Should I use LED Drivers or Resistors?

[titancrusher1]

I've posted two other threads pertaining to my LED build. I was wondering if I can just purchase Resitors to regulate the LED current of my bulbs or do I have to buy the actual Buckpucks for them? If I can use resistors what resistors should I be getting?

I'm going to be putting together 9 10w LED's. 5 of them Cool whites at 1000ma 12v and 4 of them Actinic Blues at 900ma 12v

[uncleof6]

Resistance in ohms = (Source voltage - voltage drop across LED string)/current in Amps.

Voltage drop across LED string = V1 + V2... +Vx

I wouldn't worry about it a whole bunch-- these guys will never let you run resistors instead of a driver......

[titancrusher1]

Thanks for the heads up lol. Question though...i'm not an expert electrician at all and im not understanding your equation. what is v1 and v2? if it matters these are the specs for the LEDs i'm installing..


Blues:

Emitting color: 'Extreme Royal" blue.
Wavelength between 445-450nm
Deep blue and ideal for the rapidly growing reef lighting industry
Luminous: 150-200LM
Input voltage: 10-11V
Input current: 900mA
Power: 10W

Cool Whites:

High quality aluminum alloy material
SMD
Luminous Flux : 800-810 Lumen
Rated voltage: 10~12V DC 10W
Color temperature: 12000K Cool White
Forward Current (IF): 1000mA
Viewing Angle: 120 Degree

[widmer]

Originally Posted by uncleof6

I wouldn't worry about it a whole bunch-- these guys will never let you run resistors instead of a driver......

Do we need to have this conversation again?

titancrusher1 - Here's an excellent thread to help you set up resistors if you want to go that route.

http://www.reefcentral.com/forums/sh...ght=led+budget

What made you decide to use those particular LEDs for your build?

[titancrusher1]

I wanted to go with a system that had a thinner profile than a bulker 2 sq foot footprint. I'm attaching them to a 72x3" piece of Metal Flashing that is conveniently designed to fit a Plexiglass shield in

I know this is probably a pain to do, but can you calculate the exact type of resistor i would need for each bulb? I'm assuming i need one resistor for each bulb correct?

[kcress]

Did you look at widmer's link??

[titancrusher1]

I did, not understanding it completely. I'm a total newbie here. My initial intention was to use a 12V power supply with 20 amps. Going by his writing I would need 9 resistors. I'm having an issue though with my blue leds being rated 10-11V and not 12v. Does taht mean I can't use a 12v power supply?

[widmer]

Some miscellaneous observations:

1. Individual LEDs are generally referred to as "emitters" rather than "bulbs".

2. I'm pretty confident that aluminum flashing wouldn't give you much of any heat dissipation which is necessary to keep the lifespan of the LEDs. Flashing is just so thin it doesn't have the capacity to propagate heat from the emitter... Especially taking into account that those emitters are not all that efficient, creating an enormous amount of heat in tiny footprint.

3. Which brings me to my next observation. I'm guessing the emitters you would like to use seem like a great deal because they give you lots of watts per $ spent up front. But unlike with halides and fluoros, it's a totally different ball park with LEDs. The amount of watts that they require says close to nothing about how much light they produce. To see what I mean, find a few different LEDs and compare the amount of watts they use with how many lumens they create. For instance, the latest Cree LEDs can literally produce twice as much light per amount of electricity they use as the LEDs you have posted.

4. Hang in there, it's like riding a bicycle; Once you know how LEDs work, you'll probably always know. Take another look at kcress' thread I linked to.

[titancrusher1]

Looking at the actual material it's 1/16" Stainless Steel. I was told the overal square footage of it should be enough to dissipate heat and once i add a fan the heat should not be an issue. I also need to add quality thermal epoxy. I was told this should be okay from the guys who sell the Cree LED's at LEDsupply.com

I realized taht the lumens will not be as bright, thats why i went with 9 bulbs. My original intention was to put 5. 3:2 ratio. I believe the 9 bulbs will add the extra light needed plus make it physically look brighter as well. I always kind of hated how LED fixtures dont make the water as bright as a good t5 setup.

