UPS with dead batteries reborn as a whole-house power backup

[Woodporterhouse] must deal with regular power black outs in his area. He recently converted a rack-mount uninterruptible power supply to feed a portion of his mains wiring. This one is not to be missed, since he did such a great job on the project, and  an equally remarkable job of documenting it. It’s one of the best examples we’ve seen of how to use Imgur as a project log.

The UPS still needs to have a case, but it doesn’t need room for batteries as he’s going to use a series of high-end sealed lead-acid batteries. So he cut down the enclosure to about half of the original size. That’s it mounted just above the new batteries. For this to work you need some type of transfer switch which can automatically patch between incoming line voltage, and the battery backup. He already had one of these switches in place for use with a generator, that’s it in the upper left. The entire system powers a sub-panel responsible for his essential circuits — the electronics in the home and a few lighting circuits (we’d assume this includes utilities like the refrigerator).

One really great feature that the reused UPS brings to the project is a monitoring card with a NIC. This way he can check the server to see if the UPS is being used, and how much of the 14 battery life remains.

[Thanks Ross via Reddit]

60 thoughts on “UPS with dead batteries reborn as a whole-house power backup

  1. My only beef with this is the UPS will charge the batteries rather slowly, as their AH capacity is MUCH higher than the original batteries. You might be able to adjust the charge rate in software or tweak the unit itself.

    If you dont feel QUITE as brave, and have around 300 spare dollars, you can get 99% of this in a quality, safe, and warranted unit. Look at triplite’s Inverter/Charger units. I dropped about 1800 on my unit, and its capable of 12,000 watts for nearly 5 minutes straight, and capable for 9000 watts for hours. Totally worth it if you wanna go big.

    Nice hack none the less!

    1. They do charge slowly thats for sure. This style UPS is most likely set for a “slow & low” charge for the 8 pack of 7Ah batteries that come standard.

      They’re made for quick blips(1 second to 5 minutes), and all computers attached to it are supposed to have the client software installed to take care of an orderly shutdown if the loss of utility is longer then spec.

      But yes, if someone has a few bucks and wants to invest in a charger/inverter, definitely a good idea. This is my 2nd setup, because the first one crapped out after about a year and a half. UPS capacitors like to dry out and either explode or catch on fire…the fire suppression is a different project though. :)

  2. I would assume that it wouldn’t include the refrigerator unless you aren’t worried about letting the magic smoke out. Motors are a terrible draw on inverters. Right at the startup time.

    1. Nah no fridge…just the electronics in the house, and some lighting in case the Zombies, Soviets, Terrorists, or whatever the fear of the day is and the power goes out.

      The generator subpanel is for the fridge, well pump, furnace and giant spotlights and speakers to annoy my neighbors when they have no power.

    1. No electrician necessary, but it does help…

      Just adhere to code, otherwise your homeowner’s insurance won’t cover you if the place burns down.

      The fault in the FrankenUPS project is with the batteries. Teh plywood is fire code, but they are not in an enclosure which is required by code.

      Its on my immediate list of upgrades for this project.

        1. Any time that a fire is reported to the insurance company for a claim, an investigation is done. There will ALMOST ALWAYS be enough evidence left behind to indicate where and what started the fire.

    1. I used to do flea markets in Fl where I sold refurbished computers, rather than going out and buying an inverter,(people want to see a computer WORKING before they buy it LOL), I hooked up an inverter directly to my car battery and had no problems running my equipment all day. I ran my car engine for about 20 minutes every 2 hours just to be on the safe side, but I experienced no problems. In an off grid situation, your solar panels would be charging your batteries so that you would not need to rely on the slow charge that is built into the inverter.

  3. How is the UPS software determining the battery run time? Was the software recalibrated using the new high density batteries, or is it falsely reporting the original numbers?

    1. Excellent question. The APC mon card I believe, has preset battery life presets for the model it is connected to, and when you enter the number of battery packs, it calculates the runtime, using the current wattage load.

      Being that I used non-APC spec’d batteries, the time is obviously off. I had no problem posting the picture of the 14 hour runtime though, because the longest outage I’ve had here running purely off of this setup, was about 11 hours.

