65W vs 90W power supply: how does it know?

X200, X201, X220 (including equivalent tablet models) and X300, X301 series specific matters only.
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mvan
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Joined: Mon Feb 13, 2006 8:10 pm

65W vs 90W power supply: how does it know?

#1 Post by mvan » Sat Jan 07, 2017 12:27 pm

Hi,

I have a small problem and a question.

I have an X220 with a 65W power supply of which I replaced the DC cable.
Oddly enough it is now recognized as 90W.
This is usually ok, but under combined heavy load and charging, it is overheats and shuts off.

So:
1) how does the laptop know which powersupply is attached?
Is there a circuit in the powersupply, is there something in the cable, or does the laptop measure the max current?

2) How can I make it be recognized as 65W again?

Thanks,

dr_st
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Re: 65W vs 90W power supply: how does it know?

#2 Post by dr_st » Sat Jan 07, 2017 12:53 pm

The resistance between the center pin and the outer shell / ground is different for each PSU type. That's how it knows. Your DC cable probably matches the one from a 90W PSU.

Read this and the subsequent posts:
http://forum.thinkpads.com/viewtopic.ph ... 90#p682644
Current: X220 4291-4BG, T410 2537-R46, T60 1952-F76, T60 2007-QPG, T42 2373-F7G
Collectibles: T430s (IPS FHD + Classic Keyboard), X32 (IPS Screen)
Retired: X61 7673-V2V, A31p w/ Ultrabay Numpad
Past: Z61t 9440-A23, T60 2623-D3U, X32 2884-M5U

mvan
Posts: 12
Joined: Mon Feb 13, 2006 8:10 pm

Re: 65W vs 90W power supply: how does it know?

#3 Post by mvan » Sat Jan 07, 2017 12:59 pm

Cool, many thanks.

I should be able to correct this...

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