5V for raspberry pi from 12V power supply

[jnesselrotte]

So due to my limited electronics knowledge, I need some help. I want to add my raspberry pi under my 3d printer for Botqueue. I want it to be powered from the power supply that's also mounted under my printer. I'm not overly sure what components I need but I do have some minor specifications:

• I currently have a molex power connector that I was going to try to use.
• No modification to the raspberry pi. (Although if it needs to attach to the pins instead of the USB port to handle proper shutdown, that's okay)
• Handle shutdown on power removal.

I don't know how difficult or expensive this would be. I can cut off the molex connector and solder the connectors directly onto a board if need be. Also, how much in amps does a raspberry pi usually handle? I think I have around 5 amps left over after the heated bed and extruder. My main concern is that something weird like turning on the heated bed would turn of the raspberry pi.

So all in all, I have no idea what I'm doing and would like some help on it.

Thanks,

Justin Nesselrotte

P.S. I can't buy you a beer.

[Paul Bonser]

Since it is powered over USB usually, it shouldn't draw more than 500mA.

You could use a simple 7805 to drop your voltage or you could get a cheap switching regulator. There are some cheap adjustable ones on Ebay for like $2 each.

Or you could get an auto-style 12v socket and a USB car phone charger. With that you could just use a standard USB cable to provide your power and just wire the 12v socket straight to your supply.

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[dan...@austin.rr.com]

Switching reg. The 7805 could easily overheat in this duty. 500mA=3.5W of heat. I have some of these regs.

There will be no provisions for shut-down. You cut power, it's off. Generally this doesn't create a problem, it's not a mechanical hard disk, but write errors to the flash disk can occur. There is no easy way to gracefully shut down the system. Well really you're not likely gonna intentionally cut power while the Pi is doing an op that writes to the disk.

The power supply should NOT cut out when you pull 5A.

Danny

---- Paul Bonser <mist...@gmail.com> wrote:
> Since it is powered over USB usually, it shouldn't draw more than 500mA.
>
> You could use a simple 7805 to drop your voltage or you could get a cheap
> switching regulator. There are some cheap adjustable ones on Ebay for like
> $2 each.
>
> Or you could get an auto-style 12v socket and a USB car phone charger. With
> that you could just use a standard USB cable to provide your power and just
> wire the 12v socket straight to your supply.
> On May 27, 2013 11:14 PM, "jnesselrotte" <graph...@gmail.com> wrote:
>
> > So due to my limited electronics knowledge, I need some help. I want to

> > add my raspberry pi under my 3d printer for Botqueue <http://Botqueue.com>.
> > I want it to be powered from the power supply<http://www.lulzbot.com/?q=products/12vdc-20a-240w-power-supply> that's

> > also mounted under my printer. I'm not overly sure what components I need
> > but I do have some minor specifications:
> >
> >

> > - I currently have a molex power connector that I was going to try to
> > use.
> > - No modification to the raspberry pi. (Although if it needs to attach

> > to the pins instead of the USB port to handle proper shutdown, that's okay)

> > - Handle shutdown on power removal.

[dan...@austin.rr.com]

[Hans L]

The quick lazy solution is to just wire a cheapo car to usb charger to your 12v power supply.

[Riley]

yeah I'll second (third?) that suggestion. you can organ donor a dollar store cigarette lighter to usb adapter for the 5v switching regulator on a tiny pcb

[Erik Olson]

For Raspberry Pi, make sure your USB charger is rated to output 700 mA or better. I have seen glitches while using supplies rated at 500 mA. Such as, host USB bus can't reliably power a keyboard. (I know, you're supposed to get a powered hub for USB, but it ruins the form factor.)

My preferred AC adapter is actually a BlackBerry 700 mA charger.  I have the original Raspberry Pi B.

[John Dolecek]

I've had good luck with the iPhone charging bricks and a spare micro USB cable. I know we have a ton of them floating around the house and they're 1000mA IIRC. I've run the Pi with USB wireless keyboard/mouse dongle and wifi dongle on it without problems. This is on the Pi with ethernet. I don't remember which model that is.

JTD

--

[graphmastur]

Model B is the Ethernet one. I wanted a power supply that could run Wi-Fi, so I'll probably get a 1A supply if possible.

[Tom Davidson]

Discount Electronics sells a ciglighter - USB adaptor with 2 ports rated at 2.1A, It's a single switching converter. 

There is also a 2 port 1.2 and 2.3A model that has 2 DC-DC converters in it, it's much binger and of course costs more.

DE on I35 past Hester's Crossing in RoundRock and on Anderson near Lamar.

[Akarsh Simha]

In general, if one wants to convert a 12V supply down to 5V, what is a
good solution? I've used 7805 in the past to convert 15V down to 5V.
Surprisingly enough, it is rated for that, but it throws out an awful
lot of heat. I put a bunch of aluminum wrap as a heat sink and it does
prevent the 7805 from melting, so to speak, and everything works fine.
I'm faced with this issue once again, and I'm wondering what the best
way to do it might be. Maybe some sort of buck convertor?

Regards
Akarsh

[Jerry Rutherford]

The 7805 comes in a variety of flavors... 500mA, 1A, and a 3A version. How much power do you need?

If you use the 7805 with a 12v supply... it should run just fine... but be sure to have a good sized capacitor on the input as well as the output so that the chip won't have to work as hard to filter out the spikes and ripples. Something around 470uf 35V for the input would work... larger if you have it. If you don't want to use the 7805 you could also look into using a Zenner diode.

Here is an example of another chip... the LM323K... poor Engrish... but you should get the idea...
http://pictureofgoodelectroniccircuit.blogspot.com/2012/11/circuit-regulator-lm323k.html

Here is another variant... they are taking 220VAC and dropping it to 9VDC then regulating it... but the circuit would work just as well with a 12VDC input... just build from the full wave bridge rectifier outward... you won't need the rectifier or anything left of it. If you wanted to do this with a 120VAC input... you could buy 120VAC to 9VAC transformer and then everything from the transformer out would be the same.

Askjerry... everyone else does.
Visit me online at http://askjerry.info
See my projects, video links, tutorials, and blog today.

Akarsh

[Danny Miller]

Just get a cheap buck converter:

http://www.ebay.com/itm/1pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/251066005460?pt=LH_DefaultDomain_0&hash=item3a74b337d4

They're amazingly cheap, and live up to their specs.

Pretty low quiescent current (they don't drain the batt unless a load is
using it). They're very efficient- and hella cheap.

Danny