A coworker insists wall warts charge simple devices like mp3 players, ipods, and cell phones considerably faster.
I might agree with a power drainer like a Smart Phone. But an mp3 player?
What’s the Straight Dope on charging by wall wart vs usb port?
If it’s charging through a USB port, the source of the charging current will likely be 1/2A or 1A. Many devices will charge just fine on a half-amp source (aka 500 mA), but most phones and other high-power devices will charge MUCH faster on a 1A port. I believe most computers are limited to 500 mA source power on any one port, so unless the wall charger is also a half-amp model… the wall charger wins.
I am not sure if there are any higher-current USB sources, or if they’re a good idea unless used with specifically matched gear.
ETA: I rediscovered the truth of this when I only took a compact 4-port USB charger on a trip. Even though rated at 2A total/500 mA per port, It could barely get our phones, an iPad and a camera to half charge overnight. Never made that mistake again…
I need to check my chargers then. See what mA rating they have.
We have a request into physical plant to change one receptacle in each staff member’s office to the newusb style plug. Still waiting to see if it gets approved. At least half days work to switch out 14 receptacles for our dept. They aren’t cheap but will rid our office of wall warts.
I’d make sure they’re good, brand-name quality and have 1A ratings. Otherwise, it will be an annoying half-solution.
I also wonder what the standby/waste wattage on those wall USB ports is. May be zero to trivial, but…
Man, I wish we had those… we’re not allowed to plug USB devices into our computers at work.
Grainger gives the full specs. 3Amp at 5V that should be plenty.
USB Charge Recp, 15A, 125V, 3A@5VDC, White
Can charge 2 tablets at once
I would have thought they’d have an energy saver feature. Only power up the transformer when a usb cable is plugged into the jack. But they don’t mention it in the listing.
Wouldn’t that be a code requirement? Could be a fire hazard if that transformer is on 24/7 and in a enclosed space.
My experience is that voltage can vary significantly from one source to another. Some wall warts seem to eat their Wheaties and supply a lot of power (and so a fast charge), others not so much. Same with USB ports, from PC to PC, there’s variation.
Surprisingly, the fastest charge I find for a smartphone is using a 12Volt plug in the car (into what used to be called the cigarette lighter). I also have a 110 volt socket in one car (it has a built-in inverter) and for some reason that also seems speedier than 110 in the house.
I just plugged in a wall wart with my Sav-A-Watt device - with nothing connected to it, the draw was 0 - no amps, no watts. When it is charging, I’ve measured before that the draw is miniscule. If you’re talking about the new USB sockets that you can have with your regular 110 socket plate, wouldn’t it be the same as for the regular sockets? No flow, no electricity used?
For charging phones and tablets there are various protocols for the device to decide how much current to use. Naturally Apple and Android do things differently which is why on some USB chargers with higher current plugs there will be apple sockets and android sockets.
Also many new laptops (say within the past 3 years) will have USB ports that can supply more power for charging phones and tablets.
It’s still converting the 110V AC to 5 V DC it’s the step down transformer that draws power just sitting there. Unless they’ve got an internal switch to shut it off when nothing is plugged in. These days the switch wouldn’t be mechanical. It would be a SCR or some other component.
I suspect that a consumer-grade wattmeter has poor resolution under 5-10 watts. I think you’d have to use a bench-grade multimeter to get a meaningful reading, and even if it’s only a watt of standby, that’s kind of a lot 24x365xThe number of such devices.
It probably doesn’t have a transformer at all; it’s more likely a switching design. So in theory it could draw nearly zero power with no load, but in practice, there’s always reasons a little power burns up.
Generally speaking, you can take anything that can be charged by a USB port and plug it into any USB port and you’ll be fine.
USB chargers, on the other hand, are a whole different beast.
There are two types of wall-wart style USB chargers. The first are the ones that conform to the USB spec, so they put out 5 volts. These are safe to use with any device.
The second type are the ones that don’t conform to the USB spec. Why make a USB wall-wart that doesn’t conform to the USB spec? So it can charge faster, of course. SOME of these are safe to use with generic USB devices, as they only go into “fast charge” mode (often just a higher voltage level) when they detect that the device that they are intended to charge is present, and otherwise they drop down to standard USB voltage levels. Others are NOT SAFE to use with other devices because they put out a much higher voltage than the device may be expecting, and they don’t switch down to standard USB voltage levels. Ever.
