need to build a UPS for computer

it might work out if you can scrounge the bits from crap. maybe an old car battery being charged by a pc power supply and an old inverter could do the trick

I don't know what sort of PC HS3 has but I have recently been measuring PC wattages and have found that my old PC 1.4GHz with 19"CRT uses 150W,
newer quad core 2.4GHz with two LCD screens used 45W, with a decreasing power consumpution for newer PCs. The start up watts would be higher these are just the steady operating watts averaged over a week, no power saving turned on, even the screens were left on.
A UPS shouldn't be involved in rebooting a PC, that is why you get a UPS, so if the power does fail then I would need a UPS to provide 150W until I started the genset.

Yea it's like knitting a stove out of steel wool...or making a computer from seperate discrete transistors ,possible but quite time consuming...just buy one

hello friend seand me 1000watt upsdagram

wont battery and inverter makeup a good ups?
i only need it to provide non stop power in case power failures

personally have a UPS pretecting my machine but I was VERY lucky in that I picked it up from a local junk stall for £1. Yes you see correctly £1.00 Fair enough this one needed a new set of batteries but they only cost £20. Maybe you should keep looking around on junk stalls, You never know what you might pick up!

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True,you never know what you may find from one day to the other in dumpsters too...I"ve actually found good computers with maybe a minor problem which was quickly fixed and bingo..working computer

nasibrahim said:

wont battery and inverter makeup a good ups?
i only need it to provide non stop power in case power failures

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A UPS is a little more than a battery and inverter, it's also a charger and often a conditioner.

Point is if you need a UPS just go buy a UPS.

I didn't think that electronics guys are so cheap that they pick through garbage.
I have picked up a few things from the curb just before the garbage truck mixes it with garbage and my so found a 27" colour TV that works perfectly (CRT type).

My best win was when my son found a guy who worked for a home electronics store. He was moving. Hundreds of "unrepairable" products with nothing wrong with them (maybe the wrong color?).

I didn't think that electronics guys are so cheap that they pick through garbage.

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I wasn't implying that they were cheap,only that one mans "garbage" is another mans treasure....like the electronic keyboard that was just left by the dumpster that nobody wanted.
Also I believe in recycling so im just doing my bit here to help the planet.

Hi PICers,

I want to design a 24V DC to 50Hz/240AC power inverter. My choice of PIC is the 18F452 (HWPWM). But I am not sure whether the ADC conversion time would be short enough for dynamic correction.

Any thoughts

Regards
nasib rahim ph+92939555213

If you need a good and working inverter of any capacity of your choice that can fit the size of your load then log on to www.micinverters.blogspot.com or visit **broken link removed**.

micinverters

UPS/Inverter System.

Hi folks, I'm new here and was reading through this thread on UPS power systems.

I have an idea that may help you to build a large UPS. I have a houseboat and a large set of batteries (2x 12vdc 1000ah). I already have a large modified sine wave inverter (2000w, 240vac) running on this system and It provides me with 12-14 days power with only 3x 120w 12vdc solar panels feeding the system (no 240vdc charger) what I am aiming for is a "no-break" power supply with an automatic generator switch. I have attached a diagram of my desired setup.

The questions lie in the circuit that switches the generator on.

**broken link removed**


The generator already has inputs to accept the DC circuit to tell it to start, all I need to do is provide it with one.

I hope I've given you enough details so that you might be able to help me out with a circuit that will suit my needs, or at least point me in the right direction.

Thank you in advance for your help.

Cheers

Zach Fleming
zach.fleming_at_tekace.com.au

Having seen all the requests for UPS and inverter designs from 3rd world countries posted on this and other forums over the last couple of years has sure opened my eyes and sure made we aware of how lucky I am to live in a country with reliable electrical power distribution.

I do some what sympathize with the many people asking for help. Imagine having a real interest in electronics and having to deal with daily power outages, brown outs and all the other electrical nasty stuff they have to deal with?

Even on a few vacations to Mexico, I was amazed when just looking up at the power poles on the streets. There would be dozens of illegal taps with drop lines going all over to buildings, stealing unmetered power probably. I'm sure there must be many many electrocutions from such activities.

Depending on what type of battery charger you have, the automatic changeover from mains to generator might be easy, and no actual switching device needed.

If it is a switch mode battery charger, it will work like this:-
Main in -> rectifier -> 350 V dc.
350 V dc -> switch -> 350V pulses at 20 kHz ish
50V pulses at 20 kHz ish -> transformer -> 14V pulses at 20kHz ish
14V pulses at 20kHz ish - > rectifier -> 14V DC

If your battery charger is like that, you can buy a couple of rectifiers rated at 600V and 20 A (MULTICOMP|GBPC2506|BRIDGE RECTIFIER, 25A, 600V | Farnell UK). Connect the AC side of each to the mains and the generator, and the DC sides in parallel and connect to the input of the battery charger.

This will not work if you have a linear battery charger. Tell us the make and model or the rating and the size and weight and we can probably work out what type it is.

(A linear battery charger needs a transformer that runs and 50 Hz. A switch mode battery charger needs a transformer that runs at 20 kHz, and if far smaller and lighter)

Some other comments:-

The scheme looks OK. Everything looks possible.

I would charge the batteries way before 10V. By the time lead-acid batteries are down to 12V with a light load they are about to drop.

You need a separate battery for starting the generator.

You need something to decide when to stop charging. Time might be good as you don't want to wait until the batteries are full, as you might have the sun come out or the mains come back on, either of which is cheaper than the generator to run.

