DaRk_dOg
Posts: 4
Joined: Wed Apr 18, 2018 3:39 pm

Noob case modding

Wed Apr 18, 2018 4:01 pm

Hello everyone,

I just got my new Raspberry Pi 3 B+ and I'm really happy with it however... I want to make a modded case to serve two basic purposes: Air intake AND looks for my desk.
For that I need to use an external 120mm fan + an on/off LED switch. The switch I chose is a typical momentary reset 5v button, but the fan is 12v/0,35A/4.2W so the idea is to connect a step-up module from the 5V of the Raspberry to reach the 12V (or less to make it run slower) of the fan.

Can it be done or I will fry the raspberry, the desk, the neighborhood and my whole dignity? :lol:


Best Regards.

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Imperf3kt
Posts: 758
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Noob case modding

Wed Apr 18, 2018 11:25 pm

Many 12v computer fans will happily run on 5v or even less. Some, however, will not start below a certain voltage (they run fine once spinning)

Try just plugging it in and see if it works.
Stephen Hawking, rest in peace.
8 January 1942 – 14 March 2018

DaRk_dOg
Posts: 4
Joined: Wed Apr 18, 2018 3:39 pm

Re: Noob case modding

Thu Apr 19, 2018 6:05 am

Imperf3kt wrote:
Wed Apr 18, 2018 11:25 pm
Many 12v computer fans will happily run on 5v or even less. Some, however, will not start below a certain voltage (they run fine once spinning)

Try just plugging it in and see if it works.
Thank you for your reply,

I guess I'm worried of overdrawing current from the board, and if the LED fan will start anyways... I guess i'll know once I try.

Thanks again for the info :)


Best Regards.

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Imperf3kt
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Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Noob case modding

Thu Apr 19, 2018 8:13 am

If the fan tries to draw too much current, your Pi will simply crash. Usually, not a big problem (during boot)
At 5v though, it shouldn't draw too much. As long as you have a decent power supply and cable and don't plug in a hundred devices (or a large-drain device such as a mechanical HDD without its own power supply) you should be fine.
Stephen Hawking, rest in peace.
8 January 1942 – 14 March 2018

DaRk_dOg
Posts: 4
Joined: Wed Apr 18, 2018 3:39 pm

Re: Noob case modding

Thu Apr 19, 2018 10:12 am

Imperf3kt wrote:
Thu Apr 19, 2018 8:13 am
If the fan tries to draw too much current, your Pi will simply crash. Usually, not a big problem (during boot)
At 5v though, it shouldn't draw too much. As long as you have a decent power supply and cable and don't plug in a hundred devices (or a large-drain device such as a mechanical HDD without its own power supply) you should be fine.
Well the main idea is to:

-Power the fan (12V but will try to make it run in 9v or less through a DC-to-DC step up module, 5v seems too low for the LEDs)
-Use a power button (5v)
-And maybe use a spare 120GB ssd I have, as the boot source (through usb to sata cable)

My power supply is the official universal power supply.

The backup plan if the above fail, is just to use the power button and a typical 30mm pi-fan.

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Imperf3kt
Posts: 758
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Noob case modding

Fri Apr 20, 2018 12:23 am

Converting 5v to 12v will take too much current.

LEDs typically operate between 1.85v and 3.3v. To run from 12v they're probably just four white LEDs in series or they have a resistor connected to vcc
Stephen Hawking, rest in peace.
8 January 1942 – 14 March 2018

DaRk_dOg
Posts: 4
Joined: Wed Apr 18, 2018 3:39 pm

Re: Noob case modding

Fri Apr 20, 2018 6:07 am

Imperf3kt wrote:
Fri Apr 20, 2018 12:23 am
Converting 5v to 12v will take too much current.

LEDs typically operate between 1.85v and 3.3v. To run from 12v they're probably just four white LEDs in series or they have a resistor connected to vcc
I did not think about the current, you are right. I'll try to use the fan on 5v and see from there.

Thanks for the info!

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