obarthelemy
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Re: 1 PSU to rule them all ?

Tue Sep 20, 2011 4:57 pm

MMmmm dumb question (I'm Sales, okayyyyyy)

My ADSL box, my external hard drives, and my soon-to-be Raspi both take 12V. Assuming I get a powerful enough PSU, can I get just 1 PSU for them all and hack together a Y (well more than Y, 4 to 1 since I have 2 HDs) passive cable ?

I have no clue if there's a risk of feedback during normal operation and/or connect/disconnect.

ShiftPlusOne
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Re: 1 PSU to rule them all ?

Tue Sep 20, 2011 5:10 pm

I don't see why not. As long as you don't get anywhere near the current rating. I am not 100% sure though.

doobedoobedo
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Re: 1 PSU to rule them all ?

Tue Sep 20, 2011 7:36 pm

Just about any ATX PSU will happily supply enough current at 12V for all those things. I use an old one I had kicking around to power all sorts of things.

jamesh
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Re: 1 PSU to rule them all ?

Tue Sep 20, 2011 9:18 pm

Good idea on the ATX PSU. Never thought of that, but a relatively cheap source of voltage I reckon. Lots of dead PC's out there with still working power supplies. Perhaps we should sell a molex to Pi converter cable. The I could mount one or more in standard desktop case....along with what'a already in their of course.

Hmmm.
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Re: 1 PSU to rule them all ?

Tue Sep 20, 2011 9:28 pm

Quote from jamesh on September 20, 2011, 22:18
Good idea on the ATX PSU. Never thought of that, but a relatively cheap source of voltage I reckon. Lots of dead PC's out there with still working power supplies. Perhaps we should sell a molex to Pi converter cable. The I could mount one or more in standard desktop case....along with what'a already in their of course.

Hmmm.
+1 to that idea from me :)

obarthelemy
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Re: 1 PSU to rule them all ?

Tue Sep 20, 2011 9:28 pm

a bratxble ? Sounds nice ^^

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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 4:38 am

An ATX PSU has 12v and 5v rails so you are covered no matter what they decide. Just be carefull as the 5v rail is the one that usually fails. You could easily power at least one RasPi per power connector.

Two devices off a wall wart, through a "Y" connector would be OK I would not risk more than that as Surges from the devices might cause problems. If you want to power more than than a couple of devices I would look to some sort of distribution board. I say this as I tried running an ADSL modem and a wireless router from a power 150watt power supply on 1 connector. Even though the connector was rated over the amperage drawn, and the power supply had more than enough overhead, I still had errors that I eventually tracked down to surge current. The problem was using a "Y" connector. When the devices were moved to separate molex connectors the problems disappeared. Of course each of these devices drew a lot more than a RasPI does. Each was rated at 1 amp apiece or 12 watts.

one drawback is that an ATX power supply uses an aweful lot of energy just idling. Way worse than a wall wart.
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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 11:10 am

ATX power supplies also have a minimum load on the 5V line, so if you use only the 12v you will need to add a power-wasting resistor on the 5v line.
http://vincentsanders.blogspot.....nized.html is about using an ATX supply as a 12v power supply. (found via planet.debian.org)

doobedoobedo
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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 12:39 pm

Quote from Blars on September 21, 2011, 12:10
ATX power supplies also have a minimum load on the 5V line, so if you use only the 12v you will need to add a power-wasting resistor on the 5v line.
http://vincentsanders.blogspot.....nized.html is about using an ATX supply as a 12v power supply. (found via planet.debian.org)I couldn't see that in the spec. I've never had any problems in that regard. The spec does say:
ATX / ATX12V Power Supply Design Guide
3.4.3. No-load Operation
No damage or hazardous condition should occur with all the DC output connectors
disconnected from the load. The power supply may latch into the shutdown state.This might also be useful for any who want to use an ATX supply for whatever. Although I think it would be complete overkill just to run a raspi.

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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 2:26 pm

Crossposting from the Bramble thread, srarthur had the awesome idea of using guitar effects pedal power daisy chains as a potential power source:

Quote from srarthur on September 15, 2011, 19:14
Would something like a Guitar effects power chain / snake not do the job?
Similar to:
http://www.amazon.co.uk/Power-.....038;sr=8-4 - would support an 8 branch bramble plus hub plus HDD
or
http://www.amazon.co.uk/Stompb.....038;sr=8-3 - would support an 4 branch bramble plus 4 port hub plus HDD
or even just something like:
http://www.amazon.co.uk/PSU-FX.....38;sr=8-43 and daisy chain them together to support a larger bramble?

I'm not up on my electronics personnally

They are cheap enough to give a try. I plan on order one along with a few berries.

stuporhero
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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 2:34 pm

I have a few WD External PSUs (which were in use before I ripped the drives out and made a proper NAS box!) if anyone is interested, maybe a donation to the RasPi guys?

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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 2:46 pm

I would have expected that being Arm based, that this would require somewhere between 3V and 5V. If it were to use a 5 pin micro usb socket supporting MHL (mobile high definition link) instead of a HDMI socket, it could still put out Full HD & 7.1 channel sound, but also supply the raspberry pi with power all through the one cable. When connected to an MHL compatible display, this would do away with the need for a dedicated power supply.

