Dell Laptop Power Supply

[darrellx]

Hi All

I am just curious about a Dell Laptop power supply. I have an old one that I was going to "repurpose". So I cut the cables off the transformer. On the Output side of the transformer it is rated as 19.5 v (3.34A), Centre positive.

When I cut the cable there are actually three wires inside - White, Black, Blue.

My meter indicates that the centre pin is indeed positive. The outside of the plug is indeed negative. BUT, inside the plug but on the outer wall appears to be positive. The Blue wire seems to be connected to the inside wall of the plug but only carries 1 volt DC.

I haven't seen this before. I have only seen two wires on a DC circuit.

I am wondering if anyone can shed some light on this. It's no big deal, as I don't have a Dell Laptop anymore. I am just curious.

Thanks
darrell

[mill]

the blue wire is there so the computer recognizes an original Dell power supply.
any other power supply will make the laptop saying that a non genuine power supply is connected and there could be damage to the laptop because of it.
Money maker i call it :P

[leon]

Yes I have had this happen when my wife's power supply died and she used mine from an older lappy.
It said exactly that (what Mill mentioned) as it was not the power supply supplied with the original lappy.
I ignored it and it still worked fine

Leon