
------------
2400mA

same as 2.4A

Your supply must be capable of providing at least 2.4A You would be wise to find one that was rated at perhaps 3A or more so the components aren't all running at high temperatures and your supply will last a long time.
 
Here are some pictures of my LEDs, I used the Cree LEDs and instead of using only dark blues and cool whites, I used six plane blue along with six dark blue leds plus the 12 cool whites. I'm not yet finish with the whole project but my corals seem pretty happy with them so far. I plan on hanging the lights over the 29 Gal. tank.


IMG_0005.jpg


IMG_0006.jpg


IMG_0009.jpg


IMG_0010.jpg


IMG_0012.jpg


IMG_0014.jpg
 
Impressive! Very clean looking. What is the fixture made out of, acrylic? My nano will be rimless and have no conventional hood, so I want to build a fixture that's nice to look at.

I see you have optics. How high above the tank will the fixture be? If you have a standard 3' 29g tank, are you sure you'll have good coverage from end to end? It looks like the LEDs are bunched near the middle quite a bit.
 
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