laptop transformer

[pimster987]

I am going to use a laptop transformer to power an amp that I am going to build that needs +18V. My question is which wire is the +18v once the tip is cut off. there are three layers inside the cord. in the middle there is a thin wire wrapped in blue insulator then around that there is a thick layer of a bunch of small wire surrounding the blue wire. This section makes up most of the cord. Last outer layer is a thin layer of thin wires. I am guessing the thicker wires wrapped in the blue insulator is the power wire. What are the other wires for?

[ea6b607]

The outer shield is usually ground. The last wire (the thinner one) is likely a digital signal wire. I know Dell uses a coded identification chip to make it harder for people to use the wrong charger or a charger not made by them.

[sofaspud]

If you don't have a multimeter (shame shame ), put a rectifier diode and LED in series with a 1k ohm resistor. Use it to determine the 18V + and - from your power supply.

[firechief]

Originally Posted by sofaspud

If you don't have a multimeter (shame shame ), put a rectifier diode and LED in series with a 1k ohm resistor. Use it to determine the 18V + and - from your power supply.

Yep that would work.
I for one can never remember the polarity of an LED just by looking at it so this is handy.

[N-Channel]

ea6b607 is right. I have gutted many of these AC-DC Adapters and made my own DC-DC Step-up adapters using the original case. I noticed this chip in a TO-92 case near the output pins, and at 1st I thought it was a TL431, part of the voltage-sensing network.

Upon closer inspection, it is really a Dallas Semiconductor DC2501 battery IC. It tells the Dell laptop that the adapter is a genuine Dell AC (or DC) charger. I incorporated this into all of my DC-DC boost Laptop adapters by taking the chip out of the AC charger and putting it in my design, thus getting around their little security measure. The only difference this ma\kes is w/o this chip, you can power the laptop, but it not charge the batteries.

Hope this helps.

Steve

[pimster987]

Originally Posted by sofaspud

If you don't have a multimeter (shame shame ), put a rectifier diode and LED in series with a 1k ohm resistor. Use it to determine the 18V + and - from your power supply.

I have a multimeter and will test the power supply once I get home today. I just thought somebaody has used a laptop power supply as a voltage source before and would know the wiring. What part of San Antonio are you from?

[sofaspud]

Northwest, close to the Leon Valley area.

[pimster987]

Cool, I live in Schertz and goto UTSA.

[sofaspud]

Ah, well UTSA main campus is close by me. If you have any problems or a desperate part need give me a shout. I'll try and help.

[pimster987]

I found a better power supply that I found laying around my house. It was a supply for a old surround system. Its says it has an output of 15VDC. I measured the output to be around 19VDC. My question is this +-15V. Here are some pictures of the supply. I took it apart to take a look inside and I see it has a fullwave rectifier. So I am assuming this is +-15V.