If geeks love it, we’re on it

Beating brownouts: building a super UPS

Beating brownouts: building a super UPS

It’s public knowledge that South Africa’s sole electric company is battling to keep up with demand. You only have to look at my UPS performance summary to appreciate the amount of brownouts we experience in our area of Margate.

Sometimes the brownouts last up to eight hours or more. As a result, I have collected all manner of uninterruptible power supplies which are linked to all the computers scattered around my house. This ensures I’m not left in the dark halfway through a game or a spreadsheet I spent the last hour compiling. Those of you who have experienced this know how infuriating power loss can be.

apc performance summary

At most, the UPS I own are only designed to run one PC and hold sufficient battery backup to give me 7-10 minutes of power – enough time to save my work or game and switch the computer off. This may suit most people who wish to prevent that dumb-struck moment when you find yourself staring at your reflection in a black screen, sick with the knowledge that whatever you were busy with is lost forever.

My application, however, demands a bit more. I have a fully kitted-out office at home with a workstation that runs two PCs, a 4-in-1 digital scanner/printer, an inkjet printer, a DSL broadband router, a wireless network router, and two sets of speakers. There are also a fax machine, and a mobile handset that is useless when its base goes dead.

home office

This space is used by my wife during the day, who runs a busy bookkeeping business. I invade it in the evenings. Having no power for half the day or night is no fun for anyone, least of all for somebody trying to run a business.

In search of a solution

It is with this background that I went in search of a decent, cost effective UPS that could run all the electronics in the office for at least a few hours. I quickly came to realize two things:

1. There are no intermediate UPS. You either get the off-the-shelf cheapies or lay out a small fortune. The cheapies are designed for one or two home computers (readily available in most computer stores). Generally these contain “gell cell” batteries which are cheap, don’t leak and are very standardised. They provide only back-up time and little or no protection. The small-fortune variety are much larger and suited for a small- to medium-sized business.

2. Most decent home-use UPS are designed to provide a clean power source, eliminating under and over voltage as well as electrical noise. They are generally not intended to provide hours of backup time. Five to 15 minutes seems to be the norm.

My search eventually led me toBocal Electronics, a local company who specializes in UPS, standby systems and associated products. That’s where I learned about DC-to-AC inverters. Their function is to take power from a battery source, normally 12 or 24 volts DC, and convert it to anything from 110 to 230 volts AC. This is ideal in remote locations where there is no power grid to tap into and allows you to run just about any electrical appliance off a battery.

The unit I bought is the Inverex 1000 with a 1000VA / 600W capacity. It is essentially a DC-to-AC inverter with auto line-to-battery transfer and an integrated charging system. It can serve as an UPS, standalone power source or an automotive inverter. It’s also quite compact, with a footprint roughly the size of a sheet of paper, slightly over 3″ tall, and weighing under four pounds. With those specifications, you may have guessed it does not come with its own dedicated battery storage and that’s where it gets interesting. Provided you stick to the DC voltage rating of the unit, use the same type of batteries (typically lead-acid) with the same Amp Hour(ah) rating, you can pretty much use any combination of battery in parallel or series to meet your specific requirements.

ups with batteries

My unit came fixed to the top of the battery housing and comprised of two 12V 45 ah semi-sealed lead-acid batteries, wired in series to produce a total of 24V. The batteries that came with my setup are deep discharge batteries and are well suited for UPS applications.

lead acid battery

Factors to consider when making a purchase

The technician that put my setup together would at this point argue that he did not sell me an true inverter. To a large extent, I would agree with him. Inverters usually run independent of a main electricity supply, so they do not normally come standard with a 110/230V plug that you can connect to a wall socket. My unit plugs into the mains and uses an integrated charging system to automatically switch the unit to batteries when the power dips below a pre-determined voltage and back to mains when power is restored. It also re-charges the battery once it has dropped below optimum voltage. Pretty much how a UPS functions, so what are the differences?

Well, price for one. A quick search on the Internet showed me I was getting excellent value for money. An industrial type UPS rated to provide backup power for the 4-5 hours I required would have cost me a lot more than I paid for my setup.

On the subject of pricing, when making your choice it’s important to note that there are two types of UPS’s and inverters. One produces a pure-sine wave and the other a modified-sine wave.
The pure or true-sine wave is the closest you can get to the power produced by the public utility power grid system. The modified or square-sine wave models (mine falls into this category) are the most common of the inverters and are much cheaper than their thoroughbred cousins. Be sure to check which model you buying before settling on price.