My brains not working with me today. I can't figure out the type of resistor i would need. I guess i first need to figure out if i can power the 10-11V rated Blue LEDs with the same 12v power supply that would power the White LEDs.

[widmer]

In spite of how remarkably stainless steel appears to be similar to aluminum, it actually only has somewhere between 1/3 and 1/20 the capacity to conduct heat. For more reading:

http://en.wikipedia.org/wiki/Thermal_conductivity

If you do end up using the steel flashing, let us know how it goes.

[Tbduval]

[QUOTE=titancrusher1;17995335]
I I always kind of hated how LED fixtures dont make the water as bright as a good t5 setup.

QUOTE]

I don't think this is an accurate statement. It's like saying all 20k's look like a Radium, which we all know is not true. There is a major difference with LED than T5's. Most people light their tank from end to end, front to back, or very close to. In return it lights every nook and crannie of a tank. With LED's you can control how many LED, what spread, and what color you like. Light a 65g up with 150 LED 40 degree optics and I promise you it will just as bright as a T5 setup! Not trying to agrue, just trying to compare apples to apples. I really want to see how you place everything together and how those LED's will work.

[titancrusher1]

well, Home Depot says its Tin. Guess dad doesn't know everything lol :P What would be better than Aluminum? remember, the idea is to create a longer Thin structure if possible...

By the way, spoke to Blasterman on here who has built a ton of LED structures, he told me the resistors can get red hot with the bulbs im using and has suggested Drivers "hands down" I think i'll be going the Driver route...*cha ching*

The last thing to figure out here is Where can I find a proper power supply and how the heck do i wire this thing assuming I buy a driver for each LED.

[uncleof6]

Originally Posted by titancrusher1

well, Home Depot says its Tin. Guess dad doesn't know everything lol :P What would be better than Aluminum? remember, the idea is to create a longer Thin structure if possible...

By the way, spoke to Blasterman on here who has built a ton of LED structures, he told me the resistors can get red hot with the bulbs im using and has suggested Drivers "hands down" I think i'll be going the Driver route...*cha ching*

The last thing to figure out here is Where can I find a proper power supply and how the heck do i wire this thing assuming I buy a driver for each LED.

Told you not to sweat it didn't I? Using resistors is not supported here. Chuckles.

[titancrusher1]

I really want to try the resistor route because at the bare minimum i can save some money. The trick is to find the EXACT resistors for the two different bulb types. I have no idea how to calculate that. I'm also having a hard time finding a 10v power supply with at least 10amps, where would i be able to find something like that?

[kcress]

Originally Posted by titancrusher1

I have no idea how to calculate that.

You have NOT read or have not comprehended the thread link given above.

You are about to waste a lot of people's time and your money.

It was very clearly explained how to do what you want in great detail there. If you cannot read and understand the first post in that link or cannot be bothered to, you should not be attempting this build.

[uncleof6]

With a 12VDC power supply: to run @ 10 forward voltage for each LED (not bulbs) in parallel.

Blues: 2.2 ohm 10 watt ballast resistor at 900mA (resistor dissipates 1.8 watts)

Whites: 2 ohm 10 watt ballast resistor at 1000mA (resistor dissipates 2 watts)

Neither will get red hot.

12VDC 10 amp power supplies are easy to come by.

http://www.google.com/products/catal...=0CJQBEPMCMAc#

However, with the whites you will be pushing the limits of it, and would be better off with 15 amp capacity. You need one for the blues and one for the whites, though there are a couple ways to go about this.

If you can find a 100 or so volt driver.......its doable with a ~100VDC power supply with a 3 amp capacity or so, and just a couple resistors..... different values than above though.

