Solve : How can I tell if a USB port is powered or not? Thank you, I

1.	Solve : How can I tell if a USB port is powered or not? Thank you, I got an answer?
Answer» I have a desktop PC with 4 USB ports in back and two in front and would like to hook up my new laser printer via USB, but the directions say it must be a "powered USB port". How can I tell before hooking the printer to it? Thanks anyone for an answer.Typically, the front USB ports are not powered, however on some models they are. The back USB ports are ALWAYS powered, since they are a component of the motherboard.Thank you. How can I now close my post so nobody else needs to answer me?You can't and don't need to close the thread. If you want, you can always edit your post, and put a [SOLVED] at the beginning of the Topic title.Quote from: AgentX on October 03, 2009, 09:51:42 PM Typically, the front USB ports are not powered, however on some models they are. The back USB ports are ALWAYS powered, since they are a component of the motherboard. If front USB ports are not powered how the heck would they work ? ? I thought ALL USB ports are powered...All USB ports are powered. It is USB hubs that are powered or unpowered, with an AC adapter. a hub requires this type of configuration because, by definition, it plugs into a single USB plug on the host machine, and is, itself, a USB device. each USB device is limited to drawing only (IIRC) 200mA of current from the USB connection. Therefore, devices plugged into an unpowered USB hub would be required to "SHARE" the available current, in most cases, they end up having to require less then around 170mA, when added together. (because the Hub itself requires power for it's circuitry). chances are, the Printer is designed to draw the full amount from the USB connection, 200mAs, and therefore requires a port capable of delivering it- a Powered USB hub, or any built-in connection on a PC - is capable if this. The directions are specifically referring to USB hubs or the USB connections of CERTAIN devices whereby it would be unable to draw the full amount as allowed via the USB specification.Actually... no they're not. There are low powered one, and then full powered. On my old tower, the front USB ports were low powered, so I couldn't charge my iPod with them. I had to plug it in from the rear in order to get it to charge. All internal usb ports are powered on as soon as the system boots.Quote from: GRIFF on October 04, 2009, 11:12:58 AM Actually... no they're not. There are low powered one, and then full powered. On my old tower, the front USB ports were low powered, so I couldn't charge my iPod with them. I had to plug it in from the rear in order to get it to charge. This is usually a manuf.'s budget speaking...it's not the rule of thumb. Hang on... Quote Important You experience longer charging times when you use low-power 100-milliampere (mA) USB ports. USB ports that are located on the front of a COMPUTER or in some USB hubs are frequently low-power 100-mA ports. Typically, you can find high-power 500 mA USB ports on the back of the computer. Additionally, when you suspend the computer or put the computer to sleep, high-power USB ports may change to a low power 100 mA mode. http://support.microsoft.com/kb/938069what cheap sub-standard components support has nothing to do with the specification but rather the fact that they don't adhere to it. In such a case, sometimes the manufacturer cheaps out by only using a single front panel USB header, and having a small piece of circuitry act as a hub. In this case, the power of the front panel USB is reduced in the same way as would occur with a unpowered hub, that is, < 200 mA. The actual Front panel header on a motherboard gives 200mA, which is the full power available via the specification. In this case your iPod may simply not charge from the front panel due to another quirk. Many front panel USB connections on PCs are built to the USB 1.1 standard; the iPod may simply not support USB 1.1. That being said, however, I imagine a printer would gain significantly... (in fact, it does, considering now my printer and it's performance now versus when I used it with USB 1.1) and so if it turns out that the front panel connections of the OP's computer are in fact USB 1.1, or if their PC manufacturer used a cheap "I'll use a cheap hub instead of a cheap USB header" technique, then the connections on the machines rear would be best. In fact, considering the printer isn't likely to be often plugged/unplugged, it would probably best to plug it into the rear anyway, and save the front panel connections for things like USB drives. EDIT: AHH yes, replace 200mA with 500mA in this and my previous posts, heh. 500mA is the standard requirement. Not meeting this standard- and not being a unpowered hub - means that it does not conform to USB (strictly speaking). However the front panel ports, as I've indicated are often implemented using a low cost USB hub, whose limitations I have outlined previously. The charging of the iPod is more an issue of voltage than current. Unfortunately, many designers are unaware of the implications. Charging Batteries Using USB PowerWow. Great thread on what at first seemed to be such a simple issue. Thanks to everyone involved, I've learned something today.

