Thinkpad T420: Im buyin a t420 and i didnt can put on, becouse i have not the original

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Oct. 10, 2022, 3:23 a.m.

Guys would u help me with something?? Im buyin a t420 and i didnt can put on, becouse i have not the original charger but i wont spend money buying something that ill cant use, the thing is that i have a lenovo carger 90watts without the plug but this original charger have a resistance above signal and - or + at the plug if u have a multimeter and would make this read in ohms for me ill be grateful with u for u help i really want this computer. Pls help me

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6
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Oct. 10, 2022, 3:23 a.m.

Say again?

sure, i talk in spanish thats the problem. I explain again im trying adapt a universal charger to mine thinkpad t420. I have an adapter with the same plug but without a resistance that works to do a correct voltaje at the signal plug, what i need is that someone help me to test one of those thinkpad chargers in ohms to know wich resistance i need to adapt mine charger correctly

this is mine adapter

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Oct. 10, 2022, 3:23 a.m.

AFAIK any barrel end charger will work with any Thinkpad with the appropriate socket, aka most up to the T440 I believe. Wattage does not matter unless you are intending to power some hungry external devices. I mean, wattage does control how fast the battery will charge, and it must provide more than the laptop itself is drawing from the battery, but a 45 watt charger and a 90 watt charger will both charge the battery just at different rates.

this isn't true. As the laptop specified for 90watts, (which is 20V•4.5A) has a resistor in the tip of the connector and it does a "handshake" with the device and that confirms the charge rate. And a laptop like the w540 persay, wont charge with a 90watt charger.

Hope thats helpful information!!

Yes I am familiar that the chargers have a sensor circuit I believe between the center pin and the inner barrel that can tell the laptop which adapter is plugged in. Maybe I said it poorly but I acknowledged that the adapter "must provide more than the laptop itself is drawing from the battery" aka it must meet the minimum requirement for the laptop. The W540 was considered a mobile workstation and as such, either the 135w or 170w supplies were needed. Regarding the OP question, I have a T420 and a bunch of different barrel chargers and they all work just fine.

I run a t440p, it wants a 90 watt charger but I don't mind hooking it up to a 135 or whatever. I get it.

the resistance change the voltaje that comes from the laptop at the signal plug, what i need is the resistance in ohms to repair an chinese adapter that i have

thats correct but mine problem is diferente i need to know wich resistance use the charger to the signal plug in ohms

dude i seem to remember seeing a forum where someone breaks down the resistance values and the chargers. Cant find it..

If you're brave you could set up a potentiometer and "sweep" for the needed resistance values and jot them down.

im not brave for that bro >:v thats the reason why im asking for a resistance test in one of those chargers if u would help me Will be great

Ok well keep in mind there are 3 connectors in that barrel, the outside, the inside and the center pin. On my 90w charger, I see open circuit between the center pin and either/both inside and outside of the barrel. I see roughly 200 ohms between the inside of the barrel and the outside. This was not under power as I did not want to accidentally short the supply and fry it or my meter. Hope this helps.

this is diferent over all thing iv read about this charger i have one 90w charger without plug, ill test it to review this, u says that the signal plug a have not resistance above others? Would u send me a video testing this would help me a lot, i did a try with a 250ohms resistance above external the (negative) and central plug (signal) without energí is the perfect testing, with energí u would test dc v that would help too

If you refer to the Thinkwiki posted below by Bird Sof Panik, the reading I got of open circuit seems correct for the 90w adapter. This also gives you the signal pin resistance for the other adapters. Checking resistance of the two live wires is likely not much value due to the internal impedance of the different adapters. Sorry but taking these readings needs 3 hands as it is, doing a video is not practical for me.

thanks bro. ill keep trying turn on mine laptop

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Oct. 10, 2022, 3:23 a.m.

this would help me bro thanks u

i have one of 90w but im not sure about "no conected"

Its a +- with no resistance in circuit, no handshake. 🤷

i try but didnt worked 🤔very strange, ill keep trying and thinking how solve mine problem, mine batery is died apart.... 0.01v 🙄

If you learn something along the way then maybe that's enough.

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Oct. 10, 2022, 3:23 a.m.

This charger is OK for a T420

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Oct. 10, 2022, 3:23 a.m.

Charger provide suitable capcity for machine, I mean you can used charger 230W without issue for T420.

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Oct. 10, 2022, 3:23 a.m.

I used 90W charger also for my T420




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