If you really want to go after this stuff, you really should learn ohms law, and some basic electronic principles and terms, or not bother with this stuff. Agree with Keith on that.

[Jeff000]

Originally Posted by titancrusher1

well, Home Depot says its Tin. Guess dad doesn't know everything lol :P What would be better than Aluminum? remember, the idea is to create a longer Thin structure if possible...

By the way, spoke to Blasterman on here who has built a ton of LED structures, he told me the resistors can get red hot with the bulbs im using and has suggested Drivers "hands down" I think i'll be going the Driver route...*cha ching*

The last thing to figure out here is Where can I find a proper power supply and how the heck do i wire this thing assuming I buy a driver for each LED.

Just buy dimmable meanwells. You will be into it for 60 bucks, and the cost of LED's.
How bit is your tank?

better then aluminium?
You need to start looking at peoples links, and reading what they post
http://en.wikipedia.org/wiki/Thermal_conductivity there are a few that could be used, but the big thing is that aluminium is by far the cheapest.

You say you do not want a bulky build but you are attaching to a 72x3" "heat sink"? Thats very long and very narrow for a tank, unless you have a 72" tank, but then you will need a LOT more LED's

And why the plexi shield? how close to the water are you putting it?
How close to the LEDs are you putting the plexi?

Originally Posted by titancrusher1

I really want to try the resistor route because at the bare minimum i can save some money. The trick is to find the EXACT resistors for the two different bulb types. I have no idea how to calculate that. I'm also having a hard time finding a 10v power supply with at least 10amps, where would i be able to find something like that?

I have no idea how much the LEDs you are looking at cost, but the Cree 3w are what most use for their builds and are proven. And then just use the buck pucks. Both are at LED supply.

I'm not sure that LEDsupply would have said thin stainless would be a good heat sink, stainless is a poor heat conductor, and with plexi covering the leds I would worry about over heating

[der_wille_zur_macht]

Resistors certainly can get "red hot" when used to limit current through an LED. They can be terribly inefficient and dangerous. However, the same things can be true of any active driver you might use. The key here is that you need to understand the advantages and disadvantages of the available methods of current control, and you need to understand the correct application of the various methods of current control.

Commercial, off-the-shelf drivers are nice because they're fairly "plug and play" and as long as you follow instructions, things will basically work out. There's documentation and support from vendors and manufacturers. They're also extremely common and are used in a very large percentage of the build threads on here, so if you can bother to spend a few minutes reading, you'll get all the info you need.

Resistors can appear trickier to those not familiar with the basics, but essentially, it's very simple math to choose the correct resistor, given you know your way around a simple circuit. kcress's thread, linked by widmer above, contains exactly the information you'd need to go that route. There's really no need to rehash things in another thread, as he did a great job documenting it there, and there was even plenty of discussion about resistors vs. commercially available and DIY drivers right in that thread. The obvious "danger" is that you're more or less on your own to make sure it all works out. There's no vendor support.

One final thought. You've started several threads over the last two days asking some basic questions about LEDs, and proposing plans that go harshly against the grains of "established" norms. While this is not in itself a bad thing, it is going to be a very difficult path considering your lack of experience and understanding of the basic principles involved. I don't mean this as an insult, but rather as helpful advice. Your chances of success would likely be much higher if you'd choose to do a more typical build, at least for your first try - then, once you understand the basics and have some hands-on experience, you can experiment with some of your different ideas with a bit more confidence.

[titancrusher1]

ok. Looks like i've figured it out. (the Resistor route that is) I did the math a few times to understand it and unclueof6 has it spot on. Luckily I can get my hands on a 12v 20amp power supply.Would I only need one or do i need two power supplies, one for the whites and one for the blues, i noticed you mentioned a couple of way to go about it....

are you saying if I went the 100v 3amp or so route, i can use just one power supply coupled with the right resistors?


