eco-ants --> eco inventing <-- - Targus PA350 12v Laptop Charger

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eco-ants --> eco inventing <-- - Targus PA350 12v Laptop Charger
I bought this laptop charger from a second hand shop about 10 years ago..... I knew one day I'd use it..... and heck, it was $10 !!

The Targus PA350 is a clever wee beast, it runs off 12v - from a car cigarette lighter socket - and has an adjustable output, so it's suitable for most laptops.
The output voltage is set by a plug at the end of the output wire, there is a full range of these plugs, sadly the 2nd hand store didn't stock the whole range. The plug it came with outputted 19.5 volts and I needed 18.5v

I searched the internet, but NOWHERE could I find any useful information :(
Well, I found this list of tips and their outputs.

Targus Power Tips voltage by Tip Number:
1 +16.00 volts
3 +18.00 volts
4 +12.00 volts
6 +15.00 volts
7 +16.50 volts
8 + 8.40 volts
5 -12.00 volts (tip negative)
10 + 2.95 volts
11 + 6.00 volts
12 +10.00 volts
15 -10.60 volts (tip negative)
16 + 5.50 volts (wide variation)
17 + 8.50 volts
18 + 9.40 volts (wide variation)
19 +16.60 volts
20 +13.00 volts
21 +19.00 volts
24 +19.55 volts
25 +18.25 volts
26 +19.50 volts
27 +15.00 volts
28 +22.00 volts
34 + 7.00 volts
36 +18.26 volts
38 +24.00 volts
44 +18.90 volts
47 +13.00 volts
48 +18.20 volts
57 + 4.10 volts (wide variation)
58 +20.00 volts
74 +16.00 volts (wide variation)

But I didn't have access to any other tips -> I wanted to know how to make my own !

So I did some experimenting...

The following information is published in the hope that it helps someone use one of these great little powersupplies.

Setting the output voltage:

The output voltage is set by a resistor inside the tip.
Back when they were sold you bought the correct tip for your laptop thus you got the correct voltage.
However, ten years later.... no one is selling the tips.... luckily I'm smart enough to make my own :)

The tip has 4 connections, by measuring the resistance from pin to pin inside the tip I had, I worked out that there was a resistance between the grey and yellow wires.
So I rigged up a variable resistor from the grey wire to the yellow wire.
Here are my results:

Output Voltage	Resistance

17.5           259.5k

18             198.2k

18.5	       162.5k

19	       138.3k

19.5	       120.6k

20             108.4k

21	       90.8k

22	       79.4k

23	       71.1k

Here I am testing the voltage sag under a 25W load -> less than 4% is pretty damn good :)

Now of course I didn't have a 162.5k resistor (that doesn't exist !)
So after scratching around in my resistor box I used two resistors in parallel to get a voltage of 18.44. I'm happy with that :)

The next challenge was to find a DC barrell plug to fit the laptop. More scratching around in my workshop unearthed a multi plug kit, there was one that fitted the ol laptop.

All done, now I can finally get around to tweaking the controller settings in my home made electric car :)