UPS Supercapacitor Conversion for Cyberpower GX1325U (seeking debug help) - Page 1
Forum section: electronics / projects

author: compostea
author_rank: Newbie
timestamp: September 19, 2025, 10:02:57 pm
content: Hi, inspired by the UPS Supercapacitor Conversion thread (seehttps://www.eevblog.com/forum/projects/ups-supercapacitor-conversion/) I wanted to share my initial attempt at trying to do it on a Cyberpower GX1325U. It's a rather common pure sine wave UPS for Home PCs in the United States, typically sold online and in retail stores. I'll share some initial testing results, though I ran into an issue and am seeking help on how to debug/repair.# MotivationThe original two series Sealed Lead Acid batteries died on this unit after about 8.5 years, and more frustratingly the when the batteries fail and fall below a certain voltage the UPS will shut off hard, potentially causing issues for the device you're trying to uh...have power supply protection for. Additionally, I've just wanted a supercapacitor-based UPS for about a decade, from a standpoint of wanting less maintenance & waste of replacing batteries though being aware of the tradeoffs of limited capacity (i.e. runtime) and expense of such a setup. Think more in terms of wanting coordinated soft-off support of a server in case power goes out.I also happened to find some used Maxwell BMOD0058 16.2V capacitor banks at a decent discount, and talked myself into trying the modification.# SetupSo the original batteries are two 12V Sealed Lead Acid batteries hooked up in series for 24V output. So I used two of the Maxwell BMOD0058 capacitor banks in series which, when cutting out some of the original plastic battery housing as seen in the photos, can just barely fit which is nice.When first plugging the UPS in with uncharged caps, it will not turn on. You'll at most hear a little periodic chirp. It is however slowly charging the battery/supercaps and if you have a voltmeter attached you should be slowly seeing the voltage rise. After I think 30min or an hour you'll start to see it display a 'Time to turn on' with a counter of how many minutes until the UPS can turn on.# Rough math sketches(note, I haven't actively practiced my EE theory skills in many years, so feel free to correct me if I'm getting something wrong here)Two 58 Farad capacitors in series, so(1÷58)+(1÷58)1÷0.034482759=> 28.999999681 farad ,supposedly at supporting up to 16.2 * 2 => 32.4 voltsQ = CVQ = 28.9 * 24Q = 693.6 coulombsI don't remember the formula, but somehow I ended up calculating 2.319 Wh for this setup before losses. Or an estimated runtime of 0.02319 hours * 60 min/hour = 1.39 minutes for a 100W load, which in practice proved false.# Initial testing resultsAssuming things work (keep reading on for when they didn't), I tried a few different tests to see how long the UPS would run.## No load runtimeNo load, nothing plugged into any terminal: around 1 minute 21 seconds until hearing continuous beep indicating turn-off imminent.## 60W incandescent bulb runtime testTime to shutdown beeps: around 40 seconds, likely less since plugging in required a waiting period where the capacitor-battery needed to recharge a bit before the light turned back on while plugged in.## Server testI was testing with an old intel-based fileserver that eats supposedly 80-120 watts depending on load, and takes (based on a couple time trials) around 15.4 to 18.8 seconds to shut down properly. There's a wait setting in the OS I use when detecting a UPS signal over USB, and ended up setting the wait time to 2 seconds (much less than the default) in order for the server to shut down before the UPS ran out of energy from the supercaps.With a 2 second wait time, I counted about 6.17 seconds between unplugging to seeing a message on the server's remote shell broadcasting "Executing automatic power-fail shutdown", and roughly 25.4 seconds from unplugging to seeing the server shut off.## The problem.It's been a while since but after about a day or so, I think I found the UPS off. I disconnected the server, tried plugging the UPS in with no load. Later on it showed an error F03 , which supposedly indicates a 'charging circuit error'.Any clue how I could go about diagnosing or fixing it? I have seen forum threads likehttps://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-power-supplies-and-power-supply-design/92714-cyberpower-cp900epfclcd-f03-error, and about to check if are any exploded capacitors.

