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frolen13
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PC power supply

Fri Jan 31, 2014 1:02 am

Ok so I am working on a project that involves a computer power supply. Can I power the pi with the supply the 5 volts coming from the supply is at 22.0 amps how will the pi like that? Will it fry it lol thx :lol:
-Collin

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Raspruss
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Re: PC power supply

Fri Jan 31, 2014 1:34 am

frolen13 wrote:Can I power the pi with the supply the 5 volts coming from the supply is at 22.0 amps how will the pi like that?
It SHOULD say "Thanks, may I have more?"...

Unless something is really unusual, the Pi will take what it needs and leave the rest for your external peripherals...

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 1:36 am

Raspruss wrote:
frolen13 wrote:Can I power the pi with the supply the 5 volts coming from the supply is at 22.0 amps how will the pi like that?
It SHOULD say "Thanks, may I have more?"...

Unless something is really unusual, the Pi will take what it needs and leave the rest for your external peripherals...

Thanks bro!
-Collin

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Raspruss
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Re: PC power supply

Fri Jan 31, 2014 1:38 am

BTW - a 22 amp (!!!) 5V supply sounds like something from my TTL days...yow!

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FLYFISH TECHNOLOGIES
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Re: PC power supply

Fri Jan 31, 2014 1:47 am

Hi,
frolen13 wrote:Can I power the pi with the supply the 5 volts coming from the supply is at 22.0 amps
22 amps is the "capacity" of the power supply. Since it is 5V voltage generator, it tries to maintain voltage at 5V. If it would be 22A current generator (but it is not), it would try to "push" this amount of the current into RasPi.
frolen13 wrote:how will the pi like that?
Perfectly well.

But, (there is always but...) there is another problem. You should be aware that these power supplies (so-called switchers) require a load with some power consumption in order to regulate voltage properly... Attaching only a single RasPi to the output might not be sufficient load (it represents just few percents of the capabilities). This is the reason why I would recommend you not to use this power supply.

Try to get 5V power supply with max current in the range between 1 and 5 amperes.


Best wishes, Ivan Zilic.
Running out of GPIO pins and/or need to read analog values?
Solution: http://www.flyfish-tech.com/FF32

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 2:14 am

Also can I feed the 5v directly down the GPIO? :?:
-Collin

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FLYFISH TECHNOLOGIES
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Re: PC power supply

Fri Jan 31, 2014 2:30 am

Hi,
frolen13 wrote:Also can I feed the 5v directly down the GPIO? :?:
I always supply it via a power connector.
The reason is that when you feed the RasPi via this USB power connector, its protection is in place (over-voltage, over-current). When feeding the RasPi elsewhere (GPIO or USB ports), this protection is bypassed...


Best wishes, Ivan Zilic.
Running out of GPIO pins and/or need to read analog values?
Solution: http://www.flyfish-tech.com/FF32

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 2:33 am

FLYFISH TECHNOLOGIES wrote:Hi,
I always supply it via a power connector.
The reason is that when you feed the RasPi via this USB power connector, its protection is in place (over-voltage, over-current). When feeding the RasPi elsewhere (GPIO or USB ports), this protection is bypassed...


Best wishes, Ivan Zilic.
Ah ok thank you.
-Collin

klricks
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Re: PC power supply

Fri Jan 31, 2014 2:42 am

Many people use the 5V standby power line from an ATX power supply instead of the main 5V. The standby line has enough power to supply the RPi and it is always on even when the main power supply switch is turned OFF.
No fans blowing and no worry about a minimum load to start it up.

If you use the main 5V you will need to have a dummy load such as a fan, light-bulb or even an old hard drive.

Google [computer bench power supply] there are many many tutorials videos etc.
Last edited by klricks on Fri Jan 31, 2014 2:57 am, edited 1 time in total.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 2:46 am

klricks wrote:Many people use the 5V standby power line from an ATX power supply instead of the main 5V. The standby line has enough power to supply the RPi and it is always on even with the main power supply switch is turned OFF.
No fans blowing and no worry about a minimum load to start it up.