      I still have to do some calculations and such, but I would say the runtime meter is +/- 30%

      Still not bad though…

      1. If you’re using one of APC’s monitoring cards you can load the UPS above 30% and perform a calibration through the monitoring card. This runs the load off the battery until it goes flat (when it switches back to the mains) and uses the run time to recalculate the battery capacity. APC recommend this is done regularly as the batteries age and lose capacity so that the predicted run time is kept accurate. I found it much more reliable than faking the number of battery packs connected.

    1. It would probably run the fridge without issue, but I haven’t tried.

      Motors and other “big draw” items aren’t a good thing to run off of UPS unless its critical life safety, or some other exception. They’ll kill the batteries quick, and cause wonkiness if they are 3-phase for sure. Don’t have to worry about 3-phase though at the house… :)

  4. This and questions of whether the fridge will blow it makes me wonder what the difference is, internally, between a high-end, high-wattage UPS and the storage/inverter setups usually seen with solar installations.

    Do the solar installation inverters merely have beefier sub-components or do they use a completely different circuit?

    1. Large inverters (like the Outback solar inverter) usually bank together multiple inverter circuits and sync their output waveforms. They have additional capacitors and coils to help handle motor surges.

      1. Just about every UPS system ever marketed for computer use produces “Pure Sine Wave” output, This means that ,unlike “modified sine wave” inverters,(some of them), the current produced by a UPS is almost identical to that which comes from your wall socket. Most motors and compressors have a problem with “Modified” but will run fine on Pure.
        Hope this is helpful.

    2. as far as ive seen/heard/read, 90% of all “ups/sps inverter”s are not TRUE sinusodial(sinewave) output and thus the unit’s internals are MUCH simpler and CHEAPER.

      fridges, and to a lesser extent all 60hz ac motors HATE “modified sinwave” outputs and often either stall(veryvery bad) or blow the crap out of your mosfets… (or just get warmer and have less torque). im talking about the mosfets that turn your “inverted” 180vDC into an average of 120vAC@60hz-mod.sinwave

      the fridge as well as other specific applications of motors have existing extra stress / torque requirment during startup. fridge has load of frefrig. gas/liquid backed up ready for pumping. if it stalls from lack of tourque bcuz the mod.sinwave, then it will start to draw WAY much more current, destroying things. (motor-brushes, inverterparts, ect)

      PS: on a fridge, I THINK the overheat sensor is inside the sealed chamber, which is okay, but on other equipment, check to make SURE the sensor is NOT bypassed before trying this! … or use an extra temporary fuse.

      PPS: this equipment is designed for computer backup, and thus a computer backup ups/sps will almost never have the more expensive (and less eficient) true sinewave inverters.

      PPPS: ive heard of very bad things happening when you go to charge a nicad-built in pawerfailure rechageable flashlight/nightlight from squarewaves, modsinewave is a cross between square and sine waves. most user manuals that i have read say “WARNING: DO NOT USE THIS PRODUCT TO CHARGE NI-CAD BATTERIES AS THEY MAY OVERCHARGE AND CAUSE BATTERY TO LEAK OR CATCH FIRE.”
      i assume they are talking about slow-dumb-simple chargers, and not the computerized ones.

    3. I don’t know anything about solar inverters, but industrial VFDs that run motors at the end of very long cable runs can use sine wave filters (google it) to achieve very nice looking sine waveforms from choppy inverter outputs.

      1. i think

        and me

        are all correct. im sure you could use extra coils and capacitors ect to run a tempermental motor on squarewave ect

        just wouldnt fit inside your SPS/UPS with limited space. (and DEFINATELY not inside your “travel” inverter XD )

        i havent seen the circuits you two describe in person, but im pretty sure it would be a unit itself, and as big as or bigger then the inverter itself. (without battery box of course)

        which does not lend itself to “portable” or “compact” or “visualy appealing” or “cheap” or “lightweight” or “i use a mac and my sister would kill me if it wasnt white with silver trim…” == all things i dont care for.

        PS: i know they sell 12vDC fridge compressors, and i know they sell 120vAC60hs fridge compressors,,,

        but do they sell 180vDC fridge compressor-motors????

  5. For anyone who’s interested I contacted APC about this sort of thing some time back (wanting to add a battery bank to a UPS) and their response was that the charger circuits in their UPSes are only designed to handle the internal battery capacity. They said that the more batteries you add, the more current they will draw when charging and it was likely that adding too many could overload the charging circuit.

