Safely wiring and housing PSU's - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 17, 2021, 12:27:18 am
content: Hi,I mean Meanwell (see what I did there) must sell a heap of these "enclosed" PSU's, heck I have a few lying around.The AC terminals are exposed on these "enclosed" PSUs. I know they're supposed to be part of a larger systems enclosure but a lot of hobbyists (some with little kiddies I'm sure) are buying these for PC modding et. al. I for one don't wanting to be putting my hand in a PC case and touching live 220V AC terminals.So I guess the first question is, has anyone seen a cost effective (close to Meanwell prices) PSU family that just has an IEC320 on the back, the Excelsys Xgen stuff is lovely but costs the earth?I'm looking for 60A@5V and 25A@12V,Say I can't find PSU's with IEC320, so I go with a Meanwell LRS-350-5 and a LRS-350-12, can I connect the 5V and 12V to the same set of PC disk "Molex" connectors (AMP Mate-n-Lok 1-480424-0)?So if I can do that, what the heck can I put these PSUs into to safely cover the AC side, I'm not much of a handyman so an enclosure you can buy online would be good, obviously I would add a fan and IEC320 with fuse and power switch?Basically I want to power a lot of DIY disk shelves, with lots of 5V 2.5" drives inside.Thanks.Richard

author: Faringdon
author_rank: Super Contributor
timestamp: July 17, 2021, 06:37:54 pm
content: Yes , good idea to be safe..I mean, any metal enclosure you like...https://www.metcase.co.uk/en/Enclosures/Metal-Enclosures.htmJust make sure to have the enclosure earthed to be extra safe.Your PSUs probably already have fans in them....so just drill a few holes in your metal enclosure to let the air through....holes small enough so little fingers cant poke through.Or use a plastic case if you want.Yes...chassis mounting power switch and even fuse too if you want, though the meanwell will be fused inside.

author: james_s
author_rank: Super Contributor
timestamp: July 17, 2021, 07:19:28 pm
content: What's with all these people wanting to run lots of disk drives? Cryptomining idiocy? Or is there something more legitimate?

author: calzap
author_rank: Frequent Contributor
timestamp: July 18, 2021, 12:13:47 am
content: Attached photo shows my solution. Did not feel like taking it apart for more photos. I found a cast aluminum box that would fit nicely over the end but with about a 6 mm gap to allow passage of wires but not fingers. The aluminum box is mechanically attached and electrically bonded to the PSU. And yes, there is a strain relief for the 120 VAC cord which is plugged into a GFCI (RCD) outlet. Blue and yellow wires emerging from the bottom carry the 9 VDC output. The little hole in the aluminum box was put there for the PSU LED to shine through. It has since burned-out. The PSU supplies power to switch and other indicating LEDs in a pump house.Mike in California

author: Ian.M
author_rank: Super Contributor
timestamp: July 18, 2021, 05:40:34 am
content: @Rthorntn,You obviously either weren't around, or don't remember, the insides of PCs over the decade or so before the introduction of the ATX formfactor in 1995 and its accompanying PSU with low voltage control for the power switch. It was extremely common for clones to have exposed live mains pins on the back of the power switch, protruding through a cutout in the chassis into the case interior. One did *NOT* fumble around the drive bays without pulling the power cord. The better clones had a rubber boot over the back of the switch.The traditional way to touch-proof PSU terminal strips was to mount a Perspex barrier just above the terminals, wide enough that a finger couldn't reach the terminals, so long as the PSU was bolted down to a chassis. Often there was a threaded standoff either end of the terminal strip to facilitate mounting such a cover. Your Meanwell LRS-350 series PSUs don't make that easy as there are no mounting holes in the terminal area, but there's nothing to stop you adding a couple of standoffs to whatever chassis you are mounting it to, just past the end of its footprint to support a Perspex cover plate.

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 18, 2021, 05:47:03 am
content: Thanks @Ian.M, yeah, I was a small child all of the 70's.By the tine I had my own computer it was the late 80's.I do have a IMSAI 8080 so I know exactly what you mean, honking big open PSU, it scares me just looking at it!Perspex is a great idea!I haven't purchased the PSU's yet, if there is a better type (available from DigiKey) that has threaded standoffs I would love to know about it.

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 18, 2021, 06:12:27 am
content: I should add, I have a tap and die set so could I just add standoffs, what are the standoffs, are they like the PC standoffs that go under your motherboard?

author: Ian.M
author_rank: Super Contributor
timestamp: July 18, 2021, 10:07:01 am
content: Depends. If you've got a high quality case that came with all brass threaded hex standoffs, maybe, though personally I'd prefer to use hex internally threaded spacers with a screw from underneath, just so I didn't have to tap a thread in thin sheet-metal!(Hint: if you must tap thinnish sheet-metal, a thread-forming tap produces a much stronger thread than a thread-cutting one)The OEM standoffs in high volume applications would often be internally threaded round steel posts staked or welded into place.

author: timenutgoblin
author_rank: Regular Contributor
timestamp: July 18, 2021, 11:40:07 am
content: Quote from: rthorntn on July 17, 2021, 12:27:18 amNo, not really, but I think you meant well by it...

author: Terry Bites
author_rank: Super Contributor
timestamp: July 18, 2021, 01:36:05 pm
content: A word of caution. I had an entire raid array destroyed by a single faulty PSU.A sad server day, and of course it happend during backup. ShieeeeT!I'd use more than one PSU and reduce the risk or put some overvoltage protection on the PSU output(s) or both.There are two kinds of HD as I'm sure you know. Those that have failed and those that are about to.

author: wizard69
author_rank: Super Contributor
timestamp: July 18, 2021, 09:07:31 pm
content: There are all sorts of power supplies with IEC inlets, I'm not sure why this is a huge problem. Many of the supplies designed for 1U servers are very compact for example. You can get TDK's QS series with an IEC inlet and I'm sure othhers exist.You also have other options for increased safety. For example Bel Power has power supplies with protected (well better than nothing) barrier strips for AC in. Also many supplies are offered with plug terminals instead of screw connections. Then you have the industrial rated supplies commonly sold in DIN rail mounts, these have to meet tighter safety requirements even if the AC is somewhat exposed. For some applications these DIN rail supplies are the best compromise on safety vs. the alternatives.Now given all of this you do realize that when you implement one of these supplies you are responsible for the safety of the installation? That means there should be minimal risk if the enclosure is opened. Frankly if you think of yourself as "not much of a handy man", I'm not sure you should even be working on mains connected equipment. There are real safety issues that impact both you and anyone that might come near your installation and again if something happens you are responsible.Beyond all of that if you want to run a bunch of PC hardware why not go out and buy a PC power supply that already has the outputs and connectors you require? You say you are looking for "I'm looking for 60A@5V and 25A@12V, ", that is at least a good 600 watt power supply. You will likely pay far more trying to cobble together a bunch of chassis mount supplies. You might have to shop around for the right current mix or go to a larger than 600 watt supply. Also I have to wonder where the 60A @5VDC came from, seems like a lot for modern hardware. In any event an ATX supply solves a lot of problems for you and is far safer if you are not well versed in mains work. If you don't like ATX form factor server supplies come in all sorts of configurations.

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 18, 2021, 10:49:29 pm
content: Thanks all!@wizard69 modern ATX PSU's have piddly 5V rails, the 600W you describe, lets pick the Corsair SF600, the 5V rails on nearly every PSU I found are within 75W of each other:SF600Peak power = 660W+12V = 50A+5V = 20A+3.3V = 20AMax. combined power 3.3V + 5V = 120WThe other thought I had was what about a 12V to 5V DC/DC converter, does such a supply (60A output) exist?

author: wizard69
author_rank: Super Contributor
timestamp: July 21, 2021, 08:12:32 pm
content: Quote from: rthorntn on July 18, 2021, 10:49:29 pmYes I know which is why I said:QuoteEven if you go to larger ATX supplies they still hold the 5VDC at around 25 amps.So I'm still wondering why any modern implementation would be trying to pull 60 amps from a 5VDC supply. This just seems odd to me when everybody has gone to the 12 VDC supply and uses local regulation.QuoteYou can get over 80 amps on the 12 volt rail on ATX power supplies. That is a lot of power!!! Which brings up another issue, the supply I'm looking at online right now couldn't possibly deliver rated power into every rail at the same time. Just the 12 VDC and 5 VDC power ratings puts you over the supplies 1000 watt rating. So you need to know what you are doing and how you are allocating power off a ATX supply.I'm still trying to understand where you power numbers are coming from. You can buy all sorts of DC to DC converters but the problem I see here (beyond the cost) is that you need to know how to properly install them. This isn't something trivial in that you can dismiss safety concerns, thermal management and so forth. Rather you need to be safe and have the ability to manage the thermals in the system, or have an unreliable and not so safe system. 60 amps through the wrong wire and you will have a lightbulb for a brief moment.You can get the voltages and currents in standard supplies that will come real close to what you want but I still have to wonder why. A 300 watt, or even a 600 watt, supply is not a big deal these days so that in itself isn't a problem. I think Digikey will list out over >100,000 different supplies via parameter search so there are plenty to choose from. Frankly there are a lot more suppliers and manufactures than what is at the Digikey store.

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 21, 2021, 09:15:57 pm
content: Thanks, the numbers I'm getting are from the ST5000LM000 datasheet.Spinup (max) 5V 0.75AAnd I have 64 drives currently.Now I can't guarantee that I have staggered spinup and so, to be safe I wanted to be able to provide 240W of 5V just for the drives, to be safe (for the backplanes 5V consumption) lets say 300W, there is the 60A.Now some posts here (Terry Bites) have me thinking about running $5K worth of drives off of a single PSU and so now I'm thinking multiple smaller PSUs.