Thinkpads Forum

Hi Y'all,

Are any of the Thinkpad 'smart' power supplies?

What I mean is, if a power supply is rated to provide 90 watts, and only 50 watts are needed by the laptop, does the power supply pull the full load from the wall outlet or does it pull just enough to output 50 watts?

Am guessing that there have been improvements to power supplies over the years?

Thanks and good health, Weogo

I might be slightly wrong on what I'm saying, or I might be very right: (Not an electrical engineer.)
The powersupply should not be drawing full load unless your laptop requires it to draw the maximum output. In the case of the Thinkpad bricks, they are not 100% efficient so they will draw more from the AC end of the plug than they output on the DC end (Your laptop end) of the plug. Some of that is wasted as heat (Your bricks will heat up, yes?). In practice, if you were drawing 50W (! Charging and benchmark?) then the brick might be drawing 55W at first and as it heats up (Resistance increases, inefficiency of components as temperature rises), it might start to draw more than 55W and move into the 60W range.

You wouldn't be trying to use the powersupply for a hobby project, would you?

If the power supply were "dumb" enough to draw all 90W/72W/etc when only a small fraction of that is needed, then when the laptop is idle, the power supply would be about as hot as an incandescent light bulb of the same wattage. Like hot enough to burn your finger instantly.

As Navck says, they aren't 100% efficient either, and waste some electricity when converting. I'd expect some to be more efficient than others, especially among the 72W or 5xW supplies which have existed for several years, but don't have info on that. If anyone finds it, maybe they will share.

Hey Weogo,

Your topic title reveals the flaw in thinking, "power [supplies] - energy draw." It's the connected laptop that "draws" power, the transformer doesn't actually draw power on it's own (well, very little). The wattage rating is only the maximum the power supply can safely provide without overheating. Any "smart" circuitry is contained within the laptop itself, not the power supply, and yes there have been significant advances in that technology over the past ten years.

Hi All,

Thanks for the replies!

I do know power supplies create waste heat.
Doesn't Lenovo have some some lightweight, switching power supplies that create less heat?
Which ones create the least heat per watt going to the laptop?
(And yes, I know laptop and power supply voltage need to match.)

Neil, we might have a semantics difference going on here.
The laptop draws power from the power supply, the power supply draws power from the wall, right?

What I'm after is a laptop/power supply combination that can run off a small photvolatic/battery/inverter setup with minimal draw.

My X41 Tablet has a 56 watt power supply, but an X200s and its 65 watt power supply could possibly draw less power from the PV system?
Anybody know of a table showing actual power used for different Thinkpads/configurations?
I do know heavy use of CPU/GPU/hard drive, etc. increases the load.

And you would think I would know how to spell supplies!

Thanks and good health, Weogo

Weogo wrote:Am guessing that there have been improvements to power supplies over the years?

You are guessing wrongly then

The type of power supply used on ThinkPads has not changed in any significant way over the past decade I have been using ThinkPads (and has probably not changed in quite bit longer than that). They are all switched mode technology based power supplies.

In any case, just about any type of power supply you are likley to find for most personal-use electronic equipment will only ever "consume" a tad more than the power the attached device is actually and instantaneously drawing out of the power supply.

Transformer style power supplies require a small "magnetising" current which they will draw even under no load, while switched mode power supplies will draw a small "switching" current event under no load conditions.

Cheers,

Bill B.

Hi Bill,

Thanks for the clarification!

It appears that what I really need to be looking at is the smaller laptops with minimal draw, and sticking with my X41 tablet is probably fine for much of what I do.

Good health, Weogo

Seems you may have had two different questions:

1. Which power supplies are more efficient/lower electricity use, if any?

2. Which thinkpads are more efficient/lower electricity use, if any?

For the first question, I still suspect, but do not know, that there may be some measurable differences among different power supply models. However, if there are, they will be tiny in comparison to # 2 above. A large screen Pentium 4 (G model?) with ATI will take much more power than a small screen Pentium M LV, for example. Your X41 is pretty good on this scale. If it's very important to use as little electricity as possible (sorry if I'm not using exactly the right words, long time since college) there might be somewhat better models. You also can do better by turning down screen brightness, undervolting CPU, shutting off unused hardware like serial&parallel&wireless, etc.

That will only cut your power consumption by 1-2 watts in practice. I've manually terminated everything including the USB ports on my T43 leaving it on the lowest screen brightness level and wireless on, practically with undervolting that was a 12 watt idle to 9 watt idle. Powering off the display when you're not planning to use your Thinkpad would contribute more power savings.

Then again, 10-20 watts isn't a lot of power draw compared to everything else around you.

Think of the "power supply" more of as a "pass-through" component. The load (the laptop itself) will determine how much energy will pass through it.