Apart from a few exceptions, the modified-sine wave inverters will run just about any household appliance. Laptops and desktop computers have no problem running off these.

Another difference I found, and probably the most significant, is the fact that my model and most other inverters like it does not have any built in surge protection against lightening strikes and power spikes. It is essential to run the inverter/UPS through a surge protection unit.

A lot of the better off-the-shelf UPS’s come with monitoring software which enables you to interface with your PC via a USB cable. This is one feature you will be very hard pressed to find when shopping for inverters or UPS of this nature.

Your standard home UPS (600 VA) only has a 0.5 or 1 amp charger at best.
The models from the Inverex range come with a much larger charge capacity (up to 8 amps) which enables you to recharge a large battery to 80 percent of its capacity within 6-8 hours.

Ordering the UPS

Apart from that I couldn’t find any reason not to go ahead with my purchase. After an initial phone call to Bocal to establish what unit was suited for my application, the rest of the transaction took place via e-mail. Any further questions I had were replied to promptly and the invoice was e-mailed to me along with the time and date my unit would be ready for collection. Due to weight constraints, I opted to fetch my package directly from the supplier. The three hour round trip from my home to the supplier and back was still significantly cheaper than paying the shipping costs for a 60 pound package. The UPS was waiting for my collection at the depot, packed in very sturdy cardboard boxes with the appropriate “Fragile” and “This side up” stickers stuck on them.

As soon as I got home I eagerly set the unit up so I could put it through its paces. As already mentioned, all the wiring was already done. The batteries were already in their housing and the actual Inverter was very sturdily mounted on the lid of the battery housing. All I had to do was literally plug the lead coming from the one battery housing into the socket mounted on the second battery housing to close the 24V circuit and I was good to go.

connecting two batteries

The only modification I had to make was to cut the kettle plug fitting off the end of the lead from the outlet and connect the cable to a multi-plug adapter with sufficient sockets to take the bulk of my appliances.

Setting up the test

For my test application I rigged up the two PC’s, the ADSL Router, the wireless router, a 19” widescreen LCD monitor, a 17” CRT monitor, and the 4-in-1 laser printer.

The computer that connects to the 19” LCD monitor runs with an AMD 64 3000 chip at 2GHz, 1GB RAM, a Radeon X800 graphics card, two 80GB hard-drives and two CD/DVD drives. Along with the standard keyboard and optical mouse, it also has the laser printer plugged into it.

The second computer connects to the 17” CRT and hosts an AMD 64 3500 at 2.2GHz, 1GB RAM, an Nvidia 7800GT graphics card, a single 80GB hard-drive and one CD/DVD drive. The standard keyboard and optical mouse completes the roundup.

I run Folding@Home on both computers, so the CPU’s are already running at 100 percent capacity. To put extra strain on the setup, I got my son to play a succession of FPS games on the second rig and I printed out 20 pages of full page print, pictures, and spreadsheets from various files on the first computer. Then for good measure, I downloaded a huge game demo file from the computer farthest away from the wireless router (about 30 feet) to make sure it was working hard too. The rest of the uptime was spent playing an FPS LAN on the two computers.
At this stage it must be noted that the Inverex 1000 comes with deep discharge, overcharge, and overload protection, so under normal operating conditions there should be no fears of overloading the system. I was about to see if it could handle what I threw at it.

Crunch time

I ran two tests. The first was to see if the unit could handle successive power outages over very short intervals without any restarts of the PC’s or dropping the Internet connection and wireless signal.
The second test was to see what discharge time I got out of my unit before it went completely dead on me.

Please note that I had no monitoring equipment I could attach and there were no control units or benchmarks I could work with, so please don’t shoot me down for my methods not being scientific enough. I hope I have given you sufficient information regarding my setup for you to gauge for yourself what sort of power I was drawing and hopefully it is a good enough benchmark for you to compare against your particular application.

I must say the results were quite startling:

When I disconnected power from the wall, the unit switched to battery-backup seamlessly. The Inverex 1000 is rated with a typical transfer time of 8ms. There wasn’t even a flicker on the monitor and the download progressed without a hiccup. Apart from the led that lit up to show it was running off batteries and the cooling fan in the unit becoming audibly louder, there was no other indication to show I was no longer running off mains.
I flicked the unit on and off at 30 second intervals for 2 minutes then increased the intervals to 10 seconds for a further half a minute.
Everything remained rock solid.

By this time my son was already into an advanced stage of ‘Medal of Honour’ so I left him to it and proceeded onto the second test. Leaving the mains switch off I set my timer to zero and embarked on printing photos and documents to the laser printer.

