mymon
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One PSU for all

Mon Jun 29, 2020 1:47 pm

What do you use to power multiple Pi devices?
I have 3x Pi v3 (with at least 2 USB in use on each) running different projects
now I need 4th one and running out of power sockets
I'm looking for best practices to power multiple devices from a single PSU


LTolledo
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Re: One PSU for all

Mon Jun 29, 2020 2:08 pm

my solution
12v mother source,
12v to 5.1v buck converters for each device

get total power requirement for each setup (in watts)
add all of those
multiply by 1.1 (or 1.2)
divide by 12v
you get ampere rating
get the next higher available rating
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ejolson
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Re: One PSU for all

Mon Jun 29, 2020 3:40 pm

LTolledo wrote:
Mon Jun 29, 2020 2:08 pm
my solution
12v mother source,
12v to 5.1v buck converters for each device

get total power requirement for each setup (in watts)
add all of those
multiply by 1.1 (or 1.2)
divide by 12v
you get ampere rating
get the next higher available rating
The buck converter solution seems reasonable. I was going to use similar in my microscale cloud prototype

viewtopic.php?f=36&t=272660#p1678218

However, it turned out the 5V rail on that old ATX power supply delivered 200W. That and some strategically placed fuses seem to be working at present.

The fashion way to power a bunch of Pi computers is with a POE switch and a bunch of POE hats. Here is an example of a converged NAS, switch and server:

Image
https://www.servethehome.com/our-switch ... 0p-review/

This would not only power a bunch of Pi computers, but could network boot them as well. After seeing how much time and soldier the do-it-yourself solution I chose is taking, a converged NAS and switch is looking very attractive.

W. H. Heydt
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Re: One PSU for all

Mon Jun 29, 2020 4:26 pm

When I saw the thread title, my first thought was, Pi4 PSU plus a USB-C to USB-microB adapter.

PoE HATs are limited to 12.5W, so a bit marginal for a Pi4B, which can require up to 15W.

My solution is a breaker bar or surge protector with well spaced out sockets. My largest group of Pis in one spot--requiring that solution--is 4 Pi4Bs. That group is also limited by the 4-port KVM switch they're connected to.

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thagrol
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Re: One PSU for all

Mon Jun 29, 2020 5:59 pm

Don't know whether it's best practice but I've been powering three Pi off the 5v rail of an ATX PSU for quite some time now.

Well, I say off the 5v rail. One of them is actually running of the 5v standby rail.
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lurk101
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Re: One PSU for all

Mon Jun 29, 2020 7:04 pm

thagrol wrote:
Mon Jun 29, 2020 5:59 pm
Don't know whether it's best practice but I've been powering three Pi off the 5v rail of an ATX PSU for quite some time now.

Well, I say off the 5v rail. One of them is actually running of the 5v standby rail.
Yep. Been using a recycled PC power supply to power multiple Pi's for years now. Some recommend fusing but I haven't bothered.
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Heater
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Re: One PSU for all

Mon Jun 29, 2020 9:30 pm

Fuses are like seat belts and air bags.

Ones car works just fine without them.

Until one day...
Memory in C++ is a leaky abstraction .

lurk101
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Re: One PSU for all

Mon Jun 29, 2020 9:43 pm

Heater wrote:
Mon Jun 29, 2020 9:30 pm
Fuses are like seat belts and air bags.

Ones car works just fine without them.

Until one day...
Not quite. All PC supplies I've used have builtin short circuit protection, and fuses won't protect from over voltage.
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Endgame
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Re: One PSU for all

Mon Jun 29, 2020 9:53 pm

I can second the Anker 6 port 60 watt supply. 85% efficient according to Anker and I’m happily running 6x pi 4s at 100% cpu (boinc) on it with no problem.

What would be really awesome is a 80+ titanium power supply with 50+ usb c connectors. A whole pi cluster off of one psu.

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thagrol
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Re: One PSU for all

Mon Jun 29, 2020 10:02 pm

Heater wrote:
Mon Jun 29, 2020 9:30 pm
Fuses are like seat belts and air bags.

Ones car works just fine without them.

Until one day...
I admit I haven't bothered with fuses. Partly because I'm lazy but mostly because I've never seen fuses between PSU and motherboard/HDD/ODD/GFX cards/etc.

All thsoe things can potentially short, with no inline fuses I assumed (correctly it turns out) that protection is inside the PSU.
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Heater
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Re: One PSU for all

Mon Jun 29, 2020 10:44 pm

thagrol wrote:
Mon Jun 29, 2020 10:02 pm
I admit I haven't bothered with fuses. Partly because I'm lazy but mostly because I've never seen fuses between PSU and motherboard/HDD/ODD/GFX cards/etc.
Indeed.

That is to be expected where the PSU and all the parts that are powered by it are in the same metal PC box and the risk of starting a fire or whatever is pretty low as a result.

But I can imagine people pulling a PC supply out and trailing wires all around the place to their Pi. I whole different situation in a different environment.

All depends what you are doing. Just be aware of the risks.
Memory in C++ is a leaky abstraction .

JMK8
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Re: One PSU for all

Tue Jun 30, 2020 11:12 am

I use one of these...

https://www.amazon.co.uk/XKTTSUEERCRR-S ... 356&sr=8-2

...to power 3 Pis (2x3B and 4B) . I know some people say "Don't do it!!!" but I power them via the GPIO pins and I've have not had any problems since I started doing this a couple of years ago. The PSU runs just slightly warm with the 3 Pis connected and running (plus some leds, an SSD and ancillary components), the ripple and regulation seem pretty good, they also have a voltage trimmer so you can adjust for 5V at the Pi.

