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solar3000
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One large 5 volt supply?

Thu Mar 16, 2017 7:24 pm

I have many dozens of pis all over the place. I have many power supplies to go with them.
Would anybody object to the idea of a really large 5 volt supply for a batch at a time?
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edo1
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Re: One large 5 volt supply?

Thu Mar 16, 2017 7:31 pm

It isn't a good idea to deliver 5V via long cables.

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solar3000
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Re: One large 5 volt supply?

Thu Mar 16, 2017 7:58 pm

edo1 wrote:It isn't a good idea to deliver 5V via long cables.
No long cables, just short thick ones.
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sparkyhall
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Re: One large 5 volt supply?

Thu Mar 16, 2017 8:54 pm

You need to think very carefully about potential fault conditions before doing something like this.

If, for example, you connect 10 PiZero to a 5V@20A PSU, a fault such as a short circuit in a connected USB device may well cause a fire due to severely overloaded cables and PCB tracks. Clearly using the correct 5V@2.5A PSU protects against this under such fault conditions.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 8:57 pm

solar3000 wrote:
edo1 wrote:It isn't a good idea to deliver 5V via long cables.
No long cables, just short thick ones.
I think the problem was "all over the place", which implies they are separated by significant distances. For insight into the issues, read up on the early--DC--power distribution systems put in by Thomas Edison and why the Nikola Tesla (by way of George Westinghouse) AC systems beat it out.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 9:51 pm

W. H. Heydt wrote:I think the problem was "all over the place", which implies they are separated by significant distances. For insight into the issues, read up on the early--DC--power distribution systems put in by Thomas Edison and why the Nikola Tesla (by way of George Westinghouse) AC systems beat it out.
DC is the best way to transmit power long distances. Certainly it provides more energy transfer for a given cable technology and it decouples grids so if one goes down, it won't necessarily be disaster for others. Rolling blackouts are bad, I blame Tesla.

But if you get a spark going, DC sustains that spark much better than AC. Previously it was difficult to change voltages with DC so AC was the winner but if you take most electronic devices apart nowadays, pretty much you've got a power supply that converts your line AC to several DC voltages. There are losses in doing this. AC line voltages are also higher than would be necessary with DC.

There have been people who've advocated increasing the voltage in car electrical systems to 24 volts but apparently in the situations where this is done, in some large trucks, the higher voltage rapidly erodes things like relay contacts. I've wondered if issues like this could be mitigated with a DC scheme that had, say, a 90% duty cycle and then 10% off. Perhaps something like that could make DC the king again.

The real cool thing would be a globally standardised home power voltage of, say, +45 volts on one line and -45 volts on the other. Between any hot line isn't enough voltage to usually harm someone and the full 90 volts would only be available between those two hot lines meaning that with the one hand rule, ever getting shocked beyond your hand would be pretty hard to do. I guess you could get hit on your arm, but the point is no through body threat, at least it's as minimised as possible.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 9:55 pm

sparkyhall wrote:You need to think very carefully about potential fault conditions before doing something like this.

If, for example, you connect 10 PiZero to a 5V@20A PSU, a fault such as a short circuit in a connected USB device may well cause a fire due to severely overloaded cables and PCB tracks. Clearly using the correct 5V@2.5A PSU protects against this under such fault conditions.
Also the possibility that, before the fire starts, all your Pis will be starved of power. Ideally you want to automatically disconnect the faulty one at a safe power level. So distribute through a fuse or MCB for each system, rated for 2.5A per system to allow for Pi3s.
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stderr
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Re: One large 5 volt supply?

Thu Mar 16, 2017 10:36 pm

sparkyhall wrote:If, for example, you connect 10 PiZero to a 5V@20A PSU, a fault such as a short circuit in a connected USB device may well cause a fire due to severely overloaded cables and PCB tracks. Clearly using the correct 5V@2.5A PSU protects against this under such fault conditions.
What you are counting on with your individually powered pies is that the potentially dodgy wall wart you bought at the walmart has a working fuse somewhere inside its sealed case. We already know that sheets you buy at target that say they are egyptian cotton don't contain any egyptian cotton. We also know that the retailer simply took the word of the producer and never bothered to verify the claims. We already know that walmart is notorious for pressuring suppliers on every penny. Do we really believe that they will regularly crack open power supplies to verify they are up to snuff?

Computer power supplies seem to advertise that they use a single 12 volt rail and then go on to claim to provide 1000watts or more of power. So one might ask whether it is safe to dump that much power into a short without risking fire. It would seem that these power supplies are depending on the devices plugged into them to have their own fuses. I don't think that trusting that is ever a super good idea. It would be nice to have inline molex connector plugs with replaceable fuses that could be set at whatever was needed for that device. But the cost of such a thing for 10 pies seems like a lot. Perhaps cut the line and crimp in a fuse based on the needs of a couple of pi at a time.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:04 pm

Google raspberry pi atx power
If you can recycle a good ATX power supply from an unused PC, you solve several problems. A fuse per Pi is still a good idea.

