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Building an Alternative UPS

Building an Alternative Power Supply

Page One: What am I talking about?

By: Orinthical

What am I talking about? Well, chances are that no matter how involved with computers you are... you've heard of a UPS. And un-interuptable power source that powers your computer for a small amount of time in order to let you save documents and such in case of a power outage.

Well if you're like me, you're probably wondering why in the world you should pay upwards of two hundred dollars just for twenty minutes of power? Well, what if I could tell you how to get allot better results for just about the same amount of money or less? Personally, I'd be happy... but wait, it gets better.

How about 10 hours or more of power for around $200? or even $250? Yes, you heard me right... 10 HOURS of power for the same amount of money. Well, I suppose right now you'll be going crazy and asking me to explain how to get this done, no?

Well, let's start with the basics...

UPS's (Un-interuptable power supplies) used to only be found in bank branch offices or industry giants where mainframes were in use and millions or billions of dollars were at stake if the power ever failed during a number crunching affair. Well, like everything else in the world... times have changed. These smaller devices have now found their way into almost every serious computer users office collection.

How they work is by using a set of voltage regulators and a few relays to measure input voltage and then react by switching over to an internal power supply (batteries) if the input voltage should fall shorter than a given range. The idea is, that it will switch over within enough time that the device(s) it is protecting won't feel the fluctuation. Therefore, allowing them to continue running as if nothing had happened.

While you are probably thinking this project will be hard to do, let's start with just the base idea....

Let's just build the alternate power supply...

Well, since UPS circuits would be a bit complex to design, I'll cover that in part two of this guide. But let's cover how to make the first part, which you can use with... or without a UPS. Since an "alternate power supply" refers to the batteries inside of the UPS unit... guess what I'm referring to when I say the same thing.

The batteries inside of the standard UPS are "sealed lead acid" type batteries which are sealed in nature and offer better safety to the consumer than the standard wet cells that we use in our cars, boats and other vehicles.

Contrary to popular belief, the liquid that you see in wet cell batteries is not strong acid. It is usually a diluted mix of sulfuric acid and water that is put in at either point of purchase or at the factory. The acid which is in the water usually soaks into the lead plates, causing the chemical reaction which creates and stores energy.

This doesn't mean that it still won't burn or hurt you... because it will. But if you get some on your hands, your skin won't melt into a puddle either. Believe me because I've had allot of acid on my hands and they aren't deformed.... or so I've been told. haha

Anyway, I say this because I want you to understand that batteries are dangerous. When charging, the wet cells we are going to use emit low levels of hydrogen gas. This stuff is flammable. Now, I've seen many people smoke around these things and know that they for the most part are safe, but please use some caution and don't smoke right next to them.

This is the Yuasa 12volt, 7Ah (Amp hour) SLA (Sealed Lead Acid) Battery. In most smaller UPS's, this is the battery that you will find when it comes time to replace them. These batteries usually cost around $22-30 each and last 3 to 5 years. For something comparable to the wet cell below, you'll pay something like $200 to $400. Why? Because this battery, unlike the one below, can be mounted in any environment, at any angle and without fear of leakage or explosive gas venting.

This is what we'll be using... Well, close anyways. See the difference? If you turned this battery upside you'd have a big mess. So please, don't try to do that. And btw, sulfuric acid likes to eat cotton so please don't wear clothes that you care about when doing this project. Because polyester is plastic based, it is safe clothing to wear. But please realize we aren't liable for you destroying your clothes of course. Oh yea... and I shouldn't have to tell anyone this, but please do not mess with batteries without wearing anything.... it burns, okay? 'Enough said? haha

Let's talk about what you will need....

To assemble this unit you will need the following items...

Total Project Cost:
30 Minutes of your time
$220 - $270 (US Dollars)

To be honest with you, you'll probably already have some of this stuff if you own a car or better yet... a boat.

