Backup Battery Box

yes, you can make an 'always on' system.

The inverter runs your system from the batteries. The charger keeps the batteries fully charged and has to be good enough to charge the batteries and run the system.

If the power fails your system run on the battery as long as it can. Often these UPS systems have detectors that do an orderly shutdown. The interval between power loss and battery loss is your powered life. At any time you can start a generator and resume operations.

A large 24 volt truck battery might be 400 ampere hours and 40 amps = 1 kilowatt, so it might run your system for 10 hours. You can often create a standby regime with zero to the monitors and the drives all stop for less draw.

Go to http://www.apc.com and use their product selector to calculate the backup you need. You can get a used one from eBay or local resellers. The only part that ever need changing is the battery. There are reseller which install new battery and resell the unit.

You can't just use a 12V charger with battery and inverter. First you'll need to use the inverter all the time. Is it design for such duty? Second how much amp could the inverter supply continuously? Third how many amp of current draw will that be on the battery? Could your charger charge at same or higher current? With such high amp discharge and charge cycle, the battery will die pretty fast. It also won't shut down the computer when the battery ran out.

Of course you can get components that works but with such high current they'll be costly. I doubt it'll be much less then a UPS.

The UPS not only protect the computer from brown out/ black out. It also protect the computer from harmful surge. Remember you can size the UPS to supply power form network routers and other equipments. It'll also last longer then then your computer.

The peace of mind from knowing power can go out any time without corrupting or removing hours of work make the UPS well worth its price.

BTW I've been using APC UPS since University. I'm using a 1000VA BackUPS Pro at home.

Yes, it's that simple if you are talking about the basic components. However, remember that you are depending on an EMERGENCY backup, which must operate, period. An emergency system that fails is worse than not having an emergency system. Bite the bullet and go for a UPS........

Seems you should be able to get the offline UPS for far less than 1000. You should try looking to not pay such a high markup. You might be able to get as many as three for Dell's price, and you could use use all of them ganged. Sides that, you will get the UPS shutdown and monitoring service software mentioned above as well as GUI, and probably about seven or more years battery life. In addition to software controlled computer or network shutdown, you can also get startup as well...for power failures while you are not in attendance, or for automatic computer and UPS shutdown according to a normal work schedule. Just a thought...and you might not really be able to save all that much, considering the risks, trying to put something together yourself. UPS's in that price range also come with built in tests which would not be available on a homemade setup. Remember also that the computer will probably never run at the rated capacity...probably less than 20-30 percent on average. Biggest power uses being the HDD(s). Figuring runtimes on batteries is fairly simple once you know the power and backup spec for the UPS.

When I worked for Best Buy several years ago Christmas season was approaching and we needed additional POS terminals that we could place throughout the store. The solution was a mobile cart that held a complete spare POS terminal, radio link, and a setup very similar to what you describe. It really was "as simple as that" and worked very well for a quick, cheap, solution made only with parts on hand plus 1 trip to the auto parts store. What you described is essentially an online UPS.

Make sure this is really what you want/need. It is a hack with no warranty or "connected equipment replacement insurance" like some UPS have. It may even violate the strict terms of your computer warranty, read it to be sure. Also you need to comply with Canada's electrical code which I am not familiar with. That isn't an issue with a TUV approved UPS or whatever they use up there.

If you decide to go ahead, verify your computer's power requirement. Is 1400watts the supply's input or output power? Maybe what you have is 2 redundant 700W supplies and marketing called it 1400. In which case you get away with a much cheaper system. Also, computer power supply ratings are getting almost as reliable as car stereo amp ratings. (Digression; A friend excitedly showed me the new 2000Watt car amp he picked up at a traveling liquidator show. It had a 3ftx1ftx2in extruded aluminum heat sink and 2AWG power terminals. And a 7.5A fuse. Yes, 7 point 5. I opened it up and showed him the 4inx5in circuit board inside connected to those massive 'gold colored' terminals with 16AWG wire.)

Back on topic. Inverter. I always choose a supply that has at least 7% headroom. More if I don't trust the rating. Why 7%? Because it's as arbitrary as 5 or 10% and I never again have to explain myself for violating my own guidelines when I say the 9% unit is good enough. A modified sine wave inverter is usually good enough as long as you get a unit with a fair amount of filter capacitance. If you are unlucky, the switchers in the computer, inverter, maybe even the charger will be the same or harmonics of each other. (this happened on the first Best Buy units) This sets up a beat frequency that can wear stuff out quicker than normal and/or make noise. If this possibility concerns you get a pure sine wave inverter, but that is likely to blow the cost advantage. If you can find the specs for switcher frequency you could be sure.

Don't use 2 or 3 batteries. It adds cost, complexity and additional failure and maintenance points. Copper and good connectors are getting expensive. If you absolutely must for some odd reason use identical batteries from the same lot, off the same pallet if possible. A single 4D will do fine, or an 8D if you have the need, space, and ability to lift one. These are available for a variety of end uses and you can sometimes get great surplus deals if you can avoid shipping costs. House batteries may even carry necessary code approvals. There is alot of stuff I could tell you about choosing batteries but its all on the net somewhere. Flooded LA batteries generally require separate ventilation to the outdoors, sealed units do not. But in either case it is a good idea to avoid keeping your battery and electronics in the same confined area. Batteries can release hydrogen gas and/or sulphuric acid. (musing; RoHS. Why must we remove every trace of lead from our circuit boards, but keeping hundreds of pounds of lead and acid in a thin plastic box in our homes to store wind or solar power is considered green? I should shut up lest they replace my time proven safe lead for expensive exploding Lithium.)

