Tapping power from a USB port?, and multimeter questions

[NoahsMyBro]

There are countless gadgets that serve no useful purpose, yet draw power from USB ports to do something. ( http://www.thinkgeek.com/gadgets/lights/7825/ )

These gadgets don't have any meaningful connection to or interaction with a computer they are attached to, they only use the USB port as a power source.

I have a 92mm internal PC case fan with a 3-pin fan connector, and also an adapter cable to plug the fan's 3-pin connector in to a standard molex 4-pin connector (like what you plug in to desktop hard drives or optical drives.

I *WANT* to fabricate a wire that would connect to the fan on one end, and plug into a standard USB port at the other end, to supply power to the fan.

This seems to me like it should be simple. BUT, a couple of nights ago I cut off the end of a standard USB cable, and attached the red & balck wires from the USB cable to the red & black wires on the fan. I plugged the USB end into the sole USB port on the back of a very old laptop, and of course the fan did not power up. I then tested the wires with my multimeter, and no power was on the line. In hindsight, I probably was testing the line improperly.

Surprisingly to me, I can only find one hit via Google for a cable that does what I'm talking about - http://groovygamegear.com/webstore/i...roducts_id=299

Questions:
1) Has anybody heard of GroovyGameGear.com ?
2) Does anybody know how I could make a cable like this myself?
3) How could I test the cable for the presence of power? I should be able to draw the 5v from the USB jack. I believe it's 500milliamps, but I'm not sure.

My multimeter has two separate pair of jacks to connect the probes, and did not come with any substantive instructions, so I've always sort of muddled through figuring things out as I go, and I really have no idea when/why/how to use one of the pairs of probe jacks. The pair of jacks I ordinarily use to test voltage are labelled with a + & -, with a lightning bolt between the two. Of the other two jacks, one is labelled 10A, and states 'Unfused' below it. The other is labelled AΩ. Between the two is the warning '10A MAX'.

The multimeter has ranges for AC-V (voltage), DC-V (voltage), AC-A (assuming amps), DC-A (again, assuming amps), hFE (transistor testing I think), OHMS, and 'F'.

As stated above, I don't know how or when to use the probe inputs labelled 10A and AΩ. I also don't know what the 'F' range is for. It's values are labelled with the 'micro' symbol or a lower-case n.

Thanks for any info that may help.

[selfdestroyer]

I found the information below .. might be usefull.. I know you can build a upconverter with a transformer to up the voltage.

USB powered devices

The USB connector provides a single 5 volt wire from which connected USB devices may power themselves. A given segment of the bus is specified to deliver up to 500 mA. This is often enough to power several devices, although this budget must be shared among all devices downstream of an unpowered hub. A bus-powered device may use as much of that power as allowed by the port it is plugged into. Bus-powered hubs can continue to distribute the bus provided power to connected devices but the USB specification only allows for a single level of bus-powered devices from a bus-powered hub. This disallows connection of a bus-powered hub to another bus-powered hub. Many hubs include external power supplies which will power devices connected through them without taking power from the bus. Devices that need more than 500 mA or higher than 5 volts must provide their own power. When USB devices (including hubs) are first connected they are interrogated by the host controller, which enquires of each their maximum power requirements. However, seems that any load connected to USB port may be treated by operating system as device. The host operating system typically keeps track of the power requirements of the USB network and may warn the computer"s operator when a given segment requires more power than is available and may shut down devices in order to keep power consumption within the available resource.
USB power usage:

Bus-powered hubs: Draw Max 100 mA at power up and 500 mA normally.
Self-powered hubs: Draw Max 100 mA, must supply 500 mA to each port.
Low power, bus-powered functions: Draw Max 100 mA.
High power, bus-powered functions: Self-powered hubs: Draw Max 100 mA, must supply 500 mA to each port.
Self-powered functions: Draw Max 100 mA.
Suspended device: Max 0.5 mA
USB voltage:

Supplied voltage by a host or a powered hub ports is between 4.75 V and 5.25 V. Maximum voltage drop for bus-powered hubs is 0.35 V from its host or hub to the hubs output port. All hubs and functions must be able to send configuration data at 4.4 V, but only low-power functions need to be working at this voltage. Normal operational voltage for functions is minimum 4.75 V.

