USB Wall Charger

[clintbradford]

>> ... Will a 500mA one work?

Absolutely.

SOURCE: Personal experience with 500mAH, 700mAH and 1AH charging setups and my Kobo.

[DNSB]

Originally Posted by 3d0g

The USB spec is no longer 500mA. It's actually quite complicated now as there was an IEEE USB Battery Charging Spec started back in 2006 (as I recall), that allows up to 1.5A over USB. Devices negotiate how much they need / can get from the host. So, for a true USB host port, the USB device (kobo) will sort out how much it can have. For a "dumb" USB wall-charger, you'll want to be able to deliver the full rated requirement of 700mA.

I seem to remember it 1.5A at low speed, 900mA at high speed and whatever current can be safely supplied when there is no data communication.

Your definition of safely may not be the same.

My motherboard uses (I think) self-resetting fuses that open after about 6 minutes at 650mA and take about 5 minutes to reset under no load conditions.

I built my own charger back in 2005 when USB chargers were really expensive. Please excuse the ugly looks of that circuit - my soldering skills were not yet up to my usual high standards back then

The 7805 regulator delivers 1A at 5V, and completely "unintelligent" at that, so to say Since then, I have fried not a single device with it, using it on a regular basis. Will try it with my new KT

[jackastor]

Originally Posted by Duiker

Anyone tried their Blackberry wall charger yet? I'm afraid it might overload the kobo.

it cant. If its designed to run on a usb port and be charged then the ac wall charger can not over charge any thing that is plugged into it, its that simple. Anyone that may tell you differently is misstaken.

So that goes for any and all usb wall charges from belkin, to apple, to crackberries, to what ever knock off usb charger out there that will ever be. The only time I would err on caution is if I purchased at Xscargo or LW where it may be a lot buy of substandard electronics (means they failed quality testing and do not perform correctly).

Otherwise your good to go.

regards

jack

[DaleDe]

Originally Posted by jackastor

it cant. If its designed to run on a usb port and be charged then the ac wall charger can not over charge any thing that is plugged into it, its that simple. Anyone that may tell you differently is misstaken.

So that goes for any and all usb wall charges from belkin, to apple, to crackberries, to what ever knock off usb charger out there that will ever be. The only time I would err on caution is if I purchased at Xscargo or LW where it may be a lot buy of substandard electronics (means they failed quality testing and do not perform correctly).

Otherwise your good to go.

regards

jack

You are correct that you cannot overcharge the Kobo but a charger that doesn't put out the minimum current required can, itself, be destroyed. You need to insure that the mA available meets or exceeds the minimum requirements for the Kobo. Note that a device can tell the difference between being hooked to a computer and being hooked to a charger so it may intentionally expect more current be available from a charger. I believe it wants about 800mA from other posts and to give it less would be a mistake.

[jackastor]

Originally Posted by DaleDe

You are correct that you cannot overcharge the Kobo but a charger that doesn't put out the minimum current required can, itself, be destroyed. You need to insure that the mA available meets or exceeds the minimum requirements for the Kobo. Note that a device can tell the difference between being hooked to a computer and being hooked to a charger so it may intentionally expect more current be available from a charger. I believe it wants about 800mA from other posts and to give it less would be a mistake.

That is not an issue that needs consideration. If your device charges from the computer then they will charge from all usb chargers plain and simple. I agree that providing less current would be disaterous but its not an issue in usb charging, as they have to provide the current of your usb port on the computer. They all do. You can always have more then you need that again will not affect things, your device will only draw what it needs. So if you needed 50 ma then thats all it would draw. From my understanding a typical usb port provides 500 - 900ma Depending on the version of the device. This is why when we use say an unpowered hub that devices start to fail as there is more demand then what the port can supply.

So bottom line the usb wall charger will provide all the power the device needs. And seeing as the Kobo works in usb1 to usb 3 its never going to be an issue with current usb charging tech.

jack

[DaleDe]

sorry but that is not true. Some devices throttle down the charging requirements for CPU use on a USB port. As I said they sense that they are plugged into a computer. They typically list a longer charge time when hooked to a USB port than when hooked to a charger.

When these same devices are hooked directly to a AC charger they pull more current to charge faster. However this depends on the AC charger being able to supply more current. Devices are smarter now than they used to be but they can outsmart themselves if you use a charger with lower capacity than they are expecting.

Dale

[jackastor]

Originally Posted by DaleDe

sorry but that is not true. Some devices throttle down the charging requirements for CPU use on a USB port. As I said they sense that they are plugged into a computer. They typically list a longer charge time when hooked to a USB port than when hooked to a charger.

When these same devices are hooked directly to a AC charger they pull more current to charge faster. However this depends on the AC charger being able to supply more current. Devices are smarter now than they used to be but they can outsmart themselves if you use a charger with lower capacity than they are expecting.

Dale

Actually Dalede, I belive you are wrong.

http://anythingbutipod.com/2009/08/usb-charging-guide/

here is a link that explains how usb charging works. Bottom line no matter what you think when you are using a usb charger your going to draw 500ma min at all times. The kobo works quite fine for that. There may be devices that can draw more current to recharge but there are limits to that.

Bottom line here is and will always be any usb charger will work period. no ifs buts or anything about it.

If a user is using extreme power management on a desk top then yes some comptuers can regulate the power in the usb ports. But we are not talking about computers we are talking about usb power adapters for the wall. In which case they will always be compliant to the inudstry standards period. They will always produce a min 500 ma. There are four connectors ona usb and 2 for power and 2 for data. In an ac usb charger there is no need for the data to be used.

regardless I think you and i will have to agree that we cant agree.

