Werks3d
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Powering multiple Pi Zero’s? (Again)

Wed Apr 18, 2018 6:16 pm

Thoughts on powering up to 50 Raspberry Pi Zero’s daisy chained off a 5v 30amp power supply? This is just a jump off point to get this discussion started.

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DougieLawson
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Re: Powering multiple Pi Zero’s? (Again)

Wed Apr 18, 2018 10:05 pm

https://www.pidramble.com/wiki/benchmar ... onsumption gives you some numbers for each model in a cluster.
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Re: Powering multiple Pi Zero’s? (Again)

Wed Apr 18, 2018 11:19 pm

Werks3d wrote:
Wed Apr 18, 2018 6:16 pm
Thoughts on powering up to 50 Raspberry Pi Zero’s daisy chained off a 5v 30amp power supply? This is just a jump off point to get this discussion started.
By "daisy chained" do you mean powering each Pi (except the first) from the previous Pi's USB socket (or any other method passing the chain's power through each Pi)? Work out the effect of the total current for 50 Pis passing through one Pi.

Powering many Pis from one PSU needs a low impedance distribution bus. You may also want to consider the consequences of a power short on any Pi -- shorting a 30A supply would be catastrophic. I would want to divide and rule the power distrubution, with sections of maybe four or five Pis sharing a fuse/polyfuse/MCB, thus limiting the damage (and consequent outage of other Pis) in the event of a fault.
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Re: Powering multiple Pi Zero’s? (Again)

Thu Apr 19, 2018 2:03 am

I've got two words for you:

Track Lighting

My dream is to just have a rail that runs the length of my desk and from any point I can just attach the RPi (or similar USB device) I want to power. Some EE needs to explain why this kind of thing doesn't already exist.

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Re: Powering multiple Pi Zero’s? (Again)

Thu Apr 19, 2018 9:12 am

Werks3d wrote:
Wed Apr 18, 2018 6:16 pm
Thoughts on powering up to 50 Raspberry Pi Zero’s daisy chained off a 5v 30amp power supply? This is just a jump off point to get this discussion started.
I'd agree with what davidcotton has already said. Split the Pi's into groups, choose suitable cabling and fusing for them. 30A down a single cable will need a large cable. If you had 10 groups of 5 on a cable from the PSU the current (and so cable size) would be much smaller and also easier to work with. The biggest issue is likely to be voltage drop across the cable.

Depending on what the distances involved are between PSU and Pis I'd potentially also consider running the distribution at a higher voltage (probably 12V or 24V) and then use switching regulators near groups of Pis to drop the voltage to the required 5V.
droleary wrote:
Thu Apr 19, 2018 2:03 am
My dream is to just have a rail that runs the length of my desk and from any point I can just attach the RPi (or similar USB device) I want to power. Some EE needs to explain why this kind of thing doesn't already exist.
I'm sure that sort of thing exists in many home labs, although likely home brewed to fit the environment and requirements (I'd probably have something that provides both 12V and 5V, and possibly 3v3 as well).

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Re: Powering multiple Pi Zero’s? (Again)

Thu Apr 19, 2018 8:58 pm

droleary wrote:
Thu Apr 19, 2018 2:03 am
I've got two words for you:

Track Lighting

My dream is to just have a rail that runs the length of my desk and from any point I can just attach the RPi (or similar USB device) I want to power. Some EE needs to explain why this kind of thing doesn't already exist.
Economics is why.

Not enough people will buy it so the sales price to cover the tiny production run gives the device a high price. Then because the price is so high even less people would buy it, especially the target market who looks at the price and says I can build that for a lot cheaper*. So no second production run is made but hopefully you broke even (been their, done that, got the T-shirt, too many times).

* Of course you can build it cheaper you don't have the overhead of a manufacturer and don't need to show a good profit margin to the investors.

