For you really smart computer WIZZES

[chopperman]

Hey guys, I have a charger that needs a power supply, but What I am thinking is usning a usb cord, and hook it up to my computer and the other end goes to the charger. What I would like to know is, if the usb cord has positive and negaive parts to it so I can hook up the charger, thanks, and any ideas are welcomed

[pmackenzie]

The USB port has only 5 volts on it, and is only rated 100 ma.
Pinouts can be found here (http://www.starmount.co.uk/s_usbpin.htm) .
Pat Mackenzie

[chopperman]

is there a way where i can hook up 2 usb cords together to get 10 amp

[jperch]

Chopperman,
You might want to take another look at Pat's post. It says that a USB port can only provide 5V at 100mA. That is 0.1 amps. Even if it would work (which I don't recommend trying), you would need 100 of them in parallel to get 10 amps. Two just won't cut it.

Joe

[pmackenzie]

You could tap into the PC's power supply inside the computer. There are generally extra connectors for adding hard drives , fans etc. Both 12 volts and 5 volts are available.
A connector could be brought out through the case.
However if you don't know how to go about it, it is better to not mess with anything that is powered by line voltage, or anything more expensive than you are willing to "let the smoke" out of if you make a mistake.
Pat MacKenzie

[Zeta Phoenix]

If you use USB 2.0 ports on the computer you get 500ma, but that is no where near the 10A you are looking for. If you do decide to tap into the case, red is +5, black is gnd, and yellow is +12v.

-Jon

[clively]

One thing you might take a look at is:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2536

This chip is specifically built to charge LIPO from USB power sources; however you will still be limited to a 100ma or 500ma max depending on if your port is USB 1.0 or 2.0 compliant.

[jswjimmy]

If you use USB 2.0 ports on the computer you get 500ma, but that is no where near the 10A you are looking for. If you do decide to tap into the case, red is +5, black is gnd, and yellow is +12v.

-Jon
also the +12v (yellow) with the -5v (ground next to red or +5v) will give you 7v

[Afroman]

Pat's post is a misinterpretation of the data on that site. The USB spec allows for a total of 500mA to be drawn from the port. The figure of 100mA is the maximum allowed for USB external hub designers to use in their hubs. The reason for this is presumably so that cascading multiple USB hubs will not have a combined quiescent draw that would pop the USB ports. USB 1.0, 1.1 and 2.0 all have this 500mA limit.
USB.org has a lot more information if you search around (http://www.usb.org/developers/usbfaq/#pow1)

But yeah, basically like Pat was trying to say, there is no way on earth you are going to get the kind of current you want from USB.

[pmackenzie]

I saw the 500 ma listed, but I thought it was for an external hub, and that 100 ma would be more appropriate for a PC connection.
You are probably correct, but I would not trust the tiny wires going to the USB in my computer to provide much voltage at at 0.5 amp draw.
Pat Mackenzie

[westfw]

I think you're only allowed to draw 500mA from a USB port if you "negotiate"
that power draw. For a dumb peripheral, you should only draw 100mA (of
course, actually implementing hard and variable limits is pretty tough, so many
USB ports may provide 500mA whether or not you "negotiate."

[Eric Brouwer]

The USB gets their +5V from a dedicated USB supply inside the PC power supply. On my 350W power supply, it indicates that the USB +5V rail is rated at 1.2A. When this level is exceeded, V-USB drops. It also has some kind of current limiting circuit, as I made a mistake on a USB project, shorting out the supply via two PIC I/O pins. Although the chip got hot, there was not enough power to damage the chip itself.

[Munkey]

If you want you can buy an ATX power supply if your worried about frying your all computer gear they are relativly cheap, I got one for 30bucks austrailian and i use it to charge my gear. Heres how you do it: