Racks and Power Supplies

On a sunny day (Wed, 16 Jan 2019 13:34:32 +1300) it happened snipped-for-privacy@f377.n35.z1.binkp.net (Rick Christian) wrote in :

I have several Meanwell power supplies. Yes those have screw terminals and we have 230 V here. I do not see the problem? Those are meant to be mounted into some industrial type of housing. Very good quality.

Cooling will be you biggest challenge perhaps.

compatible?

pi?ref=

I believe that pi's are generally acknowleged to require 1 amp or a bit more under heavy load, so would be more like 15 amps for 10.

I would suggest you might look at some mini-itx power supplies. Still a bit of overkill, but they are compact.

Neither do I provided they are used in such a way that the power source and PSU do not move relative to each other. A flying lead to a plug on the wall would be erm, foolish, as would using a PSU like that without some kind of outer casing.

Many good ATX supplies are really 12V supplies with a set of DC/DC converters, not much is going to waste by using just the 5V rail, there'll be some excess capacity on the 12V rail - you could run some LED lighting off it if that bothered you. IME it's usually cheaper to repurpose a good quality ATX PSU (ie. the ones gamers buy and run at the rated capacity without blowing them up) than to buy an equivalently rated dedicated PSU.

On a sunny day (Thu, 17 Jan 2019 06:24:26 +0000) it happened Ahem A Rivet's Shot wrote in :

You mean like this?

You are absolutely right, although I do habe the opinion that it is safer than those skying competitions. Do not do this at home.

I have 'm stacked 3 high too, 3 x 7.5 adjustable to make 24 V:

I also have 300 kV somewhere, well that is what it says anyways.

Sorry. ;-)

Yeah lab benches are the only place, not because it's safe but because you know it isn't and the occasional belt is an occupational hazard that you learn to avoid with (hopefully not too much[1]) experience.

On a sunny day (Thu, 17 Jan 2019 08:51:16 +0000) it happened Ahem A Rivet's Shot wrote in :

I worked in a TV studio for many years, also in TV repair. The danger was taking a CRT out (after discharging the HV), it then slowly builds up voltage again [1], and if you got bitten while holding it in your hands dropping it would cause an implosion and glass pieces would pierce you. We had an CRT implode all by itself, colleague heard a funny ticking noise, and decided that that was a good moment to go get coffee, when he came back the pieces of glass were sticking in the 1 inch thick metal armed soundproof studio door. Handling CRTs I have learned to control the 'drop it' reflex. Been bitten by that direct 25 kV several times, step aside, break contact.

Anyways, raspies are safe :-) LCDs are sort of safe (if LED backlight) as far as HV goes.

I still have a color CRT monitor in the attic, colors are better than LCD IMO, no burn in either.

Yep seen that, discharge capacitor (big paper, high voltage), leave for a week with nothing across terminals - regret touching it! The corona discharge around the terminals, when it was built into the GBFO strobe light it (and three others just like it) was destined for, was very pretty if a little perturbing. These days I'd just use a bunch of LEDs and a switching transistor (switching a hundred watts or so of LEDs isn't exactly hard), too easy, no fun.

modern CRT's are implosion protected, but i would still not want to chance it.

It depends how homebrew you want to get...

I've not done this specifically for the Pi but for other boards in the past I've used dirt cheap generic rack shelves and self-adhesive PCB standoffs - those things stick very firmly and the result is suprisingly robust. For the Pi though the problem I see is that you're unlikely to find suitable standoffs that will fit the holes

- most boards use mounting holes in the 3-4 mm range which is what the standoffs target.

Suitable nuts/bolts through the shelf would be an option but would probably foul on whatever is below the shelf in the rack unless it is something shallow like a patch panel - I wouldn't fancy your chances of countersinking them - some nut rivets come fairly close to flush fitting but never seen them in M2.5 or smaller.

An alternative that comes to mind would be to glue a sub-base of e.g. 9 or 12mm ply to the shelf surface. You can then screw the Pis in place using suitable woodscrews and cylindrical standoffs. A quick back of an envelope calculation suggests you'll get between

As for power I'll leave that to you since you are obviously best to decide what you find acceptable. The enclosed powers supplies of the kind you seem to be referring are really intended for equipment mounting and need further enclosure, but to be honest if the screw terminals are used with insulated crimp terminals they're generally reasonably touchproof - they'd certainly qualify for an IP2x rating. My biggest concern would be ensuring some form of strain relief to ensure a tug on the cable doesn't pull it out of the terminals.

The problem reading between the lines is you want the mains side fully enclosed but the low voltage to be freely rewireable. Bench supplies with 4mm socket/binding posts come to mind but tend to be quite tall and the budget models (the ones with a few fixed voltages as opposed to continuosly variable voltage and current) tend to be difficult to track down. The final option would be to stay firmly in consumer territory and get one of those multi-output USB chargers with 8-10 outlets.

Some time in the 1980s at a trade show I saw one poor sod demonstrating how strong the protection on a CRT, by hitting it square in the middle with a claw hammer over and over again all day long. You couldn't have paid me enough, it would have shredded his legs if it imploded.

Me too.