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Re: Powering multiple Pi Zero’s? (Again)

Fri Apr 20, 2018 2:10 am

Paul Hutch wrote:
Thu Apr 19, 2018 8:58 pm
Economics is why.
What are the economics that make it prohibitive? I can't imagine any other solution that is cheaper than a couple rails to carry the current. Presumably it could actually be done with existing low voltage track lighting equipment, just with 5V instead of 10-24V.

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Re: Powering multiple Pi Zero’s? (Again)

Fri Apr 20, 2018 3:24 pm

droleary wrote:
Fri Apr 20, 2018 2:10 am
Paul Hutch wrote:
Thu Apr 19, 2018 8:58 pm
Economics is why.
What are the economics that make it prohibitive? I can't imagine any other solution that is cheaper than a couple rails to carry the current. Presumably it could actually be done with existing low voltage track lighting equipment, just with 5V instead of 10-24V.
See the rest of my reply for the general answer. ;)

Specifically it will require a lot of custom fabricated components that meet fire and electrical safety requirements and getting custom parts made in quantities of less than 100,000 per batch is costly. Non-recurring engineering and tooling charges also become a big factor with smaller batches.

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Re: Powering multiple Pi Zero’s? (Again)

Fri Apr 20, 2018 3:59 pm

Werks3d wrote:
Wed Apr 18, 2018 6:16 pm
Thoughts on powering up to 50 Raspberry Pi Zero’s daisy chained off a 5v 30amp power supply? This is just a jump off point to get this discussion started.

Why not use a 10 Port USB Hub, you should be able to get 500mA on each port:

http://m.dx.com/p/high-speed-10-port-us ... ray-194655

https://www.raspberrypi.org/help/faqs/#topPower
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Re: Powering multiple Pi Zero’s? (Again)

Sat Apr 21, 2018 1:25 am

Paul Hutch wrote:
Fri Apr 20, 2018 3:24 pm
See the rest of my reply for the general answer. ;)
I was hoping for hard numbers rather than "general" hand waving.
Specifically it will require a lot of custom fabricated components that meet fire and electrical safety requirements and getting custom parts made in quantities of less than 100,000 per batch is costly. Non-recurring engineering and tooling charges also become a big factor with smaller batches.
That's true for any new product; by your logic, nothing would ever get made. And, again, it sure seems the work has all essentially been done for existing low voltage track lighting setups. You haven't mentioned anything that is obviously going to make it more costly than a full USB hub.

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Re: Powering multiple Pi Zero’s? (Again)

Sat Apr 21, 2018 1:33 am

fruitoftheloom wrote:
Fri Apr 20, 2018 3:59 pm
Why not use a 10 Port USB Hub, you should be able to get 500mA on each port:

http://m.dx.com/p/high-speed-10-port-us ... ray-194655
Run away! The spec for that hub says (typo and all):
With 1A (acutal 700mA) power supply
So while one port could give you 500mA, use all 10 and you'll be lucky to get 70mA each. Not suitable as a power supply.

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Re: Powering multiple Pi Zero’s? (Again)

Sat Apr 21, 2018 8:55 am

droleary wrote:
Sat Apr 21, 2018 1:25 am
Paul Hutch wrote:
Fri Apr 20, 2018 3:24 pm
See the rest of my reply for the general answer. ;)
I was hoping for hard numbers rather than "general" hand waving.
If you think its a viable product then do some designs and talk to some investors.

I think the issues you'll have are that the potential customer base is relatively small, and they'll have a wide variety of requirements. They're also more capable of making something themselves.

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Re: Powering multiple Pi Zero’s? (Again)

Sat Apr 21, 2018 9:34 am

What about using a PC ATX PSU some can provide 5V 36A:

https://www.ebuyer.com/566861-ace-black ... suace500br
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Re: Powering multiple Pi Zero’s? (Again)

Sat Apr 21, 2018 1:04 pm

mfa298 wrote:
Sat Apr 21, 2018 8:55 am
I think the issues you'll have are that the potential customer base is relatively small, and they'll have a wide variety of requirements. They're also more capable of making something themselves.
That's certainly a problem with any market full of creative people. I mean, we all could make our own cases, too, but most of us will still buy one. All I'm saying is that if I had a project that required 16+ RPi to be clustered together, I'd see how viable it would be to do it using track lighting rails, and make a product of it if it beat screwing around with a bunch of USB hubs that weren't really designed to be power supplies.

