LED Light Panel Build, Part 1

Ok, ok. This is finally the first post that even remotely relates to what the website is all about. However, I confess. This isn’t exactly a step-by-step build. More of a build that’s about 75% complete. But I’ll go through some of the steps on this build.

The main purpose of why I wanted to build 3 of these LED light panels was that it would be relatively cheap and provide the necessary lighting that I wanted to use for either photography or shooting video.  There’s a whopping 468 daylight white LEDs on each light panel! A brand new unit would cost around $500-$800, whereas the cost of each panel built is about 25%-30% of that!

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The LED array and wood box frame.

I drew inspiration from DIY Perks build (you can check out the Youtube video here). I picked up a few reels of daylight white LEDs (I’ll have links to the stuff I’ve implemented under a budget breakdown table in either Part 3 or Part 4). Since there are 468 LEDs, I had to use two reels to do a single panel (each reel comes with 300 LEDs on the strip). I decided to go with the cheapest jelly roll pan as a heatsink surface to apply the LEDs to, instead of applying it to a non-metallic backer. The jelly roll pans were unfortunately covered with a non-stick coating, so I had to rough up the surface with a cheap chisel to allow the LED strips and any adhesives to adhere better to the surface. If I had to do this over again, I would probably use an aluminum baking sheet that didn’t have a nonstick coating on it.

DSC_0087 (3)I epoxied blocks of wood onto the jelly roll pan to raise my flat tinned copper braids, off the surface, for my positive and negative terminal power bars. A bit crude, but it does the job. Before applying the LED strips down, I also made sure the ends of the LED strips would lay over some electrical tape, since I would be soldering the ends to my terminal bars. I didn’t want to risk a short by accidentally solder directly to the metal surface. That’s why you see the black electrical tape. Once the LED strips adhered in place onto the jelly roll pan, then came time to solder the respective points on the LED strips to the terminal bars. As you can see, the left side of the panel had all the positive connections, and the right side of the panel had the negative connections.

DSC_0085I used some 24AWG magnet wire to bridge the terminal bars to the LED strips. These are coated in enamel which burns/melts off quite easily with a soldering iron. Once this was done, I decided to make a wooden pine box frame to hold the jelly roll pan. I made a dado cut within the box to make space for the jelly roll pan to sit in. Nothing too fancy. I didn’t want to waste my time and effort hacking the jelly roll pan to fit in the pine box frame. I also made a second dado cut to allow a 1/8″ piece of plywood to sit right behind the jelly pan, just so it would be easier to attach the electronic components onto the surface easier.
I made some 45 degree mitered cuts on the plywood frame, to create the box. Instead of using splines (since I don’t have a real spline jig yet), I used some screws to hold the box together. For those that aren’t aware, mitered joints are weak, due to the joint being end-grain to end-grain. Woodworkers will use a wood-type joinery, instead of metal fasteners, as they’re more elegant and they don’t look awful.

The build quality of the wooden box frame doesn’t scream “fine woodworking.” I know. If I took the extra time to build a decent spline jig, this wouldn’t look so horrid with the screws showing. But the screws will be covered up with some wood putty and this will be painted, eventually.

I wanted to make the LED panel versatile. I wanted to add legs onto back of the panel so I can prop the light panel at an angle on the floor, to light up a background or whatnot. This is composed of a single block of wood with a carriage bolt through the top. I drilled a hole through each side of the back portion of the light panel, to accommodate the bolt through the panel. This would be held on tight with a 5-star plastic knob.

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DSC_0092-(2)I also wanted the ability to use this on a light stand, so I snagged a few brass Manfrotto threaded studs that would thread onto some t-nuts. I only needed to attach a stud to either the bottom (for the panel to sit horizontally) or one side (for the panel to sit vertically). So only two sides had the t-nuts installed. Again, nothing too crazy. Unfortunately, the Manfrotto threaded stud was longer than the thickness of the wood box frame, so I had to notch out one of the legs to make room for the threaded stud clearance. I could’ve ground down the Manfrotto stud, but I didn’t want to waste time grinding down several brass studs. Notching out the leg (as shown below) is way easier! Also note in the below picture, that I made sure the t-nuts would stay secure with some screws on both sides of it.

Oh, the reason why I had to recess the t-nut from the inside panel was because the dado that I cut in the pine wood, for the 1/8″ plywood, had clearance issues. So I decided to recess the t-nut with a Forstner bit on the good ol’ drill press.

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That was the bulk of the main panel build. A lot of planning was involved, trying to figure out how to make the cuts that I wanted, as well as the features that I wanted to add. This was definitely not a lightweight build by any means. The box alone was weighing in at under 10lbs. I would probably try my hand in some ultralight MDF next time. But the features that I had were well worth it. The ability to prop the light panel up on itself was a huge plus for me, as well as propping it onto a regular old lightstand with a tilt attachment (see picture below).

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The dimmer circuit.