A Pi does not contain a lithium battery so it will not burst into flames like an iPhone. Heat is the main danger with the Pi processor chip automatically slowing down at maximum temp. An ATX supplies 12 volts to drive case fans. In hot climates, a small heatsink on the chip plus a case fan blowing over the chip will keep everything cool.

SD cards rarely melt. When they melt, it is cheap rubbish or the sort of hot weather where you need a fan for the processor. A pi inside a plastic or wooden box will heat up and any part of it can melt first. Airflow is important. A case fan will help when the air temp is 40 degrees.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:30 pm

RPi boards already have a fuse when powered via the micro USB port so adding a fuse is redundant.
I would definitely use fuses if powered by GPIO pins.

Most listed power supplies have short circuit / over-current and thermal shutdown built in.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:34 pm

solar3000 wrote:I have many dozens of pis all over the place. I have many power supplies to go with them.
Would anybody object to the idea of a really large 5 volt supply for a batch at a time?
MY advice is , if all is working well with each PI is fed from It's own adapter, leave it that way
If you use one common 5v supply,and that fails all Pi's will lose power, Also long cable runs
Will create voltage drop
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davidcoton
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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:39 pm

klricks wrote:RPi boards already have a fuse when powered via the micro USB port so adding a fuse is redundant.
I would definitely use fuses if powered by GPIO pins.

Most listed power supplies have short circuit / over-current and thermal shutdown built in.
It's not that simple. A short could occur at the board input, before the polyfuse. The size of wire that could be connected to the board cannot safely carry 20A for long. So all the thinner cable routes should be protected by a suitable fuse/MCB. (Note this can be downstream, since shorts actually on the cable are less likely.) But all the wiring to multiple Pis (or at least to multiple fuses) must be thick enough to carry 20A indefinitely without overheating.
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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:39 pm

I am running 24 pi 3's from a 5V 60A 300W power supply which is linked to 24 usb female sockets arranged in 12 x 2 pattern and housed in an aluminium channel. This allows all pi's to be connected to power with a micro usb to usb lead. Must take pictures......

I basically used the 300W supply to power a 24 bank usb hub.

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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:41 pm

stderr wrote: Computer power supplies seem to advertise that they use a single 12 volt rail and then go on to claim to provide 1000watts or more of power. So one might ask whether it is safe to dump that much power into a short without risking fire. It would seem that these power supplies are depending on the devices plugged into them to have their own fuses.
Most of the power in a modern PC goes to the 5v rail. 12v is used for fans, liquid cooling pumps, and 3.5" HDDs. And the PSUs have built in circuit breakers (a feature is lacking in the wall warts typically used with Pis).

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Re: One large 5 volt supply?

Thu Mar 16, 2017 11:53 pm

stderr wrote: DC is the best way to transmit power long distances. Certainly it provides more energy transfer for a given cable technology and it decouples grids so if one goes down, it won't necessarily be disaster for others. Rolling blackouts are bad, I blame Tesla.
Long distance transmission using DC only works if you can boost voltage to high levels, typically 375Kv and up (way up). Edison had no way to do that. He was using small, localized generating facilities that output house current voltage levels. He even went so far as to try physically moving rechargeable batteries around to extend his coverage. From the use of transformers, the AC systems could generate power where convenient to do so (like Niagra Falls), boost the voltage for transmission, and then drop it down again for local usage in places like New York City.

Edison ran an ad campaign against AC because the state chose an AC system to power their electric chair. NY state made that choice because Edison simply couldn't deliver enough power to make it work.
But if you get a spark going, DC sustains that spark much better than AC. Previously it was difficult to change voltages with DC so AC was the winner but if you take most electronic devices apart nowadays, pretty much you've got a power supply that converts your line AC to several DC voltages. There are losses in doing this. AC line voltages are also higher than would be necessary with DC.
The "previously difficult to change voltages" is what killed DC for general use. If your generator put out a suitable voltage for household use, the range was too limited to be economical. Sure...AC has line losses, but you can easily kick the voltage up high enough to make long distance transmission economically viable, plus you can make comparatively few, large capacity generating plants--situated to take advantage of energy sources--instead of a zillion little plants forced to be close to where the power will be used..

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Re: One large 5 volt supply?

Fri Mar 17, 2017 1:35 pm

You can get multi-drop USB power supplies. I have a 40 W (8 Amp) 5 drop one in my setup with a number of single board computers running off it.

e.g. https://www.amazon.com/Anker-6-Port-Cha ... 7AT3QNYTTM

This gives you individual USB compliant (current limited) ports for several processors in a single package. I doubt you can find one that has "dozens" of ports.

Distributing regulated voltage such as USB 5 volts over more than a couple meters distance without endpoint voltage sensing (which USB doesn't allow) is a bad idea.

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Re: One large 5 volt supply?

Fri Mar 17, 2017 2:51 pm

If they are in the same location then you might be looking for something...
like this :
http://www.ebay.co.uk/itm/Sipolar-Real- ... 1641900159
Or this :
http://www.ebay.co.uk/itm/20-Porte-USB- ... 1641903556
Then it's just a case of running USB cables to the desired Pi. ;)
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Re: One large 5 volt supply?

