High quality DC 19V PSU? (for use with a DC UPS) - Page 1
Forum section: electronics / projects

author: marber
author_rank: Regular Contributor
timestamp: November 09, 2015, 01:43:31 pm
content: Last Monday we had a large scale power outage in this area, and unfortunately one out of three HD drives in my home server/NAS system died. I do have a very old UPS (APC SU620INET with new battery) which caused more outages than it prevented, so I wasn't using that anymore especially as power tends to be fairly stable here. Still, using a UPS is evidently a good idea.I'm considering a decent new UPS (e.g. Eaton 5P, or perhaps just a simple 3S), but still it doesn't quite feel all that optimal. I'd be using it to protect my home server, a few routers/switches and a cable modem in my wire closet, *all* of which are fed by cheap DC power bricks. Line-interactive UPSs with pure sine wave output seem nice and common, but are they really all that useful here? Line-interactive UPSs help with slight under- or over-voltage situations using their autotransformers, but a) those don't seem all that common here, and b) the switched PSUs of this equipment probably wouldn't really care. Online UPSs are more expensive and generate more heat due to the double conversion - and for what? To convert it back to DC again?Then again, the external PSU of my NAS/server (in aChenbro ES34069)seems to be a 19V laptop adapter, and my impression is that it's not the most resilient (and why would it be, for a laptop).So instead of going the conventional UPS route... wouldn't it make sense to use a nice quality industrial (DIN-rail) DC power supply for this equipment, coupled with a DC UPS? That might actually improve reliability over a 230V UPS for the cheap walwarts. Should be simple for most of the devices, which have 12V DC plug packs. I had a look at some industrial DC supplies, e.g. the Puls Dimension power supplies that Mike did a few videos on. However I didn't yet find a good industrial DC power supply for 19V output for my home server, they all seem to have outputs tunable only around 12/24/48V (which makes sense of course).Is anyone aware of a good alternative here? Or are there any general flaws in this plan?(Yes I am aware that one of the most important functions of a UPS is actually signaling a server to shutdown before battery runs out - I'll deal with that separately

author: Fungus
author_rank: Super Contributor
timestamp: November 09, 2015, 02:03:40 pm
content: 20V switching power supplies aren't uncommon. Most of them will have an adjustment pot that will let you tweak it to 19V.If not, get a 24V supply and put a 5V supply in series but backwards.24V-5V = 19V

author: Karel
author_rank: Super Contributor
timestamp: November 09, 2015, 02:23:42 pm
content: Quote from: Fungus on November 09, 2015, 02:03:40 pmFor a moment, I thought you were serious.I guess the smily meant you know this is a very bad idea...

author: Fungus
author_rank: Super Contributor
timestamp: November 09, 2015, 02:38:11 pm
content: Quote from: Karel on November 09, 2015, 02:23:42 pmYou're right. It's better to put the 5V PSU low-side like this:+----+| || LOAD (19V)| |24V +| || 5V| |+----+|GNDThis keeps all the GNDs common to all power supplies.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 09, 2015, 03:19:47 pm
content: Quote from: Fungus on November 09, 2015, 02:38:11 pmBetter notDon't put two supplies against each other unless you are sure that the lower voltage supply (in this case the 5V one) cansinkall required load current.CheersAlex

author: SeanB
author_rank: Super Contributor
timestamp: November 09, 2015, 03:56:14 pm
content: Buy a few buck boost converters off eBay, rated for the load of each item ( with the eBay ones get double the power for each,m they are very likely being overspecced) with 12V input and appropriate output voltages. Isolated ones for things like cable modems and such that have a connection to the outside world, and non isolated for things like the NAS and your network switch. Then get a 12V deep cycle battery of appropriate capacity to cover the longest outage, and a float charger that can charge it and supply the load as well. That way you get the best efficiency at the lowest cost, and adding more equipment on is simply a matter of adjusting the converter output to suit.

author: marber
author_rank: Regular Contributor
timestamp: November 10, 2015, 11:42:46 am
content: Quote from: SeanB on November 09, 2015, 03:56:14 pmIsolation is a good point - the home server doubles as a media (Kodi) server as well, and has HDMI out via a HDMI-over-CAT6 converter to elsewhere in the building.I'll first see if the internal DC-DC converter (for ATX power) can support lower voltages (12V?) as well...

author: eas
author_rank: Frequent Contributor
timestamp: November 10, 2015, 09:51:12 pm
content: For what it is worth, there are some commercial UPSs intended for providing DC power to home/SOHO networking equipment. I think they may exist, in part, because telcos want to kill POTS (plain old telephone service), but haven't been able to shake requirements for providing 911 service.I think they may be labeled as "broadband gateway" UPS, or something like that.

author: taylor12
author_rank: Contributor
timestamp: November 10, 2015, 10:38:46 pm
content: belkin makes the one for my att uverse router. it a 12v out if i remember. its nice to have wifi when the power goes out