[PeterT]

May I suggest Wikipedia... http://en.wikipedia.org/wiki/USB#Power

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 2.0, the voltage supplied by low-powered hub ports is 4.4–5.25 V.[34]

A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. Low-power devices draw at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. High-power devices draw the maximum number of unit loads supported by the standard. All devices default as low-power but the device's software may request high-power as long as the power is available on the providing bus.[35]

Some devices like high-speed external disk drives may require more than 500 mA of current[36] and therefore cannot be powered from one USB 2.0 port. Such devices usually come with Y-shaped cable that has two USB connectors to be inserted into a computer. With such a cable a device can draw power from two USB ports simultaneously.[37]

A bus-powered hub is initialized at 1 unit load and transitions to maximum unit loads after hub configuration is obtained. Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e. one device connected on a four-port hub will only draw 1 unit load despite the fact that all unit loads are being supplied to the hub).[35]

A self-powered hub will supply maximum supported unit loads to any device connected to it. A battery-powered hub may supply maximum unit loads to ports. In addition, the VBUS will supply 1 unit load upstream for communication if parts of the Hub are powered down.[35]

In Battery Charging Specification,[38] new powering modes are added to the USB specification. A host or hub Charging Downstream Port can supply a maximum of 1.5 A when communicating at low-bandwidth or full-bandwidth, a maximum of 900 mA when communicating at high-bandwidth, and as much current as the connector will safely handle when no communication is taking place; USB 2.0 standard-A connectors are rated at 1.5 A by default. A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V. A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port shorts the D+ and D- pins with a resistance of at most 200 Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured. The increased current (faster, 9 W charging) will occur once both the host/hub and devices support the new charging specification.

So devices MAY draw as little as 1 unit load.......

[DaleDe]

I agree, from the computer side of things a USB port is exactly as described. But you are missing the point. A USB charger, and I have many of them, can supply only 500mA but many of them are rated at 800 mA or more. I have some that can supply 1 Amp, all at 5 Volts or there about. I worked, before my retirement, for a PDA company that used such a charger. Now why would you design a charger that uses a USB connector that can supply 1 AMP of current? Why make it more expensive when you only need to output 500 mA.

The reason is simple. A eBook reader is a smart device as is a PDA. They can decide if they are plugged into a computer or plugged into a charger. Haven't you ever noticed when you plugged in your device to a computer a message appeared saying do you want to charge, or attach to the computer for data transfer.

My Hanlin says: To connect press OK. To charge press any other key. How does it know? Well, technically I could get into handshaking but that is un-important. The important thing is that is does know. A it takes 6 hours to charge my eBook Reader. However, if I plug into my charger it will charge in 3 hours. How come? Because it uses more current. The eBook reader knows it can yank 1 AMP out of my charger and does so. But it I were to use my poor little cell phone charger I would probably blow it up.

Dale

[PeterT]

Actuqally with the Kobo it makes no difference if you plug into a computer OR a USB charger. You are still prompted as to whether to go into device mode or stay reading

[jackastor]

Originally Posted by JPenguin

MonoPrice.com sell USB Wallwarts with shipping for less than $5, I'm going to pick one up for a different use but I'll test it with the Kobo too. It's rated for 1A so it should be plenty for the Kobo's 700mA.

It doesn't matter what it is rated for it will work no it's buts about it. If kobo charges via the computer port and it does. It will charge whether it is 1 amp or not.

Good luck let us know how it works out.

[G0AT]

Originally Posted by jackastor

It doesn't matter what it is rated for it will work no it's buts about it. If kobo charges via the computer port and it does. It will charge whether it is 1 amp or not.

Good luck let us know how it works out.

This is correct assuming the USB AC adapter has a built-in current limiter. The PC USB port is limited in its output, so even though the Kobo is looking for 700 mA, it only gets what the port can supply. If the adapter does not have a current limiting circuit, it could potentially overheat if it is rated at less than the Kobo's input rating. I'm sure there are some cheap USB AC adapters out there that are at risk of overheating.

On a side note, this means that any adapter rated at 700 mA or higher will charge the Kobo in the same amount of time. If you use an adapter rated lower than 700 mA, it will take longer, with the length of time proportional to the output rating of the adapter.

[Wicked]

Originally Posted by DaleDe

Yes, it should work fine. 5V plus a number bigger than or equal to 700mA. 1.0A is equal to 1000 mA.

Dale

This number stuff gets me. So I have a sony charger that is 5v and 1500 ma, is that going to harm my kobo? I can buy one off amazon but will wait until I find out, hate to buy if it's not required to do so. Hope you see this, not sure how old this thread is.

okay and another thing, if I plug my kobo into the computer it doesn't ask me about charging, it asks me if I want to connect to the computer, I say no I think, oh I am not even sure anymore but nothing about charging so getting confused and the pfd file just says plug the sucker into the computer....... ugh but whatever I end up doing, oh I do tell it to connect to the computer and then I close the little window asking me what do you want to do, use as storage or blah blah I close that down and then it says it's charging....

[robko]

See other thread for answer on the charger itself.
The behaviour when you plug it into the computer is so that you can continue to read while charging. If you select "connect to computer" it mounts it to allow you to play with the file system on the device, but you won't be able to read on it until you disconnect. If you decline to connect it should still be charging but will allow you to continue reading on the device while it charges (but you won't be able to play with the files on the device).