Build an LED COB Grow Light

There are so many advantages to building your own LED grow light, from savings to customization to output. Making your own light is a lot of fun and if you put money towards creating your own light rather than buying a premade unit off of Amazon or eBay, you’ll end up with a final product that’s FAR more powerful and efficient.

Since I first wrote this article, it’s gotten much, much easier to build your own lights. The part that proved most difficult in the early days was finding a heat sink for your DIY COB grow light, but now there are all sorts of heat sinks available that come pre-drilled for a variety of popular COBs, so I think it’s worth revisiting this and giving it a little revamp. We’ll start with examining how to build your light the easy way, then have a look at the original, more involved option, where you’re drilling your own heat sink.

METHOD 1: THE EASY WAY

Let’s use a common build for this tutorial:  4x 36 volt COBs on a Mean Well HLG-185H-C1400. This setup works out to be about 50 watts per COB, 200W total. A light like this will cover a space of about 2.5’x2.5′ for flowering plants and will cover up to 3’x3′ for vegetative growth or leafy greens. Everything but the driver in this tutorial was provided to me by the good people at Horticulture Lighting Group so a special thanks to them for helping out the DIY community and be sure to check out their kick-ass Quantum Boards!

Of course, you can always pick and choose your own components to build your system, and if you decide to switch it up, be sure to read our post on Selecting COB LEDs and Matching Drivers and then check out our constant current driver selection tool to easily design your system using the current most popular COBs and Mean Well HLG series drivers.

 

Components

My parts list for this build is as follows:

An LED driver, pin fin heat sinks, COBs, COB holders, wire, wagos, a potentiometer with cap, a power connector, and thermal compound.

All the components for the build.

4x Citizen CLU048-1212 Gen. 6 COBs in 3000K color temperature.

4x 120mm Pin-fin heat sinks from Horticulture Lighting Group

4x IDEAL COB holders for the CLU048 chips.

A tube of thermal compound to help transfer heat between the COBs and the heat sinks. One tube does 4 COBs.

Wago 2-conductor lever nuts. These things are amazing.

A 100K ohm linear taper potentiometer.

This potentiometer came with a nice cap.

An LLT-L20 waterproof connector that I’m using for my AC power connection between the driver and the wall.

A Mean Well HLG-185H-C1400B LED driver.

 Tools

Here’s what I needed for tools for this build:

Assembly

1. Installing the COBs in COB Holders

The first step is an easy one. Take your COB and fit it into one of your COB holders. There’s generally a springy little tab that you’ll need to depress, and a couple corners you’ll need to fit your COB into. The back of the holder will likely have a plus symbol to indicate which side you need to match with the positive side of the COB. The front of the COB will have this same symbol – just make sure to match them up.

 

2. Apply Thermal Compound to the Back of the COB

There are a few different ways to do this. You can use thermal compound, which is the way I always do it, or you can purchase handy little thermal pads that are sized for your particular COB – though these may be more expensive. If you go the thermal compound route, put a pea-sized amount of it on the back of the COB and spread it out with an old plastic card:

 

3. Fasten the COB & Holder to the Heat Sink

If you’ve purchased the right heat sinks for your particular model of COB, they will have come with pre-drilled holes that match the mounting points of your holders. When you line the holder up, make sure that not only do the screw holes line up to fasten it down, but the screw holes for attaching an optional reflector also line up:

4. Terminate Your LED Driver AC Connection

If you’re unfamiliar with working with electricity, consider enlisting some help on the driver terminations – otherwise, do this at your own risk. Make sure everything is unplugged until you’re 100% complete and certain everything is wired correctly.

I really like the connector I used to terminate for this example because it’s waterproof and provides excellent stress relief for the cable (if the wire gets tugged on, it won’t rip it out of the connector). You can use a connector like I did, or a number of others like a NEMA 5-15P or IEC-style power connectors.

Consult your driver’s manual for information on wiring the AC connection. Some may have information printed on the case of the driver – mine tells me that the brown wire is my line (hot), the blue wire is neutral, and the green wire is ground. Make sure you screw the connections down very tightly no matter which style connector you use, and be sure there aren’t any stray strands of copper that manage to poke out. I terminated my driver into one side of the connector, then attached my power cord to the other side of the connector. I matched the black of the power cord to the brown of the driver, the white of the power cord to the blue of the driver (neutral), and the green of the power cord to the green of the driver (ground). Make sure you’ve properly identified the colors of your specific power cord – they may not be the same as mine.

For more info on terminating a standard power plug instead, read this instructional post.

