Change power output?

[Cliff Karlsson]

I have a small waterpump that runs on 12v max. I want to be able to change the power to the pump from 3v up to 12v. I have a 12v power supply. Do I use mosfets, transistor or other componet? And could someone show me how to connect the parts and show a small example code of how to change the voltage output from the arduino?

[sundberg84]

Depending on which arduino you run you can connect 12V to RAW pin and the internal voltage converter will fix the rest for you... or i might have missunderstood the question?

[rvendrame]

Just to add my two cents, the cheap pro mini clones that I bought didn't went well with 12V on raw pin, as 12V is the absolute maximum on their regulators. Some of them simply burned after some minutes , some got installable.

To be on safe side, I don't put more than 9V on raw. You can use a 7809 for example to get 9V out of original 12V

[Cliff Karlsson]

I probably explayned bad. I want to be able to set the voltage to the pump to values between 3v and 12v. Like 5v, 7v and similar to have the pump run at different speeds.

But I just realised that what I am asking is exactly like the dimmer sketch. Led dimmer

[Oitzu]

@Cliff-Karlsson said:

I probably explayned bad. I want to be able to set the voltage to the pump to values between 3v and 12v. Like 5v, 7v and similar to have the pump run at different speeds.

But I just realised that what I am asking is exactly like the dimmer sketch. Led dimmer

I'm not sure if it is save to use this circuit to control a pump.
The circuit is designed for resistive loads like LEDs but a pump (electric motor) is a inductive load probably killing the mosfet while turning off.
There are special IC's for this situations called motor drivers.
Maybe have a look at this:
http://www.instructables.com/id/Arduino-Modules-L298N-Dual-H-Bridge-Motor-Controll/

[Cliff Karlsson]

@Oitzu said:

The circuit is designed for resistive loads like LEDs but a pump (electric motor) is a inductive load probably killing the mosfet while turning off.

Ok, but it is a really small pump. Does this matter? Pump

[peka]

Using an H-bridge can indicate that you want to reverse your engine. I guess that's not the case with the water pump?
The easy (quick and dirty) solution is to use a FET like in the "LED dimmer". But you should probably add a fly-back diode because of the inductive load.
Proposed solution depends on how robust you want it to be.

[Cliff Karlsson]

thanks for the answer, I don't really know what a fly-back diode is or have any non-light diodes at home right now. I have a couple of
optocouplers, mosfets and transistors lying around. Can I use any combination of those components to control the pump?

[Oitzu]

@Cliff-Karlsson said:

thanks for the answer, I don't really know what a fly-back diode is or have any non-light diodes at home right now. I have a couple of
optocouplers, mosfets and transistors lying around. Can I use any combination of those components to control the pump?

At this small pump a mosfet will probably also work yes. To the fly-back diode:
As you may already know a diode only conducts in one direction.
And you may also know that a electric motor can also be used as an generator.

When powering off the motor the motor will be act for a short time as "generator" due to the momentum and the stored energy in the magnetic field.

The diode will be connected between the mosfet and the motor to prevent flow of current back to the mosfet in this event.