Solve : How can I tell if a USB port is powered or not? Thank you, I got an answer?

Answer»

I have a desktop PC with 4 USB ports in back and two in front and would like to hook up my new laser printer via USB, but the directions say it must be a "powered USB port". How can I tell before hooking the printer to it? Thanks anyone for an answer.Typically, the front USB ports are not powered, however on some models they are. The back USB ports are ALWAYS powered, since they are a component of the motherboard.Thank you. How can I now close my post so nobody else needs to answer me?You can't and don't need to close the thread. If you want, you can always edit your post, and put a [SOLVED] at the beginning of the Topic title.Quote from: AgentX on October 03, 2009, 09:51:42 PM

Typically, the front USB ports are not powered, however on some models they are. The back USB ports are ALWAYS powered, since they are a component of the motherboard.

If front USB ports are not powered how the heck would they work ? ?
I thought ALL USB ports are powered...All USB ports are powered.

It is USB hubs that are powered or unpowered, with an AC adapter.

a hub requires this type of configuration because, by definition, it plugs into a single USB plug on the host machine, and is, itself, a USB device. each USB device is limited to drawing only (IIRC) 200mA of current from the USB connection.

Therefore, devices plugged into an unpowered USB hub would be required to "SHARE" the available current, in most cases, they end up having to require less then around 170mA, when added together. (because the Hub itself requires power for it's circuitry).

chances are, the Printer is designed to draw the full amount from the USB connection, 200mAs, and therefore requires a port capable of delivering it- a Powered USB hub, or any built-in connection on a PC - is capable if this.

The directions are specifically referring to USB hubs or the USB connections of CERTAIN devices whereby it would be unable to draw the full amount as allowed via the USB specification.Actually... no they're not.

There are low powered one, and then full powered. On my old tower, the front USB ports were low powered, so I couldn't charge my iPod with them. I had to plug it in from the rear in order to get it to charge.
All internal usb ports are powered on as soon as the system boots.Quote from: GRIFF on October 04, 2009, 11:12:58 AM

Actually... no they're not.

There are low powered one, and then full powered. On my old tower, the front USB ports were low powered, so I couldn't charge my iPod with them. I had to plug it in from the rear in order to get it to charge.

This is usually a manuf.'s budget speaking...it's not the rule of thumb.
Hang on...

Quote

Important You experience longer charging times when you use low-power 100-milliampere (mA) USB ports. USB ports that are located on the front of a COMPUTER or in some USB hubs are frequently low-power 100-mA ports. Typically, you can find high-power 500 mA USB ports on the back of the computer. Additionally, when you suspend the computer or put the computer to sleep, high-power USB ports may change to a low power 100 mA mode.

http://support.microsoft.com/kb/938069what cheap sub-standard components support has nothing to do with the specification but rather the fact that they don't adhere to it.

In such a case, sometimes the manufacturer cheaps out by only using a single front panel USB header, and having a small piece of circuitry act as a hub. In this case, the power of the front panel USB is reduced in the same way as would occur with a unpowered hub, that is, < 200 mA.

The actual Front panel header on a motherboard gives 200mA, which is the full power available via the specification.

In this case your iPod may simply not charge from the front panel due to another quirk. Many front panel USB connections on PCs are built to the USB 1.1 standard; the iPod may simply not support USB 1.1.

That being said, however, I imagine a printer would gain significantly... (in fact, it does, considering now my printer and it's performance now versus when I used it with USB 1.1) and so if it turns out that the front panel connections of the OP's computer are in fact USB 1.1, or if their PC manufacturer used a cheap "I'll use a cheap hub instead of a cheap USB header" technique, then the connections on the machines rear would be best.

In fact, considering the printer isn't likely to be often plugged/unplugged, it would probably best to plug it into the rear anyway, and save the front panel connections for things like USB drives.

EDIT: AHH yes, replace 200mA with 500mA in this and my previous posts, heh.

500mA is the standard requirement. Not meeting this standard- and not being a unpowered hub - means that it does not conform to USB (strictly speaking). However the front panel ports, as I've indicated are often implemented using a low cost USB hub, whose limitations I have outlined previously.
The charging of the iPod is more an issue of voltage than current. Unfortunately, many designers are unaware of the implications.
Charging Batteries Using USB PowerWow. Great thread on what at first seemed to be such a simple issue. Thanks to everyone involved, I've learned something today.

Solve : How can I tell if a USB port is powered or not? Thank you, I got an answer?

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