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Old 12th September 2011, 18:34   #451
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Default Re: Inverter capacity?

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Sorry Aroy. By the time I finished typing I saw that you have covered the main points.
No problem. You added some more substance to my post anyway.
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Old 29th September 2011, 18:45   #452
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Default Re: Inverter capacity?

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I'm shopping for a true sine-wave inverter for my house. Our house is old and does not have any special provision/wiring for an inverter. (Of course the house is new enough that we have a separate wiring for heating and lighting.) I contacted a few dealers today. Some of them visited my house and left me totally confused. Here is my dilemma:

A. Let's say I have 8 lights, 3 fans, a CRT TV and a computer being used simultaneously with raw power supply.

B. Let's say I want to use only 5 lights, 2 fans and a TV when there is a power cut for about 2 hours.

So far I believed I had to plan only for B and that A didn't really matter because I could choose to switch off stuff and reset the UPS in case of a power cut. However one gentlemen who visited says that A is equally important because even when the power supply is available, the load is actually being connected to the inverter and therefore I need to plan with A in mind or else the inverter fuse will blow off frequently.

Is this how it actually works? As per his calculation I might actually require a 2kVA inverter which will be a mighty expensive affair.
If you do not have a provision for an inverter, you can get additional wiring for the lights and fans and have skirting boards to conceal the wiring. If you don't mind the sight of the wires, you can just get U-shaped plastic bits with nail to hold up the wiring. You can get two separate inverters if you have a duplex - one for upstairs and one for downstairs.

For a really really cheap sasta-tikaav solution, get one of the computer UPSes (they're 600VA to 800VA) for Rs.1.2K to 1.8K. The cheapest of the lot (1.2K) can power a table fan (or one with a long neck that stands on the floor) for 45 min. and a slightly more expensive model (1.8K) can get you a few lights for the same duration or instead you can get an emergency lantern. If you connect a computer, the power draw is higher and these UPSes will get you just 10-15 mins for the computer alone.
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Old 30th September 2011, 10:01   #453
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Default Re: Inverter or generator?

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For a really really cheap sasta-tikaav solution, get one of the computer UPSes (they're 600VA to 800VA) for Rs.1.2K to 1.8K. The cheapest of the lot (1.2K) can power a table fan (or one with a long neck that stands on the floor) for 45 min. and a slightly more expensive model (1.8K) can get you a few lights for the same duration ...
The cheap computer kind of UPS won't give you sine wave. It will give you only a square wave ( computers won't object as they use SMPS) and your table fan/pedestal fans will strongly object. They will get burnt out in some cases.

One of my employees hooked a USHA vertical fan to such a UPS and it failed within a hour.

But you can hook up lights. Choke based tubelights are problematic too. Electronic chokes are ok with square waves. Incandescent bulbs will work ok with any wave form. But you shouldn't be using them in the first place.
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Old 1st October 2011, 02:07   #454
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Default Re: Inverter or generator?

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The cheap computer kind of UPS won't give you sine wave. It will give you only a square wave ( computers won't object as they use SMPS) and your table fan/pedestal fans will strongly object. They will get burnt out in some cases.

One of my employees hooked a USHA vertical fan to such a UPS and it failed within a hour.

But you can hook up lights. Choke based tubelights are problematic too. Electronic chokes are ok with square waves. Incandescent bulbs will work ok with any wave form. But you shouldn't be using them in the first place.

almost all of the old inverter designs (a decade ago) were square wave. Even the "sine wave" designs of today have a substantially squarish wave.

No major harm can come to fans or tube lights due to this (except they make a little noise and heat up slightly) unless they were faulty in the first place. My family and neighbours used old inverter systems (we shifted to sine wave years before others did) for a long time - no problems.




BTW I'm surprised that a UPS of the same rating as an inverter is available cheaper - does this include battery prices?
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Old 1st October 2011, 10:23   #455
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Default Re: Inverter or generator?

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No major harm can come to fans or tube lights due to this (except they make a little noise and heat up slightly) unless they were faulty in the first place. ..

BTW I'm surprised that a UPS of the same rating as an inverter is available cheaper - does this include battery prices?
I beg to differ. The 'cheap' computer kind of UPS gives squarewave output with harmonics extending upto several kHz. Your fans and tubelight chokes are designed to work with sinewave of 50 Hz. Any other wave form will skew their impedance. Bottomline is they eventually fail.

The computer type inverter comes with sealed lead acid battery of about 7 Ah. A normal house general purpose inverter will use a heavy battery rated at 80 Ah or more.

A computer inverter is not designed for continuous duty whereas the household inverter is designed specifically to run longer hours. That is why computer kind of UPS costs a lot lesser.

Last edited by Prowler : 1st October 2011 at 10:25. Reason: Added more information
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Old 1st October 2011, 13:56   #456
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Default Re: Inverter or generator?

The simplest Inverter is a square wave one as that requires the active element to just switch the DC on and off. The harmonics can be filtered out, but require added component. As computers rarely use raw AC, and route all power requirements through the SMPS, square wave output of the UPS does not matter, but in home appliances which use the sine wave directly, square wave can create problems. The high end Sine Wave Inverters use systems akin to Class D amplifiers as well as filters to provide pure sine wave.

