Forum Thread: Raspberry Accessories

So im gonna buy a raspberry pi 2 model b
So I know that the power supply is 5v 2a.. so

  1. Ive seen that that the fan or other things are 12v.. so they wont work??
  2. If not.. then how many 5v accessories can I plug in??

11 Responses

The 12v fans run at 5v will spin alot slower then if fully powered at 12v.

I don't own a pi but would assume you can use a 12v power supply as long as it has the amperage to support it. I may be wrong though.

I use pc fans/led lights/etc I have spliced directly to 12v random power supplies with 0 issues for various projects. You just need to do some reading I guess.

I have a large duffle bag full of power supplies and cordage collected over time. You can pick up power supplies from a thrift store for a 1$

I have the same, although mine is a box full of them. :D

future electrician here, you're wrong indeed.

there is a law in electrical engineering, called Ohm's law, that says: R = U/I. which means: resistance equals electrical voltage divided by current. the raspberry pi's resistance is made that it delivers 200mA at 5V. if you are going to put 12V on the Pi without adding an extra resistor, there will be too much current flowing through the Pi, because the resistance is too low. which will lead to the Pi being overloaded.

you can, however, add a resistor inbetween the 12V power supply and the raspberry pi, to "increase" the Pi's resistance. if you have a resistor big enough, you can even hook up the Pi to a 300.000V DC line!

here is a schematic of a power supply i made myself for the raspberry pi. you plug it in a 230V AC outlet and it outputs a super-stable 5V DC. here is how it works:

first, it transforms the 230V AC to 12V AC using a transformer. then, the 12V AC is converted to DC using 4 diodes. the electricity is now DC, but it is still unstable (it goes from 12V to 0V 50 times a second), so i added 2 capacitors with a capacity of 1000µF (farads) to store this electricity, so it will always remain a stable 12V. then finally, i added the 7805 voltage regulator to convert the 12V DC to a super-stable 5V DC.

EDIT: since the Raspberry is popular on Null-Byte nowadays, do you guys think i should make a post about this power supply?

-Phoenix750

Yea I studied that 2 years ago lol.. ohms law is R = V/I I think... cause U is potential energy I think...

Well anyway thnx!! Ill just hook up a 5v fan...

But now the question that remains is..can I hook up 2 fans of 5v or a fan of 5v and something else of 5v or less??

U is electrical voltage, I is current, R is resistance.

you can hook up as many fans as you can. but keep in mind that when you are connecting a fan that is under 5V to a 5V pin, that you use the right resistor to prevent any damage.

now i am just wondering, if you already knew what Ohm's law was, you could've answered your own question easily, could you? no offence, it just caught my attention.

-Phoenix750

Idk but I studied voltage as V haha...

I just learnt it for exams you know.. never really had any applications... I mean most of stuff we study.. 0 use I must say..

EDIT - BTW IT SAYS V FOR VOLTAGE ON WIKIPEDIA TOO ;);)

nope. V is the abbreviation of "Volt", which is the UNIT in what electrical voltage is expressed. the symbol for electrical voltage itself is U

U = the SYMBOL of electrical voltage.
V = the abbreviation of the UNIT "Volt", in which electrical voltage is expressed.

it is like the symbol for electrical current being I, but is expressed with the abbreviation of Ampére, A. and Resistance has the symbol of R, but is expressed with the Omega token, which somehow is an abbreviation of Ohm.

a more correct name for U would be "electrical tension", but i preffer saying Electrical Voltage.

-Phoenix750

I'd appreciate a knowledge-able post about the Pi, including the Power supply.

But wont using a 12v power supply spark the board??

And question 2??

not if you increase the resistance of your Pi by adding a resistor to it.

-Phoenix750

Ok thanks!!!

And question 2??

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