So, if you have a device that is designed with some sort of quick charge capability, and if you attach it to the wall-wart that it was designed to use, it is certainly possible that it will charge a lot faster. However, if you are using all generic stuff that all conforms to the USB spec (5 volts, no fancy high speed charge modes, etc), then a wall-wart will charge the device at exactly the same rate as a USB port from a computer will.
An Apple iPhone will charge faster from its wall-wart than from a computer’s USB port. An iPhone charger is also one of those devices that is friendly to non-iPhone devices, meaning that if it doesn’t detect an iPhone attached to it, it puts out standard USB voltage levels and won’t harm your device.
Generally speaking, it’s the el-cheapo crap from China that sometimes has the quickie charger that doesn’t conform to the USB spec.
An mp3 player might have a quick charger. You never know.
Wait a minute. Legit wall chargers all put out 5 volts, but they may put out different amps, which can significantly affect charging speed.
Anything stepping down from line voltage to low-voltage DC almost certainly still has a transformer. However, the transformer is tiny because they can run it at many kiloHertz instead of 60 Hz.
Low-voltage DC-DC switching regulators generally don’t have transformers, though. And you’re right that they should only use power when there’s a load, though bad designs may not operate that way.
Pretty fascinating tear down of real and counterfeit Apple USB adapters here: iPad charger teardown: inside Apple's charger and a risky phony - they all do still have a tiny transformer for the switching power supply. And the counterfeits can be very dangerous - turns out paying for the name brands really does get you quality and safety.
As for idle draw, some of the USB outlets actually switch off the power supply when the door over the USB socket is closed. Inserting a USB plug slides the cover and turns on the power supply. Idle draw in that case should be insignificant.
This doesn’t actually make sense. But is close. No device with a constant voltage output “puts out” different current (amps). They are capable of different current, but the current delivered depends upon the load, up to that maximum current.
As much as possible a properly designed device will deliver a constant output voltage into different loads, and will shut down if the load exceeds its capability. Cheap and nasty devices are not so well regulated, and the voltage will sag as the load increases, still with an eventual shutdown/failure if the load is too great.
The problem with USB charging is that the spec was written so that the supplying device and the supplied device were supposed to talk and negotiate the current draw. Further, it was never really intended as a power supply socket for charging things. Initially, nobody implemented the spec. USB ports on computers simply provided power, and if you drew to much anything from the port shutting down to wrecking the port (or worse) was possible. Now most USB ports on computers do provide negotiation capability. But the same has been true of devices. Lots of devices just treat the USB port as a power source - they don’t even connect the communication port wires. So no negotiation happens.
But some devices and chargers do negotiate. iDevices will negotiate with chargers if they can. Older iDevices (30 pin connector) used specific resistors in the 30 pin connector to signal different conditions to the device. In both cases the result is that the device is told that it may draw more than the normal maximum USB current. So they are able to charge much faster. But they won’t if they can’t determine that they can do this safely.
There is a big difference between cheap and simple devices and complex devices that are charged (say a torch versus a smart-phone). The complex device will usually incorporate various switch mode power supplies and a proper power management and battery charging system. There are dedicated chips that do this with considerable sophistication. They will guarantee to draw exactly the current they say they will. Faced with an unknown source of power they will stick within the spec. Given a smart source, they will negotiate the maximum power that can be safely supplied.
No all charging leads are the same. Some are two wire only, and only supply power. They can’t provide negotiation. Apple Lightning cables actually have a chip in them that can provide some part of the negotiation. iDevice 30 pin connectors may or may not have the additional resistors in them to code for the various possibilities of what is connected, and to allow the device to draw greater current.
In all, it is a historical mess. You can get everything from poor performance to way past expectations performance, and it matters what device you use with which charging source, and the cable can matter as well.
They are not the same. Some devices will draw more power than the official maximum USB current rating/power draw if they are connected to “their” wal wart. This means that ipads may not charge if they are used at the same time they are plugged into a USB port (it takes too much power to run that screen and there’s not enough left to charge the battery at an appreciable rate)