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Re: Powering multiple Pi Zero’s? (Again)

Sat Apr 21, 2018 7:07 pm

droleary wrote:
Sat Apr 21, 2018 1:04 pm
mfa298 wrote:
Sat Apr 21, 2018 8:55 am
I think the issues you'll have are that the potential customer base is relatively small, and they'll have a wide variety of requirements. They're also more capable of making something themselves.
That's certainly a problem with any market full of creative people. I mean, we all could make our own cases, too, but most of us will still buy one. All I'm saying is that if I had a project that required 16+ RPi to be clustered together, I'd see how viable it would be to do it using track lighting rails, and make a product of it if it beat screwing around with a bunch of USB hubs that weren't really designed to be power supplies.
What I'm saying is that if I had a project that required 16+ RPi to be clustered together I would not even consider to use "track lighting rails" to avoid a potential single point of failure. One little hiccup on the rail while servicing a node would be capable of downing the complete cluster.

As an exercise: with +/- 2A for each RPI would need at least +/- 32A to power 16+ RPi, what do you think will happen if you cause a short circuit on the rail ?
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Re: Powering multiple Pi Zero’s? (Again)

Sun Apr 22, 2018 12:34 pm

5V 10A supplies are already out there, I have one of these, https://www.adafruit.com/product/658 It only powers one Pi though. A Pi 3B, Pi foundation screen and some other odds and ends.
Mate it to something like this, https://www.adafruit.com/product/658 or this, https://www.adafruit.com/product/610
Then wire that to multiples of these, https://www.adafruit.com/product/2225 Fuses on each one if you wish. Mount it all on proto boards, https://www.adafruit.com/product/1606

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Re: Powering multiple Pi Zero’s? (Again)

Sun Apr 22, 2018 2:21 pm

Ernst wrote:
Sat Apr 21, 2018 7:07 pm
What I'm saying is that if I had a project that required 16+ RPi to be clustered together I would not even consider to use "track lighting rails" to avoid a potential single point of failure.
Odds are pretty good there's going to be a single point of failure in the power system regardless. Could be at the wall, could be at the building. It just seems silly to jump to the "last mile" and pretend you've solved that problem.
As an exercise: with +/- 2A for each RPI would need at least +/- 32A to power 16+ RPi, what do you think will happen if you cause a short circuit on the rail ?
Probably trip a circuit breaker or blow a fuse. The better question to ask is how likely such a failure is compared to the failures that could happen by powering those 16+ RPi some other way. If you're the type of person that constantly shorts out circuits, you're going to have problems with anything you do with electronics.

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Re: Powering multiple Pi Zero’s? (Again)

Sun Apr 22, 2018 6:05 pm

droleary wrote:
Sun Apr 22, 2018 2:21 pm
Ernst wrote:
Sat Apr 21, 2018 7:07 pm
What I'm saying is that if I had a project that required 16+ RPi to be clustered together I would not even consider to use "track lighting rails" to avoid a potential single point of failure.
Odds are pretty good there's going to be a single point of failure in the power system regardless. Could be at the wall, could be at the building. It just seems silly to jump to the "last mile" and pretend you've solved that problem.
As an exercise: with +/- 2A for each RPI would need at least +/- 32A to power 16+ RPi, what do you think will happen if you cause a short circuit on the rail ?
Probably trip a circuit breaker or blow a fuse. The better question to ask is how likely such a failure is compared to the failures that could happen by powering those 16+ RPi some other way. If you're the type of person that constantly shorts out circuits, you're going to have problems with anything you do with electronics.
I would thank you for your valuable contribution on the subject of occupational safety and disaster prevention.
Most human activity will be at the "last mile" and there for an "accident" is most likely to happen there.
A short circuit on a single rail system powering 16+RPI will cause a nice spark, may not even cause a circuit breaker to trip, but may cause damage to power supply / rail so badly that it is a total loss while downing all the cluster nodes. Let's hope that there is nothing inflamable lying around that could start a fire.
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Re: Powering multiple Pi Zero’s? (Again)

