Thinkpads Forum

Hi all. This is a question for y'all electric enthusiasts.

I know running a lower wattage AC adapter can be damaging for the computer but i have a question regarding this.

I know that all the T540p model ship with a 90W power supply adaptor regardless of the chip's power consumption (35W or 47W). But the problem is that it's a really heavy cumbersome brick to carry around (about three times the weight of a 65W ac adapter!)

I presume Lenovo ships de facto the 90W in prevision of the worst case scenario happening; when you actually need 90W.

Now i would like your advice as of carrying instead my 65W power supply with me on my daily basis. Yes, before knowing this was potentially dangerous for the laptop i acquired a 65W from kijiji locally simply to carry one and have one at home at all time (This is what i had with the previous T420).

Consider the following :
- My T540p has a 35W chip (i7-4600M).
- I removed the HDD (using m.2 ssd).
- Running under Linux, the second GPU (the 730M) is off on demand (using Primus).
- Screen is only 1080p (not the 3k screen).
- Bluetooth is disabled in BIOS (might save some Watts).
- I rarely use the CD drive bay which i think sucks a lot of wattage, and when i do, usually the GPU is off.
- I used a 65W PSU daily for the last couple months, and nothing happened.

Here this guy says it's dangerous only once the laptop asks for too much power. Is this true?

I'd like to know if you think i should be ok with a 65W? And if possible, is it safe to even go lower with a 45W brick instead? (The brick is even much smaller)

Also, do you know if there's a way to do a power assessment for laptops? Is it linear? Like if it's 90W MAX but i have a 35W chip instead of 47W does that mean i can never go over 78W because they planned ahead of me?

Thanks.

If you want to check power, you can use a kill a watt. Check the power consumption on the 65 watt and 90 watt adapters. If 65 reads 65+, the laltop draws 65+ watts. The 90 watt adapter should be 10% higher than the actual laptop because of the internal circuitries.

Thinkpad4by3 wrote: ↑

Thu Jun 22, 2017 8:50 am

If you want to check power, you can use a kill a watt. Check the power consumption on the 65 watt and 90 watt adapters. If 65 reads 65+, the laltop draws 65+ watts. The 90 watt adapter should be 10% higher than the actual laptop because of the internal circuitries.

Thanks.

I'll try to acquire one of these. This is the EXACT thing i need.