author: jwet
author_rank: Frequent Contributor
timestamp: September 25, 2025, 07:47:37 am
content: Supercaps, even these monsters that you found can't compete with batteries. Your calculations are correct but assume 100% efficiency of everything- its not nearly so high. The missing equation is E=1/2*C*V^2. Somehow you got to the right value- 8352 joules (watt seconds) and converted to watt hours give 2.32 as you calculated. You might want to multiple this by 60 to give you watt-minutes= 139 which is closer to your reality. The fact that you get an alarm after 1.3 minutes says that you have something like a 100W equivalent idle load from the UPS- that might work for a battery but won't work for you. The other issue is that all this relatively cheap electronics is probably 60% efficient, its been optimized for cost with batteries. You'd need to redesign for your criteria.I think you can use supercaps to give you a minute or so of hold up time but you probably can't use a low cost UPS designed for batteries to get you there. The biggest problem I think is that your UPS draws a lot of power in PF mode. I don't know what that is but I suspect its the base power of boosting the 12v back up to AC. The inverter draws a lot of current just to do its thing without a load- its like efficiency but its more like an offset before you even start drawing current.Supercaps keep improving but they have a ways to go...Good luck.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 25, 2025, 01:37:17 pm
content: I started that UPS supercap test on 6-28-2018. It is still in operation today. My goal was seconds of operation. Over the years, the AC mains were replaced and the short power outages are far less frequent.I have not measured the run time for at least a year now and assume the cheap capacitors I used have continued to degrade. We had an outage a couple of weeks ago and it seemed to ride it out for roughly the expected time.

author: jwet
author_rank: Frequent Contributor
timestamp: September 25, 2025, 05:22:51 pm
content: Seconds of holdup are very doable.I worked on project a while ago at Maxim that's related. Power failure duration is sort of a 1/T distribution. Most, 99% ?, of power failure are less than five seconds. We had some appliance manufacturers (kitchen stoves, fridges) and consumer electronics (set top boxes) that wanted a way to ride out these very brief power outages to keep their clocks from flashing 12 all the time. I studied the problem for a bit and talked to EPRI (Electric Power Research Institute) and got the statistics. The appliance guys didn't want any batteries for obvious reasons but really couldn't afford a real crystal controlled RTC even that could be backed up with a cap. Most of their stuff counted power line cycles with an interrupt into a small uP. I couldn't come up with a solution cheap enough and similar enough to make them comfortable.Regards.

author: fourfathom
author_rank: Super Contributor
timestamp: September 25, 2025, 06:57:05 pm
content: I've been developing gear for use in ham radio propagation research, and we've seen problems where the small computers we use with our SDR receivers can't tolerate the brief power glitch when a typical UPS goes into holdover. So I took a friends supercapacitor design and "productized" it:http://wb6cxc.com/?p=520It turns out that the supercap ESR is a fairly big deal. I could have added a switching regulator to harvest more power from the cap, but decided I wanted to not have the design be voltage-specific (and to keep it simple). Anyway, it does the job...And yes, you can buy an "online" UPS that supposedly has a glitchless switchover.

author: 5U4GB
author_rank: Super Contributor
timestamp: September 26, 2025, 05:40:02 am
content: Another possible option is to use LiFePO4 battery packs that come in the same form factor as SLAs but use, obviously, LiFePO4s instead. These have a built-in BMS so work with SLA chargers, and are rated for a 10+ year life. I've never used them, and reviews often disagree as to whether they're fine or not (typically under high load you get limits on current draw from them and problems with heat buildup in the sealed units), but for just running a few low-power devices through outages which won't stress the batteries too much they should be fine.

author: jwet
author_rank: Frequent Contributor
timestamp: September 26, 2025, 03:05:02 pm
content: Fourfathom: can you send me a PM? I'm interested in your propagation project- I'm working on something related.

author: fourfathom
author_rank: Super Contributor
timestamp: September 26, 2025, 03:24:55 pm
content: Quote from: jwet on September 26, 2025, 03:05:02 pmPM sent

author: joeqsmith
author_rank: Super Contributor
timestamp: September 26, 2025, 04:10:58 pm
content: Quote from: fourfathom on September 25, 2025, 06:57:05 pmThe one I am using for my tests is a double conversion. For example you can supply it with 110V 60Hz and convert that to 120V 50Hz. The output waveform is much cleaner than the mains coming into our home.Quote from: 5U4GB on September 26, 2025, 05:40:02 amI had seen these and wondered how they would hold up in a USP. They are fairly inexpensive.Don't most of the new ones now use NiMH?

author: compostea
author_rank: Newbie
timestamp: September 27, 2025, 01:06:34 am
content: QuoteThanks for the info @jwet . Even losses aside, this technically (albeit just barely!) works for my needs aside from the errors I bumped into. I suspect it'll still be usable for some lower-power setups (think UPS for soft-off needs on a 3D Printer that just uses an ARM SBC).Been busy with other projects but hoping to eventually debug what went wrong with the UPS. Apologies if I'm a bit slow with replies.

author: 5U4GB
author_rank: Super Contributor
timestamp: September 27, 2025, 06:19:24 am
content: Quote from: joeqsmith on September 26, 2025, 04:10:58 pmAFAIK the SLA-replacements went straight from nothing to LiFePO4, meaning that at about the time they became fashionable the best option was already LiFePO4.