5. Terminate Your LED Driver DC Connection

The same safety rules apply for the DC side of the driver as the AC side. Get help if you’re not comfortable with this and be sure to double-check all the connections, then only power it on when you’re positive everything is done correctly.

The DC side is much easier than the AC side. Most people use Wago connectors for the DC side, and they’re a breeze. Just strip back the driver output wires a little and then snap them into 2 separate Wagos. When you’re ready to connect all your COBs, the positive side of the COB run will be connected into these the positive Wago and the negative side of the COB run will go to the negative Wago (we’re using a series connection in this build).

5. Terminate Your Dimming Potentiometer (“B” Style Drivers Only)

If you buy a Mean Well driver that ends with a “B” (e.g. an HLG-185-C1400B), you’ll need to terminate an external potentiometer on it in order to dim the light. If you get the “A” version of the same driver, it will come with a built-in screw terminal that can be used to dim the driver. Here’s how to terminate an external potentiometer on a B type driver:

5. Build a Frame

This video covers the frame build process from start to finish for these 4 Citizen COBs.

6. Connect the COBs to the Driver

09/06/17: Coming soon… hang tight! For now, check out this post on wiring in series and parallel.

METHOD 2: THE HARD WAY

If you don’t go with a pre-drilled heat sink, you can make your own out of a CPU cooler. Here’s how.

Components

My parts list for this build is as follows:

LED Grow Light Components

A Mean Well LPC-60-1400 LED Driver

12V Power Supply

Tools

I was able to complete this build using the following tools:

  • Cordless Drill with Drill Bits (I ended up using a 3/32 bit which didn’t prove big enough, so I went up to a 7/64 drill bit for my #6 screws)
  • Digital Multimeter
  • Wire Strippers
  • #6 x 3/8 Screws with a Matching #1 Screwdriver
  • Sharpie
  • Grinding Bit
  • Plastic Card to Spread Thermal Grease

A selection of tools required for building an LED Grow Light

Assembly

There are 3 main steps to assembly: Attaching the COB to the Heat Sink, Wiring the LED Driver, and Wiring the Fan.

1. Attaching the COB to the Heat Sink

Of the 3 steps, this step will require the most patience. I have found in the past that if I rushed the drilling of the holes or even screwing in the screws, I ran into big problems. If you break off a drill bit or over-tighten a screw and break the head off of it, you’re going to have a very bad time. It takes a long time to fix screw-ups like that (you’ll need to drill new 2 new holes, plus try to flatten out all the crap that’s now broken off in the heat sink), and it’s so much easier in the long run to take the few extra minutes to do it properly the first time!

Now, first thing’s first. The CPU coolers I ordered to use as heat sinks came with a patch of thermal grease installed. You could get away with reusing this, but I decided to wipe mine off in order to get a cleaner application. I used a paper towel to get rid of the stock grease.

A CPU cooler with stock thermal paste

Cleaning thermal paste off of the CPU cooler with paper towel

The CPU cooler with thermal paste removed

Once the grease was gone, I mocked up the COB on the heat sink where I wanted it, and marked the screw holes with a Sharpie.

Mocking up the LED COB on the heat sink

Marking the LED COB holes with a Sharpie

LED heat sink with COB holes marked

In order to make things easier, I detached the fan from the heatsink. This allowed me to lay it flat for drilling.

Fan removed from heat sink

I highly recommend using safety glasses when drilling into metal. I’ve gotten little flecks of metal in my eyes both at work and at home when drilling metal, and it’s absolutely brutal to have to get them removed after they have literally rusted into your eye. My boss gave me these particular glasses as a joke, since they’ve got this goofy yellow color to them. Safety first, right?

Safety glasses for drilling out LED heat sink

Drill out your 2 holes as precisely as you possibly can. If you have access to a drill press for this part, use it! In the past, I have drilled the holes out, then tapped them and used a machine screw to fasten the COB into place. Today, I decided just to drill the holes out so they were close to the size of the screw, then use self-tapping screws to anchor the COBs. Tapping can be a pain in the ass, as it’s easy to break the tap off in the hole.

Drilling holes for LED COB in heat sink

LED heat sink with finished holes

If you have any burrs around the holes you drilled, be sure to grind them off. Otherwise, the COB may not sit flat. The holes I drilled were pretty clean, so I had hardly any grinding to do at all.

Grinding holes on LED heat sink to deburr them

The holes after drilling and grinding smooth

Apply the thermal paste to the back of the COB. You really don’t need much for this part – ideally, you have just enough to cover the COB in a very thin layer.