Charger. Newer computer controlled chargers are smaller, cheaper, more efficient, full of monitoring and other cool options, and have a cleaner dc output. I use my Schumacher all the time but I do NOT recommend it. Make sure the one you choose is rated for continuous duty at the rate you will be using, has an automatic float mode and that the float voltage is appropriate for your battery. Don't want to boil it away. Do NOT use the anti sulfation mode if it has one, unless you first disconnect the inverter load. Avoid fully discharging your battery. Besides severely reducing the ultimate battery capacity, a very large dead battery will try to draw alot of current. I found out the hard way after leaving my truck dome light on in -10F weather for 3 days. My charger which "features" short circuit protection saw my dead battery as a dead short and completely shut down. How convenient is that feature? Isn't a dead battery the whole reason for owning a battery charger? A better design would provide a current limited output, maybe a timed output at a low rate then recheck. Anyway...

Some inverters are available with a charger built in. Some even have a serial output to signal your computer to shut down when the battery is low or trigger power saving mode when AC mains is lost. This duplicates all the major functionality of a commercial UPS, but a low voltage audible alarm on inverter or charger would have the same affect as long as you are around to hear it. So far I've assumed commonly available cheap 12v equipment. But now that I think of it, thats alot of juice. You would be moving around upwards of 110Amps constantly. You can keep current,heat and cable size down by going to a higher DC voltage. 24, 36, 48volt and others are available but you probably wont find em at Wal Mart. So far we have only discussed online solutions, meaning several conversions are going on continuously. AC to DC, back to AC to 3 or more different levels of DC for use inside the computer. Not the model of efficiency but with 0 switching time and highly filtered power it has advantages. Another option, the one I would probably choose would be to replace the computers power supply with an AC/DC unit. These are the same form factor as what you have now, PS2 ATX or whatever and plug into the wall just like yours does now. The difference is they also have DC terminals which you wire to batteries you supply. The charging circuit is built in and a separate inverter is not required. The 12v units I've seen are barely enough for a plain Jane PC, limited I suppose by the required high current components would have to withstand. I know the higher voltage units are available with higher wattage ratings but I don't know if they go as high as you need.

I can't believe I typed so much. If I was rambling and incoherent I apologize, its the insomnia talking.

(musing; RoHS. Why must we remove every trace of lead from our circuit boards, but keeping hundreds of pounds of lead and acid in a thin plastic box in our homes to store wind or solar power is considered green?

Because RoHS is concerned with recycling or disposal of electronics and they ASSUME you are already doing the right thing in recycling your lead acid batteries. When I was in Germany in the 1980s they had already put up public battery recycling boxes everywhere for typical consumer batteries (AAA, AA, C, D, 9V, hearing aid, etc.) like carbon zinc, ni-cad, and alkalines, and presumably had automotive and similar large battery disposal systems working as well. Here in the US many states charge an extra fee for battery disposal if you are NOT returning a dead automotive battery when you buy a new one. Kind of like collecting deposits on returnable bottles. Of course we all know how well THAT worked! Funny thing is, tire sellers charge the disposal fee only if you do NOT take your old tires home with you. Presumably you can recycle your old tires yourself, but not old batteries. Sure, we love to make tire swings, yard planters, even cut out sandal soles from the tread....Yeah, right, if you are a redneck (tire swings and planters) or a hippie (sandals). Most of us simply pay the disposal fee, but a few cheaters take the tires home, where they sit in the garage for years collecting dust, and eventually get sneeked into the trash to wind up in the landfill.

Something that nobody has raised is that unless you engineer this properly you may end up with something that is less reliable than running on the raw mains power. Most inverters aren't that reliable so you could end up going backwards. A good UPS has some sophisticated monitoring that can automatically bypass the inverter and run your system on raw mains in the event of a failure within the unit.

The question is, how often can you expect to have the power fail unexpectedly and how much work could you expect to loose with each failure. I don't know about how reliable the power is where you are but where I am nobody can remember exactly how long ago the last power outage was. In any event there has only been one in at least the last 5 years. That would mean that to be better off the inverter must operate 100% for at least that length of time for your system to be even as reliable as the mains on their own.

My advice would be that if you data is so valuable that power outages are a concern then its worth spending the money on a properly engineered UPS rather than a hack job that is more than likely less reliable that the mains power.

THANKS EVERYONE FOR THE ENLIGTENING INFORMATION.

KEITH

Your stuff looks good.

Even though you are rated at 1400 watts you may not typically use that much. Put a meter on it and find out how much line power is going into it because that is what you really are designing for. Use a precise inverter that delivers "filtered" power. Some one the solar power people make really good ones. Read up on the batteries a little and make sure you get a charger that stops crystals from forming between the plates regaurdless of the lead acid, battery type. Again solar power sites have the best information. I think you are on the right track. I made one of these from a 8D battery and I intend to add another. I will use it for other purposes too since I live in South hurricane FL. My upgrade will include 300 to 600 watts worth of solar panels.

Try an autosave setting with a short time interval, in the first instance. The inconvenience of autosave may be preferable to a sizeable investment in an UPS or the demands of home-brewing one, depending on the vagiaries of the local power supply.

You don't need massive battery capacities.... my UPS uses a tiny 10 Ahr 12 Volt sealed lead acid battery...

Its only rated for 5 to 10 minutes of use, but that fine and gives me enough time to save work close applications and power off the computer....

John.

Belkin make a UPS built into a 4 way extension lead similar to their anti-surge leads. It sells for about £30 in the UK for 5-10 minutes duration.