DIY UPS leads?

[danb35]

It's pretty OT for this forum, but the depth and breadth of knowledge here never ceases to amaze me, so...

The sealed lead-acid (SLA) batteries in my UPSs are getting annoying. They don't last very long, and they lose capacity quickly before they become completely useless. And in a lower-end unit that doesn't do regular, scheduled self-tests, they can die on you without warning. And replacing them every few years can get expensive. So, I'm looking into alternatives.

The easy answer would be to replace the existing battery packs with LiFePO4 packs. They have a long cycle life, and if managed properly (i.e., with a halfway-decent BMS) can easily retain 80+% of their capacity for a couple of decades. And packs of four of them to a pretty good job of imitating 12-volt SLA batteries in terms of charge/discharge voltages--so they could be pretty close to a drop-in replacement for SLA. But that does lock me into using whatever voltage the UPS uses, which limits my choices of amp-hour capacity.

The other possibility coming to mind is to build my own UPS. In principle, this is pretty straightforward--a charger, a battery bank, and an inverter give you the effect of an online double-conversion UPS. But what this doesn't do is give you any kind of monitoring. So, after that excessively-long introduction, does anyone know of plans/instructions/documentation for a monitoring system that could be made to work with nut?

 

[Basil Hendroff]

You've piqued my curiosity. (Caveat: I could be feeding you garbage) In my mind, the battery monitor would, on the battery side have to monitor battery voltage levels, and on the server side emulate a NUT aware UPS. This way you can utilise existing NUT drivers on the server. See fig. 1 below (crudely done on OnlyOffice ;)). A more ambitious project might have the monitor feed into a dedicated NUT server (fig. 2).

The tricky part would be to try to emulate what a NUT driver is expecting to see. This feels like something I'd try building using an Arduino. I found this Arduino based UPS that emulates a Megatech

Maybe some other useful leads:

1. Monitoring a LiPo battery while powering the Arduino UNO with it
2. Power Outage Detector & Arduino UPS
3. UPS device pinouts
4. Using a raspberry-pi as a UPS server with nut

 

[danb35]

In my mind, the battery monitor would, on the battery side have to monitor battery voltage levels, and on the server side emulate a NUT aware UPS.

Kind of what I was thinking (with, I guess, the additional requirement that it monitor the state of the mains), keeping in mind that one way to "emulate a NUT aware UPS" would be via SNMP--which puts it on the network, so there wouldn't seem to be a reason to have a separate NUT server in the mix. And I was kind of thinking Arduino as well, though it looks like you've found some links I hadn't. Interesting...

 

[dak180]

@danb35 I think UPSide might be just what you are looking for; you can read more about the dev work on esr's blog.

 

[danb35]

I think UPSide might be just what you are looking for

Very cool, I hadn't found that one with my Googling. It looks a bit more comprehensive than what I was thinking of, but it sounds like a very neat and ambitious project. Though it's somewhat disappointing to see how far they still have to go, after over two years of work...

 

[dak180]

Though it's somewhat disappointing to see how far they still have to go, after over two years of work...

From what I can tell this is more a matter of scheduling than anything else; esr in particular only just finished converting the gcc code base history to git if I recall correctly. I do not know if he has any other large projects on the immediate horizon.

 

[CompuGlobalHyperMegaNet]

Have you looked into the batteries being sold for other purposes?

I know that the batteries for my UPS are a hell of a lot cheaper when bought as replacement batteries for a mobility scooter rather than specifically for a UPS.

 

[danb35]

Have you looked into the batteries being sold for other purposes?

Mostly. I've been buying, e.g., these:

Power-Sonic PS1250F2 12V 5Ah Rechargeable Battery for sale online | eBay

Find many great new & used options and get the best deals for Power-Sonic PS1250F2 12V 5Ah Rechargeable Battery at the best online prices at eBay! Free shipping for many products!

www.ebay.com

They're a little cheaper than buying the batteries individually (they're running $12-15 each from what I find with a quick Google), and they're much cheaper than buying a replacement APC-branded pack, though the eBay listing still list them for a UPS application.

I'm seriously considering replacing those with a pack of 16 cells like these:

98.0US $ |lifepo4 3.2v 20Ah lithium battery Lithium iron phosphate deep cycle for DIY 36V 48V 72V 40AH scooter bike motorcycle inverter|Rechargeable Batteries| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

That would have the nominal capacity of two of the SLA packs (and in reality, it would be better--the rated capacity of SLA is at a much lower discharge rate), and should last much longer--if they last twice as long, I break even (allowing a bit extra for the cost of a BMS and cabling), and everything after that is gravy, as long as I'm not too picky about it looking good.

 

[jgreco]

Funny, I was just thinking of you as I noticed these --

https://www.ebay.com/itm/12V-3S-7P-...DIY-18650-Powerwall-Battery-Pack/174217605702

I wonder if that could be made to work in the normal APC UPS's.

 

[danb35]

https://www.ebay.com/itm/12V-3S-7P-Li-ion-Battery-Case-Holder-for-DIY-18650-Powerwall-Battery-Pack/174217605702

Very interesting. Total capacity would depend on the cells used, but with (say) 2500 mAh cells, that would be a 12V, 17.5Ah battery, more than doubling the capacity of the standard SLA batteries in that size. I'd be more concerned about the charging settings, though--I don't think LiIon can substitute as easily for SLA as LiFePO4 can. But it'd sure be nice to have everything self-contained...

 

[cobrakiller58]

oh that is interesting if you can work a BCM into that little package this could be really interesting.

Edit:I was just looking at pricing to convert one of my old school Liebert's and pricewise I can't justify it. @danb35 are you seeing this or are the prices looking more sensible to you for this adventure?