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I have always wondered what is in a USB cable. I learned that it transfers data in and out. Another thing I learned it that the USB cable also provides current electricity. This fact led me to try to convert a cheap (cost about $2) hand-held battery-operated fan to a USB-powered fan.

There are lots of USB-powered fan out there in the market. This project does not save one's money. Personally, It is just a hobby and learning journey for me. So in that spirit, let us start.

Step 1: Materials and Tools

With electrical projects, chances are that soldering is involved. I do not have a soldering iron nor the skill to operate them. So I found alternative ways to soldering.

Gather the following materials:

  1. 1 x Battery operated fan powered by 2 AA batteries (It cost me about $2. Batteries not included)
  2. 6 x wire connector (Refer to picture. This wire connectors enabled me to avoid soldering)
  3. 4 x 10 Ohms Resistor
  4. 1 x USB cable (I used a 2m cable. You can choose any length)

Gather the following tools:

  1. Scissors
  2. Wire Stripper
  3. Screw Driver

Step 2: Calculate Current and Voltage

The following questions need to be answered:

  1. How much voltage does the fan need?
  2. How much current does the fan require?
  3. How much voltage does a USB host supply?
  4. What is the maximum current does a USB host supply?

Answer to Question 1

The fan was built to be powered by 2 AA batteries. One AA battery has an EMF of about 1.5V. So these facts suggest that the motor requires 3 volts.

Answer to Question 2

The answer to this question required that I used a multimeter to measure the current when the fan is supplied with 3v. So I measured the current to be about 500 mA to 600 mA.

Answer to Question 3

Research using google and wikipedia suggest that USB has a potential difference of 5v

Answer to Question 4

I googled and found out: It depends. It ranges from 100mA to 2A.

Conclusions

When the fan, rated at 3v, is applied with a 5v potential difference supplied by the USB host, then overvoltage will result. Basically 5V source supplies too much current to the fan. To counter the overvoltage, the circuit must then have another component that will used up the excess 2v so that the fan will receive a proper 3v supply. That component is resistors. So that's why I needed resistors for this project.

How much resistors?

I calculated using Ohms law, Voltage = Current X Resistance

Therefore Resistance = Voltage / Current

Current required by fan= 500mA or 0.5A (I measured the current to be between 500mA to 600mA at 3 volts)

Voltage drop by resistor = 2V (Because the fan was built to be operated at 3 volts : 2 x AA batteries in series)

Resistance = 2 / 0.5 = 4 Ohms

So I needed a resistor rated at 4 Ohms. The closest I can get is a 10 Ohms resistor.

How to convert 10 Ohms resistor to 4 Ohms resistor?

Back to school again. In principle, connecting a bunch of resistor in parallel formation will decrease the circuit's total resistance. So I calculated 2 or 3 of the 10 Ohms resistors connected in parallel will result in the circuit having 5 Ohms or 3.3 Ohms. I shall initially use three resistors as that comes closest to 4 Ohms. Later, I will try with four resistors.

Warning

Resistors alone may not be enough to protect your computer that is supplying the USB power from harm. Please be aware of the risk that you are taking. There is another instructable dealing with a motor where some people suggested:

"......protection diode will help, but you really should have a 1/2A (or less) fuse to protect the port."

I shall not be held responsible for any damage resulting.

Step 3: Setup Up the Resistor

The materials needed in this step:

  1. 3 x 10 Ohms resistor
  2. 4 x Wire connectors
  3. 2 x wire

The tools needed in this step:

  1. Screw driver
  2. Wire Stripper

Do the following:

  1. Get 2 resistors and a wire connector
  2. Strip the ends of the wire to expose the metal core
  3. Connect one end of a resistor leg to the connector's slot and screw tight.
  4. Connect the second resistor to the empty slot of the same connector in #2.
  5. Connect the free legs of the 2 resistors with another connector
  6. Compare your setup with the one shown in the video.
  7. Get 2 wire connector and 1 resistor
  8. Connect the resistor's 2 legs to each slot of the wire connector
  9. Compare your setup with the second video
  10. Get 2 pieces of wire.
  11. Connect the 2 pieces of wire to the connector as shown in the video.
  12. Measure the resistance using multimeter as show in the video if you desire. (I measured 3.6 Ohms.)
  13. You have created a resistor component rated at between 3.3 to 3.6 Ohms

Step 4: Modify the Fan

You need the following materials:

  1. 1 x Battery-Operated Fan
  2. 2 X pieces of wire

You need the follwing tools:

  1. Screw driver
  2. Wire Stripper

Do the following steps:

  1. Strip both ends of the 2 wires to expose some metal
  2. Open up the fan using screw drive or using any tool you deem fit for your situation
  3. Connect one wire to one side of the battery terminal
  4. Connect second wire to the other side of the battery terminal
  5. Compare your setup with the video attached.
  6. Connect one of the two wires connected to the fan in #3 or #4 to the resistor component that was completed in previous step.
  7. Compare your setup with the second video attached.

Step 5: Setup the USB Cable

You need the following materials:

1 x USB Cable

2 x Wire Connector

You need the following tools:

Wire stripper

Do the following:

  1. Position wire stripper at the end closest to the USB type B connector.
  2. Cut the USB type B connector
  3. Strip off the insulator
  4. Observe that there are 4 wires as shown in the video: Red, Brown, White and Green
  5. Cur the green and white wire (because these are data wires and not needed in this project)
  6. Strip the red wire to expose some metal
  7. Strip the brown wire to expose some metal
  8. Compare the USB cable with the one in the second embedded video
  9. Connect the exposed metal of the 2 USB wires with 2 wIre connector as shown here.

Step 6: USB Cable and Fan

You need the following materials:

  1. The fan and resistor component completed in the previous step
  2. The USB cable completed in the previous step
  3. 3 x wire of different colour with metal exposed at both ends

You need the following tools:

  1. Screwdriver
  2. Wire Stripper

Do the following:

  1. Connect 1 wire to the resistor component as shown.
  2. Connect the wire in #1 to the wire connector of USB that joins with the red wire as shown.
  3. Connect the blue wire of the fan to the free slot in wire connector of the USB as shown.
  4. Connect the USB cable to a USB host (This can be a PC) or a Wall-outlet USB Charger.
  5. Switch on the fan
  6. Observe the fan turnin
  7. Optional: Measure the voltage of the fan. (I measured the voltage and it showed 2.74 volts)
  8. You have successfully transformed battery-powered fan to USB-powered fan

Optional:

I added one more resistor to make it 4 resistors in parallel as shown in the video embedded in the introduction page. This has the effect of lowering resistance in the circuit and thereby increasing the current. I measure the voltage of the fan and found it to be 3 volts. In my opinion, 3 volts hitting the fan is within acceptable range and it turns slightly faster.

I love converting stuff to usb. great explanation on the electical calcs. very sound and correct.
<p>Awesome. USB powered things are so much more useful for the office so you don't have to keep replacing the batteries!</p>

About This Instructable

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Bio: Systems Administrator and Software Programmer.
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