Thinkpads Forum

Does a 90W (larger) AC adapter charge the battery faster than the 65W AC adapter - or is the charge rate limited by the battery hardware and the 65W is already charging at the battery's limit?

On an X series system at least, you will not be able to use up more than 65W of power, even charging and running the notebook at the same time. So there really is little point in buying a 90W power supply -- although some people have speculated that they may run cooler ...

thanks for the reply tom - but you may have misunderstood my question.

I'm wondering if the *charging* time for a dead battery (lets say on a system that is powered off) will be faster with the 90W charger compared to the 65W charger - or if the charge times will be the same. In other words, is the battery limited to accepting a certain amount of power - which the 65W supplies and therefore the 90W is useless for an X-series?

I would tend to think that the charging time is a function of how much current is being poured into the discharged battery. Since there is probably an Analog Devices ADP3806 (or similar) Li Ion battery charger IC in your system, it's going to regulate the proper amount, regardless of what the current capability of the AC adapter you are using. In short, no, a 90W probably will not charge the battery any faster than the 65W.

Ray does the tech talk much better than I do.

I'm not so sure about this. The charging time is shorter, if the notebook is off. So I think it would charge faster with the 90W, at least if the notebook is in use.

d3 wrote:I'm not so sure about this. The charging time is shorter, if the notebook is off. So I think it would charge faster with the 90W, at least if the notebook is in use.

OK, a quick test (on an X31, since my X61 still has not arrived ). Running on battery, battery at about 25%. Power usage on battery is about 14-15W.

Now, plug into a 72W adapter. 72W - 15W = 57W, so there should be lots of charging capacity left. However, the charging rate is only 31W, no matter how I change screen brightness, wireless etc. (And charging rate will drop as I get closer to full capacity.)

So on the conventional 54W adapter for the 31X, I would use 15W to power the system, and still have 39W available, more than the 31W it will charge at. No difference at all in the charging rate.

The difference will come in when you are playing a heavy 3-D game on a T61p with a 15" display, discrete graphics and 4 GB of memory, with WWAN enabled, and using 30W+ of power -- that's when the 90W adapter will enable you to charge at full rate even while using the system.

For the x61, lenovo specifies different charge times if on or off.
15W, that is when the machine is idle?
a x61 can consume far more power (it has no low voltage CPU).

15W is light usage, disk spinning, wireless on, full screen brightness. With appropriate power settings you can bring it down to 8-10W, but that wasn't the objective here.

yes, my 90w wall adapter charges my x61t faster than the 65w connected to my x base. Can not give you actual time frames though.

The easy thing is to check in the battery properties -- you can see the charging rate without waiting for a full charge cycle. (Just make sure you check at roughly the same battery level as the charging rate drops as the level approaches 100%.)

Can you check this with the two adapters? I may be proven wrong yet ...

and me as well... Good idea there Tom!