DC-DC UPS are there any drawback that I am neglecting? - Page 1
Forum section: electronics / projects

author: SaleB
author_rank: Contributor
timestamp: May 03, 2020, 12:51:30 pm
content: I am in the process of making a home server. As you all probably know it is advisable to have a UPS device connected to any redundant storage solution, at least to give it enough time to get into sleep when a power outage comes. After looking at the UPS devices, and seeing that many consumer-level devices use lead batteries that should be changed every 2-3 years I have come to a conclusion to use Li-Ion. It was interesting to find out that just the newer models made by top brands use Li-Ion or Li-Polymer batteries. Another interesting thing was that there are very few power supply brands that even make PC power supplies with DC input. I found a few low power solutions intended for automotive PC solutions, ranging from 130 to 450W and that was it.So, my idea is to make a kind of voltage distribution board, that would generate all the voltages needed in a PC, by taking a 12V or 24V from a battery source or a Meanwell external SMPS power supply. It is complicated to e to believe that I have come to a solution that no one taught of before, so the other conclusion would be that there is some major drawback to that solution that I am not thinking about. Please, tell me what would be a drawback.If there are no substantial drawbacks I would like a suggestion for a circuit or a single IC switch that would monitor the AC input and send the command to switch power sources when AC is lost, but before the power brick losses voltage on the DC side. I am assuming those few hundreds of milliseconds are enough to do the switching. If your suggestion is is a single IC I prefer it to be something that can be soldered by hand, so I would like to avoid a BGA or QFN package.Thank you

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 03, 2020, 12:58:46 pm
content: Just use a 3S pack with a BMS and then 12V (4V/cell) will be pretty much a perfect float voltage. To connect it to the DC bus, the easiest way would be to use a relay with a Schottky diode to cover the time it takes for the relay to switch. Then add a resistor, PTC, or even an automotive incandescent bulb in parallel with the diode to give a limited charge current.Another possibility is to use a MOSFET.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 03, 2020, 02:13:15 pm
content: There is a new motherboard standard going : Intel ATX12VO Power Connector You juste need a powerful 12vdc to supply the board and everything else (5v, 3.3v ...) is generated by the boad himself.I would go with the standard ups solution and wait for this standard to come out on many boards / brands ... or replace your cell with Li-Ion or Li-Polymer batteries as you wrote.Or simply buy an newest generation ups ... for me to replace batteries at 3 years intervals is fine with me, my ups runs at 24v and can use an external 24vdc pack.Some threads here mention super capacitors instead of batteries ....

author: SaleB
author_rank: Contributor
timestamp: May 04, 2020, 12:55:18 am
content: I have just now read about ATX12VO. I did not know about it. It will be many years until something like that comes to second-hand servers or consumer motherboards, but it gives me confidence that I am thinking in the same direction as they are.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 04, 2020, 01:31:13 am
content: Already started :https://www.tomshardware.com/news/asrock-z490-motherboard-intel-atx12vo-10-pinIf youre willing to make tryouts of your "new" ups design and put time, efforts and maybe more than you're willing to spend go for it.You have efficiency loss to convert a dc source to smps / ups and convert it again to the needed 3v, 5v, 12v and -12v, for the motherboard needs, and the rest of the computer case hardware like vdo card(s), ssd, sata hdd...Each voltage you need will have a loss somewhere, and finally you'll need lots and lots of amps ... and some protections ??I have a 1k watt psu for a computer with 12 hard drives, my 1.5kw apc ups last 10 minutes with the original 24vdc internals batteries, 20 to 25 min with the added external pack. I dont know your computer power requirements ?My 1kw corsair psu.3.3v is 25 amps5v is 25 amps12 is 83 amps-12v is 300 milli amp5v standby 3 ampsA big total of 137 ampsSome of my friends are using deep discharge cells, they have put an seconday charger on them, when the charger operate it select a battery pack and open the battery circuit to charge them outisde the ups system, once the charge is complete they are put back in the circuit, while the other pack begin a charge. But they are 3kw or more ups ... in rack mount enclosures.I do understand the 2-3 years change, my old / died ups had a charge problem, it busted the batteries after 2 years, but i must say it saved my ass so many times ...

author: ogden
author_rank: Super Contributor
timestamp: May 04, 2020, 01:35:21 am
content: Worth to mention what Google did long ago:https://www.cnet.com/news/google-uncloaks-once-secret-server-10209580/Consumer motherboard with 12V or 19V input:https://www.gigabyte.com/us/Motherboard/GA-B75TN-rev-11#ov