@Jeff000 I dont know how high off the water i will be putting the fixture but i'm playing around with the idea of putting it 8" above the tank line.

the LED's will be about 1" away from the Plexiglass shielding. I did get 1/8" plexiglass that's pretty thick, in case of heat buildup against the glass. I do have a 1/16" laying around but haven't fabricated the pieces to make the plexiglass shield out of it yet. Keep in mind the Fixture has 3 4" long holes on the top that i'm going to be using for air circulation. I may attached some small fans too it if it looks like it will get too hot.

[der_wille_zur_macht]

Originally Posted by titancrusher1

ok. Looks like i've figured it out. (the Resistor route that is) I did the math a few times to understand it and unclueof6 has it spot on. Luckily I can get my hands on a 12v 20amp power supply.Would I only need one or do i need two power supplies, one for the whites and one for the blues, i noticed you mentioned a couple of way to go about it....

are you saying if I went the 100v 3amp or so route, i can use just one power supply coupled with the right resistors?

You can essentially use as many power supplies as you like. The difference between using a 12v supply and a higher voltage supply is the wiring between the LEDs. With a 12v supply, you'd put several of them, each with their own current limit resistor, in parallel across the supply. With a high-voltage supply, you'd put several LEDs in series, with a single current limit resistor. With a "medium" voltage supply, you'd likely do several parallel strings with several LEDs in series in each string.

Basically what it boils down to is matching your string length to the voltage of the supply (add up the Vfs of the LEDs), and matching your number of strings and intended drive current with the current capacity of the supply (with a margin for safety).

With just your 20A 12v supply, you could indeed power all of the LEDs you've mentioned - you'd put them all in parallel with each other, each with their own current limit resistor. Keep in mind that this is about the least efficient way to drive the LEDs, since you're incurring a "hit" of wasted power for each LED. It would be more efficient to get a higher voltage supply and build some series strings to run on it, but that may be a moot point given your plans.

And now I'm going to sound like a broken record, but please read the thread linked above by widmer. Besides laying out all the information you'd need in practical terms, it includes some very meaningful information on exactly how to go about arranging and building an array controlled by resistors in a safe and effective manner. It is VERY important to understand that, while the math is all nice and simple, the real world isn't as accurate. Seemingly small differences in the equipment you're using (i.e. that 12v supply might actually be generating 12.8v, and that LED rated at 10v for a given current might actually only need 9.2v to hit that current) can be VERY significant both for the effectiveness of your array AND your personal safety. It's common for these LEDs to be "off" in terms of V/I relationships by enough that using a poor-tolerance resistor or a power supply that's off by a few tenths of a volt can create a dangerous situation, so please make sure you understand these nuances before you start wiring things together.

the LED's will be about 1" away from the Plexiglass shielding. I did get 1/8" plexiglass that's pretty thick, in case of heat buildup against the glass. I do have a 1/16" laying around but haven't fabricated the pieces to make the plexiglass shield out of it yet. Keep in mind the Fixture has 3 4" long holes on the top that i'm going to be using for air circulation. I may attached some small fans too it if it looks like it will get too hot.

Check your other thread for some comments about heatsink design and thermal management. Your current plan to use the stamped sheet steel is not going to work. You need to start from scratch with respect to heatsink design.

[Jeff000]

Originally Posted by titancrusher1

the LED's will be about 1" away from the Plexiglass shielding. I did get 1/8" plexiglass that's pretty thick, in case of heat buildup against the glass. I do have a 1/16" laying around but haven't fabricated the pieces to make the plexiglass shield out of it yet. Keep in mind the Fixture has 3 4" long holes on the top that i'm going to be using for air circulation. I may attached some small fans too it if it looks like it will get too hot.

How big is this tank you are putting this on going to be? Sounds like you are going to be spacing these emitters pretty far from each other and not many over the tank.
Being that far from the water I am not sure I would bother covering the LEDs unless you have something that is causing a lot of splashing.

As mentioned already I think you need to reevaluate your heat sink idea.