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. ;)

Were those metric watts or imperial watts? That is what the "m" in mW means, isn't it? :D

And also remember that when boiling water in the southern hemisphere, you also need to turn the jug upside-down :p .

Why are you troubling us with all this information? We have a hard enough time with those blasted southern hemisphere toilets. :)

FewMiles..

I understand they have an adapter available now that makes them flush in the correct direction. This post would be a lot funnier if my Google search had turned up the picture from the Simpsons "Booting" Episode. Though I'm sure a half-dozen people would still have turned up trying to prove me wrong. :rolleyes:

With all the talk of VOLTAGE differences, I am surprised no one mentioned FREQUENCY differences...

Oh, yes, that's right, its the frequency that hertz :D .

Sorry, that's ample of those silly puns. If I'm not careful, you'll charge me, put me in a dry cell, and send me ohm.

Frequency doesn't matter in this case because the AC voltage is converted to DC voltage, which is converted to DC current.

The formulas you guys are using for Power, Current, and Voltage are linear, which doesn't take into account the use of transistors and other signal conditioning circuitry which a laptop charger most assuredly has.

To answer the OP's question, given the lack of harmony in these responses, I'd say it isn't worth trying because you could really screw something up. However, if you're in the mood to experiment with your (expensive?) laptop, plug the charger in by itself overnight and if it hasn't burned a hole in the counter by morning, plug it into the laptop and see what happens, then post.

Also, please note that no one here has an "I've tried this...." story, probably for a good reason.

Interesting thread..... does anybody know why on earth we still have various AC standards around the world? Wouldnt it be more efficient to just standardize the worlds voltage to one unified setting? I realize doing this now has cost issues, but... does someone here know the history behind all this?

Last time I was in a 240 volt, 50 hz country, I also noted my batteries charged significantly faster than my US based experiences. While I am somewhat technical, I can think of no reason why that would be so, but it is my anecdotal experience.

Sorry I asked the question
 

Now I am completely lost in all of this technical literature?

Am I correct to assume that it doesn't matter the AC voltage? The converter will still charge at the same rate, and that I am just fooling myself thinking that the charge is faster on 240v vs 110v?

SO why then do we have two different types of voltage?

Well, from the technical perspective, using 220/240V is a more efficient approach as the transmission losses are lower than at 110/120V.

However, the original power networks that were designed in the late 1800s - early 1900s did provide for 110/120V as the voltage standard.

As an example, Russia (and, I suspect other European countries) went through a massive swith-over from 127V standard to the 220V one. However, this was done gradually, starting in 1960's and it took almost 25 years to fully complete it.

North America did not want to switch when it had an opportunity to do so (i.e. in the 1960s when it would have been much easier) and now it's probably too late...

All AC-powered equipment will be labelled with the input voltage and current requirements for which is it designed. Before using any electrical appliance on a power grid other than that for which it was purchased, read the label. Many portable devices are now auto-sensing and operate with anything from 110 to 240 Volts input, and 50 to 60 Hz. I am yet to find a modern laptop computer power supply that will not operate correctly with anything from 110 to 240 volts.

However, many smaller or cheaper devices do not operate from the full AC voltage range. For example, I recently purchased a new Nokia mobile/cell phone in Australia (my home country) and specifically purchased a tri-band phone so I could use it in the USA. But it was supplied with a 240V only charger (read it on the charger unit). I had to purchase the optional Nokia "universal" charger to get one that operates from 110-240 Volts.

And has already been stated, the battery charge rate is a function of the current being sunk into the battery. The output DC voltage of the laptop power supply is constant (my IBM Thinkpad power supply outputs 16V DC) no matter if the input voltage is 110V or 240V. And the current being consumed by the laptop is a function of the laptop load, not the power supply (assuming it is not being limited by a poorly designed, under-rated power supply).

The major factor that affects a laptop battery charge time is whether the laptop is being used or is powered off. If the laptop is on while being charged, some of the power from the supply is being used to operate the laptop and the battery charge rate is reduced. If the laptop is switched off while charging, it can divert more current to the battery and chrage it more quickly.

Higher voltages suffer less loss through the transmission system, so 240V is a more efficient delivery environment that 110V. However, higher voltages are a bigger safty risk. The dangerous part of electicity is not the voltage in isolation, it is the power that must be dissipated through a load, and when a person receives an elctric shock, they themsekves are the load. A load is just a resistance and the resistance of a person is the same if they are in the USA (110V) or Australia (240V). The power to be dissipated in the load (person) is the square of the voltage divided by the resistance. So you see that given a constant resistance (the person in the case of an electric shock)as the voltage goes up, the severity of the shock increases as a square relationship.

So the efficiency benefits of a higher voltage power grid must be traded against the risks associated with misuse.

Frequency is less of an issue when comparing 50 to 60Hz. However, it does come into play. Some devices rely on the AC frequency to establish timing functions (ie my parents have an old clock that relies on the 50Hz mains power to keep time, and it does do extremely reliably).

For a laptop powersupply, the AC frequency is much less important than for devices using less efficient wound transformers. Most laptop powersupplies use what is known as a switch-mode power supply. A switch-mode power supply is very efficient and can be made small and light, but requires more components and is more expensive to manufacture than a traditional transformer/recifier/regulator power supply. Transformers consist of a ferrous material core with multiple wire windings. A higher frequency AC source permits a much smalled amount of ferrous material to be used in the transformer, making it lighter. This is why weight limited environments such as aircraft often use higher frequency AC power systems (eg 200Hz). However, the extensive use of switch-mode power supplies had reduced the need for bulky and heavy transformers and hence the benefits of higher frequency power systems are reduced.