It is not advisable to run any laser printers on UPS or inverters unless they are of an on-line type and have been specifically rated to handle the current required to heat the element.
If you are running a laser printer directly off batteries you are likely to blow your unit.
I ran the laser printer off batteries only once, and only as a means to
push the inverter to its maximum in order to gauge its performance.

My printer is set to conserve energy, so it takes about 40 seconds to heat the drum before it begins a print job. Clearly the Inverex 1000 backup unit did not like this. It issued a single audible warning every time the printer had to heat up before it printed. Other than that I printed all the jobs I had lined up with no printing errors.

At this time I checked my download progress and was disappointed to find that it was hanging. I was unable to establish if it had lost the connection permanently, but the progress bar had frozen. I could only assume the extra power demands from the printer had to come from somewhere, and the wireless connection to my gaming rig (which is farthest from the router and arguably the weakest link) made the ultimate sacrifice.

I refreshed the site and restarted the download. This was about 20 minutes into battery time. We then proceeded to load up ‘Call of Duty 2’ Multiplayer and got onto a map that was probably far too big for just two players, but we managed to have fun with it. 86 min into battery time, the unit began to issue an audible beep at two second intervals. This was the low battery warning.
Being used to my much smaller UPS’s, I found this sound very disconcerting as usually by this time I would have mere minutes of uptime left. So it was with bated breath that I waited for the final death knell. 1Hr 56min into battery time everything went dead. In one way I was quite grateful. My son was giving me a serious hiding at ‘Call of Duty’ anyway.

End result

With everything operating at max, I got just short of two hours of battery time. Considering my application consists of two 12V batteries wired in series to give me 24V, I am effectively running off one 24V battery.

sketch batteries in series

Series battery connection

I was extremely happy with the time it gave me. Under normal office operating conditions, had I switched one computer off while the power was down and used the other for tasks that are nothing more stressful than spreadsheets, I am quite sure I could get at least double the time out of it, if not more.

It took just on four hours to recharge the batteries. I restarted the PC’s immediately after reverting back to mains so everything was on while the unit was recharging the batteries. I’m not sure if leaving the computers off would have made a big difference to the charge up time.

In conclusion, I would have to say I am extremely happy with my UPS.
I paid R 3,003.00 for it. That included the batteries and the battery housings. In US dollars, at our current exchange rate, that translates to around $411.00

The beauty of this system is if you get an inverter that has the same features as the one I got, you can custom fit it with batteries of your choice and then add as many as you need in parallel depending on what application and backup time you need. With a bit of research and common sense, it should be easy to make your own backup unit with a few lead-acid batteries that can be bought from the local battery retailer.

sketch batteries in parallel

Parallel battery connection

Putting together a UPS of your own

As my unit was already made up for me, I am not going to go through a step by step dialogue on how to make one of these from scratch. Using my unit as a guide, I’m hoping that I am able to provide you with sufficient specifications, diagrams and pictures for you to make your own setup or be able to make an informed decision should you wish to go out and buy one, or have one made.

For this project you will need the following hardware:

  • A DC-to-AC inverter, with auto line-to-battery transfer and integrated charging system.
  • 12V semi-sealed lead acid batteries or valve regulated lead acid batteries (VLRA) which are completely sealed.
  • Polyethylene battery box (This is optional although highly recommended from a safety aspect.)
  • AC wiring no less than 18-gauge copper wire and rated for 167°F (75°C) or higher cut to the desired length.
  • Battery cables no less than 10-gauge and rated for 167°F (75°C) or higher.
  • Metal battery terminals to fit the positive and negative contacts on your particular model of battery.
  • Ring cable terminals to secure the battery cables to the DC input connecter on the back of the inverter

I would suggest getting the cables made up at your local auto electrician as it involves the use of specialized crimping tools, which unless you already have in your toolbox, seem to be an unnecessary outlay for the single use you would have for them on this project.

The back of my inverter unit is very clearly marked and shows exactly where to connect the various terminals. The following diagram and close-up of the wiring on my unit should hopefully provide a sufficient guide.

inverex 1000 wiring diagram
rear view Invarex inverter

To the left, are the terminals for the DC input(battery terminals). This would take the 10-gauge wire that runs from the positive and negative terminals of the batteries. It is advisable to keep the length of these cables as short as possible. Using cables that are too small in diameter or too long will cause a resistance buildup and could stress the inverter, resulting in lower efficiency, lower peak output power, and reduced surge power. At worst, the cable could generate sufficient heat to start a fire.