Applying thermal grease to LED COB

A pea-sized amount of thermal compound on LED COB

Use a plastic card to spread the paste and smooth it out.

Spreading thermal compound on LED COB

Thermal compound applied to LED COB

The screws I had were pretty much the perfect length. If the screw is long enough to get down into the fins of the heat sink, it can  go off in weird directions once it hits the fins and becomes more prone to snapping. #6 Screws are definitely overkill for this application, but they fit in the COB holes and I had them handy, so I made use of them.

Screwing into LED heat sink

Before you put the COB in place, do a test fit of the screws. Screw them both into the holes and make sure they go in properly. This will also tap the holes, making it easier to put the screw in once the COB is ready.

Screwing into LED heat sink

A test fit of the screws in the LED heat sink

Place the COB and line up the holes. This is where all that precision and patience pays off!

Lining up the LED COB holes with the holes drilled in the heat sink

Screw the COB down, alternating between screws for even pressure.

Screwing the LED COB down onto the heat sink

The LED COB screwed down to the heat sink

2. Wiring the LED Driver

Wiring up the LED driver to the COB is pretty simple – it’s even easier if you can do it without having to solder. If you end up using Veros like I did, make sure to order a Pico-EZmate wire harness for each COB. If you’re using a Cree COB, see if you can get it with a solderless holder like these.

The first step to wiring the COB to the driver is to hook up the COB. In my case, all I had to do was plug the harness into the COB.

LED COB and wiring harness

Vero Pico-EZmate harness

The connector on the LED COB for the Pico-EZmate harness

Pico-EZmate plugged into LED COB

Now, connect the other end of the wire harness to the driver using the push-in connectors. Again, I’d recommend using the Wago connectors from the first build rather than the yellow connectors I used on this build. While these connectors do the trick, they’re harder to use and very difficult to get the cable out of when you’re done.

Ideal push connectors for wiring LED

Ideal push-in connector

Place the wire next to the connector to figure out how much you need to strip off. Be sure to read the instructions the connectors come with.

Gauging how much wire to strip

LED COB harness with wire stripped

Push the stripped cables all the way into the connectors. You’ll need one for each polarity.

LED COB wire harness complete

Time to hook up the LED driver. First, I did the AC side. The hot wire goes into one connector, and the neutral goes into another.

LED driver AC wires in connectors

In order to plug the whole assembly into the wall, you’ll need to either sacrifice an existing power cable or make one using an AC plug end. I chose to use a cheap extension cord and cut the end off. If you’re reusing a cable, make sure to check the specs to see how much power it’s rated for. This cable was rated to handle over 1,600 watts.

Do NOT plug this cable in until you’re 100% done with the project and have checked everything. Be very careful when working with anything that involves connecting to mains electricity like this!

Extension cord for AC power connection

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Cut the end off the cable and use the continuity function of a multimeter to determine which conductor is hot, and which is neutral. On a 2-prong plug, the smaller prong will be the hot wire and the larger prong will be the neutral. Identify each conductor. If you’re using a cable with a 3-prong connector, you’ll have a 3rd conductor, which is ground. Plug the hot side of the cable into the connector containing the hot conductor for the LED driver input. Plug the neutral into the connector with the LED driver neutral. Take the time to ensure that the cables are seated properly and will not pull out. Make sure no stray wires are poking through anywhere. Do not plug into the wall until the project is 100% complete and checked.

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Now, hook up the DC side. Plug the positive side of the driver output into the same connector that you plugged the positive side of the COB into. Repeat for the negative side.

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That’s it for wiring up the LED driver. Only one connection remains.

3. Wiring the Fan

When wiring up your CPU fan, you’ll need to know which of the wires on the fan are +12V and ground. In my case, the red wire is +12V and the black wire is ground, which is fairly common.

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Cut the connector off and strip back your wires.

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Since I’m too lazy to solder and heat shrink these splices and they are too small to fit in the push-in connectors, I used little crimp connectors.

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If your power supply has a barrel connector on the end of it, cut it off. You will need to use a multimeter to identify which conductor is +12V and which is ground (just touch one lead of your meter to each conductor when the power supply is plugged in, and see what it reads. If it reads +12V, then the conductor you have your positive probe touching is the positive conductor. If it reads -12V, then the conductor you have your negative probe touching is the positive conductor).

Double check your power supply to make sure it produces enough current to run the fan. The specs for my fan state that it only draws 160mA. My wall wart produces up to 350mA, so I’m good to go.

