Using Lenovo laptop PSU as general purpose PSU

[vk3em]

I grabbed a 20v 10A DC PSU from the waste bin thinking I might be able to use it to power a bank of 12v battery chargers that need 18v DC input. Checked it on my Lenovo docking module and it works fine. However, disconnected from the docking module there is no dc output on the rectangular connector.

Have searched but can only find reference to laptop PSU with constant voltage output. Wondering if there is something I need to satisfy to enable the output like a minimum load. Have not probed it on a CRO yet. Any ideas would be welcome.

[abeyer]

Perhaps you need a sense resistor per this:

https://www.thinkwiki.org/wiki/Power_Connector#slim_tip

[Jwillis]

Centre pin is Called an ID pin. Some say its for the laptop to identify if the correct supply is connected , Others say its to power up the supply when connected to laptop. I think it does both. Ran into that issue fixing a friends lenovo.
By connecting a resistor from ID pin to the Ground (-)  the power supply should start . I'm not certain of the value of the resistor.

[vk3em]

Connector does indeed have center pin - will try the sense resistor to ground. Many thanks.