I have two e-readers (Kobo). One came with a charger that you plug into the wall. The other came with a cable and directions to plug that into a computer USB port. The other end of both cables are indentical, what I will call, for want of the correct word, a mini-USB connector. Is it safe to plug the one that didn’t come with a charger into the charger?
Incidentally, the instructions that came with the larger device, the one with the charger, say that you can plug it into a computer, but it will charge very slowly.
Like any power supply, a USB brick is labeled with its input and output characteristics. Typically it’ll be 5V 1A for a modern phone charger. Some tablets require even more power. The problem is, USB was designed as a data interface, not a power interface, and according to the specifications, shouldn’t put out more than 300mA. Motherboards adhering to this spec won’t charge your phone quickly, or at all, so your phone charges poorly in the computer.
But there’s more! Cheap, poorly designed power supplies can have many faults that make them ineffective or downright unsafe. You may only be getting a reasonable approximation of 5V when under full load. Under no load the voltage fluctuates as high as 15V, which can damage equipment. Also, you have AC mains voltage and 5V DC within very close proximity inside a ~1" cube. If the cheap design improperly isolates these, you can get a nasty shock. USB charger counterfeiting is a serious problem and it’s difficult to know if you’re buying something legitimate, even if you’re at a reputable retailer.
Finally, the connector usually used on phones is a ‘micro’ USB. Mini USB is a different, slightly larger connector that isn’t seen much any more.
The USB power spec is 500 mA, not 300, at least for USB 1 and 2. USB 3.0 and above raise the maximum power draw to 900 mA.
USB ports on a computer are supposed to be protected, at least according to the spec. In the real world, they often aren’t protected. If you try to draw too much power, sometimes you will blow out the USB ports and sometimes you can blow out the entire motherboard.
Generally speaking, most devices that will plug into a USB port for charging will charge just fine on any standard computer USB port or any standard equivalent USB charger (like a wall-wart type). They may charge fairly slowly, though. Many devices have special functionality where they can detect if they are plugged into their own special charger instead of a standard USB port, and if so, they draw a lot more current than the standard USB can source. This allows the devices to charge much more rapidly. If the device detects that it is plugged into a standard USB port, it just charges at the lower power rate (so it takes longer to charge) and nothing gets damaged.
There are a few oddball pieces of equipment out there that use the standard USB connector but don’t adhere to the spec, and those can damage your computer. Fortunately these types of devices are pretty rare.
I’ve seen phones that use standard USB hardware, but which have some means of detecting their own branded chargers, and refuse to charge on anything else. It still doesn’t hurt anything, though.
From what has been posted, I would say that you can safely plug either e-reader into either a standard computer USB port or a standard USB type charger.
But the charger that came with the larger unit is not a standard USB charger. It’s a special charger designed to quick charge that particular unit. It may not conform to the USB spec with respect to voltages and currents and such and may damage the other unit.
However, nowadays most wall chargers supply more than the “standard” 500 mA, so I think it’s misleading to imply that such a “quick charger” is somehow unusual or device-specific.
From everything I’ve read (and personal experience), there is absolutely no harm, and possibly some benefit, to using a charger that supplies more than your device actually needs (assuming a reasonably modern and properly-designed device). Here’s one cite; here’s another (with a caveat that this is assuming that the chargers and devices involved follow the standards they’re supposed to); and here’s a thread on a message board that specifically addresses Kobo e-readers (see especially post #5).
On the other hand, I do see that the “official” word from Kobo itself is “Charge your Kobo eReader with any 5V, 500mA Micro USB adapter” (bolding mine); so there’s no official guarantee that a more powerful charger would be safe to use.
Note on terminology: The small USB port you see on most non-Apple phones these days, and a myriad of other devices, is a micro-USB connector. Mini was a thing briefly, but is a little bit bigger. One of the phones I worked on started with a mini-USB because the micro parts weren’t available yet - the standard was just being finalized - so we had to design around it. The micro part had a meaningfully smaller footprint on the PCB, which is a good thing.