1) Marine Deep Cycle Battery -- "Group Size 27"
Estimated Cost: $80
Specs: BCI (standardized) group size: 27
Reserve Capacity: 160-180 minutes at a 25Amp discharge rate.
Terminal type: Dual Marine (Car style posts plus screw posts)

2) 300 Watt Power Inverter Estimated Cost: $50 - $80 Input: 12 V Nominal DC Output: 115V AC If you want the same one that I've got... get a SIMA SPV-3 300 Watt Power Inverter. It'll come with a cigarette lighter adapter as well as two alligator clamps. Guess which ones we're going to be using. If you guessed the clamps, you guessed right. These can range in price from $50 all the way up to the $80 I have listed. Really, the best thing to do would be to search for "Sima SPV-3"... Trust me, you'll get a lot of results and some excellent prices. If you're going to be running more than one computer or if you are going to be running a LARGE monitor and lots of accessories, I might suggest that you try a 600W inverter instead. The conclusion page will have a simple equation to follow in order to determine how much that'll cut out of your runtime. 3) 12Volt "SureCharge IV" Float Charger Estimated Cost: $30 - $40 These little beauties will never over-charge the battery by automatically sensing when the battery needs to be charged. With lead acid batteries, their care is exactly opposite of most Ni-cad and Nickel Metal Hydride (NiMH) batteries and should always be kept at a full charge. This little thing can be had for around $30-40 and keeps me from ever having to charge the battery to maintain it.

However, these little chargers won't charge the battery back up to it's full capacity if you should happen to run this battery for a long time and drain it. So for that, I'd recommend picking up a cheap 6 amp automatic charger from your local walmart for $20 too. This you can use on your car battery too so you won't be.. *cough* wasting money. Don't leave this on the battery all of the time, only after you've run off the battery for a few hours. And despite what anyone else may tell you fairy tails about charging your batteries in only a couple of hours, you should leave your battery on this thing for no less than overnight after a good run. Otherwise, let the float charger do the work for you.

4) 12Volt Car Battery Charger 2Amp, 6Amp or 10Amp Estimated Cost: $20 - $30 There's no need to go spend a fortune on this but it's important to get an automatic battery charger (designed for cars) which will charge at, AT LEAST two amps. To be honest, you really want to try and get a 6Amp or 10Amp variant because they will charge the battery up from dead alot quicker. This charger will only be used to charge the battery back up after a long use. Like if the power goes out for a few hours, you'll want to disconnect the float charger mentioned above and the connect this for a few hours to bring it back up.

Well, if you've come this far chances are you rush over to your local Home Depot and collected the few things that this project requires. Either that, or you're really really curious. We like simple projects which have large gains, don't we? I think we do... Well guess what folks, this one is really easy too... and to show you that it is indeed simple, I made you a pretty diagram. haha

Well, as you can see from the diagram there folks, "A" (The 2A/6A/10Amp Charger) is not directly connected to the battery because it is only used when the battery is used for few hours. The float charger "B" will keep the battery fully charged for you all of the time. Now, it IS possible to do this project without a float charger. Just make sure to charge your battery overnight, every three months it sits and within 24 hours of when it is used. Of course, if you don't use a float charger... you won't be guaranteed a full charge every time you go to use the battery. That's the beauty of having a float charger.

Connect the inverter using those "clamp" type connectors or if your has actual permanent connectors, like eyelets, you can go ahead and connect that first. Positive side to the + sign or red side of the battery and Negative to the -- or black side of the battery. Now with nothing else connected, make sure your inverter works by firing it up once. If you get signs of it working, turn it back off and go to the next step.

Connect the float charger by using the eyelets that it comes with or by attaching the clamps from it to the battery.

Red to positive, Black to negative... If you purchased a marine battery with dual purpose terminals then connect the float charger to the wingnut set and clamp the inverter to the pole (auto post) terminals.

Well now that we've gotten this far, wouldn't you like to know how exactly I came up with saying that this small little battery will last thirty hours? Hard to believe isn't it? Well it's all in the math and before anyone jumps on my back about this being wrong... I've tested my equation and it works as it is supposed too. For those of you who are going to be angry at me for using math.... don't worry, it'll be really easy.

You need to obey the law of power conservation. Power = Voltage * Current.
The battery has 12V * 25A = 300W for 180 minutes.
The inverter, generating 300W (without any efficiency loss) would only run for 180 minutes (less if it was not 100% efficient).

However, the PC is not drawing the full 300W when running, maybe it's using 50W - 80W (without the monitor).
The total time would be 180 minutes * 0.9 (inverter loss) * 300W (output) / 80W (usage) = 750 minutes (12.5 hours).

That equation will work with any battery as long as you get the minutes reserve time and what discharge rate those minutes were counted at from the sales clerk. If he or she doesn't know and doesn't know where to find this information.... find another store to shop at. But, most of the time this information is printed directly on the battery label.