If you use the main 5V you will need to have a dummy load such as a fan, light-bulb or even an old hard drive.

Google [computer bench power supply] there are many many tutorials videos etc.
What is the ground for standby? i know positive is purple :)
-Collin

klricks
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Re: PC power supply

Fri Jan 31, 2014 2:56 am

Ground is any black wire they are all the same.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

achrn
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Re: PC power supply

Fri Jan 31, 2014 8:41 am

FLYFISH TECHNOLOGIES wrote: But, (there is always but...) there is another problem. You should be aware that these power supplies (so-called switchers) require a load with some power consumption in order to regulate voltage properly... Attaching only a single RasPi to the output might not be sufficient load (it represents just few percents of the capabilities). This is the reason why I would recommend you not to use this power supply.
Most relatively recent PC supplies do OK at this. They tend not to require a significant load to regulate, and will generate a decent stable voltage on all outputs even if some are open circuit. The first PC power supply I hacked about needed a dummy load resistor, but none I've done in the last 10 years have needed it.

As I type, one of my Pis has been on a hacked PC power supply for some months.

So the regulation could theoretically be an issue, but probably won't (unless it's a really ancient PC supply you're using), but it would be prudent to check the voltage under zero (or minimal - say put a 100 ohm resistor on so you've got 50mA) load.

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FLYFISH TECHNOLOGIES
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Re: PC power supply

Fri Jan 31, 2014 10:40 am

Hi,
achrn wrote:So the regulation could theoretically be an issue, but probably won't
I'm rather on the safe side... specially when discussing about some remote equipment I don't know much about.
But of course, it's always on each individual to check/read/investigate what exactly is applicable to his/her case...


Best wishes, Ivan Zilic.
Running out of GPIO pins and/or need to read analog values?
Solution: http://www.flyfish-tech.com/FF32

blc
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Re: PC power supply

Fri Jan 31, 2014 1:40 pm

The idea of using a PC power supply for electronics stuff, or the RPi, really scares the crap out of me. Most modern power supplies put out a ridiculous amount of power - my next upgrade will use over 330 watts for the CPU & GPU alone. If there were some sort of problem or short circuit then there would be an awful lot of amps being pumped out...

That said, many people use PC PSUs with no issues, and there's always the +5vSB line as already mentioned. Google about for the ATX PSU pinout - there's plenty of info out there in this. It's all at your own risk of course... :)

achrn
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Re: PC power supply

Fri Jan 31, 2014 1:46 pm

blc wrote:The idea of using a PC power supply for electronics stuff, or the RPi, really scares the crap out of me. Most modern power supplies put out a ridiculous amount of power - my next upgrade will use over 330 watts for the CPU & GPU alone. If there were some sort of problem or short circuit then there would be an awful lot of amps being pumped out...
About 20, after which the current limiting circuitry defined in the PSU specs kicks in. 5V at a potential 25A is not a terrifying amount of electricity, in my view.

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 2:15 pm

Well I am already using the supply in the project I just wanted to take advantage of it.
-Collin

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panik
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Re: PC power supply

Fri Jan 31, 2014 2:22 pm

For those that don't like the mess of cables involved in a PC power supply, this might be handy: http://dangerousprototypes.com/2013/09/ ... pply-case/
It also has room for an optional load resistor for power supplies that need it.

blc
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Re: PC power supply

Fri Jan 31, 2014 2:48 pm

achrn wrote:About 20, after which the current limiting circuitry defined in the PSU specs kicks in. 5V at a potential 25A is not a terrifying amount of electricity, in my view.
It might not be terrifying, but 25A is more than enough in my view! That's 125W! :)

To be honest, unless you're using good quality gear then I would seriously doubt the ability of most PSUs to meet the defined ATX specs - many probably can't even meet the +/- 5% voltage regulation spec. The situation is certainly a lot better than it used to be but there's still a lot of guff out there, especially when it comes to spare components you've had lying round for a while; chances are that if you do have a good quality PSU then you're going to re-use it in another PC rather than just chuck it into storage somewhere. At least I do anyway!

