I’m a huge fan of Big Clive, and watch his videos regularly. Back in December he built a DIY LED bulb kit from China, and as soon as I finished the video I ordered a couple for myself! It’s a fairly simple kit with a lot of potential for customization. There’s a lot of solder joints but the overall assembly isn’t too complicated, and the theory behind how they work is fascinating and not too hard to comprehend. Best of all, with prices well below $2 shipped, they’re cheap fun! I recently assembled one of these kits so I can review it and share what I’ve learned so far.
Disclaimer: I’m not an electrical engineer, just a hobbyist having a little fun who wants to share what he’s learned. If you build one of these LED bulbs, you do so at your own risk. Be careful. These kits are really cheap, run on mains power, and have no safety certifications whatsoever. Some are not properly isolated, which means they could potentially expose you to high voltages even when they’re fully assembled. There’s a potential for serious injury, death and property loss, so exercise caution when building and using these bulbs. Personally, I think they seem fairly safe enough to use (the ones that offer proper isolation), but I’d never leave one running unattended, or use it anywhere a child or animal may reach it.
Seriously folks. Don’t even think about building one if you don’t have a solid understanding of the dangers of working with mains electricity. Also, read Bob Paradiso’s article on Capacitive Droppers and Big Clive’s article on hacking an LED lamp before you attempt to use or build one of these bulbs.
Ordering the kit
These kits are widely available on Ebay and AliExpress. Searching either site for “energy-saving 38 leds lamp diy kit” or some other variation of those keywords should return several results. I’m focusing on the 38 LED version, but there are also 60 and 120 LED versions which I haven’t got my hands on yet.
Some kits include the LEDs, and some do not so it’s important to read the description carefully so you know what you’re getting. Also, some kits do not include the plastic “bubble” cover that fits over the LEDs once the kit is assembled. This cover provides isolation from the circuit so you don’t get electrocuted when touching the bulb. This is important since since the the capacitive dropper circuit offers no electrical isolation. The kit I’m reviewing here does not have the cover, but I’ve made sure to get it included in later purchases of the kit, and you should too.
For the kit shown here, which included the LEDs but not the “bubble” cover, I paid $1.53 total shipped from China to the USA. Other kits I purchased which include the cover but no LEDs were just $1.18 each shipped! So it’s possible to pick these up very cheaply.
The values of the included resistors and capacitors can very depending on where the kits are sourced from. The value of the main dropper capacitor is of particular importance, since it affects the amount of current that will pass through the LEDs.
Below is a schematic of the power supply used in these kits, and a description of what each component does. I’ve included notes indicating which component values I’ve received, and whether I made changes based on the information I’ve picked up from articles and videos concerning capacitive dropper power supplies.
- 1N4007 Diodes – Together, they form a bridge rectifier to convert the incoming AC current to DC. This part been consistent on all kits I’ve purchased so far.
- C1 – The actual dropper capacitor. In all the kits I’ve received so far, it’s been 470nF or 680nF. For countries with 120V mains (such as the USA, where I live), 470nF is a really low value, and will cause the LEDs to receive much less current than they can handle. Even 680nF (which the reviewed kit includes) is a bit small. More on that later.
- R1 – Bleeder resistor for C1. Lower values will discharge the capacitor quicker, but will also waste more electricity while the bulb is powered. The reviewed kit came with a 100KΩ resistor; I swapped it out for a 1MΩ resistor for efficiency.
- C2 – Smoothing capacitor. Helps smooth the rough DC voltage coming from the bridge rectifier. This kit came with a 2.2uF capacitor, and it seems like it’s “good enough” as I don’t detect much shimmer in the LEDs when looking at them.
- R2 – Another bleeder resistor, this time for C2. 100KΩ in this kit.
- R3 – Inrush current limiting resistor, to protect the LEDs when power is first applied. Should be 100Ω, but some kits ship with a 10Ω resistor instead. In those cases I’ve swapped it out for a 100Ω resistor as Clive does in the video below.
- LEDs – I ordered this kit with the LEDs included. They’re warm white, 5mm “straw hat” LEDs. I measured a forward voltage of 2.5v when I metered a couple of them.
Building and Testing the Kit
I won’t try to cover assembly of the kit; instead I suggest you did what I did, and watch this video from Big Clive. Assembly begins around the 5:17 mark:
Using Clive’s video as a reference, I got through the build without much trouble. There are a lot of solder joints that need to be made, but it’s a great way to practice! I did have one LED right in the center which was was bad, and I didn’t have an exact match for it in on hand. That’s why the center LED looks different than the others in the photo at the top of the article. But with that replaced, all was well. Here’s a photo of the bulb before I replaced the bad LED and snapped it together:
One thing Clive suggests is insulating the power supply board using heat shrink tubing. I didn’t have large enough tubing on hand, so I just placed some electrical tape over the leads of the 680nF capacitor instead to ensure they don’t touch the bottom of the LED PCB board.
Power Usage and Brightness
The completed bulb draws very little power. Using the formulas from Bob’s article on capactive dropper circuits, it’s possible to determine the amount of current going to the LEDs. The dropper capacitor is 680nF, and I’m in the USA where the mains AC frequency is 60Hz. So the capacitive reactance of the dropper capacitor in this case is:
1/(2π60 * 0.00000068) = 3901
The LEDs have a forward voltage of 2.5v, and there are 38 of them wired in a series of 19 parallel pairs. So the total forward voltage is:
19 * 2.5 = 47.5v
And I’m in the USA where mains is approximately 120v. With that information the current to be supplied to the LEDs can be determined as follows:
(120-47.5)/3901 = 0.0186
Approximately 18.5mA. Since the LEDs are wired in parallel pairs, each will see approximately 9mA of current.
That isn’t much, and it shows when I tested the bulb for the first time. It’s not very bright at all. Here is the output of the bulb compared to a Cree 60w equivalent LED bulb:
The Cree is significantly brighter, and spreads the light out more. This isn’t terribly surprising, given that the DIY kit is much less expensive than the Cree bulb (which I can no longer find for sale, but I believe it cost between $6 and $9 when I bought it), and it uses much simpler technology. It also draws less current; the Cree is rated at 81mA; I measured it at 86mA. The DIY bulb by comparison measured 23mA current for the entire circuit, which is approximately a quarter of the power used by the Cree bulb.
Could the bulb be made brighter? Possibly. I noted earlier that the 680nF capacitor is a bit small for the USA where mains power is 120v @ 60Hz. This results in each LED seeing less than 10mA of current. Clive’s bulb by contrast is supplying 15mA per LED, which is ideal given the LEDs are probably rated for 20mA max. Swapping in a larger capacitor will increase the current, which might produce a little more light output. Then again, maybe an extra 5mA won’t really do that much. This is something I plan to test and write about in a future article.
This was a fun kit to build, and worth every bit of the $1.53 I paid for it. I learned a lot about capacitive dropper circuits, and I got to assemble one and see it in action. Sure, it’s not really all that useful as a light bulb, since it’s not very bright and there are some safety concerns. But as an educational tool, it’s great, as long as you’re careful and are comfortable and knowledgeable enough to work with mains voltages.
But really the best part of these kits is they’re cheap and they’re fun! There is a lot of room to hack and customize the circuit, and that’s what makes it exciting and leads to further learning and understanding. Different color LEDs can be used, which could produce some very nice accent lights. And swapping the dropper capacitor will allow the current to be adjusted to accommodate different LED forward voltages and differences in the world’s various mains power standards. I look forward to building additional kits with some customization added, and I’ll be sure to write about it when I do!