ThinkPad adapter resistor values

Upon looking for ways to use the W520/W530 with lighter adapters we've started figuring out at forums.thinkpads.com how a ThinkPad identifies what adapter is plugged in.

The findings are the following:
1. There is only 2 wires coming out from the adapter
2. There are 3 connectors in the plug
3. The electricity is between the inner and the outer side connector on the circle
4. The inside pin is used to identify the adapter, by a simple resistor connected between the pin and the outside connector.



So to identify what adapter is what, we need to measure the resistance values between the outside metal and the inner pin.

• 65W adapters have 10K resistance, confirmed.
• 90W adapters have no connection, confirmed.
• The 170W adapter has 1.5K resistance, confirmed.

What I would like to ask, if you have a ThinkPad adapter, could you measure the resistance between the inner pin and the outside of the circle?

 

Well done! So it looks like getting 90W to work with W520 should be easy.

Same 10K/no connection/1.5K as above for 65/90/170W adapters I have.

 

Did you measure the 90W? Just because it wasn't confirmed before. If yes, I put it in the first post!

 

Yes, actually measured all 3. 90W shows up as disconnected.

 

Thanks, first post updated.