Mon Apr 23, 2018 2:27 pm

Ernst wrote:
Sun Apr 22, 2018 6:05 pm
I would thank you for your valuable contribution on the subject of occupational safety and disaster prevention.
You're welcome!
Most human activity will be at the "last mile" and there for an "accident" is most likely to happen there.
Now you're conflating the likelihood of accident with the "single point of failure" issue you raised. You still haven't addressed that issue, so unless you're trying to move the goal posts, you now have two issues to investigate.
A short circuit on a single rail system powering 16+RPI will cause a nice spark, may not even cause a circuit breaker to trip, but may cause damage to power supply / rail so badly that it is a total loss while downing all the cluster nodes. Let's hope that there is nothing inflamable lying around that could start a fire.
This smacks of FUD. Do you have any evidence that track lighting systems are more prone to the incidents you're describing than other forms of high-Wattage power delivery? What mechanisms would you suggest are likely to be the problem? Keep in mind that people handling an RPi are going to be exposed to the bare PCB and components. So, again, if shorting out circuits is something a person is prone to do, maybe an electronics hobby/career is not for them.

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Re: Powering multiple Pi Zero’s? (Again)

Mon Apr 23, 2018 3:37 pm

Talking to you is a waste of time, I hope that you are able to learn from your mistakes.
I suggest that you do not make the mistake to bridge GPIO pins 4 and 6 while plugged into your track lighting system, that could lead to an excessive state of sorrow.
My first computer was an ICT1500, my first "personal" computer was the Sinclair MK14

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Re: Powering multiple Pi Zero’s? (Again)

Mon Apr 23, 2018 5:48 pm

Ernst wrote:
Mon Apr 23, 2018 3:37 pm
Talking to you is a waste of time, I hope that you are able to learn from your mistakes.
I suggest that you do not make the mistake to bridge GPIO pins 4 and 6 while plugged into your track lighting system, that could lead to an excessive state of sorrow.
Please don't offend other posters here...
Its against our rules. :twisted:

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Re: Powering multiple Pi Zero’s? (Again)

Tue Apr 24, 2018 12:25 am

droleary wrote:
Sat Apr 21, 2018 1:25 am
Paul Hutch wrote:
Fri Apr 20, 2018 3:24 pm
See the rest of my reply for the general answer. ;)
I was hoping for hard numbers rather than "general" hand waving.
If you want hard numbers my employer and I could work them up for you but the cost would be $10,000+ paid up front (actually we have no free time is our schedules right now so we couldn't start until some time next year). Sorry, good engineering isn't cheap and a lot of the complete design needs to be done before a reasonably accurate hard estimate can be calculated.

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Re: Powering multiple Pi Zero’s? (Again)

Tue Apr 24, 2018 1:05 pm

Paul Hutch wrote:
Tue Apr 24, 2018 12:25 am
Sorry, good engineering isn't cheap and a lot of the complete design needs to be done before a reasonably accurate hard estimate can be calculated.
I didn't ask for anything formal or excessively accurate, I was just hoping you could back up your vague "Economics is why" answer with at least the smallest bit of evidence. In the spirit of the RPi being an educational platform, let people know the basis for your objections so that they can make their own calculations.

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Re: Powering multiple Pi Zero’s? (Again)

Wed Apr 25, 2018 11:19 pm

Ernst wrote:
Sun Apr 22, 2018 6:05 pm
...
Most human activity will be at the "last mile" and there for an "accident" is most likely to happen there.
...
Ah! I hadn't thought of that. I guess that comes from having a software & not hardware background.

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