Agreed that it’s mostly safe, but I want to highlight your our caveat - a properly-designed device.
A properly-designed device has layers of safety with charging a battery. The battery itself should have some safety mechanism. The charge circuitry on the device itself should manage the amount of current being drawn from the charger. And the charger itself should limit the amount provided. If you have a cheap, poorly designed device, it might have a crappy battery and charge circuit, relying on the charger itself to limit the current. That’s when things get dangerous.
Luckily, outside of development activities, I haven’t run into anything like that recently.
Umm. Unless the device manufacturer really worked on doing it incompetently, the current capacity of the charger should make no difference whatsoever.
This is true for all electrical circuits. If I plug, well, anything into a power source capable of delivering more current than I need, nothing will happen unless the device is faulty.
If I, for instance, connected a space heater directly to a pole transformer capable of supplying 500 amps at 120 volts, with no circuit breakers or fuses in the circuit, my heater will still use only 10 amps. Now, if my heater has an internal short circuit, it would explode rather dramatically in this case, but under normal operation it’s V= IR.
The charger in any battery powered device with an internal battery is an electronic circuit that has to monitor and detect the battery’s state of charge. It has to deliver a specific voltage to the battery at specific times, and limit the flow of current. It has to cut off charging when the battery is full, to prevent damage.
It isn’t difficult to get it right enough to be safe, but it’s pretty easy to be incompetent.
Doing a proper charging circuit takes money, board space, and time. In the race to the cheapest for commodity level consumer electronics, I wouldn’t be at all surprised if short cuts are taken. Combine that with a manufacturing or in-the-field defect, and you can get a direct short pretty easily.
Name brand manufacturers aren’t doing that…but the really cheap knock-off from a company you’ve never heard of? I’m not going to trust it, unless I really understand where their cost structure comes from. Just not worth it to me - I’ve seen what can happen when the safety circuits are bypassed.
The charger in question comes from the company that makes both e-readers. The obvious thing to do is ask them, but they never answer questions you send them in. I asked them last week, then went to the Dope. Which leaves me still uncertain.
Oh. Right. We have a real world question here.
Sorry about that.
I’d have absolutely no qualms about interchanging the chargers that came with various Kobos. You’ll be fine. The risks I’m discussing are extremely unlikely in that case.
All the information has been supplied already, but in a fairly confusing way.
First and foremost, if it has a USB port you can connect a USB charger and it won’t blow up. (Vendors aren’t that stupid.) All USB stuff works at 5 Volts. However, there are some really cheap chargers that don’t quite hit 5 V and if you use those your touch screen may not work properly. They still won’t blow up your device.
Second, pretty much anything will charge off of a standard USB port or standard USB charger. Those provide up to 500 milli-Ampères (mA) = 0.5 A for a total of 2.5 Watts (5 V x 0.5 A = 2.5 W).
Third, many devices really want more than that 0.5 A / 2.5 W. There is a USB charger standard that describes how USB chargers can provide more power. *Most chargers and devices that provide/draw more power conform to that standard and will work together, a few work differently so some combinations won’t charge.
Fourth, you don’t have to match amps/Watts between chargers and devices. If the device wants more than the charger can deliver, either it takes what the charger can give it and charges more slowly, or not charge at all. If the charger has a higher rating than the device, the device simply draws what it needs and charges at its maximum rate.
Bottom line: yes, chargers are different. Avoid the cheap knockoffs but don’t worry too much about it otherwise except for really big devices such as iPads.
I think the opposite: it’s not that there’s a “quick charger” out there that you can plug into wall sockets and somehow get more power out of them than they’d usually give*, just that computers are slower because they send fewer volts out of their usb ports than wall sockets do because the primary purpose of a USB socket is not power.
*Is this possible? Is there any kind of charger you can plug into a wall and increase the voltage it sends out? Sounds like a recipe for either hardrive or even human meltdown.
