What’s inside a cheap Chinese LED light?

LED lights have become cheaper and cheaper in the last years. But they are still a bit more expensive than Halogen lamps. To save money, some people might have a look at Chinese shopping sites. I wanted to know what you get if you pay less than 5$ for an LED lamp.

My delivery arrived like this:

led-lamp-china-broken

Yes, it fell apart already during shipping. It consists of some PCBs with LEDs soldered together by hand and a cheap plastic cap. You don’t really want to use something like this on mains voltages – right?

However, this gives us the chance to look what’s inside of this thing.

led-lamp-china-broken-inside

Ok, this is really the simplest circuit you can think of. You see a suppressor capacitor (the red one), a bridge rectifier (the small black part with the 4 pins), a small 4.7uF electrolytic capacitor and a few resistors.

The two 51Ohm resistors are connected in parallel and they limit the current flowing through the LEDs.

Better designs use switching mode power supplies with a fixed current output. However, you won’t get this if you buy the cheapest stuff on the internet.

Especially the fact that this ding falls apart on the slightest touch and every part of the circuit runs at mains voltages makes them extremely dangerous. After the the rectification you can expect almost 300V DC on the board. This is even more dangerous than 230V AC.

Do not use something like this!

Hacking the H801 LED dimmer

I just received the H801 LED dimmer. I couldn’t figure out, what the “W1” and “W2” connectors on this device were. So I removed the case and checked the board. I was pleasantly surprise to see that this isn’t a 3 channel (RGB) but a 5 channel device. The W1 and W2 connectors are 2 additional channels.

Installation isn’t complicated. You connect the power supply and the LEDs and turn on the device.

With a laptop or mobile device, you connect to the WiFi network HCX_856705 (the numbers might be different) and use the password “88888888”.  Now, the trouble begins if you don’t have an Android phone. I was expecting there is at least a simple web interface available that allows to configure WLAN credentials. Nope! The only way to control the device with the initial firmware is an Android app.

You now have 2 options if you don’t own an Android phone: flash another firmware or install an Android emulator on your PC. It used Droid4X. However, I wasn’t able to connect to the device. I’m note sure if this Application supports using the WLAN connection from the Mac.

Ok, back to the start. Flash another firmware. This is usually something that I don’t do easily, but on a device that costs less than 20$ and isn’t useable for me otherwise, I tried this. Luckily the board design makes it easy to flash a new firmware. The board is already prepared with 2 headers: RX/TX/GND/3.3V and J3. Just solder headers and use your existing ESP8266 programmer.

h801-header

As software I used the Arduino sketch from Eryk.io and adapted it slightly. My sketch can be downloaded from Github.

The GPIOs are used as follows:

Pin Function
15 Output red
13 Output green
12 Output blue
14 Output white 1
4 Output white 2
1 Internal LED green / Signal
5 Internal LED red / Power

Power supplies for LED installations

If you look around on the Internet you will find a lot of interesting DIY LED installations. Most projects are stripes for lighting and Ambilight clones. Last week I stumbled across a very good guide how to build your own Ambilight clone. I won’t link to this guide as it had one big problem: safety!

Many projects use power supplies similar to this one:

pl8886134-short_circuit_protection_standard_led_display_power_supply_100w_5v_20a_ip20_60hz_en1122

Why? Because they are available quite cheap from many Chinese suppliers. I can’t say if a specific power supply itself is safe. With this type of power supply, the build quality is usually quite good because you can see most parts and people wouldn’t buy them if you can already see that parts are not soldered correctly. Note that this doesn’t say anything about the quality of the parts. But let’s just say, the manufacturer designed this power supply well and it is safe. Why shouldn’t you use something like this? Why isn’t it safe?

Many DIY installations install power supplies in places where they are hidden, but can still be accessed  from the outside. Check out this picture:

powersupply-unsafe

You won’t see the power supply from the front, however, the mains is still relatively easy accessible. Even if you don’t have kids at home, this is unsafe!

There is an easy way to deal with this problem: You should use fully capsulated power supplies with standard AC cables like this one:

laptop-adapter-ac-adapter

This type of power supplies is also available in many different voltages with a power range of up to 100W – more than enough for usual LED installations.