Question about laptop ac adapters

[dotkel50]

So I have this very old IBM Thinkpad 750CS laptop that I rediscovered in the back of a closet. Of course it's dead as a doornail and I can't find the power cord and ac adapter. So I go to Google and find a bunch of replacements....BUT..... the bottom of the laptop says 20V 2.50A and all of the replacements so far are 16V, with various A (for amps?). Do I need to find a 20V 2.50A adapter or will the 16V ones be ok?

[Collector]

I'd go by what the laptop says.

[Tawmis]

Weird. Everything I have seen/found is 16V also.
http://www.nevershopping.com/ibm-thinkp ... apter.html

Even Amazon.com...
http://www.amazon.com/Adapter-Numbers02 ... B00080L0SS

Although the replacement is a wee bit expensive...

[audiodane]

Just a bit of background.. V is volts, A is amps. Multiply the two and you get power (i won't get into the differences between VA and Watts here).. in the most fundamental sense, 20V at 2.5A is 50W.

Assuming the connectors were the same and the laptop in mind WOULD work at 16V input, it would need at least (50W / 16V = ) 3.125A to still be at 50W power supply. However reducing the voltage and increasing the current can cause other problems. The higher a current a wire carries, the more it warms up. Your power supply would be fine, but an internal wire could get too hot. 2.5A to 3.125A is not much of an increase however (around 25%). The next question would be those pesky connectors. They're all so different...

With all that said, I'm not sure what the laptop is rated to take as an input. Sometimes they may say 20V but can take between 16V and 24V. That's to be expected. I would keep looking for a 20V, 2.5A supply for a while first. And asking around on some IBM Thinkpad forums if you can find a good one.

my two cents,
..dane