Fri Mar 17, 2017 3:08 pm

solar3000 wrote:I have many dozens of pis all over the place. I have many power supplies to go with them.
Would anybody object to the idea of a really large 5 volt supply for a batch at a time?
So long as they are all fairly close to the supply, it works great. That is what I am doing, my 3D printer controller RPi (I do not use arduino), my house control RPi, and my 2 desktop computer RPi's are all powered off a single 10A 5v converter (that is powered off of my 12 volt solar system).

I would recommend using 12AWG wire for any run over 20 feet. Shorter runs 20AWG is more than enough.
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Re: One large 5 volt supply?

Fri Mar 17, 2017 8:04 pm

S0litaire wrote:If they are in the same location then you might be looking for something...
like this :
http://www.ebay.co.uk/itm/Sipolar-Real- ... 1641900159
Or this :
http://www.ebay.co.uk/itm/20-Porte-USB- ... 1641903556
Then it's just a case of running USB cables to the desired Pi. ;)

Power supply 5V 4A to 16 USB ports?
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Re: One large 5 volt supply?

Fri Mar 17, 2017 8:17 pm

solar3000 wrote:
S0litaire wrote:If they are in the same location then you might be looking for something...
like this :
http://www.ebay.co.uk/itm/Sipolar-Real- ... 1641900159
Or this :
http://www.ebay.co.uk/itm/20-Porte-USB- ... 1641903556
Then it's just a case of running USB cables to the desired Pi. ;)

Power supply 5V 4A to 16 USB ports?
Near enough, (2.5 - 3 amps) they are used with usb asic Bitcoin miners.
So they need a stable strong supply over long periods.
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Re: One large 5 volt supply?

Fri Mar 17, 2017 8:56 pm

S0litaire wrote:
solar3000 wrote:
S0litaire wrote:If they are in the same location then you might be looking for something...
like this :
http://www.ebay.co.uk/itm/Sipolar-Real- ... 1641900159
Or this :
http://www.ebay.co.uk/itm/20-Porte-USB- ... 1641903556
Then it's just a case of running USB cables to the desired Pi. ;)

Power supply 5V 4A to 16 USB ports?
Near enough, (2.5 - 3 amps) they are used with usb asic Bitcoin miners.
So they need a stable strong supply over long periods.
Cheaper one states 350A /port,more expensive 750mA /port.
I think all my Pi drain 400mA minimum peak (A+ and Zero). The 2B &3B i know take more.

I just use a variable voltage 100W desktop PSU, it shows me the voltage and current draw and i chopped the usb side of usb cables and hook a few up for play time :-)

Personally i would go the ATX PSU route for a more permanent solution if i need one. Since they are cheaper.

At the moment an IKEA 3 Port Plug charger does a good job at home.

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Re: One large 5 volt supply?

Fri Mar 17, 2017 10:19 pm

I use one of the Anker 6-port supplies MarkTF pointed out. Completely reliable over the last 30 months or so. I consider it a very worthwhile investment of $25.

I also occasionally use a spare iPad charger to run 1 Pi when demoing stuff out-of-lab.
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Re: One large 5 volt supply?

Fri Mar 17, 2017 10:58 pm

I forget the brand, though I ended up finding a switching USB power supply, that takes 12 volt for its source and puts out a combined total of 10A, and does not isolate the 4 ports from one another (they are just all on the same power rails). This is what I am using for mine, it cost about $45, though was worth it, I have 3 of them total.
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Re: One large 5 volt supply?

Fri Mar 17, 2017 11:03 pm

DavidS wrote:I forget the brand, though I ended up finding a switching USB power supply, that takes 12 volt for its source and puts out a combined total of 10A, and does not isolate the 4 ports from one another (they are just all on the same power rails). This is what I am using for mine, it cost about $45, though was worth it, I have 3 of them total.
Hey DavidS,

I'd be interested in the power supply you mentioned. Can you possibly provide more information or even a link? In light of your other recent posts, I understand if you don't have time for that.

Thank you.

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Re: One large 5 volt supply?

Sat Mar 18, 2017 1:09 am

ktb wrote:
DavidS wrote:I forget the brand, though I ended up finding a switching USB power supply, that takes 12 volt for its source and puts out a combined total of 10A, and does not isolate the 4 ports from one another (they are just all on the same power rails). This is what I am using for mine, it cost about $45, though was worth it, I have 3 of them total.
Hey DavidS,

I'd be interested in the power supply you mentioned. Can you possibly provide more information or even a link? In light of your other recent posts, I understand if you don't have time for that.

Thank you.
Well it has two clips to go onto the 12 volt source, the box containing the PWM regulator, power rails, and USB ports is about 2.5 inches by 2 inches, by 1.5 inches deep, with a triangular rear profile. The casing is black ABS, it has no external markings, and it was sold at the local HardWare store.

That is about all the info I have, wish I could be of more help.
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