DC UPS

It currently is running on a 12 Volt Battery. The problem is if the system for some reaon spuriously keeps functioning it drains the battery and eventually stops working. Hence I want a reliable power supply so atleast the power stays on no matter if the system works spuriously and eventually dying out.

My intention at this stage is not to change the design but to only provide a relaible power supply.

Thanks

UPS is not for a continuous run of equipment. Of course the batterie will drain.

Get a back up generator for this one or have a huge bank of batteries available.

Does your system "spuriously keeps functioning" often?

Maybe teaching it how to behave would save you the bother of buying it unnecessary toys.

Do you know how much power the spurious system consumes when it is being naughty?

Perhaps a 2 AMP battery minder is all you need.

Google "UPS".

Have a clue.

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For a 12 volt 5 amp system I use a battery charger connected to a 12 volt deep cycle lead-acid battery, I use a 15 amp battery charger as the power source to this battery and from the ac line. This is in lieu of the small internal battery charger of a UPS. A few capacitors kill any substantial spikes from the ac line and the battery charger. It could easily put out 18 amps for quite a long time. Increase the capacity of the charger and add another battery and you have what you want at much less than the cost of a commercial UPS. Units with the capacity you want are very expensive.

The battery is placed in a plastic battery box from a marine supply dealer for about $10. All apparatus is located in the basement and only a #12-2 cord goes through the floor to the power users. All appropriate items are fused.

Good Luck, Old Salt

If I was given the job to design something simple, but to do a good job I would do the following:-

1) Buy a quality converter with a true sine wave output at the frequency/voltage I needed.

2) I would monitor battery drain both in current and in time 24 x 7 and using this calculate a battery size needed to bridge any mains failures both in time and current draw. (Do not forget that 12 volts to mains converters, especially true sine wave ones, are fairly heavy users of battery power! Efficiency is not as high as you might expect). Also, get a charger that can supply the 18 amp draw continually (or close to) without overheating or other problems, that way, the battery sort of runs as a filter cap.....but is THERE when needed, so to say!!

3) Do not use car batteries, leisure/deep cycle are needed. Do not plan to ever need 100% charge in the battery, too knife edge.

4) If you decide to go for more than one battery in parallel/series, DO put an intelligent charger with proper charge cutoff on each battery separately.....Batteries, even identical ones have different personalities that if run to high and too low can cause individual cells to degrade.

5) Do remember that charging above 70% of SOC will cause a dangerous gas to be formed and given off, very explosive, so good ventilation is a basic requirement with no cigarettes or naked flames nearby... Standard safety equipment is also a good idea....or you must have batteries that are sealed, but do not forget that even over charging of these can cause high pressure and gas venting....so the safety precautions stay the same.....

6) Which is why I design and build my own chargers as only top expensive chargers allow control of max SOC to be set up to suit your needs....too expensive for me personally, even when I could afford anything I wanted. Scottish blood!!!

7) You need to price/design a 12 volt system and a 24 volt one to see what suits you best of all and then go for it. I tend to think that a 12 volt one will do you OK and be slightly cheaper. Also adding a second battery (identical to the first is best) with its own charger in parallel, to the first system, would be a cheaper option than adding say 2 batteries and two chargers to a 24 volt system! Simple math!! though its better to have as big a SINGLE battery as you can afford and to look after it's health carefully.....

Pick a cool place to install the system...

I personally do not like UPSs which try and "cut" in at mains drop time to replace the missing AC, as I have never personally seen one that did it cleanly enough and did not hang PCs and the like.....I know it can be done, but few achieve it. A hung PC is as useless as one that is powered down!!!

Best of luck....

Hi, While the advice from Andy is very good I differ on the use of UPS.

Being too lazy to try and make my own and, finding that secondhand ups can
be obtained so cheaply as to make it un-worthwhile, I have used many over the
last 20+ years and can truly recommend them.

I have mainly used the APC make, and provided you obtain one which is made to
accept additional external batteries, they are easy to adapt and set up. They "cut"
in seamlessly when the mains power fails, even the PC's do not "blink" and the only
notification you get is a "click" as it changes over, and maybe something not connected
to it stops. (e.g. a printer etc.)

I have used 5kva ones to run the whole house, but naturally a substantial battery
circuit is needed for any prolonged use. At one time I connected 8 deep draw leisure
external batteries, which gave several hours of run time.
However, if you rationalise your emergency needs and cater for only your essential services
a smaller capacity will likely suffice, saving money on the size of the unit and the
additional batteries required. If you search CR4 for "battery circuits" or similar you
will find loads of advice on battery circuitry.

A generator can be expensive to run, and if not automatic, very annoying to start up
at possibly an inconvenient time. Standing capital used infrequently.
A UPS system can be sourced cheaply, prolonged with external batteries, give instant
seamless fail changeover, saving your work; but unfortunately will have a limited run time.
But during this run time alternative measures can be effected to save your day.

I can recommend APC UPS (no association) others are likely just as good. Many are
to be found on ebay and other sites at very discounted prices. Chose wisely.

Hope this helps.

jt.

I read that a cafe in London is now selling coffee at £8 a cup.
Inside the cup you'll find hints of apricot, pineapple, kiwi, and lime.

Outside the cup you'll find a daft bugger who spends eight quid on coffee....