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Cheap! Water Cooled - 10 x COB LEDs - 1 x Pump - 1 x Fan - Spinning plants


Active Member
I`ve been trying to come up with a cheap but feasible system for my flower room
using the cheap chinese LED`s. I have designed this cooling system which does away
with a load of noisy fans by using a single submersible pump which pushes the water through the
cooling tubes and then drips it out over a wire mesh with a single 4 inch fan cooling the flow
back to the tank.

The 150W LED`s generate the most heat at 70 deg C (158F)
I have a total of 10 different COB LED`s, I am not sure of the combined heat generated but the cooling system
is maintaining a steady temp of under 30C (86F) measured in the tank.

Most of the LED`s have direct 220v supply and the others use the transformers to change from 220v to 36v
This basically gives a mix of the LED`s currently available out there.
I have more room to put a few more so we`ll see how it goes.
This setup allows you to use LED`s of different spectrum`s.

The cooling tubes are just pieces of 30mm square steel tubing (what I had lying around at work) with
welded end plates and tapped holes to take the water connectors.
Rectangular Aluminium tube would work well, and as there is not a lot of pump pressure or heat
you could probably plug the ends with some plastic and silicon sealant.
Obviously Keep a very close eye out for leaks before and after powering up the LED`s.

There is hardly any weight to the LED`s and the spring clips do a great job of holding them
against the tube.

For the return flow I have a piece of plastic pipe (with a bunch of small holes drilled in a line) attached to the
top of the wire mesh. so simple.

To further aid plant growth, the pots sit on a rotating disc spinning at 2 revs per minute.
This means all parts of the plants get a chance under all spectrum`s of light.
It consists of a taper bearing bolted to the floor, the laser cut steel disc placed onto that and is driven
by a windscreen wiper motor with a cheap variable voltage supply to reduce the speed.

Hopefully these pics will inspire you to build a cheap easy system for yourself.
Pics show 9 Led`s but I have since added another one.

Simple fixture to bend and cut the spring clips from wire.

The clips

Led`s attached to tube


View from underneath

Cooling in and out

Cooling loop. Flow from one tube to the other

Side View

Submersible Pump in tank

4 inch fan mounted with a piece of flat aluminium plate.

another view of fan and mesh

Steady Temperature reading

Rotating disc setup

Thanks for looking.


Active Member
A few days on
Everything is running well.
The tank pot loses a lot of water, I have to top it up with a good couple of gallons a day
There is a big spike with humidity in the room, gone from around 45 to 65 %

So I added a normal room fan and I must make a cover for the pot and I reckon I wont lose so much water daily.

Otherwise very pleased with the setup.


Well-Known Member
Great work, love the cooling system and I love diy solutions to problems, it's all part of the fun.

It's got me thinking about alternative methods of cooling for cobs, due to space restrictions in my house, i'm looking at doing some sort of outdoor hidden grow room type build, maybe just a compost bin to start with. One of the main problems with nearby neighbours is minimising the noise from fans kicking in for light cooling and odour control systems. So you got me thinking about a water cooling system, but instead of cooling the water via a fan like you did, I might try using an old radiator, so kind of like a central heating system in reverse, pump the warm water from the leds through an old radiator outside in our cold night ambient air. That should work

Oh and it would stop that high humidity problem you are seeing with blowing a fan at water in an enclosed space.

Nice one mate.


Active Member
So you will run your light cycle during the night ?
Pumping through the a radiator sounds like a good idea.
If I could make a suggestion, I would add a cheap voltage adjusting unit which would allow you to alter the speed of your pump
and balance the speed to flow ratio to make sure the rad has time to cool the water.

The wire I used is actually a thin welding rod one of the guys use at work. Not sure why it`s copper coated.
You would have to find some thin spring wire.

Look forward to seeing your setup take shape.


Well-Known Member
Hey stage4, you might be interested in this. I spent most of the day experimenting with cooling mains powered 50W COB's with PC heatsinks.
I was hoping to find one that would work for passive cooling, but even the largest got close to 70C after around 7-8 mins of running, so tried a few heatsinks with fans, and they cooled it pretty good, but were very noisy. I've a background in electronics and do a lot of DIY, built my own hi-fi amplifier many years ago, also make guitar effect pedals for musicians, so built a simple PWM 4 wire fan speed controller using some old parts I had using a very old NE555 timer IC. Very easy to make if you have basic soldering skills.

During testing, heatsink temps were getting close to 60C after around 5 mins of operation with no fan on, so turned on fan at a very low speed and within 1 min it had settled to 30C. I have the speed turned down really low, any lower and I'm afraid it might stall, but it is really very quiet, nothing to be heard. So this cost me nothing with junkbox parts that I had, I think I won't bother with the water cooled radiator idea.

If anyone is interested in making their own I can post detailed info and pics of how I made mine.

Next step is to hook it up to a thermostat so it only comes on when heatsink gets hot, but ultimate goal here will be to have it controlled with an Arduino, maybe come on for a minute every 5 to 10 mins based on real measured temperatures. The Arduino will also control lights, ventilation, watering, feeding and heating.



Active Member
That`s great Pyr0
Do you think the pwm helps with changes in frequency which makes the fan appear less noisy.
In my compost bin, would I be able to pwm the output from my small psu and quieten down the 4 fans it runs or is pwm a single fan thing ?
I`d love to be able to pwm those hard drive motors and add fan blades to that.

I am really interested in your Arduino project, I have some arduino stuff from previous cnc stuff I did.
Please post your info on how you will build this but if you don`t mind me asking, I cant read the hieroglyphic electrical drawings,
any chance you could simplify those for me. Would you be prepared to share your code ?


Well-Known Member
Hey stage4 here's an easy tip you can try. If your CPU heatsinks and fans are anything like mine they are probably 4 wire pwm fans. I've tested a good few and you can tie the blue control wire to ground and the fan will operate on its slowest speed without stalling. Whisper quiet and should be enough air movement to keep the COB'S ok. Give it a go and see.


Active Member
I used 3 wire fans, 2 wire actually cos I cut the yellow.
Thanks for the tip as I did have an attempt at a 4 wire and couldn`t get on.

Hey I had a problem yesterday, the tank got too low and the pump was`nt doing it`s thing,
I had 2 leds `burnt out`. Well one stopped altogether and another was flickering,
they were the last 2 led`s in the cooling circuit so I guess have the hottest temp water in the circuit.
Looks like it will pay to have a float valve with fresh water supply for automatic top up.
Or your radiator idea as that will be a closed system.
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