DSC_0101 (2)To simplify the build, I went with some cheap electronic parts off of eBay and AliExpress. There are some people that complain about the Chinese DC-to-DC power converters, but I haven’t had any issues with them. There are very limited instructions/manuals out there on how to use these, so I can see the challenge for most folks trying to figure out how they work. I may consider doing a write-up to breakdown these power converters so that folks out there can spend less time tinkering and more time applying these to their projects.

The first part of the electronics that I wanted to get out of the way was the 12V dimmer circuit. Dimmers out on the market typically consist of a pulse-width modulating circuit, or PWM. The basics of a PWM is that there’s a duty cycle of an on and off “pulse”. Depending on how long the pulse-width of “on” time is, compared to the “off” time, will ultimately dictate your brightness level. There’s nothing wrong with a PWM dimming circuit, except they tend to show up on video footage as a pulsating/strobing lighting effect that can be undesirable.

Instead, I wanted to build a voltage-controlled dimming circuit, which starts off with a DC-to-DC power converter. The one I used was a DROK DC Buck Converter, which typically steps down voltages. This type of converter is great for LED strips in boats or cars, because they can protect the over-voltage when the engine’s on. Buck converters will typically step-down voltages, and step-up currents. This means an input of 1A @ 15V, can be converted to 1.25A @ 12V. DIY Perks does a great job of how to setup the DC buck converter for the dimming circuit.

As you can see in the picture above, I had to create some custom enclosures out of 1/8″ baltic birch plywood. Instead of waiting for your typical wood glue to dry, I sped up the glue process of the small custom plywood enclosure boxes with some cyanoacrylate glue, commonly called CA glue. There’s a ton of different brands out there, but I prefer the 2P-10 brand, as it was more convenient for me. There’s usually an activator spray and several “grades” of CA glue, ranging from a thin liquid to a gel-type glue. I prefer using the gel-type glue because you can reinforce the interior of these boxes with a thick gel bead, spray some activator over it, and it’ll yield a strong wood box enclosure. The cure time for CA glues is usually a minute; however, spraying a mating surface with the activator will yield a strong bond instantly.

Below, I’ve created a simplified PCB layout of the modifications that were made to the DROK DC-to-DC power converter. On the bottom of the power converter, I soldered a 6.8K resistor in series with a 22K potentiometer, parallel to the onboard trimmer potentiometer pins. This provided the dimmer circuit, to dim the lighting. On the top, I had to add an extra line from the input terminal block to wire the fan controller…I’ll get to why I had to use a fan on this circuit.

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Once I modified the buck converter, I plopped it into my small custom wood enclosures. I went with custom wood enclosures, instead of a readily available plastic enclosures, because of the clearance of the potentiometer knob. I wanted everything on the rear of the light panels to be relatively flush to the brim of the back side of light panels. This would allow me to stack these light panels on top of each other rather easily, and nothing would be sticking out and off the back side.

DSC_0098 (2)After I finished this circuit, I did a quick test with the LEDs and my 12V bench power supply. As noted by DIY Perks, the aluminum heat sink on one side would tend to heat up. This would worsen when you applied 15V to the input of the buck converter, and stepping down to 12V. So, to mitigate the issue, I decided to go with a centrifugal-type fan. They’re a bit pricier than your typical axial PC fan, but they can provide a ton of CFMs. They do tend to be noisy as well, so I had to use a fan controller to reduce the voltage being supplied to the fan.

I soldered the input of the fan controller to the input of the buck converter. But before connecting the output of the fan controller to the fan, I made sure that the small potentiometer, on the fan controller board, was turned down so that I didn’t supply the fan with a voltage greater than 12V. This is the potentiometer to control the fan speed, show in the image below. Since the fan itself was pretty powerful at 12V, but overbearingly loud, I stepped down the voltage to the fan to around 6-7V. I didn’t want to noise level of the fan to be too loud, especially if the light panels are being used in videography. This keeps the fan quiet, but still pushing a decent amount of air onto the one heatsink on the buck converter that tends to heat up.

Fan-Controller

A cheap plastic enclosure was used on the fan controller, just so I could stay consistent with keeping most of the electronic components covered and out of the way. Also, I used a sheet of automotive gasket material for the fan to sit on, which can be purchased at any automotive store. I figured that it would reduce the amount of vibrations being transmitted from the fan to the light panel.

If I were to do this part of the build all over again, I would prefer using a laser cutter or 3D printer to build a custom enclosure to house the buck converter, fan controller, and centrifugal fan in. There was some trial-and-error involved, but on future builds, I would definitely consider automating the build of the custom enclosures. Cutting each piece of plywood to the correct shape with a coping saw and hand saw is tedious and time-consuming.

So, is it worth it? Well, I did a quick test shot with two of the LED light panels. One light source was at mid-brightness, aiming down from above the subject. The second light panel was at 75% brightness and it was placed standing up, towards the front left, aiming at the subject. My faux table top is too narrow for this particular shot, but you get the idea. It’s amazing what good lighting can do to your photos!

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In Part 2, I’ll cover the battery pack system when using the light panels in remote locations where you don’t have access to AC power. One other thing I want to add to this build are some barn doors, so I can focus the light on a specific portion of a subject, and not flood an entire scene with light. Still contemplating a decent design for that!