How to get 12V 2A power through an extension cable?

Question

I have an AC to DC (12V, 2A) converter (/transformer) plug which I am using to power a wireless router. The connector has "center positive" polarity and the size of the connector is the ubiquitous 2.1mm x 5.5mm.

The nearest electrical outlet from the router is ~6m (20ft). The distance is ~3m (10ft) vertically and ~3m (10ft) horizontally as the router is placed high up on the wall to broadcast the best Wi-fi signal.

Unfortunately, the wire that comes with the supplied AC to DC power source is only 2m (10ft) long. While I do have a mains rated (230V) extension cord, I would prefer not to run this extension cord up the wall.

I bought online a 10m (32ft) 12V extension cord online, with male-female 2.1mm x 5.5mm (see picture).

When I use this cable to extend the existing wire, the router does not work correctly. The LEDs on the unit do light up, but I cannot seem to connect to the internet. Unfortunately I do not own a multimeter. I have just ordered one. When I tested the 12V extension cable with some strip LED lights, it seems the LED lights are slightly less bright with the 12V extension cable.

Do you have any suggestions on what I might be able to check to make this work? Would it be possible to get a higher voltage or amperage converter if the long extension is causing too much resistance?

Answer 1

Unfortunately while it's very easy to extend mains cables, it's very hard to extend low voltage cables. The resistance of copper bites not as the voltage ratio, but as the square of the voltage ratio. Your low voltage extension lead is not 20x worse, but 400x worse than the mains one.

You should experiment with putting the router less than 2m from your socket, you might find that the range is adequate in this 'less favourable' position.

A meter is not really going to help you, as you already know that whatever the voltage the cable is delivering, it's not enough to run your router. If you measured 10 V, or 11 V, what would that tell you?

As a destructive experiment, you could try shortening your cable, it seems to be over-long. Maybe you'd get lucky and find that your router would work with only half the voltage drop.

Another possibility is to build your own low voltage extension cable with much heavier wire. But note that a low voltage extension needs to be thicker than a mains extension to power equivalent loads.

You could replace your wall power supply with a higher voltage one, say 24 or 48 V, and then use a buck converter to drop it to 12 V at the router. This would permit your low voltage extension to be much lighter gauge than before - remember the voltage squared ratio. But now you're introducing much more equipment.

It's maybe possible your router would accept a slightly higher voltage without damage, and tweaking up the voltage of the sending end could be tolerated. But if the router doesn't specify that on its labels, do you want to risk it?

Try moving the router near your supply first.

What will definitely work is providing a mains extension lead. If the ones you can buy use flex that's too thick, and you're competent to make connections to plugs and sockets, you could buy a length of the lightest gauge 3-core you can find, and make an extension lead with that. Be sure to fuse the conductor correctly, for instance if you use 0.5mm2 wires, use a 3 A fuse in the lead, so that if it ever gets used for a fan heater, it's not going to be a fire risk.