I got a 3 wired HP charger that i want to make into a power supply.
The wire colors of the charger is blue, black and white.

How do i approach it?
How do i deal with the third wire?

 

Do you have a DVM or VOM on hand?

 

Do you have a DVM or VOM on hand?

Yes

 

Try this. Consider the black wire ground and measure the voltage from the other two wires, one at a time.

 

Black is Negative , Blue is Positive, White data.

 

SOME HP power supplies put out two voltages, with a 3 position connector.
Other supplies do have that third wire to handshake with the computer, so that a non-HP supply can not charge the battery.
So the supply might not even work

 

If that charger is for a Nicad battery the white wire is probably a temperature sensor feedback to control the charging.

 

I got a 3 wired HP charger that i want to make into a power supply.
The wire colors of the charger is blue, black and white.

How do i approach it?
How do i deal with the third wire?

Hi,

We had been talking about this extensively on another web site.
The consensus is that black is ground and white is positive, and the blue wire is to tell the Laptop that the charger is capable of a particular wattage output.

There is some variation on how that blue wire affects the output of the white and black wires. In most cases the blue wire has no effect on the output of the black and white wires. The blue wire does have an effect on whether or not the Laptop charges the battery or even lets itself be powered by the wall wart at all.
The wall wart seems to tell the Laptop that it can do a certain power output by placing a particular voltage on the blue wire. The Laptop senses that voltage and either allows some functionality or none.
There could be some that also pass data to and/or from the wall wart. The data stream would have to be recognized by the Laptop.

It does seem that in most cases the wire and black wires always put out the appropriate voltage which is usually 19.5 volts for many Laptops like the HP types, but this could be different for more modern ones.

There is usually no way to vary the voltage though that I know of without digging into the wall wart itself. The more modern ones may have a way to do this though but I have never encountered one yet. The simplest way is to add an external regulator.

 

It is likely that the two power wires are a heavier gage than the communication link wire. That should provide anadditional clue as to which wires supply the power.