[izarate]

I have a 92mm internal PC case fan with a 3-pin fan connector, and also an adapter cable to plug the fan's 3-pin connector in to a standard molex 4-pin connector (like what you plug in to desktop hard drives or optical drives.

I *WANT* to fabricate a wire that would connect to the fan on one end, and plug into a standard USB port at the other end, to supply power to the fan.

This seems to me like it should be simple. BUT, a couple of nights ago I cut off the end of a standard USB cable, and attached the red & balck wires from the USB cable to the red & black wires on the fan. I plugged the USB end into the sole USB port on the back of a very old laptop, and of course the fan did not power up. I then tested the wires with my multimeter, and no power was on the line. In hindsight, I probably was testing the line improperly.

Well, the thing is that most PC fans draw between 1.5w and 2.5w of current from the 12V rail (most fans have this info in the package or in the manufacturer's site), so the 5V aren't even enough to get the fan started and even if it was a 5V fan, the 500mA would make it run very slow or not at all.

Surprisingly to me, I can only find one hit via Google for a cable that does what I'm talking about - http://groovygamegear.com/webstore/i...roducts_id=299

Questions:
1) Has anybody heard of GroovyGameGear.com ?
2) Does anybody know how I could make a cable like this myself?
3) How could I test the cable for the presence of power? I should be able to draw the 5v from the USB jack. I believe it's 500milliamps, but I'm not sure.

1) No
2) The one you made surely works, but the current and voltage aren't enough for the fan.
3) With a multimeter

My multimeter has two separate pair of jacks to connect the probes, and did not come with any substantive instructions, so I've always sort of muddled through figuring things out as I go, and I really have no idea when/why/how to use one of the pairs of probe jacks. The pair of jacks I ordinarily use to test voltage are labelled with a + & -, with a lightning bolt between the two. Of the other two jacks, one is labelled 10A, and states 'Unfused' below it. The other is labelled AΩ. Between the two is the warning '10A MAX'.

The multimeter has ranges for AC-V (voltage), DC-V (voltage), AC-A (assuming amps), DC-A (again, assuming amps), hFE (transistor testing I think), OHMS, and 'F'.

As stated above, I don't know how or when to use the probe inputs labelled 10A and AΩ. I also don't know what the 'F' range is for. It's values are labelled with the 'micro' symbol or a lower-case n.

Thanks for any info that may help.

Most likely you'll never have to use the unfused connection. I don't have my manual so I can't tell you exactly what is it for but I've been using it for 2 years now and never had to use said connection.

The "F" is for capacitor testing, most likely. F is the symbol for Farads and most capacitors are in the uF and nF ranges, which seem to match your findings. I'd like my multimeter to do that.

[NoahsMyBro]

Well, the thing is that most PC fans draw between 1.5w and 2.5w of current from the 12V rail (most fans have this info in the package or in the manufacturer's site), so the 5V aren't even enough to get the fan started and even if it was a 5V fan, the 500mA would make it run very slow or not at all.

The label on my fan states:
12VDC
0.20A
2.4W

Looks like you're right, and my idea won't work.

Most likely you'll never have to use the unfused connection. I don't have my manual so I can't tell you exactly what is it for but I've been using it for 2 years now and never had to use said connection.

The "F" is for capacitor testing, most likely. F is the symbol for Farads and most capacitors are in the uF and nF ranges, which seem to match your findings. I'd like my multimeter to do that.

Thanks for the addl. information. I think my multimeter is a pretty nice one; I wish I knew more and could make better use of it, so I appreciate your taking the time to write the above.