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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 2:53 pm

obarthelemy: I have already setup a router to use just one wall wart. I soldered into the 12v input on the underside of the board. Look in the thread http://www.raspberrypi.org/for.....#038;t=111.
Make sure the power supply rating is well above your project usage and a little more for good measure. In that application the router is rated at .5amps and the RasPi with a full USB load is going to be less than 7.5watts or about .625amps at 12v. I am using a 12v 2amp wall wart to power it. I do not for see any problems as the RasPi will probably never reach that .625amp.

As to using the PSU I would try to find one that has separate connectors for each device rather than using a "Y", as I pointed out before. The external HDD especially surge. So definitely place them on separate connectors. You probably will be ok to put the RasPi and the ADSL on one connector. Is your router 12v also? What is the watts on the PSU? I would look into the "load" on the 5v rail as he is probably right. I did not have any problems but then I was stealing the power from a connector in my WHS so there was a load on all the rails. Put a USB coffee warmer or a fan on the 5v rail for a load. By the way; the yellow wire and the nearest black are your 12v in a molex connector. The red wire and the nearest black are 5v. The grounds are interchangeable supposedly.
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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 3:04 pm

ok thanks. I'll try to find a laptop-style external PSU with several cables.

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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 3:18 pm

Quote from iamdave84 on September 21, 2011, 15:46
I would have expected that being Arm based, that this would require somewhere between 3V and 5V. If it were to use a 5 pin micro usb socket supporting MHL (mobile high definition link) instead of a HDMI socket, it could still put out Full HD & 7.1 channel sound, but also supply the raspberry pi with power all through the one cable. When connected to an MHL compatible display, this would do away with the need for a dedicated power supply.

Current the board needs 6-24v (is that top number correct?). We have to go above 5 because you get power stability problems at 5 when you are supplying 5v to the USB and the HDMI as well.

As to the other points about MHL, I think that would require major revisions to the board (and perhaps even the SoC). HDMI is also much more common - I've never seen anything with a MHL link.
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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 4:26 pm

The last I heard it was 6 to 20v jamesh.

I do not think you will find an external with several power cords for a laptop. You're better bet would be to use a small desktop (150+watts) PSU that has several molex connectors. You then can build molex to barrel plug adaptors. You should be able to find a project box to stick it in then you can run the cables out of the box. All of these are available at most electronics stores.

I stacked the router and ADSL modem on top of the WHS server. The server box was the size of a shoebox. I then ran the cables out from an expansion cover plate. The server only pulled 64watts at max draw. Normal use was around 36watts.

You could use one of the laptop bricks and then build a power distribution board for it. there has to be something like that on the Internet as a DIY project. You would have to use some 7812's as most of those notebook bricks turn out 14+ volts. As to what else goes into the the circuit your guess is most likely better than mine. If you do build something like that please post it as I am sure some of the others (and me) could use the information. That is one of the reasons I bought a nerd kit, I just need to learn some more advanced electronics other than solder into everyone else's work. Retirement should give me more than enough time to learn!
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Re: 1 PSU to rule them all ?

Wed Sep 21, 2011 7:05 pm

I have no electronics/electricity skills at all. I was actually thinking of whom I could beg to do the dumb cable for me :-p

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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 2:55 am

As long as you don't mind it looking a little unrefined I should imagine all you need to do is take a twist on electric cap and twist together all your positive wires together then twist together all your negative wires together. Secure with duct tape. Grab a beer.
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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 3:51 am

You are just incorrigible, but it will work if need be LOL.
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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 4:20 am

It'll only be like 14 to 19 volts, stomp it out why waste an extinguisher!
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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 5:21 pm

You know those blanking plates covering the un-used PCI/PCI-E expansion slots? I drilled two holes in one of those and mounted two 5.5/2.5mm jacks, and hooked them up to a male Molex connector. Plug that into a spare PSU cable and I now have both 5v and 12v jacks on the back of my PC. Came in very handy when working with an Arduino.

A spare ATX PSU is a great idea, but if you can find an old AT PSU that'd be even better. If I remember correctly, you have to short two pins - and keep them shorted - on an ATX power supply in order to get it to power up; however the old AT power supplies use a switch. When you turn on the power supply using the switch, it stays on.

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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 9:01 pm

Could you not attach a switch to those two pins?

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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 9:07 pm

Quote from stuporhero on September 22, 2011, 22:01
Could you not attach a switch to those two pins?

You could, but I have read mixed reports of success with this. You need to short the two pins constantly to keep it powered up - so something like a simple SPST switch would do the job in theory. However I'm pretty sure I've read reports that, even in this configuration, you need a minimum load on the PSU in order to keep it running.

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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 9:50 pm

I have an old ATX power supply I use to run a 12V crossover (designed for in-car use) and a pc case fan. To make it turn on, I simple earth the green cable on the biggest motherboard connector. I was going to attach a switch to it but in the end decided to just connect that green wire to the inside of the PSU casing so it's always earthed, and just switch it off / unplug it at the wall if I don't need it on. It works great and has never missed a beat in the 5 years I've been using it like that.

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Re: 1 PSU to rule them all ?

Thu Sep 22, 2011 10:19 pm

Though I certainly appreciate the ingenuity behind reusing an old ATX power supply, wouldn't that end up using a lot more power than hooking up the r-pis with a wall wart?
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