Non-solar UPS for computer rack - is LiFePO4 even a good idea?

[Linwood]

I have a closet full of computer gear with low total load (maybe 400-500w) and several Cyberpower UPS's, that are basically disposable and I have to replace one every year or three.

I have been looking at some postings for DIY UPS setups with inverter/charger (or both separately) and battery(s) and thinking of building up something. The max current draw is modest so fits LiFePO4 and getting a longer run time is attractive.

This is not a solar setup, just pure UPS. Which brings up the question: absent some forced cycling, 99.9% of the time the battery would be charged to 100%.
How bad is this for battery life? Last thing I want to do is trade replacing cheap SLA batteries with expensive LiFePO4 batteries because I'm putting them in an abusive charge situation.

Most examples I find when searching are people trying to use charge/inverters from APC (etc) units off the shelf, I am not suggesting that. I am looking at something more like here: https://xtremeownage.com/2021/06/12/portable-2-4kwh-power-supply-ups/

Though I think I would want to do 24v at least, and maybe not as large.

Do I need to plan some technique to maintain, say, an 80% charge not 100% charge? Which may make double conversion difficult (i.e. charge while drawing power through output inverter for cleaner power to load).

If anyone has pointers to example UPS builds they are appreciated, but wanted a sanity check first -- is it even a good idea?

Linwood

 

[Steve_S]

Applying the KISS principle, this is quite easy.
24V Battery System will provide all that you need and then a bit.
A respectable smart Inverter/Charger that can operate as a UPS with VAC inputs for 1) Grid power to charge batteries, 2) Genset VAC input to charge batteries IF the grid has failed and optionally be able to accept Solar Input for charging batteries (not a huge solar setup either).

Starting with a Quality Smart Inverter/Charger look at these from Samlex. The EVO series is used by Fire & Rescue, Military, Police & other similar services and are a Tier-1 Quality product with far more features & functions than most others on the Market. They are a bit more costly but you Really do get what you pay for. All of the ATS (Transfer Switches) are built-in and more. Very low consumption, and 95%+ Efficient.
These can be easily programmed to prioritize charging etc IE, Charge from Grid, if not avail charge from solar or genset or both...

EVO™ Series Pure Sine Wave Power Inverter/Chargers | Samlex America

Samlex EVO™ Inverter/Charger for RVs, boats, cabins, work trucks and backup power. Robust 3-in-1 power inverter, battery charger and transfer switch.

samlexamerica.com

Next batteries:
24V/100AH = 2560Wh or 2.5kWh Weight approx 16Kg / 35lbs +/-
24V/280AH = 7168Wh or 7.1kWh. Weight approx. 45Kg / 99lbs +/-
You can build batteries or buy prebuilt commercial. DO NOT BUY 2x 12V and put those in series for 24V, people do it all the time, even when told not to, only to discover WHY we say don't afterwards (after the hair-pulling and self-abuse). Keep to "Native Voltage Packs" only !

FYI, at This time, I am not aware of any Rackmountable Inverter/Chargers but that doesn't mean you can't attach one to a Rack Shelf but airflow / cooling is a point you cannot mess around with.

 

[prometheanfire]

I'd bump to 48V if you can as that seems to have components more commonly available.

 

[SamDeleted]

Last thing I want to do is trade replacing cheap SLA batteries with expensive LiFePO4 batteries

Then I'd stick with the cheap SLA ? , how often do your UPS batteries get cycled , 10 times a year ?

 

[prometheanfire]

More often actually, most UPS's will self test on a certain cadence. Though that isn't a full discharge cycle I think. For me UPS batteries last about 5 years at the long end. I do have 6-10 outages a year though (waiting on this solar install...).

 

[Linwood]

I apologize I have been ignoring this thread since I got no email notifications and thought it got no responses. Not sure what's up with that, thought I had everything turned on.

Anyway.... as to the UPS batteries, I would say on average I'm getting around 3-4 years, and often they fail, despite self tests passing, during a real power failure. Luck? Not sure. So it's a combination of hoping for something more reliable and also top stop dealing with replacements.

The Samlex specs look interesting. It does look expensive, and looks like you need the remote control to program? This opens a whole can of worms I had not thought about, how I will monitor whatever I do (in a home automation sense), it's not clear Samlex has an open API, SNMP, etc. Need to dig a bit.

I see no one has commented on my core concern, does that mean it's silly? That in a UPS environment the battery stays fully charged nearly 100% of the time. Is that a concern?