    They did say that their extended run models (those with XL in the model name) are designed to have up to 10 external APC battery packs connected so the chargers in those are able to deliver much higher current. Their suggestion was to get an XL model and add batteries up to the capacity of the 10 external packs + the internal batteries, and then there would be no risk of overloading the charger.

    1. Indeed. I went through alot of specs for the non-XL models, and the one thing that I found, is that they are very similar to the XL’s.

      The model that I used, had everything set up for an external battery pack(APC connector), and I’ve had this setup for about 3 years total now(version 2 in the pics after the caps dried out on version 1).

      Obviously I had my concerns, but it has been working without issue.

      The way I’m figuring is that the charge circuit is limited no matter the type/quantity of batteries. XL or not. If a battery bank is completely depleted, the charge circuit in the UPS only knows, “time to charge”, and is internally limited as not to burn itself out.

      If there is a 1 battery, or 20 battery bank connected to it, it still only knows, “time to charge”, and is regulated.

      I haven’t researched this enough though to give a solid answer. All I know is it’s been flawless for a while, except for when the caps dried out on my last setup, but this is a known issue with all UPS’s.

  6. Any well stocked and insulated fridge is good for a day or more. If the power is off longer there is a change in living. Keep jugs of water in the bottom and frozen ones in the freezer. It will cycle less often, than if low on stuff (beer).

  7. I bought a Xantrex 3000W full sine wave unit that can handle like 6k for motor starts… I am running it from about a dozen gel cells and it works great. The inverter cost $450 on craigslist and the batteries were purchased at a local auction for under $250. The setup works great and keeps my entire entertainment center + lab going during the regular blackouts we have here. If the power stays out for more than 30 minutes, my generator starts up (or it starts up when I hit a button). It’s a pretty slick setup and has saved me numerous times.

  8. Be forewarned… you WILL be amazed at the amount current required to keep the batteries topped off as they get older (mere months). I had pretty much the same setup with two 3000VA APC UPSs and it was amazing. When the power went out, we barely knew it. UPS took over the demand during an outage and then the generator automatically kicked on to cover the load within 3 mins. It was beautiful. Then about 5 months passed by and the electric bill began to grow.
    We aren’t talking $20 over, we were in the $100+ range (over the regular) every month. Removed the UPS and the bills dropped dramatically. A friend of mine had the same plan and built it. He realized the same increased bill after approximately the same time period.
    Just food for though…

    1. An additional $100 a month is something like 1400W, somewhere around 100 amps of charge current (assuming the UPS itself didn’t need much power).

      What size of battery bank were you running that would accept 100 amps of standby charge?

  9. i dont understand the transfer switch. power is supposed to flow throuh the ups full time and the ups powers the outlets full time. if you use a generator, then use transfer switch so its seamless from mains to generator. ups covers the switchover time and delayed start

    1. I think the transfer switch here is functioning as a UPS bypass switch, so you can remove the UPS from the circuit if you need to do work on it, without having to power down the load.

    2. Under normal circumstances, a UPS won’t be backfeeding into the mains supply. It will only be powering the equipment connected to it. In this setup, there is the issue of conflicting waveforms from the inverter and the grid, which is why you don’t want both feeding into each other. The UPS won’t like it, and the grid won’t like it.

  10. I agree with many here. This is the wrong type of UPS for this application and adding more batteries like this is asking for even more trouble. It may “work”, but for how long and how well? Make sure your smoke alarm is working – and test it often.

  11. well basic ups theory says that you don’t need an Ats, the ups always syncs to the bypass source, and produces the same well basic ups theory says that you don’t need an Ats, the ups always syncs to the bypass waveform. This looks like a basic computer ups. i work on large scale UPS’s 300kva to 1000kva per module for a well known manufacturer. As far as the post for 9000 watts for hours… any ups rated battery is only specked for a discharge of 15 mins. while it may run for hours, no ups was designed to supply mains voltages for longer that 15 mins. Long enough to crank the gens and get them stabilized. The inherent fault of a ups system is that you are demanding a huge amount of current from a battery string that is in series (540 vdc for 480 vac and typically 330 vdc for 208 ac) one battery fails everything fails. And mosfets ??? no they typically use large SCR’s for the rectifier, and IGBT’s for the inverter.

