USB Fan Project - Need Help Bringing Voltage Down from 5volts to 3volts...

[techhappy]

So, this entire project was sunk from the beginning is what you're saying?

There is no way to get this to work with USB without burning out or causing damage to the usb port?

Ahhh, so this is complete waste of time then? I should scrap the project because it's not possible to run in a stable fashion?

 

[eblc1388]

So, this entire project was sunk from the beginning is what you're saying?

No. Its just the motor you are now using has exceeded the maximum current the USB port can supply.

Alternatively, I do remember seeing in shops USB powered lights, vacuum cleaner and fans or cup warmers etc. The secret is that they use a small motor that takes less current or they use a 5V rated motor so the current is only 0.4A.

So one can use a fan on USB, no doubt.

There is no way to get this to work with USB without burning out or causing damage to the usb port?!!

Not so. When current demand exceeds 0.5A, some manufacturers, like in the case of portable harddisks, uses two USB connectors in parallel to supply the extra current. But I doubt the current will share equally between the two connectors.

Ahhh, so this is complete waste of time then? I should scrap the project because it's not possible to run in a stable fashion?

Maybe you can try using a smaller motor or one that is rated for 6V so that it will take less current.

Also doesn't you now know how to measure current and to calculate resistor values? That would be a net gain in my opinion.

 

[techhappy]

Yeah, this has been an eye opener. Thanks for all the help, now that I know how to measure current an calculate resistor values, I did get something good out of it.

I only wished I knew this wouldn't work ahead of time, so I would have waited for a 5 volt fan of similar design. But on the flipside, now I know what to look for in the future, when I do these usb type mods.

Over and out..

 

[techhappy]

One last thought, what resistor was that guy using on the tutorials page that I posted in my first post about this project?

**broken link removed**

He claimed to have got it to work, using a resistor? 3 volt motor, same type of design initially.

Was he doing it the wrong way? Can it really cause damage to the usb system?

I found this article on a site discussing USB power and how it works:

Power Management

One special feature of USB systems is that they can directly supply power to the peripherals and the hubs attached to them. It can also regulate power usage for peripherals that use independent power sources. USB devices are classified based on the amount of power they supply or require. Low Bus Power devices take all their power from the bus, but no more than 100mA at a time. High bus-powered devices also take all their power from the bus, but can draw up to 500mA at a time. Self-powered devices use an external power supply, but can draw up to 1mA from the host if necessary--such as in the case of a power failure.

Hubs can also be low, high or self powered. Power flows downstream in a USB system, which means that a self-powered hub can be used to power high- and low-powered peripheral devices located further down in the network. This power arrangement has both advantages and disadvantages. For desktop systems where power is not a problem, it is extremely convenient not to have to use a separate outlet for each peripheral connected to the PC. In notebooks where battery longevity is often a problem, it might be more advantageous to use peripheral devices that have their own power source.

Any glimmers of hope? Or completely fully doomed? From the specs about USB, it seems like it would deny any requests more that 500mA. Wouldn't that effectively prevent current from overloading the usb port?

 

[eblc1388]

I only wished I knew this wouldn't work ahead of time, so I would have waited for a 5 volt fan of similar design.

Sorry, we cannot give the 100% confirmation that the project is doomed at the beginning because motors that take less than 0.5A at 3V are indeed available.

Its just the one you are using now isn't one of them.

 

[techhappy]

That's right, every motor is unique in it's current draw. Now I know better thanks to you guys. Well, I really do appreciate all the help and everyone's input in this project.

I'd be lying if I didn't say I wasn't a little disappointed, it seemed so close, so probable! But alas....I guess I can take a peak at 120 mm case fans and investigate my options there, hehe.

 

[Dr.EM]

Yeah, a 120mm case fan is a good option. Like I said, there are ones designed to run from 7v and these should work off of USBs 5v and will take under 500ma for sure. Not sure how much cooling it will provide though, but it should work.

 

[audioguru]

Did you notice that the measured current is higher when the rechargable battery was used? The rechargable battery has a lower voltage (2.4V) than the alkaline batteries so the current should be less.
It is because an AA alkaline battery cannot supply 900mA without its voltage dropping way down.
Which got hotter, the motor or the battery? Both.