How to extend the DC part of the laptop power cable without experiencing voltage problems

cablelaptoppower supply

I use my laptop for extended periods on the mains in two different rooms of the house, and for ease of use I keep a separate power cable in each room. In one of the rooms I need to extend this cable.

Each cable is in two parts. The AC part runs between the mains plug and a two-pin C7 figure-of-eight plug. This then fits into a line lump transformer box, from which it can be removed.

The DC part is moulded into the transformer box and runs to a "universal" laptop-tip female connector at the other end, into which the male tip plugs that fits into the laptop itself.

I want to extend the DC part of the cable. To be clear, I want about 3-4 metres of cable between the transformer box and the laptop, which I want to be able to tie up and leave on a shelf and then untie and bring down to the laptop. I realise I could extend the AC part of the cable, but that's not what I want to do. The extension must be on the DC side, because I do not want to keep moving the transformer box.

The issue is that the DC part of the cable has two small cylindrical boxes, one near each end, which I think are voltage regulators.

It's possible to find DC extension cables with 5.5mm x 2.1mm male and female ends, rated up 24V, but they tend to be described as suitable for CCTV equipment and sometimes other devices too, but not for laptops.

What's the best way to extend the AC part of the cable? Will there be a problem if I have 3-4 metres of cable without any regulators, running from the existing tip to a new tip?

Best Answer

It is hard to extend the DC, because you will have a higher voltage drop on the cable, the voltage will drop with the Current and resistance of the cable, according with Ohm's law, a longer cable, means higher resistance and lower voltage available to your device.

The cylindrical parts are probably not voltage regulators, they are most likely ferrite to filter out High frequency noise, giving you a cleaner DC voltage, so it will not compensate the voltage drop in the extension.

If you add a few meters of cable to the end of the existing DC plug the problem will be: voltage drop, and higher noise pickup.

With the additional voltage drop the supplied voltage might not be enough to power your laptop.

I suggest you to extend the High voltage AC side.

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