Does using different voltage speed up laptop charge time?
 

I travel quite a lot, and most times I am in regions that have different voltage from 110v-240v. Just a quick question for the forum.

Does voltage make any difference on the speed of the charge? I noticed (could be coincidence) that when I charge me computer using 240v, the charge is faster than using 110v and much faster than using the airplane Empower...

Am I right?

[QUOTE=ACfly] I noticed (could be coincidence) that when I charge me computer using 240v, the charge is faster than using 110v

That's been my experience too. And water boils faster at 2220-240..

Sylvia

It shouldn't matter, the adapter simply takes whatever it is given and converts it to the charging power the laptop needs, VOLTAGE should not be a problem.

If it did make a difference, I would be concerned about your power adapter, it's supposed to put out a constant no matter what's being put into it. If it's running hot at 240, then it could be causing damage to your laptop, it may be worth putting a meter on it.

Agreed with ScottC and cordelli. The power adapter outputs the same DC voltage, no matter what the input AC voltage is (assuming it's within range; typically the power adapter says 110-240 V or something like that).

Are you sure your expectation that 240 V > 120 V ==> faster charging is not affecting your measurement? :)

FewMiles..

Actually, it depends on the type of adapter/power supply.

If it's a simple transformer/bridge rectifier/pi filter with maybe a voltage regulator like a 7805 or 7812 (i.e., practically all of the big-and-heavy wall warts) and has the ability to automatically or manually switch between 120 and 240V, the output voltage stays constant but the available current doubles at 240V. The reason many laptops won't charge at all when plugged into empower adapters on planes is that the adaptor cannot supply sufficient current to charge the batteries. Depending upon how the charging circuit in the laptop is designed, it's possible that it will charge faster when it can draw more current.

Adapters/chargers that use a switching (PWM) power supply (most cellular phone travel chargers, many laptop supplies) generate their own high-frequency AC and the output is tightly regulated. Their current and voltage output will be constant regardless of input voltage.

The correct answer to the OP's question is: maybe.

I'd be concerned with equipment damage
 

I would be concerned with potential damage to your equipment.

Even though it is possible, for a time, to run equipment at voltages that exceed the design, you could potentially do damage to the charging equipment on the laptop.

I accidentally put an ac adapter a bit higher than the voltage allowable for my cell phone and blew out the internal charger on the cell phone.

For a lithium-ion battery, even increased applied current shouldn't make a gross difference in full-charge time, as the shorter wait for peak voltage is compensated for by a longer roll-off to maximum charge current.

First of all, all (or nearly all) modern laptop power supplies are of the switching type as a conventional transformer-based supply capable of providing 4-5 Amps that laptops require would probably be the size of laptop itself and weight a few kilos :).


Not quite sure why do you think that the available current would somehow double when running at 240V... Using the basic formula of [Wattage = Voltage * Current], if a tranformer has a wattage of, say, 110W and output voltage of, say, 15V:

• At 110V: Input Current = 110W/110V=1.0 Amp; Output Voltage 15V; Output Current = 110W/15V=7.3 Amps
• At 220V: Input Current = 110W/220V=0.5 Amp; Output Voltage 15V; Output Current = 110W/15V=7.3 Amps

And make sure you halve the cooking time when using a microwave oven at 240V.

Oh, yes, also be sure to take your own AA batteries with you since countries that have 240V mains power also use 3V AA batteries which could damage your camera/mp3 etc. And those little 18V rectangluar batteries (9V in the USA) really pack a punch :D .

Back to original topic - no difference. Its all about the output voltage (still the same) and current (still the same), which combined define the power being delivered to the device (P=V*A).

Oooh. That's good to know. Thanks.

I guess you didn't notice the ":D" at the end of NM's paragraph :) ...

An ideal transformer neither creates nor dissipates energy. "Wattage" (power that can be deposited into a load) is not a constant here, though, but a constraint. You're applying it to both sides of the equation.

Not that ideal transformers exist in real life, but my calculation was based on exactly the assumption you had mentioned.

Well, alanw was, presumably, talking about maximum power when he wrote that "available current doubles". I was only trying to prove that since neither the maximum power (in my example 110W), nor the output voltage will change, the maximum (available) output current will not and cannot "double".

Yes, but you're burning out the transformer in the process. ;)