If your mains load is big, you might want to bypass the charger - battery - inverter bit when the mains or the generator is working. The charger will be 80% efficient, the inverter will be 80% efficient so the total will be about 64% efficient. (the range could be 40 - 80%. I have made wild guesses on the efficiency of the kit). If you bypass the charger - battery - inverter bit you would save maybe 30% of your power from the mains or the generator.

Whether a bypass is worthwhile depends on how much power you use at 240 V, how much time you run from the mains or the generator, and how much electricity costs and the cost of extra fuel to drive the charger and inverter losses when the generator is running.

Thanks for your reply,

My battery charger is SwitchMode (30a @13.8vdc), my batteries are VRLA (designed to run a telephone exchange where they came from) and are aprox 2 years old (still 8 years on their warranty).

the reason for using 10vdc as the trigger for the generator is because the inverters Low Volt Ddisconnect is at 9.6vdc so I thought 10vdc should should give me plenty of time to get the generator running.

as far as when to stop the gen, i was thinking (and i didnt put this in my previous post) it would be nice for the batts to reach float voltage and stay there for, lets say 3 hours before the generator turns off.

at 10vdc the batteries (6x 2v cells, 500ah per cell, 2 banks of 6 batteries) are still 0.2v from their minimum volts per cell rating (of 1.4vdc per cell).

The generator has its own 12vdc battery used for starting.

any help on the circuit to control the switchover from "AC MAINS" to "AC GENERATOR" and the switching on of the generator would be great.

I also like the idea of bypasing the charger when "AC Mains" power is available, but would I be able to have a "no-break" power system with the bypass? I was keeping the inverters etc inline all the time to avoid the loss of power while the ac was switched from Mains to Gen.

Im hoping this can be done for a reasonable price and I hope someone here can help me out with the design of the circuit.

thanks again in advance for any help.

Zach Fleming
zach.fleming_at_tekace.com.au

When the battery is only 10V the starter will surprise it much more than you think and it will quickly dip below 9.6 and shut off the inverter, if only momentarily. It is much better to keep an independent 12V battery rated to start the motor. My friend with an RV does that, and your boat application is pretty similar.

Do you have a separate motor for propulsion? Can you tap its starting system?

yes, i do have a separate battery for the engines, but the generator has it's own 12vdc battery it uses for its starter.

the alternator output of the petrol engines is also another option for charging the battery bank, this is how the batteries were charged before i started changing the system to the current solar/charger arrangement, these could also be automatically started using the same method, but are much noisier than the generator (and why have a 5kva generator if I'm not going to use it!)

thanks again for your help.

Zach

If you are starting the generator from a separate battery, you could let the batteries drop low. However, it might affect their life. I would also strongly recommend that you monitor the voltage of each cell. The cells won't be perfectly matched so you could have one cell at much less than 1.4 V when the battery is at 10V.

The 12V alternator on an engine is usually only rated at 500 - 1000 W. However that is more than the rating of your charger.

If you have a 5 kva alternator, you're not going to be able to use much of it with a 30 A charger. You can only get about 400 W out of it. It will take nearly a day to charge the batteries. Also, your 5 kW motor will be very inefficient if all you are running from it is a 400 W charger and 500 W or so from the 12V alternator.

You either want to run the ac load directly, or get a much bigger charger.

Diver300 said:

If you are starting the generator from a separate battery, you could let the batteries drop low. However, it might affect their life. I would also strongly recommend that you monitor the voltage of each cell. The cells won't be perfectly matched so you could have one cell at much less than 1.4 V when the battery is at 10V.

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I think that monitoring each cell is a good idea, the power systems I install in Telephone Exchanges use a similar system, In fact, I have a complete system here at home I would use, the problem is it runs -48vdc and the houseboat already runs 12vdc, if I was starting from scratch, I would use the -48vdc.

The 12V alternator on an engine is usually only rated at 500 - 1000 W. However that is more than the rating of your charger.

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Running the Inverter and the 12vdc lights etc, it normally takes 12-14 days to discharge the batteries to a point where the inverter stops working, this is WITH the use of the solar panels.
Im not exactly sure on the total current draw, I will have to get on the boat with a clamp meter and turn everything on

If you have a 5 kva alternator, you're not going to be able to use much of it with a 30 A charger. You can only get about 400 W out of it. It will take nearly a day to charge the batteries. Also, your 5 kW motor will be very inefficient if all you are running from it is a 400 W charger and 500 W or so from the 12V alternator.

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The generator that is on the boat is 5kva (4kw) and I dont understand how I am "not going to be able to use much of it" with the 30a charger, it runs fine from a 10a, 240vac wall socket and the generator is capable of providing power for more then that. Even with the 2x 500w (240vac, these don't run from the inverter) flood lights running at the same time.

You either want to run the ac load directly, or get a much bigger charger.

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Im sorry if I have come across ignorant about this whole project, but I am wanting a solution and I would really like to build as much of it myself, it seems that all the products out there are way too over priced and anyway, I'd rather learn something new then spend money!

Cheers Folks

Zach

My point about the 4 kW alternator is that it will use quite a lot of fuel when just running with no load, as it will have to run at full speed to get the right frequency. It will be most efficient when producing about 4 kW. Your 30 A, 12 V charger can only convert 400 W so you are not running efficiently.

The battery is large enough to absorb the full power of the alternator so if you got a larger charger you would get the batteries charged a lot faster with less fuel.