Ok,

Here's something i always forgot to ask to the friends in the US here.

I've just spent 10 days in the US (about to board on my plane back home) and as always my devices (tablet, phone) have been taking roughly twice as much time to recharge throughout my stay (compared to EU). This is consistent w/the 240V/120V difference. But, it seems strange that a phablet takes more than an entire night to charge. Am I supposed to get some faster charger, or look for dedicated charging outlets in hotels, or what? In years, i never bothered solving this little mystery to me.

240V/120V should not make double the difference but it's likely the 240V version might be able to put out a bit more current. Shouldn't be double and it's not a linear relationship.

It's all about power conversion - 240V at 1A is equal to 120V at 2A in terms of raw power. Then it's an issue of how efficient the power supply is. Inside the supplies rectify to DC and then using a switching power supply to output 5V. They still output 5V regardless of the input (within reason of course). As the DC rail will be lower in a 120V supply that can lead to less efficiency.

A phone/tablet charge is of the order of 1-2A but only at 5V i.e. 5-10W. A 120V outlet is perfectly capable of charging a mobile device at full power BUT they just might not be as efficient at the lower voltage on the wide range supplies.

I'm surprised you are claiming it's double the time. I might expect maybe 10-20% more depending on how good the supply is.

What brand devices?

If you have Apple iDevices AND Apple brand chargers, the charge time should be exactly the same regardless of wall outlet voltage.

That said, Apple makes different capacity chargers. The stock iPhone and iPad MINI chargers are 5 watt maximum output rated.

The Apple charger sold with the full size iPads is rated at 10 watts or 12 watts (there are two variations).

The charging cable also matters. If the cable is internally degraded (excesse flexing, well used) then it can impede charging. Non-MFi cables can affect charging.

A full size iPad that is being charged using a iPhone charger (5 watts) will charge slowly. If the iPad screen is on then it will charge even slower.

If while traveling you are using the device more and the battery level is lower than you normally allow at home, then the charge times will be longer. If the device is hot when plugged in, it will not start actual charging until the internal battery cools down.

Travel tip when staying in a hotel. Sometimes the wall outlet turns off when you turn off the lights. I have had this happen more than once where I plug it in, see it is charging, then turn off the lights to sleep. In the morning, the device is not charged!

Thank you all so much.

I am using USB cables on Nokia, HP, HTC, Samsung devices. I am thinking the cheapo usb-us plug adapter has a Amp limit, which seems the most obvious reason? It does not carry any spec, but assuming it is limited to 1A, for example, than Voltage difference would explain it all. Also, that adapter is the only different variable.

What do u guys think? Does this make sense?



Edit:
To be more clear, I am not using the original devices AC Adapters. They all came with EU plugs.

Are you comparing a cheapo 120v charger with a OEM 240v charger? Odds are the cheapo one is putting out lower amps - have a read of the labels.

I've spent far too much time trying to diagnose these sorts of things. In a nutshell, the problem isn't 120V vs. 240V. It's about all the different modes of USB charging.

USB chargers, by default, put out 1A / 5VDC. There's sort of a standard kludge that jumps this up to 2A / 5VDC that's supported by everybody-but-Apple, who does the kludge differently. There are a small handful of USB charger adapters that are "universal", supplying >1A to both Apple and non-Apple devices, but it's exceptionally difficult when buying a charger to know whether you're getting the right thing.

To make matters more complicated, some Android devices are now rolling out Qualcomm's "quick charging / turbo charging" that can crank the power up even higher when the battery is lower.

The proper future answer is USB 3.1's "type C" connector, which goes all the way up to 100W (gory details). Hopefully, they'll have standardized branding and whatnot so you can know whether any given charger supports whatever power ratings. The rumors say the forthcoming MacBook Air will have it.

I really hope we get this done right. I fear we won't. Already, there's the new Nokia N1 tablet which features a "USB type C reversible connector with USB 2.0" Sigh. I don't know exactly what that it, but it's something of a harbinger of "not quite" compliance with various future devices until things shake out.

(Side note: I wanted a USB 3 hub for my Mac with a zillion ports. After much shopping on Amazon, I ended up buying an Anker device. Lots of ports. Mostly works, but it identifies itself as a USB2 hub, and some devices, like talking to my Android phone, don't work very well where they work perfectly if I plug them directly into the computer. Again with the "not quite" compliance.)

The cheap US adapter is highly likey to be the problem, causing slower than expected charging.

USB charging (and USB ports on computers) has precisely one output voltage, 5 volts. This is fixed, regardless of the AC mains voltage.

USB chargers vary from the bottom tier rating of 2.5 watts (while 5 watts is common enough, it is not the lowest/cheapest level) up to 10 and 12 watts.

The limit on charging speed (Amps current) is determined by the LOWER of the maximum output the charger can provide or the maximum rate the device can absorb power.

There are other reasons to avoid cheaply made USB chargers. One is safety risks. It is not unusual for inexpensive chargers to have poorly designed or poorly manufactured electronics which create risk of electrical shock or fire.

Another potential problem is electrical interference. If the USB charger is creating 'noisy' DC power then it can affect the operation of the touch screen device. I once had a car charger that made my iPhone react crazily to finger touches. That charger got binned shortly afterwards.

When I travel I carry a name brand dual output USB charger that is rated for the full 2 Amps (10 watts) charging on each port.

Top grade USB chargers can be hard to identify as the lesser powered dual port chargers also label themselves as '10 watts', but that is for both ports combined.

BTW, I am in the market for a compact/portable/travel sized four port USB charger that provides Apple compatible 10/12 watts on each of the four ports. If someone has a recommendation, I am interested.

I have posted previously about the general sloppiness of the USB spec and the process that creates it.

I am of the expectation that the industry will manage to screw USB up, yet again.

Unfortunately, I am back in EU and I can't test it, but I do believe at this point it is the cheap adapter I was using. Interestingly, I was using it just because it was smaller.

Anyway, a lot of info I was missing on the USB power standards. Great read. Thanks!