Need help from a Math wizzard/LED Geek

[Paul B]

I am building a water cooled LED fixture (yeah, I know) and I want to wire it in "parallel".
I have a bunch of 6 volt and 4 volt LEDs from old fixtures and I also have the drivers. But they are designed to run them, like most LEDs in series. I don't want to do that because these will be mounted on a copper tubing with water going through it and I want to use the tubing for one of the wires so I will only have to run one wire.
I know this can be done as I am an electrician but I forgot how to figure out the mili amps required and being an electrician, my mind thinks in light bulbs, not LEDs.
I have built quite a few LED fixtures, but never a water cooled one in parallel. I think it will be a cool Idea as water is much more efficient at cooling then air and the fixture will be very light and simple. The fixtures I took apart for parts are very heavy with 8 fans.
I will also build a radiator out of copper to cool the water but that is the easy part.
I can, of course wire this in series like all LED fixtures, but The LEDs I have are tiny and not real easy to solder so it would be much easier if I can solder one terminal to the pipe. This fixture will be 5' long and use about 60 LEDs but I can use any number of them to make it work.
I will post the specs of the LEDs I have later as I have to figure that out.
So any LED/math wizzards out there can help me?

 

[TheEngineer]

I'll do what I can to help you here... For starters, running in parallel and using water cooling is going to use more power, are you OK with that?

You are also going to need a lot of parallel strings, you won't be able to do one big one.

 

[Paul B]

OK. I have 4 or 5 drivers now, but they are for series strings. The drivers I have are 80-130V and 560mA. Using more power is fine as the overall comsumption will be the same. I want to use the copper tube as one of the conductors as this won't be a grounded system. The other conductors can be any size and may even be copper tubes but I didn't design that far yet. I have 5 of these drivers and a smaller one. This driver was running 36 white LEDs and another was running 24 blue LEDs. (that's how I figured out how many volts the LEDs are) I want to use the LEDs I have and see what type of drivers or power converters I need. Do you know how to figure the power requirements for each string?
As I am sure you know, this is just an experiment as my original DIY LEDs are running fine, but they are way under powered. I also like the water cooled idea because the air cooled is not very efficient, heavy and complicated. Years ago, when large commercial computers first came out, they were water cooled. They actually had small tubes of water running around the CPUs and it worked very well. I can do the plumbing with no problem so I want 3 or 4 copper tubes about 1/4" tubing where I will glue the LEDs using thermal adhesive. I can wire them in series but I would have to run 2 wires on the tubing. I would like to see if a parallel will be doable. The LEDs I have are wired to a circuit board so the terminals I will be soldering to are very tiny and not meant to be wired. I have to un-solder them from the board. I can do that but it is a little bit of a job and insulating the connections from the tubing is a little problem but with the small tubing the connections will be off the side of the copper so I won't have to insulate them.
Thank you for your help.
Paul

 

[TheEngineer]

You won't be able to use those high voltage drivers if you want to drive in parallel. The voltage drop adds in series, it does not in parallel.

You need to know the operating current and voltage drop of each color LED, then you can calculate current limiting resistors. I'm not sure how you're going to be able to isolate the liquid cooling system from the voltage coming in on the copper tube. There will be a path to ground there.

 

[Paul B]

Yeah, I know the drivers won't work. I just added the values on those so you can figure the voltage and current requirements of each LED. They can be figured by those values as the LEDs are not new so I don't know the values of each LED. But I figured some of them are about 6 volts so can't I just run a bunch of them in parallel using a large conductor to one side of each LED? I am not sure what size power supply I need or if I will need any resistors.
The copper pipe will just be used for the heat sink and will not be touching any power unless I can use the pipe for one of the conductors like I could if I were wiring regular light bulbs. The pipe will not be grounded anywhere as the water in the pipe is fresh water and not tank water. It can not be in contact with my reef tank because it will be highly copper saturated. It is a sealed system like a car's cooling system. I have no problems with that system, it is the current for the LEDs I can't figure out. I can also make any type of power supply I need. I think I can just use a 6 volt dc power supply to feed a string of LEDs in parallel but I don't know how to figure the resistors or where to put them. I also know this is a weird system so thank you for your help. I normally do weird.
These are the LEDs I am using. I repaired this fixture and can use it as it is. But it is square and my tank is 6' long so the configuration as it is won't work. I also want to use a water cooled system just for kicks.

 

[Paul B]

Here is a very simple schematic of what I am trying to do.

 

[TheEngineer]

The diagram seems to show that the LEDs are wired to the copper tube. Is that not right? You'd also want a current limiting resistor on each LED to be safe. The way you have it wired will drive more current into the first LED than the second, more into the second than the third and so on.

6VDC seems high to me for the LEDs. I'd guess they are 3.3VDC which is more standard, but I can't say for sure without testing one. Can you just tap into one and see when it lights up?

You can still do liquid cooling, but why not leave the LEDs wired as they are and run your liquid cooling between the fins of a heat sink?