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Connect the positive lead from your power supply to the positive lead of the fan, and do the same for the negatives. Crimp the splice caps.

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Done!

The Finished Product

Now that I’ve got 2 of these suckers finished, I just need to figure out where I’m going to mount them and start growing. The CPU coolers do a great job of dissipating heat and keep the COBs nice and cool. Without the fan running, the heat sink gets very hot, very quickly.

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I’ve used this grow light to grow a Moruga Scorpion pepper from seed all the way to fruiting, and it’s done a fantastic job:

 

If you end up building your own LED grow light, leave a comment below with how it went and what (if anything) you did differently.

20 Comments

  1. i use silicone thermal adhesive on mine, aint let me down and no faffing about with drilling

    • LEDGardener

      May 12, 2017 at 6:32 pm

      Hey Mark. I’ve read that the heat transfer on the adhesive stuff is not quite as good as the regular thermal compound, but it may be good enough for this application. I’d like to test case temperature with different compounds to find out one day. What brand do you use?

  2. Thank you. The best COB tutorial / website I’ve read thus far. I’m a bit of an old timer, 60 child and this technology was way over my head. I now see no reason not to switch out my hid and hps. Next step, Save up some funds.

    Great stream, I enjoy the educated conversation.

    • LEDGardener

      May 21, 2017 at 8:59 am

      Thank you! When you’ve got the cash, drop me a line if you need any help designing/building your light.

  3. Great DIY article! Lots of easy and organized information on your site. I’m currently getting parts ready for a 5 cob citizen clu048 1212 with a meanwell 240-1400setup. Learned a lot through this and growmao5. I’m Going to use same CPU coolers as you and hope to find a charger that might have enough power to power all 5 but will probably use a few.
    Thanks lucas

    • LEDGardener

      June 30, 2017 at 6:58 pm

      Nice! 5 of those fans will only draw 80 mA so you can power them all pretty easily. Tons of adapters will do 100mA at 12V .

  4. Why not solder the connections?

  5. Robert Lee Hinojosa jr

    October 13, 2017 at 10:32 am

    How could i make this build run at 150w or less for a 2×2 tent?

  6. Hey, brand new to indoor growing and very interested in building some cob leds, but I’m a little lost trying to figure out how much lighting I need for a 4’x8′ tent. If I built two of these sets would that be enough?

    • LEDGardener

      October 16, 2017 at 11:27 am

      Hi Joe, I’d recommend a minimum of about 600 watts per 4’x4′ space. To achieve this, some people run a larger number of COBs at low power (e.g. – 12 COBs at 50 watts each), which is more expensive but provides better efficiency and more even coverage, and others choose to run less COBs at higher wattage per COB (e.g. – 8 COBs at 75W each). Using the examples above, you’d be looking at 16-24 COBs total.

  7. The Budget Grower

    October 17, 2017 at 6:21 am

    Hey LEDGardner,

    I’m very interested in building a 50 watt cob light just to keep a mother plant alive and some clones in a 60x60x140 tent, no idea where to start with components though.

    Could you be so kind as to list what components I would need so I can follow this tutorial, interested in a normal pre-drilled heat sink with no fan and a reflector for the light

    Thanks

  8. The Budget Grower

    October 17, 2017 at 2:56 pm

    Thanks I appreciate the advice, just one more thing and I’ll leave you alone: )

    What would be the best spectrum for Veg I’ve heard 4000 to 5000

  9. Hi LEDGardener I only grow vegetables and consumables other then cannabis medicine.

    My grow area is 8×12 and I am on a budget that means kids and wife. 😉

    So for super hots they seem to need less light then weed in other words. I’m liking the gpu fan and heat sink because of cost it seems. We can start small and work our way up. Upon researching the cobs I find the crew to be over priced in comparison to citizen or vero cobs.

    I do want to get full spectrum for flowering and veg so as to not have to change setup. It seems i don’t need veg bloom cycle like weed just regular natural plant light or similar. We will use the kratky bucket system, DWC.

    Please suggest what I can do for 500 USD and to grow as many as possible as well as 2 heirloom tomatoes for salsa. 🙂 we plan on defying nature as usual and growing super hots all winter, then once growing season comes we acclimate them and bring them out side to become huge pepper bushes with 100s of peppers that we sell to locals for fun and to pay for the system. Please help with this build. I do have pretty extensive mechanical and electronics aptitude as well as basic math skills so it should not be hard.

    It seems I am ready to purchase yet I need one final bit of guidance because I haven’t tested these lights. Thanks for this awesome blog and your sugfestions.

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