Uninterruptible Power Supply - DIY?

[atatistcheff]

Couldn't find a great section to post this in so I'll try general, even though it has nothing to do with solar.

I'm interested in making a couple of UPS systems for my computers. Now I know you can buy an APC or Tripp Lite for this purpose but most of them use low Ah lead acid batteries which have a pretty limited lifespan and limited run-time. There are some that do use lithium batteries also but they start to get up there in price. What I'd like to do is maybe find a UPS with dead batteries (they are everywhere) and retrofit with LiFePO4. One challenge is charging it with the UPS charging system designed for a lead-acid charging profile. I'm wondering if anyone else has thought about this or even done something along these lines? I'm not looking to do anything really expensive, for one of them I need to run 250W of computers for maybe 20-30 minutes. The other is smaller, just needs to run some network equipment which is probably less than 50W.

Has anyone done any research or maybe even built something you'd like to share?

 

[gnubie]

I have a UPS board from ebay feeding two 18ah 12v AGM batteries to run my fibre internet connection, router, raspberry pi, 2 usb hard disks, a usb hub, a usb network adaptor, HDMI ethernet extender (used as a hdmi capture device), another raspberry pi, usb hard disk, usb hub, 2 dvb-t tuners and a router used as a wifi bridge. In otherwords, quite a bit. The two batteries hold all that up for 8 or so hours. The UPS board I have outputs regulated 12v using an onboard buck/boost from battery voltage. Separate bucks are run off that 12v to supply the 5v equipment. The UPS board was fed by an old Dell 19v laptop power supply.

This was all before I set up solar panels, now that all remains in place but its run off 24v from a battery which is dropped to 19v with a buck converter.

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Found the exact board but the price has gone insane for some reason. https://www.ebay.com.au/itm/UPS-122...ol-DC-backup-power-supply-10-28V/254364950490

 

[gnubie]

Keeping the full DC theme, you could even go to the extent of putting a pico powersupply in the PC to run it direct off 24v. That only leaves the monitor to think about.

 

[atatistcheff]

Found the exact board but the price has gone insane for some reason. https://www.ebay.com.au/itm/UPS-122...ol-DC-backup-power-supply-10-28V/254364950490

Mine has to put out 110VAC, I'm powering some network/server equipment that doesn't have DC inputs. I suppose it's as simple as using an old UPS, replacing the battery then getting a LiFePO4 charger and disabling the on board 12V battery charger.

 

[Supervstech]

Couldn't find a great section to post this in so I'll try general, even though it has nothing to do with solar.

I'm interested in making a couple of UPS systems for my computers. Now I know you can buy an APC or Tripp Lite for this purpose but most of them use low Ah lead acid batteries which have a pretty limited lifespan and limited run-time. There are some that do use lithium batteries also but they start to get up there in price. What I'd like to do is maybe find a UPS with dead batteries (they are everywhere) and retrofit with LiFePO4. One challenge is charging it with the UPS charging system designed for a lead-acid charging profile. I'm wondering if anyone else has thought about this or even done something along these lines? I'm not looking to do anything really expensive, for one of them I need to run 250W of computers for maybe 20-30 minutes. The other is smaller, just needs to run some network equipment which is probably less than 50W.

Has anyone done any research or maybe even built something you'd like to share?

I have several ups devices of varying output setup with lifepo4. The charge profile isnt perfect, but works fine for them.
I even have a best 5kva bank I am working on...

 

[svetz]

Not a UPS, but I was able to reuse the built in charger of a device with a BMS, see The Peak Jump Start. Just so happened the built in charger had the right voltage. You could probably get one of the cheap buck/booster converters to alter the voltage of the existing UPSes charger to what you need. My biggest issue with it was the replacement battery was ~2x the watt hours of the original, the charger takes for ever to charge it back up.

 

[Supervstech]

Not a UPS, but I was able to reuse the built in charger of a device with a BMS, see The Peak Jump Start. Just so happened the built in charger had the right voltage. You could probably get one of the cheap buck/booster converters to alter the voltage of an existing UPSes charger to what you need. My biggest issue with it was the replacement battery was ~2x the watts, the charger takes for ever to charge it back up.

You can tie them directly to the cigarette lighter socket and charge it with a bigger supply... hat little 1amp brick they come with SUCKS!

 

[Mars]

What is your budget? Aims Power sells these things https://www.aimscorp.net/600-Watt-Pure-Sine-Inverter-Charger-12V.html They can be found at Amazon, Zoro and maybe Home Depot.
I have a home made system that I am considering upgrading. This system currently has 150W PV, one dead deep cycle marine battery (originally two Trojan T5 6V deep cycle batteries, 225 Ah), 300 W pure sine wave inverter and an automatic transfer switch.

 

[atatistcheff]

Wow, that Aims Power Inverter Charger is pretty nice. If I wanted to do this "right" then that would be an excellent choice. Too rich for this project but I will definitely keep them in mind for something more serious. Thanks!

 

[svetz]

Just an FYI, @Wiley brought up an interesting concern about heat in rebuilding a UPS with a lithium battery in this post.