 

[Paul B]

I think the resistor will evenly spread the current as they are all connected to the same terminal and only a few inches apart. , but I could use a separate resistor for each LED. That would be a lot of resistors. I need to know the resistance. I figured 6 volts (which also seems high to me) but if I take the output of the existing drivers which is (tested with a meter) 130 volts. And I divide by the number of LEDs (24) I get 5.41 volts. So you are right, it is probably closer to 4 volts, but 3.3 would probably work. So if we take that number. What would be the resistor on each LED? I have plenty of extra LEDs so if I destroy a bunch of them in a test it will be fine.
The other LEDs I have are about 3 volts because the driver runs 36 of them. I can't leave the LEDs wired as they are because they are on a printed circuit board and much to close together for my needs. I want to space each LED a few inches apart in maybe 3 or 4 strings across my tank.
This is the existing fixture I have now. Since this I added another aluminum tube so there are 4 tubes with LEDs a few inches apart. Fans suck air through the tubing to keep it cool. This has worked for a number of years so I know the concept is sound. But I still want to experiment with water cooling on rigid copper tubing. I would love to get square copper tubing but no such thing exists as far as I know.
I will test the voltage across one LED

 

[Paul B]

I tested the actual voltage across each LED and you are correct, it is about 3.5 volts.

 

[TheEngineer]

Do you know what power the LEDs are rated for? I can't tell you what resistors you need without knowing how much current they can handle.

 

[Paul B]

No, I don't know anything about the power for them except what I read off the existing drivers which is 560ma. That drives 24-36 LEDs in series.

If we can't figure this out, I can just run the extra wire and connect these up in series like they are. That way I can just use the existing drivers and forget about all the resistors.

I think a water cooled system will be fairly cool. Of course if it leaks into the tank or falls into the tank, it will crash it. But that is like living on the edge anyway. For the corals anyway. If I go with series I just can't use the copper tube as a conductor, but that is not the end of the world.

 

[TheEngineer]

I missed that you said 560mA driver. OK, so then we can guess the LEDs are 3.3VDC and 500mA.

We can calculate the power then, P=current * voltage. P = 1.65W (the forward voltage is probably really 3VDC, so let's call them 1.5W)

One of the problems is we don't know how close to their peak power the manufacturer was running them. Running an LED beyond 50% of its power rating will cause its color to shift significantly faster.

 

[Jimmyb819]

Another problem that is going to arise is that instead of a 130v/560ma supply you are going to need a 3.5v/12A supply (for 24 leds in parallel). This is because voltage adds in series and current adds in parallel.

 

[TheEngineer]

Another problem that is going to arise is that instead of a 130v/560ma supply you are going to need a 3.5v/12A supply (for 24 leds in parallel). This is because voltage adds in series and current adds in parallel.

Indeed, unless there are multiple shorter strings.

 

[Paul B]

I can make as many strings as I want. I realize it will have to be 12 amps or so and that is fine. So who is going to make up the wiring diagram? I would like to use about 60 of the LEDs. I don't want them to run at full power because this water cooled system is experimental and it is hard to figure how much cooling I am going to need. I am building the frame/heatsink out of 1/4" copper pipe. I want to make 4 lines of it about 5' long. Remember I can still go with a series installation as the wiring would be much thinner but I would like to use the copper as one conductor. Thanks guys. I know it is a little math involved.

 

[TheEngineer]

Well you're going to do the wiring diagram of course! j/k I'm happy to help.

I'm still concerned about using the copper as a conductor. It is unshielded and it's going to have a decent amount of current flowing through it. It's a cool idea, but so is not getting electrocuted or burning your house down....

Ignoring my concern, how do you intend to transfer the heat from the LEDs to the copper?

 

[Jimmyb819]

I'm guessing he will be mounting the LEDS to the copper pipe and just transferring the heat by conduction.

If he uses the pipe as the grounded side of the circuit that should eliminate the potential for electrocution. Usually the danger is touching the voltage side of the circuit while grounded.

Also, I just realized that at 3.5v there isn't going to be enough potential to create the current through the body to even feel a shock let alone hurt anyone.

 

[Jimmyb819]

BTW Paul this is a very intriguing idea. I'll be following along and help where I can.

 

[Paul B]

Well you're going to do the wiring diagram of course! j/k I'm happy to help.

I'm still concerned about using the copper as a conductor. It is unshielded and it's going to have a decent amount of current flowing through it. It's a cool idea, but so is not getting electrocuted or burning your house down....

Ignoring my concern, how do you intend to transfer the heat from the LEDs to the copper?

No electrocution hazard here. It will be using low voltage and slightly high amps. Your car battery is 12 volts and can put out maybe 500 amps, but it won't shock you (no matter how much they show that in Sci Fy movies)
The copper tubing is capable of easily carrying that current from 60 LEDs. For the heat transfer I am going to glue the LEDs to the copper using thermo glue that transfers the heat. Water will be circulated through the tubing with a small pump. It will be a closed system but I want some of it to be clear acrylic so I can tell if the water is circulating. I will put something in the water so I can see it. Probably glitter. The "radiator" will be smaller tubing piped in parallel to larger tubing with a fan behind it just like a car radiator. I will build a water temp sensor and a shut off that will turn off the LEDs if the water stops flowing or gets to hot.
As I said, There is no real need for such a configuration. It is just en experiment and I think it will be cool. It is easy to build and it will be lighter and less complicated than an air cooled system. The LEDs I am using come out of a fixture that uses 8 fans and a heavy housing. This will just be 3 or 4 runs of 1/4" copper tubing (sprayed with clear acrylic just to keep it clean as copper turns green) That will be very light. If I can wire it in parallel I only need one wire to each string as the copper will be the return so the wiring is simple. I know the wiring, I just need help with the resistors. If it works, that's good, if it doesn't work, who cares?

 

[Jdmonealp]

Paul, if you are set on using the copper as one of the leads, you could just run it like a normal series of led's, and instead of having the last led go back to the driver, you could use the copper to make it go back to the driver. another issue i see though... that would mean only one series per copper tube. not sure how a common ground for multiple drivers would work.

EDIT: you beat me by a few minutes Paul