I really don't know what to tell you except to try this out for yourself! I'll try and get a second part to this article done sometime in the near future that'll tell you how to turn this into a real UPS so that it will automatically switch over when the lights go out. But until then, I'd buy a cheap $50 power strip with "5 minutes" of runtime and plug your system into that. Just keep this rig nearby and when the power goes out, your data will be saved by the cheapo UPS and all you have to do is unplug from the wall and plug into the inverter then flip a switch.

Then you'll be playing Quake III when everyone else is fumbling for their emergency supply of candles. And here's an idea.... this will of course work with anything electrical..... Playstation 2 anyone? [insert maniacal laughter here]


While my alternate power supply did work as it was suppose too, it shut itself off after 12.5 hours because of a low battery warning. Now, 12.5 hours is still impressive except when you look at what kind of battery I was running. For my test rig, as those who are active in the forum know, I used a 600W inverter and an Exide Commercial 8D-P1300 battery which is designed to deliver 450minutes of reserve time at 12 volts under a 25A constant load.

A borrowed amp-meter from a local car garage indicated a 37A draw by the inverter itself off of the battery while running the following equipment: 1) My box, 2) My 17" monitor, 3) My Cable Modem, 4) My 5 port hub, 5) My HP Deskjet 712C printer, 6) My Umax scanner, 7) 2 cordless phones, 8) A 12W Fluorescent lamp and my standard UPS which I kept in line just in case. While this setup power ALOT of equipment for 12 hours and that alone is impressive.

My Box specs:

AMD Duron 600 @ 1000 / 1.8V / 42C
Abit KT7-RAID Motherboard
OCZ Monster II Cooler
128MB OCZ Select PC133 SDRAM
Elsa Geforce 256 32MB SDRAM AGP4X
Creative Labs Sound Blaster Live! MP3+
Sigma Designs Hollywood Plus PCI DVD Decoder
Linksys Etherfast 10/100 PCI NIC
Maxtor 20.4GB 7200RPM UDMA/66
Toshiba SD-M1212 6X/32X UDMA/33 DVD-ROM
Imation 4x4x20x EIDE CDRW
Sparkle Power SPi (FSP300-60GT) 300W Power Supply
Customized ATX Full Tower Case


HP UltraVGA 1280 17" .26dp

Other Devices that were Plugged In:

RCA Digital Broadband External Cable Modem
Linksys Etherfast 5-port workgroup hub
Panasonic KX-TC1400 Cordless Phone
GE 2-6920M Cordless Phone
GE 12W Flourescent (Incandescent replacement) light bulb
Umax 1220P Scanner
HP Deskjet 712C Printer

Now according to the math which I used earlier, this battery should have delivered 36 hours of run time at a 600W constant draw. This math was obviously wrong as so many of you flooded my email and tried pointing it out. And forgetting my math, the UPS is suppose to only deliver 450minutes at a 25A discharge rate. With all of the above devices plugged in, I was averaging a 40A load. 450 minutes is only 7.5 hours so why did I get 12hours out of it? Let alone the fact that I was pulling almost 1 and a half times it's rated load. At those ratings, I should have only gotten like 5 hours out of this unit instead of 7.5 or the 12 that I actually got. How is this explained? Well, batteries vary in manufacture and the rating of 450minutes reserve is probably a "safe" median between the best and the worst batteries out there in this same class.

Being that the inverter stayed at 37A most of the time, solid, and only went up to 42A while initially booting up the machine, I do not think this jump in run time can be explained by just simple chance or by a fluctuation in power consumption.


For those of you who have stuck with me this far, I thank you for at least allowing me to explain my theories, problems with it and why I am writing this follow up to begin with. I apologize to those of you who got a heaping helping of my injured pride last night.

I would like to salute a gentlemen named, Yoav Epstein, who instead of yelling at me, presented the problems as they were and told me the solutions for them from an electrical engineer at his workplace. For your reference, I'm going to quote his email below.

I asked an electrical engineer at work about the amount of time the battery would last, and he said you had an error in your calculations.

You need to obey the law of power conservation. Power = Voltage * Current.
The battery has 12V * 25A = 300W for 180 minutes.
The inverter, generating 300W (without any efficiency loss) would only run for 180 minutes (less if it was not 100% efficient).

However, the PC is not drawing the full 300W when running, maybe it's using 50W - 80W (without the monitor).
The total time would be 180 minutes * 0.9 (inverter loss) * 300W (output) / 80W (usage) = 750 minutes (12.5 hours).

Thank you, Yoav.

That's everything I believe....

Until next time, be safe.... and play hard!