12v, 24v, 48v... yeah. Tradeoffs. One consideration: I have a nice 200ah 12v I use for astro that sits around at 60-80% all the time. I was thinking if I used 12v for the computer closet, in an extended outage I could bring that one in and replace a depleted one if I needed a bit more runtime. In fact could swap back and forth if it was useful.

I just took inventory and have only about 260w in the closet, and a total of around 500w if I also connect my office in an extended outage. So at 12v I'm looking at maybe #4 wire max, doable, but annoying to work with. Thinking...

One last question: I take it the Samlex (or similar inverter/chargers) do not do state of charge? Or does it? So I'll need a battery with SOC in the BMS or a smart shunt or similar if I want to count coulombs? Which also complicates the monitoring aspect.

Back to reading... Thanks for the input to date.

 

[krby]

I had the same thoughts back in July and posted this question: https://diysolarforum.com/threads/b...-converter-charger-or-inverter-charger.63790/ I never got a reply, but I did end up building it. Parts are: 600W AIMS inverter, 55A PowerMax converter charger, two 12V AGM deep cycle batteries.

In my opinion (I mean that, it's just an opinion, I know others disagree) LiFePO4 isn't a great fit for the UPS use case unless you happen to have them on hand already. From what I have read lithium chemistry batteries don't like to be charged full most of the time, while SLA batteries are ok with this. Also, with LiFePO4, you're paying quite a bit for low weight. For a fixed install (at least mine) weight doesn't matter much. In a UPS use case, they're not going to see many charge/discharge cycles. When I am running off batts, I have a much less usable capacity than a comparable LFE, but I got a good deal on these and they'll spend most of their life charged then I'll replace them and make a decision then what the right chemistry is.

In my exact case, I had the AIMS inverter already, my max load is about 250W, but typically 120W. I hope it's ok to run this AIMS unit 24/7. It's been doing fine since July. So, I just had to buy the PowerMax converter/charger and the batteries. From what I can tell, converter/chargers are intended to be run with 100% duty cycles and it's also only supplying 10-20A at 12VDC of it's rated 55A.

One addition not in this picture is I wanted this "UPS" to interface with my network via USB to send "AC mains present/missing" signals so my NAS would shut down 5min after the mains go away (my NAS is the least critical part of my server rack and uses as much power as everything else combined). This became a whole separate rabbit hole involving an Arduino and a Rasperry Pi running NUT.

 

[Linwood]

Thanks, @krby, indeed I am coming to the same conclusion. As I look to do this "right" and have good monitoring (automated, since I run everything in zabbix and/or home assistant) it is really getting expensive. Some old SLA batteries are easier, heck I can probably just take an old UPS and replace the tiny batteries with large ones if the charger will work. I don't need much power, duration is more relevant.

 

[prometheanfire]

Thanks, @krby, indeed I am coming to the same conclusion. As I look to do this "right" and have good monitoring (automated, since I run everything in zabbix and/or home assistant) it is really getting expensive. Some old SLA batteries are easier, heck I can probably just take an old UPS and replace the tiny batteries with large ones if the charger will work. I don't need much power, duration is more relevant.

That's basically what rack mount expansion batteries do, those tend to be dc coupled (parallel) never AC that I've seen.

 

[krby]

heck I can probably just take an old UPS and replace the tiny batteries with large ones if the charger will work.

It might, some UPS models have a capacity set in firmware and might not be happy if they have to put in more than the expect Ah. Or, may just cut off charging if it takes too long (a 1A charger in a UPS might be fine for a 2Ah battery, but would take over a day on a 50Ah replacement. I don't know how common that is.

If you have a donor UPS on hand, and it's easy for you to do, I would start with the UPS and wire in the batts you want. If that doesn't work for some reason, then start looking at inverter chargers or separate converter/chargers and inverters (like what I ended up with).

Re 24V vs 12V, i500W from 12V is doable just be mindful of wire gauge. I agree with the "don't try to wire 12V in series to make 24V", you have to worry about state of charge for each battery. If you're not sure you know how to do this, don't. In the picture I posted, I have two 12V batteries wires in parallel. Even wiring in parallel has its own considerations. IMO, doing parallel with two batts is pretty trivial, wire them + to +, and - to -, then I wired the charger and load "at the corners" (+ from one batt, - from the other). Beyond two in parallel, do some research and ask questions on this forum.

I'm happy to answer specific questions about my build if you have them. I had the inverter already so it was pretty easy to do to get to the basic "will provide AC when mains goes out" function. If you want it to report to a computer like commercial and consumer UPS do, then you've got to buy some more bits, do some soldering and flash an Arduino, but I've just done through that too so it's fresh in my head.