Place the correct polarity battery ring terminal over the battery terminal plate at the rear of the unit. This should be marked with a + or – It may also be coloured red or blue. Do not place any additional items like washers or nuts between the terminal plate and the cable ring as overheating may occur. The terminal stud (screw) is not designed to carry current. Make sure to tighten the cable ring to the terminal plate with the appropriate nut to ensure maximum connectivity.

Next up is the AC input supply. My unit provides a three station terminal block to connect the wires from the AC inlet (wall socket plug) to the inverter. The positioning for the wires have been clearly marked as HOT (positive) NEUTRAL (negative) and GROUND (earth). You would need to check the wiring colour code for your country or region before attempting to connect the wires to the terminal block. As mentioned, a minimum of an 18-gauge cable should be used. Most general purpose three core extension wires would suffice. The length of this cable is not as crucial as the cabling to the battery terminals and may be cut to a length that suits your application.

To the right of the unit is the output socket. This may take on various configurations depending on the appliance standard for your country or region. The cable that came with my unit ended with a single kettle plug connection, which was useless for my application, so I cut it off and replaced it with a multi-plug adapter. If you can find an extension lead that fits the inverters outlet and has sufficient sockets to meet your requirements, you may not have to adapt it like I did.

That is effectively all there is to putting your own UPS together. Depending on your needs and budget, you could build a UPS that provides monstrous battery capacity. Your only limitations would be weight, the need for portability, and sufficient ventilation.

There is presently no short-term solution for the electricity supply problem in South Africa.
Without spending a small fortune, the Inverex 1000 with deep discharge lead-acid batteries is the best solution for me. During the day, we can keep the office going without any downtime. In the evening, we can have fun and never get stuck sitting in the dark with nothing to do.


Comments

  1. primesuspect
    primesuspect What an awesome article. Great work, Mike!
  2. Leonardo
    Leonardo Great. I'm at work so just had time to scan the article and look at pics. This will get a detailed reading from me later! I'm already thinking about a new project for next winter. (heavy snowfall sometimes knocks out our power)
  3. RWB
    RWB Been looking for something like this, having a laptop is nice because of the battery, but mine only lasts like 2-3hrs, having a much bigger battery would make it much more awesome in the event of a power outage.
  4. keto
    keto *if* that is, as it appears to me, a car battery (or a pair of them), I sincerely hope you have the area well ventilated. They can and do give off hydrogen gas, which, if allowed to accumulate, is highly explosive. Let me reword that, it's explosive in any quantity but DANGEROUS if allowed to accumulate. Oh, the humanity, etc.

    I admit I scanned the article rather than giving it a detailed reading, so if this is covered in there I apologize for redundancy.
  5. edcentric
    edcentric You use sealed lead acid batteries, no hydrogen venting it is all internally re-absorbed.

    This is the right track for serious backup. (do you have a basement? does it have a sump pump? Does the pump run during big storms?)

    We were building these for field equipment when I was working in oil and gas. We bought lightning arrestors/line filters from one source (I wish that I could remember because they were real good), inverters from another and battery charging/monitoring stuff from a third.
    We had a small Li ion battery to back up the electronics and three or four big ass deep draw sealed lead acid batteries for power.
    They are big and don't look pretty, but they were 1/4 the price of pre-built units and worked very well.
  6. Thrax
    Thrax SM/IC/whatever needs more articles like this.
  7. RWB
    RWB
    keto wrote:
    *if* that is, as it appears to me, a car battery (or a pair of them), I sincerely hope you have the area well ventilated. They can and do give off hydrogen gas, which, if allowed to accumulate, is highly explosive. Let me reword that, it's explosive in any quantity but DANGEROUS if allowed to accumulate. Oh, the humanity, etc.

    I admit I scanned the article rather than giving it a detailed reading, so if this is covered in there I apologize for redundancy.

    Hydrogen gas doesn't tend to accumulate unless it's in a sealed area... it's a very light gas. Imagine a hydrogen balloon?
  8. BuddyJ
  9. Rob
    Rob
    It is not advisable to run any laser printers on UPS or inverters unless they are of an on-line type and have been specifically rated to handle the current required to heat the element. If you are running a laser printer directly off batteries you are likely to blow your unit. I ran the laser printer off batteries only once, and only as a means to push the inverter to its maximum in order to gauge its performance.

