Need help from a Math wizzard/LED Geek

[TheEngineer]

Yep. Double the wattage for overhead.

 

[Paul B]

I am glad you guys love this stuff. I spend most of my life designing weird things and this is a little weird. But I think it will be interesting as I don't think I ever saw a water cooled LED fixture before.
Here is the LEDs I will be using. We don't want to disapate the heat, we want to design it so it all goes into the LEds themselves with no waste. I know you guys can do it.

 

[twilliard]

Yep. Double the wattage for overhead.

Metal oxide is the way to go!

 

[twilliard]

I am glad you guys love this stuff. I spend most of my life designing weird things and this is a little weird. But I think it will be interesting as I don't think I ever saw a water cooled LED fixture before.
Here is the LEDs I will be using. We don't want to disapate the heat, we want to design it so it all goes into the LEds themselves with no waste. I know you guys can do it.

Oh my!
This is a challenge

 

[Paul B]

As I said, if it was easy, anyone could do it. I didn't go to college, there was that draft thing with the war. But I did spend 5 years in electrical school to become an electrician. But that was in the early 70s and there were no LEDso I have problems figuring forward voltage and all that so I can't figure it out. But I know you electronic Geeks can do it. If it works I will give you guys full credit.

 

[twilliard]

As I said, if it was easy, anyone could do it. I didn't go to college, there was that draft thing with the war. But I did spend 5 years in electrical school to become an electrician. But that was in the early 70s and there were no LEDso I have problems figuring forward voltage and all that so I can't figure it out. But I know you electronic Geeks can do it. If it works I will give you guys full credit.

I became an electrician in 1993 heavy industrial. Now retired at 40 and run a business in electronic restorations.
We will figure this out!
Still working on the plan with such small solder leads.

 

[Paul B]

If it helps, I can use one resistor for each LED because I still will need to solder a small wire to each LED to wire it to the copper tube. That wire could just as well be a resistor.

Twillard, I became an electrician in 1973. Now retired. I also worked heavy commercial/industrial. I was the general foreman so I had the chance to design all sorts of cool ways to do things. All my years were spent in Manhattan.

When I un solder those LEDs, there is practically nothing to solder to. But I used a bunch of them already and it's not to hard to solder.

 

[twilliard]

Wow all your time in one place?
Gosh I was one of the travelers in this world chasing the money.
How far apart are you thinking for the chips? I still think a single dropping resistor would help but when one chip fails the rest will follow.

 

[Paul B]

New York City is a busy place. You will never run out of work there and I never did. To support 9 million people we have plenty of power plants, sewage treatment plants, water tunnels and buildings.
My company would build buildings, knock them down or renovate them. But I specialized in power plants, sewer or garbage. Of course I ran the New York City Playboy Club and Penthouse Magazine so it wasn't all "work".
I will spread out the 15 LEDs along a 5' length of tubing. So if I use 4 tubes I will have 15 on a tube. If I use 3 tubes I will need to put 20 LEDs on a tube. There will be plenty of copper in between them for heat to be transferred. I realize there is very little actual metal in each LED but that's the way they were designed and they were running very hot. Much hotter I would suppose than a water filled copper pipe would be.

 

[TheEngineer]

Actually you want no heat to be dissipated by the LED. Heat is your enemy. The problem is that the conversion of electricity into light is a very inefficient process. LEDs do this better than incandescents but there are still inefficiencies.

I don't know the exact numbers off hand but say the LED is 85% efficient. That means 15% of the power you put in becomes heat not light. You need to pull that heat off. You are trying to do that by dumping the heat into a liquid cooling system. That 15% is what you need to be able to get from the LED into the copper tube.

I'm out and about now but I'll look up the thermal resistance and conductivity numbers to see what surface area is needed for the contact point.

 

[twilliard]

So roughly 3 inches between chips.
You can do individual resistors so I will have to calculate the resistance of each.
I will return!

 

[Paul B]

We can do this.

 

[twilliard]

Ok,
At 6 volts driving at 330ma would need an 8.2 ohm resistor at 1 watt as long as the chips are 3.3v fv
I had to find a combination of currents with available resistors made.
Please correct if wrong

 

[twilliard]

We can do this.

Excellent!

 

[twilliard]

Metal oxide 8.2 ohm resistor.
Just the heat from soldering would change the value of a carbon composite.

 

[Paul B]

I want to dump the heat into the cooling system and not dissipate it through resistors. Each of these LEDs only has a tiny bit of heat sink built in but that is what they were designed to use. They were bolted to an aluminum sheet and we already determined that copper is much better heat transfer so at least that is good news. Of course there is some loss because the tubing is round and the LEDs are flat. This I can help if I want to solder flat disks to the pipe about as large as the heat sink on the LED. That would be very easy and I think I will do it that way. That way 100% of the base of the LED will be in contact with the metal that would be soldered to the tubing so it will be a very efficient heat transfer. Much more efficient than this LED fixture was designed for. I know you guys can figure this out. I have great faith in you.

 

[Paul B]

OK so does this mean I can go out and buy 60- 8.2 ohm metal oxide resistors and supply each run of 20 LEDs with 3.2 volts DC? And will Radio Shack have these or I need to get them on line?

Also, how many amps will the power supply have to supply to each circuit? Or can I run al of them on one circuit?

Icecool, you have the perfect name for heat transfer.

 

[twilliard]

That is calculated at 6 volts.
Radio shack may not carry metal oxide I think they are all carbons, well where I live.

 

[twilliard]

OK so does this mean I can go out and buy 60- 8.2 ohm metal oxide resistors and supply each run of 20 LEDs with 3.2 volts DC? And will Radio Shack have these or I need to get them on line?

Also, how many amps will the power supply have to supply to each circuit? Or can I run al of them on one circuit?

Icecool, you have the perfect name for heat transfer.

Each channel would have to supply more than 7 amps

 

[twilliard]

I would set that up on your bench with a single chip and burn it for over 24 hours. This is to drive it at 330ma so not sure what chips you have.