# help on current source

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#### inconcessus

##### New Member
hi my supervisor just gave me a new project. he wants me to run a cooling fan using current source. how do i do it??

#### ccurtis

##### Well-Known Member
Connect current source to fan. Viola!

#### inconcessus

##### New Member
yes thats what i think too but i dont believe it is so easy.. im waiting for the fan to come and see what he say brb

#### inconcessus

##### New Member
erm i need to draw out a diagram how do i draw? just draw a source and a fan?

#### audioguru

##### Well-Known Member
If the fan has a DC motor then it should be powered from a voltage source, not a current source.

The motor needs a high current to start running and a lower current when it is up to speed. A current source with a current high enough to start the motor will supply too much voltage and current when the motor is up to speed.
With a voltage source the motor will start and the speed is adjusted by the voltage.

#### crutschow

##### Well-Known Member
What is the current source?

#### ccurtis

##### Well-Known Member
Every voltage source has an equivalent current source and every current source has an equivalent voltage source.

As the load is increased (such as when the motor starts), the voltage across the load will fall, whether the load is driven by a current source, or a voltage source -- unless the sources are ideal (and no real-world source is ideal).

#### inconcessus

##### New Member
can you help draw the circuit diagram for it?

#### audioguru

##### Well-Known Member
A voltage source (a voltage regulator) will have a constant voltage when the motor starts. The voltage will drop only 10mV which is nothing.

If it is a current source then the voltage will fall very far when the motor starts and when the current is set for the motor running. Then maybe the motor will not start.

#### ccurtis

##### Well-Known Member
can you help draw the circuit diagram for it?
The two sources below are equivalent. One is a current source, the other is the equivalent voltage source.

#### ccurtis

##### Well-Known Member
Incon, you say nothing about your current source. If it is a regulated current source, the equivalence does not follow.

#### inconcessus

##### New Member
ill ask my supervisor when hes back
thanks guys.

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