There's no accounting for cheap manufacturing :)

achrn
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Re: PC power supply

Fri Jan 31, 2014 3:49 pm

blc wrote: To be honest, unless you're using good quality gear then I would seriously doubt the ability of most PSUs to meet the defined ATX specs - many probably can't even meet the +/- 5% voltage regulation spec. The situation is certainly a lot better than it used to be but there's still a lot of guff out there, especially when it comes to spare components you've had lying round for a while; chances are that if you do have a good quality PSU then you're going to re-use it in another PC rather than just chuck it into storage somewhere.
The power supplies I use are generally ones that are redundant from work, from servers or relatively costly PCs (we'd have called them workstations in the good old days, but I'm not sure where the line is now between PC and workstation) . In some cases they are actually redundant spare power supplies and have been sat doing nothing.

I have only once re-used a PSU into a new PC - I don't replace my PC often enough - the motherboard specs have always moved on by the time I get that far. That and I only replace my PCs when work is chucking out some PCs anyway...

The dangerous prototypes module annoys me, because it takes a really useful high-power PSU (5V and 12V at 20-odd amps, as discussed) and then sticks polyfuses on the outputs to limit the current to 1.25A. So hey! we can easily convert a 500W high-performance PSU into a unit that performs as well as a 5 quid wall-wart. For about twice the price of the wall-wart (assuming your PC power supply is free). Who would actually want to do that? If you want a 1.25A power supply, you don't want a PC PSU.

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panik
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Re: PC power supply

Fri Jan 31, 2014 4:07 pm

achrn wrote:The dangerous prototypes module annoys me, because it takes a really useful high-power PSU (5V and 12V at 20-odd amps, as discussed) and then sticks polyfuses on the outputs to limit the current to 1.25A. So hey! we can easily convert a 500W high-performance PSU into a unit that performs as well as a 5 quid wall-wart. For about twice the price of the wall-wart (assuming your PC power supply is free). Who would actually want to do that? If you want a 1.25A power supply, you don't want a PC PSU.
You're right. I totally overlooked the polyfuses.

techpaul
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Re: PC power supply

Fri Jan 31, 2014 4:21 pm

blc wrote:
achrn wrote:About 20, after which the current limiting circuitry defined in the PSU specs kicks in. 5V at a potential 25A is not a terrifying amount of electricity, in my view.
It might not be terrifying, but 25A is more than enough in my view! That's 125W! :)
Perhaps I should keep quiet about one of my bench power supplies 0-40V and 0-25A, yes max of 1kW :D

Mind you that needs some hefty cabling ...
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 5:23 pm

I am using a old 350 watt I got from a discarded windows vista computer. My multimeter broke (blew the fuse) so I couldn't check the amperage from the PSU
-Collin

klricks
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Re: PC power supply

Fri Jan 31, 2014 5:42 pm

FYI- You cannot measure current by connecting the meter directly to the output of the PS, you will blow the fuse in the meter every time.
Current must be measured in series with the intended load connected.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

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frolen13
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Re: PC power supply

Fri Jan 31, 2014 5:45 pm

klricks wrote:FYI- You cannot measure current by connecting the meter directly to the output of the PS, you will blow the fuse in the meter every time.
Current must be measured in series with the intended load connected.
Yes I know. I blew the fuse unintentionally from a few months ago and forgot :p
-Collin

blc
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Re: PC power supply

Sun Feb 02, 2014 10:22 pm

techpaul wrote:Perhaps I should keep quiet about one of my bench power supplies 0-40V and 0-25A, yes max of 1kW :D

Mind you that needs some hefty cabling ...
That's a bench supply though, it's designed to deliver the power in the way that you're using it - it's not being used in a way that it's not intended to be used! ;)

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