Best way to solder thick cable to small PCB?

Thread Starter


Joined Nov 24, 2016
I am building a AC lamp controller with ESP8266 and a simple relay. To power things up in the "DC side" - I purchased a bunch of cheap 220v to 5v DC buck converters.

The converter unit came on a small PCB - see picture attached.
I need to solder two 220v AC input wires (to the PCB on the lower right side of the picture).

I am using a thick gauge solid copper cable (that I use to 220v appliances) and tried soldering it to the PCB points - but I can't get a good and solid solder, because the PCB is so small and the cable is thick...
I tried to solder legs to the PCB and then to the thick cable, but still - it's kinda flimsy and looks aweful...

What's the best way to do it right?
Will a smaller cable be fine for 220v?
Maybe I should connect a smaller short wire to the PCB and then that cable to the thick cable?

I am afraid of the risk of a fire hazard- because this whole thing will be in a small closed box - away from sight...



Joined Sep 20, 2005
What kind of wire are you using? A 2x0.5mm2 flexible cord (for lamps etc.) should be more than enough for the current that this tiny supply will need, and it should solder quite easily.
Just make sure it is rated for 230V and preferably double insulated.


Joined Jan 18, 2008
For solid copper, I would use a Euro-style connector ( ) with a screw to tighten the contact.

For stranded wire, I might consider solder, but would probably go with a screw connector anyway. The problem is strain relief. Of course, you need to find a connector that has the same pin spacing as the holes in your board.

If that is impossible, then I would work out a way to secure the wire and use stranded wire. You may need to mount tha converter and terminal in a box. Then have short wires between the conevrter and the terminal block. Connect your house wiring to the other side of the terminal block


Thread Starter


Joined Nov 24, 2016
It's a 2.5mm wire, seems like single isolated... (take a look at the photo attached)

Maybe I should get a thinner cable?
It will still be hard to solder to the tiny PCB...

Check out the photos - the soldering looks awful :(
Couldn't get it right...

The current should be really tiny - I guess at around 350-800mA at most, right? A thinner cable should be OK? (Maybe 1.0mm)


Thread Starter


Joined Nov 24, 2016
... Then have short wires between the conevrter and the terminal block. Connect your house wiring to the other side of the terminal block

The short wires from the PCB to the Terminals- wouldn't be dangerous? Because they might be too thin?

Thread Starter


Joined Nov 24, 2016
Maybe I'm just over-thinking this, because I'm gonna have 220v wires of the lamp itself coming into the box- to the relay.

So I can just connect two short wires to the the cables coming in to the relay? And "steal" the 220v I need for the buck unit/the DC Side of things?

This is the general box layout I am playing around with:

I can just connect the two points of the PCB to the red and blue wire?

No, I can't - because then I am closing the 220v circuit - -and the lamp will always be on... silly me :( thinking "out loud" - lol... :)


Joined Feb 5, 2010
With the voltage levels available through public utilities any commercially available UL approved AC wire will be properly insulated for voltage.
The SIZE of the conductor is for the current needed by the device.
If you need 1 amp at 12 volts and you have 240 volts as your source you will only need about 50 milliamps.
You convert voltage down current will increase to keep the mathematical product of voltage and current equal. It is called Watts.
12 volts times 1 amp is 12 watts.
240 volts times .05 amps is 12 watts.

50 milliamps is all the current you will have in your 240 volt tap line.

It can be VERY small and handle it with no problem