Also, I just re-read your original post and saw a link to portable battery rig. I built a thing a lot like that a couple of years ago. It's a portable electric "generator". It will work for a UPS, but I don't use it for that. I oversized it so it's heavier than I wanted, but it does the job I wanted and two people can move it if the ground won't support the rolling suitcase wheels.

The take away from this is that an inverter/charger will absolutely act as a online interactive UPS (like most consume UPS', AC mains passed through, then switch quickly to battery when the mains goes away). I tested it with my network rack and the switch over time didn't bother anything in it (NAS, switch, router, cable modem, some other small gear). Using an inverter charger makes wiring easy and a good one is configurable and handles things like low-voltage cutoff, max charge current, etc. I didn't use it for my network rack UPS because I only need about 300W of power, I think I found a few at the 500W range, but in general they seem to start at 1000W and are expensive. Especially since I already had a pure sine inverter, I realized I only had to buy the AC->DC charger/converter unit and I found a reasonable one for $150.

 

[Linwood]

If I'm going to build something large, a double conversion one might be better than line interactive, cleaner power. I do have at least one if not two old UPS' around but they are suspect - probably failed batteries but I didn't consider them worth investing in a new battery set. I haven't spent any real time to see if inverter/chargers support a double conversion setup though, or which do. Right now I just recognized the state of analysis paralysis and moved on to a different project. I'll return soon.

 

[krby]

RV Converter/charger + battery bank + inverter = double conversion UPS.

The converter/charger runs a typical battery charge cycle, then floats the batteries. Since the batteries are in parallel to the output of the DC output of the converter/charger, the inverter pulls from it, and then the batteries if the converter/charger is offline (because AC mains is off)

 

[n2aws]

I don't understand why UPS batteries don't last that long. I've seen lead acid batteries survive 30+ years in teleco environments, where they are kept in float 99.999% of the time. But my rackmount (and expensive) UPS batteries seem to last 3-5.

I have a UPS in my office right now that beeps a battery replacement warning daily, and I couldn't tell you the last time it actually cycled the batteries.

 

[Shimmy]

Lots of extra energy use if you go double conversion. To me, the first question is how long of a runtime you want. If you want more than ~4 hours you can justify LFP and might as well cycle it for a few hours a day. Less than four hours is really AGM territory.

I have a Cyberpower unit that the battery needed to be replaced on, and I have two 12V 30Ah batteries hooked up to it which can give me about 5 hours of runtime for my loads. I have a supplemental charger for it, but never set it up.

 

[Linwood]

Yeah... hadn't really thought through the poor efficiency of double conversion. Even if it's 500w total and 10% worse efficiency that's about $60/year at our rates. Not a deal killer but I guess it's of questionable value since I do not really think I have ever had anything damaged by power quality.

 

[krby]

Ya, I did double conversion because of my exact situation:
I had an inverter that I knew my load would be ok with. I was going to buy batteries anyway. If I added just a $150 55A converter/charger, then I had a double conversion UPS. My load is about 300W max (more like 120W most of the time) Instead, if I happened to have a lower power charger, I probably would have spent the money to buy an ATS (automatic transfer switch) and inverter and do an online interactive architecture.

 

[Whoa]

I don't understand why UPS batteries don't last that long. I've seen lead acid batteries survive 30+ years in teleco environments, where they are kept in float 99.999% of the time. But my rackmount (and expensive) UPS batteries seem to last 3-5.

I have a UPS in my office right now that beeps a battery replacement warning daily, and I couldn't tell you the last time it actually cycled the batteries.

I just saw this post and am VERY interested in anyones feedback regarding a LiFePO4 battery pack in a standard (Data Center quality) APC UPS. I recently made my post regarding my "issues": https://diysolarforum.com/threads/3s7p-18650-battery-packs.73937/ .Roughly 3 years ago I started "looking into" LiFePO4 batteries as I hate(d) how I had to maintain my Lead Acid (SLA?) batteries roughly every 2-3 years. The run time on Lead Acid batteries was not great as well (75% load gave me roughly 10-15 mins to get my servers shutdown before power gave out on the UPS). After I did extensive testing with the LiFePO4 battery packs in the UPS I saw no need for concern. After placing a 75% load on a UPS i tested the run time and at the 2 hour mark called it good enough as I did not need to know the exact amount of time to total failure. 2 hours was/still is more than enough time for me to do what I need to do...

I have no answer why UPS batteries do not last... I was/still am hoping that someone else could answer that question. I just dont see any good reason/s why LiFePO4 battery packs should not excel at UPS requirements. They fit all of the same requirements that a Solar Battery system has.