    I would never have thought of this... My laser printer dims the lights in the room, so I can believe it.
  10. profdlp
    profdlp That is a great job, Winga. :cheers:
  11. TheSmJ
    TheSmJ Fun read Winga!
  12. Winga
    Winga Well as I hinted in the beginning of my article, the inevitable is happening and the state owned power stations we have are not able to keep up with demand. At the moment they are load sharing, where they shut down entire grids for 3-5 hours so they can rout sufficient power to the remaining grids. These are rotated so everybody gets a turn.

    This electricity supply interruption is sending my folding stats to hell, but the good news is I finally get a chance to field test my UPS :)

    I shut down all the other gizmos and peripherals bar the router and the 2 PC's and LCD monitors. (Since writing the article the CRT has also been upgraded to a Wide Screen 19") The UPS has been running both PC's for the last 4 1/2 hours, both of which are still folding so are using 100% of the CPU and my kid has been gaming for about an hour and there is as yet no signs of the batteries giving out.

    I thought I would get this post out before it gives up the ghost and will let you guys know how how long it took before the final death knell :D
  13. primesuspect
    primesuspect Nice! :eek2:

    Hang in there! If you can weather an entire blackout, you could probably go into business with your setup! :D
  14. GHoosdum
    GHoosdum Wow that's impressive!
  15. Winga
    Winga :grumble: power restored before the UPS gave out. There goes my field test.
    However 5 hours 20 minutes is nothing to sneeze at in my books. The Inverter had begun to beep indicating low battery and with the test I ran the last time with it on full load it beeped for about half an hour and then died. So I guess it had another 15 minutes of life left in it max.
  16. GHoosdum
    GHoosdum I'd consider yours a successful test. It's great that the UPS didn't give out!

    I'm lucky to get 15 minutes out of my UPS total with just one PC connected...
  17. trphoto
    trphoto We have 10 computers at the office all on separate UPS's. we also have about 10 dead UPS's (sealed batteries are dead) laying about the office.

    Is there any reason why we shouldn't buy a 300 amp/hour deep cycle battery, similar to what is used on solar installations, and take those 10 cheap UPS's with dead batteries, pull out the batteries and wire them all to the deep cycle battery. Then put a charger on the deep cycle battery. Shouldn't the deep cycle battery run all those UPS's for a good amount of time in case of a power outage?

    Been looking around the Internet and wondering why this isn't done.
  18. Junkymagi
    Junkymagi
    trphoto wrote:
    We have 10 computers at the office all on separate UPS's. we also have about 10 dead UPS's (sealed batteries are dead) laying about the office.

    Is there any reason why we shouldn't buy a 300 amp/hour deep cycle battery, similar to what is used on solar installations, and take those 10 cheap UPS's with dead batteries, pull out the batteries and wire them all to the deep cycle battery. Then put a charger on the deep cycle battery. Shouldn't the deep cycle battery run all those UPS's for a good amount of time in case of a power outage?

    Been looking around the Internet and wondering why this isn't done.

    I bought a UPS from an auction, paid a US dollar for it. Dead battery. Went to local store (Walmart) and bought 6 12v lawn mower batterys. Hooked them up in parrellel (UPS took 12v) and was able to run from it for 3 hours at a time when the power went out. It finally died after 2 years of service... right after I got a laser printer, I guess I went over the max draw, didn't realise how much they pulled.
  19. Snarkasm
    Snarkasm You guys made Slashdot. Congratulations?
  20. BuddyJ
    BuddyJ We did? Where?
  21. BuddyJ
    BuddyJ
    trphoto wrote:
    We have 10 computers at the office all on separate UPS's. we also have about 10 dead UPS's (sealed batteries are dead) laying about the office.

    Is there any reason why we shouldn't buy a 300 amp/hour deep cycle battery, similar to what is used on solar installations, and take those 10 cheap UPS's with dead batteries, pull out the batteries and wire them all to the deep cycle battery. Then put a charger on the deep cycle battery. Shouldn't the deep cycle battery run all those UPS's for a good amount of time in case of a power outage?

    Been looking around the Internet and wondering why this isn't done.

    I think that'd put you on the right track provided your UPSs and the charger could handle the 300 amp/hour battery.
  22. mshiels
    mshiels Mike,
    This is an excellent article and helps me allot with a similar problem I have. I am curious though in that if, 24V (i.e. in your case, 2 times 12 batteries wired in series) provided you with approx 2 hours, what do you speculate would happen if you added additional 24 v batteries in series? Would you have in effect extended the up time by almost double? Who would the outcome be if you added another 24V but in this time in parallel?
    Cheers
    Mark
  23. Junkymagi
    Junkymagi
    mshiels wrote:
    Mike,
    This is an excellent article and helps me allot with a similar problem I have. I am curious though in that if, 24V (i.e. in your case, 2 times 12 batteries wired in series) provided you with approx 2 hours, what do you speculate would happen if you added additional 24 v batteries in series? Would you have in effect extended the up time by almost double? Who would the outcome be if you added another 24V but in this time in parallel?
    Cheers
    Mark

    Adding in series would up the voltage, a bad thing if the UPS's voltage regulator couldn't handle the extra voltage.

