If you have read my articles on power you know I yearn for the days when we get smart power so we have have universal supplies that power everything. This hit home when we got a new Thinkpad Z61 model, which uses a new power adapter which provides 20 volts at 4.5 amps and uses a new, quite rare power tip which is 8mm in diameter. For almost a decade, thinkpads used 16.5 volts and used a fairly standard 5.5mm plug. It go so that some companies standardized on Thinkpads and put cheap 16 volt TP power supplies in all the conference rooms, allowing employees to just bring their laptops in with no hassle.
Lenovo pissed off their customers with this move. I have perhaps 5 older power supplies, including one each at two desks, one that stays in the laptop bag for travel, one downstairs and one running an older ThinkPad. They are no good to me on the new computer.
Lenovo says they knew this would annoy people, and did it because they needed more power in their laptops, but could not increase the current in the older plug. I’m not quite sure why they need more power — the newer processors are actually lower wattage — but they did.
Here’s something they could have done to make it better.
In general, laptops only need the maximum power of their supply when they are trying to charge a mostly empty battery while running the computer at full power (maximum CPU, accessories on, screen bright.) Most of the time they draw far less, more like 15 to 20 watts, by running the CPU at a lower speed and of course having a full battery.
A laptop could be designed to take in both the old voltage (16V) and the new one (20V). In fact, I suspect they already are designed this way, because most laptops take the input power and put it into a switching buck converter which changes a wide range of voltages into what they really want (namely enough to charge the 10.8v battery.) The trick would be to look at the voltage, and if it’s lower, presume it’s an older, lower power supply. If so, manage the power to not take more than its maximum 72 watts.
One could do this, for example, by not charging an empty battery while the computer is on, because there is not enough current to do that. The computer could pop up a warning. “You are on an older 16V power supply. Your battery, while empty, is not being charged. You may use the computer, but to charge the battery, please turn off the computer for at least 20 minutes. The power light will blink yellow when the battery is sufficiently charged to allow operation and charging from this supply.”
In fact, this is what I do manually if I have one of the even older, 3.5 amp 56 watt supplies. Try to overdraw them and they just shut down, which is fine, and it tells you to pause and recharge — or if you need to, manually remove the battery. People do the same thing on airplanes where seat power is limited to 75 watts.
However, the computer could offer some other options. It could dim the screen, or power off accessories like USB devices, radios or the optical drive. Or more simply than all those things, it could get slow, refusing to let the CPU go full speed, which is one of the biggest draws of power. It could watch the current going into the battery and as soon as that current got lower, it could enable other functions. Still best to just take a pause, though, unless it’s an emergency. And yes, better to have a full power supply that can do everything. For those of us who liked to keep power supplies at our various desks waiting for us, but kept a full-power supply in the laptop bag, we could just get out the full-power supply if we ran into a situation where it was truly needed, like emergency need to work and recharge at once.
In fact, as laptops need more and more power — if they ever do — designers could just keep bumping the voltage on the new generation, and still run on the old supplies.
However, it is important that you not plug an old laptop into too much voltage. Now any laptop designed today can readily be set to take in just about any voltage up to 48v without much trouble, so we need not worry about the future. To prevent the new high-voltage supply from being plugged in to an old supply there are several tricks you could use:
- Use an entirely different plug, and provide an adapter that has a female for the old supply and male for the new.
- Put both jacks on the new laptop to let you plug in either. This takes room though, and adds a slight bit of weight.
- Design a clever jack that can take the old plug, and also the new one which would use a fatter central pin or fatter outer diameter. Springs would allow the smaller plug to fit in the new laptop, but the fatter plug could never fit in the old laptop.
- Design a new plug with a notch on the side or other non-round shape. It would fit in the new laptop, as would the old round ones, but not go in an old laptop.
Of course I really want a smart plug. I also admire Apple’s design of the quick release magnetic plug, since they are absolutely right — if somebody trips on the cord, I would much rather go briefly to battery than pull my computer off the desk or damage the jack! That was a change worthy of needing a new power supply.
Since all laptops use switching buck converters, it would be nice if they could just take any power from 12 volts to 30 volts. This is not at all hard to do today. Ok, I admit 12 volts is a bit hard if you want to charge 10.8 volt batteries, but being able to run on 12 volts — even if only at 54 watts — is so useful as to be worth a bit of extra electronics. And 15 volts (the airplane seat EmPower voltage) should also be native for every laptop.
Note that the above trick with the notch is a pretty standard trick for backwards compatible connectors. What people rarely do, however, is design their current connector to be forwards compatible. Ie. design it so that in the future it is possible to modify it to create a jack that this and the new generation can plug into but whose plug will not go into an old generation jack. If that’s what you want — I would prefer a smart plug that lasts for a long time.