Oh, I can confirm that the short-circuit protection works! :oops:

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davidcoton
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Re: One PSU for all

Tue Jun 30, 2020 8:59 pm

lurk101 wrote:
Mon Jun 29, 2020 9:43 pm
Not quite. All PC supplies I've used have builtin short circuit protection, and fuses won't protect from over voltage.
thagrol wrote: All thsoe things can potentially short, with no inline fuses I assumed (correctly it turns out) that protection is inside the PSU.
Yes, ATX PSUs have over-current protection. But the output will reach the full capacity of the rail you are using (maybe 50A or more) before the protection kicks in. A short under the Pi's PCB can cause a lot of damage before the PSU shuts down -- the tracks will not tolerate that level of current for long, compared with the time for which 3A is safe.

As for over-voltage, all Pis except the Zeros have a TVS protection diode, which clamps the voltage and converts potential over-voltage to an over-current. It can do this non-destructively if protected by a correctly rated polyfuse.

As mentioned above, even the distribution cables should be protected so that a wiring short does not exceed the cable's fault current rating (which is itself time-dependent, so that the cable and protection device must be coordinated).
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LTolledo
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Re: One PSU for all

Tue Jun 30, 2020 9:33 pm

if am going to use PC ATX PSUs....for powering multiple RPi .....
for over-current protection I'd probably do "old-school method"
installing DC earth leakage breakers for each RPi setup....
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

mymon
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Re: One PSU for all

Tue Jun 30, 2020 10:05 pm

JMK8 wrote:
Tue Jun 30, 2020 11:12 am
I use one of these...

https://www.amazon.co.uk/XKTTSUEERCRR-S ... 356&sr=8-2
heh.. Ive bought MeanWell RS-50-5 but having issues with USB connectors.. simply not good quality and not delivering enough so when all 4 USBs are in use I'm getting low power errors :cry: I'll try the GPIO pins :idea:

I like the @Endgame's solution even better and ordered the Anker PowerPort 10 so will switch my Google mini & chromecast as well ;)
Last edited by mymon on Tue Jun 30, 2020 11:25 pm, edited 2 times in total.

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davidcoton
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Re: One PSU for all

Tue Jun 30, 2020 10:06 pm

LTolledo wrote:
Tue Jun 30, 2020 9:33 pm
if am going to use PC ATX PSUs....for powering multiple RPi .....
for over-current protection I'd probably do "old-school method"
installing DC earth leakage breakers for each RPi setup....
Earth leakage breakers (sic) do NOT provide over-current protection.
Use a polyfuse, thermal wire fuse or an MCB if you can find a suitable one.
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pidd
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Re: One PSU for all

Tue Jun 30, 2020 10:34 pm

lurk101 wrote:
Mon Jun 29, 2020 9:43 pm
Not quite. All PC supplies I've used have builtin short circuit protection, and fuses won't protect from over voltage.
A 200W 5V supply is at least 40A before the overcurrent kicks in. If you are using anything less than 10A (may be more) cable then there is a good chance that a short/fault at the end of that cable won't trigger the overcurrent protection. So regardless of damage to the pi, the cable is likely to set fire to your house - similar to certain 3D printers.

Fuses other than those fitted on/in devices are not designed to protect devices, they are there to protect cables, they are a fire safety device.

Devices generally have thermal fuses in them to protect against overheating - again fire safety related protection.

So please stop thinking about protecting an already faulty device, use fuses to ensure your property and people don't end up as a charcoaled mess.

ejolson
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Re: One PSU for all

Wed Jul 01, 2020 1:01 am

pidd wrote:
Tue Jun 30, 2020 10:34 pm
lurk101 wrote:
Mon Jun 29, 2020 9:43 pm
Not quite. All PC supplies I've used have builtin short circuit protection, and fuses won't protect from over voltage.
A 200W 5V supply is at least 40A before the overcurrent kicks in. If you are using anything less than 10A (may be more) cable then there is a good chance that a short/fault at the end of that cable won't trigger the overcurrent protection. So regardless of damage to the pi, the cable is likely to set fire to your house - similar to certain 3D printers.

Fuses other than those fitted on/in devices are not designed to protect devices, they are there to protect cables, they are a fire safety device.

Devices generally have thermal fuses in them to protect against overheating - again fire safety related protection.

So please stop thinking about protecting an already faulty device, use fuses to ensure your property and people don't end up as a charcoaled mess.
Fast-blow fuses designed for use in automobiles seem pretty cheap compared to a new house. Would a 3A fuse from

https://www.amazon.com/gp/product/B0813Q4S6P/

would work well for a single Pi?

pidd
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Re: One PSU for all

Wed Jul 01, 2020 4:12 am

Yes, a fast-blow low voltage fuse is probably a good option, I might put 5A in so there's less chance of it randomly blowing, provided I thought the wire would handle 5A safely.

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davidcoton
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Re: One PSU for all

Wed Jul 01, 2020 10:09 am

pidd wrote:
Wed Jul 01, 2020 4:12 am
Yes, a fast-blow low voltage fuse is probably a good option, I might put 5A in so there's less chance of it randomly blowing, provided I thought the wire would handle 5A safely.
More or less agreed. 4A fuse if I could find one! The cable needs to be able to stand the short circuit current (way more than the fuse rating) for the time it takes the fuse to blow. Not usually a problem unless the short circuit current is limited (by the PSU or wiring resistance) to a smallish overload where the time to blow is long. Just use cable capable of something like 6A or 10A. The full calculation is foul: it's an adiabatic equation, because the cable characteristics vary as it heats up while carrying SC current. It requires knowledge of detailed cable and fuse characteristics and ambient operating temperature. It can be solved graphically. Details are in BS7454, or briefly in Wiring Regs (BS7671:2018) 543.1.3.
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