    If you added more batteries in parellel (I think he mentions that in the article) it would increase the up time. 2 batteries last 2 hours, 4 batteries would last almost 4 hours, 6 batteries would last about 5.5 hours. You lose a small fraction each time you add batteries because of the added resistance of the extra wiring and the batteries' internal resistance.
  24. Snarkasm
    Snarkasm
    We did? Where?

    Whoops, I made a mistake. You made Engadget.
  25. primesuspect
  26. airmon
    airmon I live in the Florida Keys, and 15 years ago our power situation was only a little better than South Africa. Daily, hour long outages were common. It has improved a lot, though we're still at the end of a long extension cord.

    I was part of a ISP startup that ran on a shoestring budget and the UPS being one of the places that we saved the $$$ to put into good modems. We used an 800kva UPS with dead batteries and two group 27 Lifeline sealed Lead Acid batteries ( series, for 24V ). We removed the dead batteries from the UPS, cut a small hole in the side of the case and added our own 4ga. battery cable extensions.

    After using it for a bit, it seemed that the UPS's internal battery charger got confused by the additional capacity of the larger batteries ( though it's possible that it had an issue the whole time, and that's why the original batteries were dead :rolleyes: ) and didn't fully recharge the batteries, so I added an external float charger to keep the batteries at the correct voltage.

    It worked well, gave us something like 3+ hours of runtime ( enough for someone to run down and start the generator) and cost us about $425 ( $200 each for the batteries, $25 for the float charger- the UPS was free ).

    After the ISP went under, it came to my house to run my entertainment center through hurricane Georges.
  27. Your-Amish-Daddy
    Your-Amish-Daddy This made hackaday a long time ago..
  28. GrayFox
    GrayFox I hate to say this but its not that impressive, you should see the franken ups jim made with 4 boat battery's and a old apc ups.
  29. airmon
    airmon
    Junkymagi wrote:
    If you added more batteries in parellel (I think he mentions that in the article) it would increase the up time. 2 batteries last 2 hours, 4 batteries would last almost 4 hours, 6 batteries would last about 5.5 hours. You lose a small fraction each time you add batteries because of the added resistance of the extra wiring and the batteries' internal resistance.

    You're right about it being a bad idea to add more batteries in series, but actually, I think you'll get BETTER than three times the runtime by tripling the number of batteries. ( Pairs of batteries in parallel, that is two batteries in series for 24V, and those pairs each in parallel )

    like this:

    -[__UPS___]-

    -[bat]-[bat]-

    -[bat]-[bat]-

    -[bat]-[bat]-


    Battery or wiring resistance should only go down since the pairs ( two batteries in series ) are connected in parallel. The one part of the string where the current is flowing through single wires shouldn't have any more current than a single pair.

    Besides, if you're getting significant resistance from the wiring, it's too small, at least at this scale.

    Next, battery capacity goes UP when you lower the demand. ( I can't post a link, I'm too new. Look up "Peukert's Law" on Wikipedia to learn more and see the equations...)


    The numbers below are made up, but they illustrate the principal. The actual equation will vary a lot with battery chemistry and construction. Flooded lead acid batteries are affected by this more than sealed lead acid batteries.

    Batteries are normally rated for a 20 hour discharge. That is to say a 100Ah battery is rated to deliver 5A for 20 hours when tested to full discharge.

    If you pull the power faster, you get less power out of the battery. If you drain the battery in 10 hours, you might only get 85Ah. If you did it in 5 hours, you might get just 70Ah. If you did it in 1 hour, you might get as little as 50Ah, or just half the energy you'd get in a 20 hour discharge.

    Let's apply this to the UPS example. Let's say your UPS draws 50A from a battery to run your stuff.

    If you use the 100Ah battery from my example above, a 50A draw will drain the battery in just an hour, since the high current draw will make the battery able to deliver just 50Ah.