The benefit to be realised by standardising the power systems used in different countries is reducing as more and more devices are being manufactured with multi-voltage switch mode power supplies. These devices can operate happily from 110V to 240V. At the same time, the cost of changing the USA's 110V system to meet the global standard of 220-240V cannot be justified.

Such a change is akin to countries that drive on the wrong side of the road. There was a proposal recently in Australia to change from driving on the correct (left) side of the road to the wrong (right) side of the road. The benefits would be in the redcued cost of importing vehicles from the USA and Europe.

This proposal involved a staged transition over 3 years. The first year would be a trial period where the experience, professions drivers would be the first to test the process, meaning busses and trucks would transition first to drive on the right. Following an evaluation of the success of this initial stage, cars would transition to the right side in the second year, followed by motocycles and other vehicles in the third year.

Power, measured in Watts, is purely voltage multiplied by current. This is the maximum power can be derived (or consumed) given a voltage and current. The "Power Factor" is what you are referring to, and that is the angular difference between the voltage and current AC cycles. The PF (cosine of the angle difference) is used when measuring power in VA (Volt Amps). With a PF=1 (ideal load) the VA is the same as the Watts. However, as the PF decreases (the angle between Voltage and Current increases) the VA will be less than the Watts measure of power.

Getting back to your statement, the use of transistors has little to do with the PF, and PF has little to do with non-linear devices. PF is a factor of the load characteristic, being inductive or capacitive. A transformer is an inductive load and can be produce a significant PF (perhaps as much as 0.7 or 0.8). However, modern switch-mode power supplies have very load inductive or capacitive loads (almost completely resistive), resulting in a PF or almost 1. So it is quite acceptable to measure the power consumption of a modern switch-mode power supply in Watts rather than VA.

Most AC generators are rated in VA rather than Watts since the load applied may be anything by a PF of 1.
All computer laptop power supplied from reputable manufacturers have the input power requirements clearly labeled. This is a legal requirement in most countries. There will be a label showing the input voltage such as 110-240V. If the device only states 110V input voltage, then don't plug it into a 240V supply! Similarly, if it is labeled for 240V only, don't plug it into 110V supply.

I have not seen a laptop power supply in recent years (at least the last 6 years) that is not designed for 110-240V operation.

Read the label before plugging it in. Don't just plug it and see what happens! That is BAD advice.
I've tried this. I have used my last three laptop computers in countries with 110V (USA) and 240V (Australia, NZ, UK, Germany, Ukraine, France, Italy, Singapore, Hong Kong, Malaysia, and many more). I have also used many other appliances in both, including my electric shaver, NiMH battery charger, cell phone charger etc.

BUT always read the label first!

But the resistance of a human body depends on many factors and is not constant. In fact, it can vary from something like 5 000 to 50 000 000 ohms. Therefore, the 110/240 variation is not really significant at all and the safety is not a factor.

There is only one true reason why North America is not switching to 220/240V standard, which as you said is

You probably meant "wrong (left) to correct (right)"? :).

Yes, it is significant. The resistance of a human body is in no way related to the voltage applied across it. There is no direct relationship between the electricity supply and the load resistance, therefore for the purpose of calculating the difference in power dissipation and hence the severity of the shock, the resistance is constant (same person, same conditions etc) and the power is increases as a square of the voltage applied.
I know exactly what I meant to write... and I wrote it :p .

That is absolutely correct, however I stand by my position.

To simplify it a bit, using the forumla of [Current = Voltage / Resistance]:

Current = Voltage {110 .. 240} / Resistance {5,000 .. 50,000,000}

The much greater (10,000 times) variation of resistance, makes the much smaller (2 times) variation in voltage insignificant for the purposes of calculating the current.

The general rule, electrical safety-wise, is that any voltage level above the safe level of approx. 36V AC can be, and is to be treated as, potentially lethal for a human being. The number of situations where 110V Vs. 240V will make any true difference is so negligible that it cannot be a determining factor.

But I am referring to a situation where the same person, under the same conditions (ie humidity, temperature, clothing etc) will dissipate more than four times the power if the voltage is increased from 110V to 240V. An, unfortunately, there are many electrocution accidents that may not have been fatal if the power absorbed by the person had been one quarter of what it was.

Having felt the effects of 240V through my own body on more than one occasion, I can honestly say that a reduction of the power by one quarter would have been desirable ;) .

I agree there can be a very great variability in the resistance of the human body, but most of the variation is to do with the type of contact made (eg, dry or wet skin, brushed against a limb or gripped tightly, contact area, amount of tissue between ingress and egress points etc). Once a good contact is made, the variation is much less than your have suggested. For the same type of contact and the same person and conditions, the more than four-fold power increase of the difference between 110V and 240V can be the difference between life and death.

Don't forget that it's the Volts that jolt, but the Amps that'll kill you.

A friend and I never paid enough attention to the instructions for physics experiments at school. Long story short, one day he zapped himself with 1100V, at about 0.01 mA (the exact number elude me). Got a nice shock, but not significant after effects.

Actually, it is a combination of the two, resulting in Power or Energy being absorbed by the body. This energy cause various problems for the human body, including:

• disrupting the operation of the nervous system and essential organs such as the brain and heart
• raising the temperature of critical organs - essentially cooking the body, normally after prolonged exposure or very large amounts of energy
• severe burns at the ingress and egress points, often multiple points especially in the case of lightning strikes.

Power/Energy varies as the square of both voltage and current.