  12. I’m running a 3KW APC rack mount UPS that’s several years old. I gutted the dead battery packs and wired in 4, 95 amp hour sealed 12V batteries (with breakers) to make a 48V pack. They were surplus, proper sealed UPS batteries from a radio station up a mountain. The UPS has a decent cooling fan and seems to charge up that massive pack without stressing anything or overheating anything.

    This runs every piece of fussy electronics in the house. Multiple TV’s, stereos, computers, etc.

    I live in an area with industry and get terrible power spikes, surges, outages, brownouts and just general noise. I finally associated all my desktop computer glitches with big welding projects on my Lincoln squarewave 185 tig welder as well. Since I did this mod, I have zero computer issues and a much quieter stereo to computer sound connection.

  13. He may have battery life and charging issues down the road. You need to have the right charger for the battery type, and UPS chargers are usually horrible at best.

    This is a very good gorilla install, but if the work had permits pulled and was done legally it would never pass inspection.

    If someone really wants to do this the legal way, there are a lit of inverters that are low cost (under $500) and a good charger will cost about $125 that will make your lead acid batteries last at least 5 years.

  14. I did something similar. I got a 2000 watt 48V UPS from a friend who recycles computers. My home-built electric motorcycle is also 48V.

    I set up the UPS with an Anderson quick-connector with a matching one on the motorcycle. That way, I can use the UPS as a charger for the cycle, and run my house from the motorcycle in a blackout!

    The UPS is rackmounted in an old rack in my garage, but after seeing this one, maybe I’ll wall-mount it!

  15. I have four XPower PowerSource 400 UPSs,
    two of them have 12v automotive deep cycle
    batteries attached, I got the UPSs to keep
    my keep my computers and TVs safe from my
    old Colman generator, from lighting, and other
    power problems, with a single regular automotive
    deep cycle battery used in place of the XPower
    PowerSource 400’s normal battery I can run my
    computer and its monitor for hours, most of the
    time longer than the power outage, it does
    recharge the larger battery slowly but it only
    seems to take a few hours to recharge it, I have
    used them like this for years, works well.

  16. Add more cooling, the original design was for less run time, and the UPS was kept in a air conditioned space. Heat is the great destroyer. Put two temperature controlled muffin fans on the bottom, and let them blow upward. Anything that you can do to cool the UPS down, will extend its life. The original fans were designed for a specific run time, and draw. It looks like you have it installed in a garage with no air conditioning. So while it is a great design, and it works, we are only talking about extending its life. Joe

  17. Hey, I love your project and getting ready to star my own. My 5.6 KW grid tied solar system is operational for 2 years now and I love it. Biggest problem is that without grid power my solar system is useless :-(, so it’s time to get this addressed.
    I came to possession of quite a few Compaq R6000 UPS’s with lots of extra batteries and planning on converting few of those to a battery backup system when my solar is out.
    I have few questions for you; how did you connected your UPS input/charging power in reference to your UPS output/panel feed?
    I’m sure they are not going to the same panel
    And how did you determined total output power out of your UPS after removing power plugs from the rear of it??
    Compaq R6000 has 4 16amp and 10 10amp breakers in the back of it, wondering how can I convert all of it to just 1 output to feed my panel like you did??

  18. I have a similar setup, but very easy to do.This is how.
    Fitted a small 4 way distrobutin board adjacent the existing one.
    Moved the lighting feed (all lights are LED), central heating feed (boiler, programmer and pump) to the new ‘board. Also added another twin socket on it’s own circuit to power the tele’ and set top box and another socket to power the internet router etc.
    This new board is fed using a 6mm 3 core flex from a 32 amp mcb in the old board. In the midle of this flex is a commando 32 amp plug and socket that are connected to a 3kw ups (commercial ).
    In the event of a power cut the lights, tele, heating/hot water all work. Nothing else exept the gas hob but we have to light that manually. I will get around to adding that socket to the system one day.
    I don’t really know how long the batteries will last because the longest power cut we have had is less than two hours.
    Took me about 4 hours to install, the hardest job was making a bracket strong enough to hang the UPS on the wall in the garage adjacent the fuse board.
    The best bit is when all the street lights and houses go dark…..exept us.(Show off)
    Cost? Minimal, less than £150 plus my time and effort.
    People tend to make things over complicated.

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