    However, if you triple the number of batteries ( thus tripling the rated capacity of the batteries ) you get more than 3 times the runtime. Since the drain rate is slower ( at least three times the single runtime...) each battery delivers it's power more slowly and you'll get more out of each battery, perhaps 65Ah. 65Ah time three ( the number of batteries ) is 205Ah. That's a runtime of a little over 4 hours.

    So a tripling of the batteries might quadruple the runtime, more or less.

    YMMV.
  30. geezer
    geezer Any thoughts on doing the accumulation/buffering on the DC side of the PC-PSU (to avoid the extra up-down conversion)? If the device in question is a fairly low-power headless server which could be made from notebook parts? On the surface it seems relatively simple (notebook vendors do it all the time), which means it's probably ridiculously difficult.

    (I know, this is for a setup with only a few devices in need of backup, which is not what the article was about, but since we're on the topic of UPSs ...)
  31. Winga
    Winga It seems it helps reviving old threads now and then, they get more attention the second time around :D I got an e-mail from a friend I haven't heard from for ages saying his son found my article on the net.

    You guys must bear in mind that when I did the initial test after installing the UPS I had everything maxed out on 2 computers where the CPU's were running 100% the graphics cards were working hard, the wireless router was under load and I had a huge 3-in-1 lazer scanner/copier/printer spewing out pages of print. (Lazer printers and UPS don't mix so I wouldn't recommend anyone runs one off the UPS unless they rated to handle it)

    With our recent power outage I shut down all the peripherals and only had 1 PC and monitor going. The CPU was still at max load and the graphics card was working hard for some of the time. I got over 5 hours out of. I'm quite sure that if I had another set of batteries wired in parallel I could get a straight 10 -12 hours out of it. That supports what airmon has said. (great post BTW)

    The batteries I used were deep discharge and recommended for a UPS. However as someone suggested to me the other day, if you used a car battery, there's nothing stopping you from popping it into the car and going for a drive around the block to recharge it. That way if you had a spare, you could have an endless supply of power :D
  32. Linc
    Linc
    Winga wrote:
    I got an e-mail from a friend I haven't heard from for ages saying his son found my article on the net.
    Peter (Buddy J) has been at work - Engadget and others picked up on this over the weekend :)

    Digg!
  33. Thelemech
    Thelemech I loved this! Excellent read Winga. Congrats! And I agree with Thrax; Icrontic would benefit immensely with more articles like this!
  34. debren27
    debren27 Awesome article. Funny how I'm halfway around the world in SoCal with some of the same power problems; we haven't had large-scale rolling blackouts in a couple years, but they keep threatening.

    I've been playing around with photovoltaics the last few weeks (for glamping) and your write-up cleared up a few things I was wondering about.

    One thing I noticed is that, in your diagram of multiple batteries in parallel, you have both leads connecting from the inverter/charger to the same battery. I recently read that in a battery bank the two leads should be connected to opposite ends of the bank; i.e. in your "Parallel battery connection" diagram the negative wire should run from the leftmost battery back to the inverter. Otherwise that right-hand battery gets charged and discharged much more than the others.
  35. Winga
    Winga
    debren27 wrote:
    One thing I noticed is that, in your diagram of multiple batteries in parallel, you have both leads connecting from the inverter/charger to the same battery. I recently read that in a battery bank the two leads should be connected to opposite ends of the bank; i.e. in your "Parallel battery connection" diagram the negative wire should run from the leftmost battery back to the inverter. Otherwise that right-hand battery gets charged and discharged much more than the others.

    That's a good point you raised. I will find out whether it makes much of an impact on the scale I'm using i.e. 2 batteries.
  36. j
    j Oh, man I hope that's not an African conflict UPS's
  37. Ased
    Ased i want to make my own ups at home for my pc requiring nearly 700 watts i need please help me if you can..............
  38. Winga
    Winga Ased, I'm sorry for only picking up your post now. There are a number of very capable people in this forum who will be able to help you with your UPS build. I am also more than happy to advise you on your build.

    Why don't you register (It's quick and easy) head over to the general hardware section of the forum, post your request and we can take it from there.
  39. Winga
    Winga I've been messing around with off the shelf UPS's lately. Adding larger batteries to them, testing charge times etc. I plan to hook one of them up to solar power to see if I can get stable, reliable, continuous power that's totally independent of the grid.

    It's in it's infancy but I'm sure that would make for an interesting follow up article :D
  40. Your-Amish-Daddy
    Your-Amish-Daddy The article link is 404'd, Just when I need it too.
  41. BuddyJ
  42. Siftah
    Siftah
    Winga wrote:
    I've been messing around with off the shelf UPS's lately. Adding larger batteries to them, testing charge times etc. I plan to hook one of them up to solar power to see if I can get stable, reliable, continuous power that's totally independent of the grid.