In the eighties, I dropped a bare 9 inch monochrome CRT after receiving a shock from the cap terminal while carrying it about. It smashed (hit concrete side on the band edge) and shredded a cardboard box that, as luck would have it, was between my legs and it. That CRT probably wasn't implosion proof, or the impact was at a weaker spot than straight on.

Throughly OT, but an intriguing thread - I have for very many years, always devacuumed CRTs by breaking off the pin cap and the glass vacuuming tube exposed within. I knew nothing about the potential severity of an implosion, but thought that releasing the vacuum was a sensible, and easy, thing to do. Oh, the innocence and freedoms of being a child of the 60s...

Hello ray!

rc> I believe that pi's are generally acknowleged to require 1 amp or a rc> bit more under heavy load, so would be more like 15 amps for 10.

Per:

"We recommend a 2.5A (2500mA) power supply, from a reputable retailer, that will provide you with enough power to run your Raspberry Pi for most applications, including use of the 4 USB ports. Very high-demand USB devices may however require the use of a powered hub. The table below outlines the specific power requirements of each model."

Rick

... NOprah!

While rounding up is immaterial for a single power supply, it gets silly if you multiply it, and could end up costing more for bigger PSU and heavy duty wiring which isn't needed.

When you start getting in to tens of units and need a high spec PSU, you need to measure the actual current usage under load, and add a suitable margin. Rather than just scaling up the recommendation aimed at stopping people having problem with cheap wall warts.

---druck

It's also general advice based on typical circumstances. In particular it assumes that the Pi is loaded up with a few peripherals e.g. mouse, keyboard, a USB stick and other random devices and that power are all coming from the same power budget. For a home user with a single device that isn't a bad assumption, but in the case of tens of them in a rack it is an assumption that breaks down, put simply they won't all be hooked up to a head and input devices at the same time. You're also far less likely to have random devices hooked up to them all, e.g. how many TV tuners or remote control sensors do you need?

I'd be perfectly happy with a good 60W PSU, that gives you plenty of headroom for the Pis without the additional expense, bulk and power wastage of a pointlessly over-rated supply.

At the risk of being crude, broomclips nicely hold Pi's in cases, there's complete freedom to install and remove individuals without disturbing neighboring units.

I understand the appeal of a single DC supply, but it's also a single point of failure. A group of wallwarts plugged into an outlet strip with cube taps to give good packing density is cheap, compact and easily fixable if something breaks.

Here's a photo of my (admittedly small) setup. The cables are a mess only because I bought stock lengths:

Everything is off-the-shelf, each pi is independent of every other pi. If off-line power is wanted a standard UPS can be added.

HTH,

bob prohaska

Hello bob!

I am really looking for more, elegant solutions.. Nice, but not for me...

DIY is not part of my skills, when it starts to involve wood or metal or other industrial arts .. I did my pennance with that in HS, not for me...

While thats a neat way of mounting Pi's in cases.... its not for me.. ..

bp> I understand the appeal of a single DC supply, but it's also a single bp> point of failure. A group of wallwarts plugged into an outlet strip bp> with cube taps to give good packing density is cheap, compact and bp> easily fixable if something breaks.

Aware of the SPOF, a spare, and possibly a hot spare system will be setup... but the whole wall wart thing is EXACTLY what I am trying to rid my house of in all forms... Pi's to all sorts of all things... if its got wart to power it, it needs to be looked for erradication.

AC distribution for long disatnce is great, but with the modern household the need for internal DC distribution is a must, especially in the nerd home.

I am actually looking to find a way to do whole home DC power distribution...and I am going to start with the main areas which have lots of stuff that needs DC and won't entail fishing wire etc...

bp> Here's a photo of my (admittedly small) setup. The cables are a mess bp> only because I bought stock lengths:

bp>

I understand the way that happens... its exactly what I am trying to prevent and get rid of...

Clean setups of stuff like I have in my radio shelters, is what I am after at home... Lots of things get in the way of doing that when you have to get things online and going now now now... I've got the result of that sitting in my "lab" room right now... Pi's sitting on desks taking up space that then need to be organized... these Pi's 99.9999% of the time need no attention.. connect LAN, SDR, power, startup OP25, rtl_fm etc.. and have them feed my IceCast server...

bp> Everything is off-the-shelf, each pi is independent of every other pi. bp> If off-line power is wanted a standard UPS can be added.

A UPS will be and is used on all electronics... to keep them active till gen set come on.

Rick

... NOprah!

Hello druck!

dr> While rounding up is immaterial for a single power supply, it gets dr> silly if you multiply it, and could end up costing more for bigger PSU dr> and heavy duty wiring which isn't needed.

dr> When you start getting in to tens of units and need a high spec PSU, dr> you need to measure the actual current usage under load, and add a dr> suitable margin. Rather than just scaling up the recommendation aimed dr> at stopping people having problem with cheap wall warts.

Well aware of the rounding error issue, I would rather over size rather than under size or just enough, with little to no room for expansion..

It might be 10 Pi's now, it could be 20-30 in the end or more.. who knows...

You can read the other post, I don't 10-20-30+ wall warts for Pi's.. I am trying to erradicate them throughout my house.

Rick

... NOprah!