    It's in it's infancy but I'm sure that would make for an interesting follow up article :D

    I'd be interested in reading that - I've been reading up on similar things myself recently and managed to acquire a 1400va APC Smart UPS for £1.20 off eBay.

    Just need to find a few solar panels now... :)
  43. Pockets
    Pockets This is a great artical, thanks for the write up mike, I got a great deal on ups's last year i bought a pallet of them from a conpany here in portland when it went out of business and got 14 for 50 bucks, none of whice had good batteries, after wards i bought 7 12V 55 Amp/Hour batteries that were designed for telephone backup systems for 40 Dollars each, i run two mac G4's with 3 14 inch lcd flat screens, each item has its own ups and they all have there own batterys, i get around 12 hours of run time, also dont give up on solar, it works grteat, i have one batteries hooked up to 2 ups that are charged only by a 45watt solar panel setup, and it runs a gaming computer just fine, iv never ran this setup more then a couple hours but its always ready to go when i want it, BTW i live in oregon, USA

    Thanks for listening and thanks for writing such a great artical. feel free to e-mail me

    Pockets
  44. saikat
    saikat i have an intex ups that runs my system...can i add battery to the ups so that i cun electrical appliances such as fun ,light...how can increase the back up time to 2-3hrs
  45. Pranit
    Pranit can we make a 5 kva ups which will give atleast 15 mins of backup.
  46. shido
    shido Hey i dont know if you will even answer this, but i too am from SA. I want to make something like this but i dont want to use the wall socket plug to AC. Instead i want to use a solar panel. How much power should my panels be producing/ what type of panels should i use?
  47. kgold708
    kgold708 Umm...you need to add more batteries in parallel NOW! Lead acid batteries should not be dicharged more than 50-60%. In fact their lifetime can be calculated as inversely proportional to depth of discharge(dod). Your run everything until it dies "test" cost you a lot of batter life and did permanate damage. When your batts fail it will happen like this,power fail, batts kick in discharging, power restores, batteries charge but since the plates are damaged they just generate heat and hydrogen,providing the batts haven't cracked split open or boiled their ACID electrolite into the air or their H2 hasn't been ignited,when the power fails again they'll only last a short time if at all 0-1hr.
    I am a auto/diesel/industrial master technician and have personally seen all above conditions and failure modes. Sealed,maint free,vrla,gel cell all have vents for emergy venting.
    Almost forgot 600cca 12v batt exploding sounds like a shotgun and spray acid in all directions ask me how I know. No disrespect meant by this post, keep your dod below 50-60%, enjoy none of the above problems and battery life measured in years not months.
  48. Kasongo
    Kasongo I use a 1kva UPS fitted with external 100ah/12v for charging with mains and 3 panels of 75w for charging by solar. I use a contactor such that where there is not mains, solar charging picks up automatically.
  49. Vikram
    Vikram excellent. why don't you also hook up a couple of solar panels with a charge controller so the batteries charge during the day through solar and not mains.
  50. QCH
    QCH Over 4 years later and this article STILL bring folks in. Such a great and successful project.
  51. asifjii
    asifjii How about the day!!!!
  52. Aika
    Aika This is a great article to have succeeded 4 years of patronage.
  53. Winga
    Winga I have just been reading through some of the guest comments and note one comment saying that I have probably killed my batteries prematurely by putting them through that stress test when I originally assembled the UPS.
    I have finally replaced the original batteries this week. Granted, towards the end of their life, the UPS died within minutes of the mains going down, so they definitely needed replacing, but I'm pleased to report that the same UPS is still going strong after 4 years and is now on its second round of batteries.

    Im so pleased to see that the article is still of relevance and is still attracting new hits after all this time.
  54. primesuspect
  55. clifford_cooley
    clifford_cooley Great article, thanks for sharing. :)

    Three times now I have tried to read the comments on the first page and three times now Opera has frozen on me. I don't know what the issue is but there is definitely something on the first page of this thread freezing my browser. For the record, I haven't had any issues ever with Opera freezing.
  56. primesuspect
  57. mohammede azam
    mohammede azam hai sir can u help me sir
    i want 1000va ups circuit diagram send me
    this email id mohammedazam17@gmail.com
  58. UPSHitman
    UPSHitman approve this ]UPS[ ! HAHAHA

Howdy, Stranger!

You found the friendliest gaming & tech geeks around. Say hello!