The older fan designs are certainly square wave unfriendly. I remember buying an Usha Fan fifteen years ago, and the sales man asked me not to use an electronic regulator as the fan was not designed to take the chopped sine wave output by the regulator. I did not believe him, but one day of using the regulator convinced me. In contrast the Compton fan was designed to take non-sine wave input and works flawlessly.

The hum you hear whether due to UPS or regulator is due to the coils resonating to the harmonics present in the input, which is easily rectified by proper design.
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Old 1st October 2011, 17:20   #457
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Default Re: Inverter or generator?

Using controllers designed to dim lights causes a lot of trouble with fans
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A computer inverter is not designed for continuous duty whereas the household inverter is designed specifically to run longer hours. That is why computer kind of UPS costs a lot lesser.
I would have thought the opposite, at least leaving aside the cheapest end of the UPS market. A computer UPS may be running for many (if not 24) hours a day. It may be trimming over-voltage or boosting low voltage regularly. In the current "electrical climate" here (and it looks bleak for TN at the moment) my UPS is likely to be giving two hours powering my PC (after that, I save the remaining capacity for the 5w desk lamp as emergency light) every day.

If it gets so bad that there is not time for the UPS to return to 100% charge after that, then a generator is going to be back on the menu :(
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Old 1st October 2011, 18:13   #458
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Default Re: Inverter or generator?

More than 80% of household have inverters that give square wave or quasi sine wave output. So what is all this fuss about using small inbuilt ups as a backup. It can be used, but it has some limitations.

It is only advisable to use max 100 w in its output in total.

Inbuild ups have stabilizer, so this will lead to a little more increased current bill.

Very less backup.

So people who can live with this can surely go for inbuilt ups. I mean connecting just one fan or tubelight etc. Lots of shops are using inbuilt ups for their small needs.

When you buy a sinewave inverter, do you think you are getting pure sinewave just like the electricity board. There are lots of high frequency ripples and wave distortions. It is easy to get sine wave when no load is connected, but as soon as you switch on a fan or other capacitive or inductive load the wave goes haywire. This I am saying after watching output of various inverters and online ups in a CRO. You can google "sine wave inverter cro output" in images and see.

It all depends on ones budget. People use inbuild ups to higher kva online ups in their houses. It is just a matter of how much you can afford.
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Old 1st October 2011, 20:30   #459
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Default Re: Inverter or generator?

Here, I don't think that "pure" and "Electricity Board" belong in the same sentence!
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Old 1st October 2011, 23:33   #460
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Default Re: Inverter or generator?

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Originally Posted by Prowler View Post
I beg to differ. The 'cheap' computer kind of UPS gives squarewave output with harmonics extending upto several kHz. Your fans and tubelight chokes are designed to work with sinewave of 50 Hz. Any other wave form will skew their impedance. Bottomline is they eventually fail.

The computer type inverter comes with sealed lead acid battery of about 7 Ah. A normal house general purpose inverter will use a heavy battery rated at 80 Ah or more.

A computer inverter is not designed for continuous duty whereas the household inverter is designed specifically to run longer hours. That is why computer kind of UPS costs a lot lesser.
several kHz in harmonics ??? 1kHz is 20th harmonic of the 50Hz. You can't possibly get it unless the guy designing the UPS/inverter messed up royally - and I mean royally - he would have bought more expensive components than he needed to to get the switching speeds needed for this.

Keep in mind that harmonic in voltage is not the same as harmonic in current if you are talking about magnetic systems - as you are once you exclude household electronic equipment and pure resistive (lamps)


Also changing of impedance doesn't mean equipment will fail - high impedance for inductive components is almost a given, and that is also desirable (that's what is filtering) while lower impedance of capacitors will cause the driver (UPS or inverter) to get current-saturated, increase the rise/fall times and reduce the amplitude of the fast harmonics in voltage.


Heating will not result from the reactive impedance - it will require resistive impedance.


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Originally Posted by Aroy View Post
...
The older fan designs are certainly square wave unfriendly. I remember buying an Usha Fan fifteen years ago, and the sales man asked me not to use an electronic regulator as the fan was not designed to take the chopped sine wave output by the regulator. I did not believe him, but one day of using the regulator convinced me. In contrast the Compton fan was designed to take non-sine wave input and works flawlessly.

The hum you hear whether due to UPS or regulator is due to the coils resonating to the harmonics present in the input, which is easily rectified by proper design.

The fan and regulator are not the same thing. Solid state regulators (as against variable resistance regulators of the old) do require smoothness of the supply voltage waveform as it usually has a thyristor and the trigger voltage of the thyristor is what is controlled.


Regarding filtering - fans etc. are essentially huge coils that provide quite a bit of filtering by themselves when you look at the current. Plus if anybody thinks harmonics are a major problem, keep in mind that ALL solid state regulators make the current/voltage waveform seen by the fan differ vastly from sines waves. In fact mains supply can have as much as 10%-20% of third harmonic present by design (transformers are operated in near-magnetic saturation to save money on core material) and given the state of our grid the harmonics are usually one the higher end.


The hum/noise can certainly be eliminated by filtering, but aside from the filtering the motor like components already have, any filtering will be prohibitively bulky or very expensive (solid state emulation of filters) - not practical for the application in question. However usually the hum is due to high order harmonics - 200Hz and above - these harmonics are easier to get rid of but better not to have them - they will not damage the coils that easily but they will overheat the capacitor choke.


As far as electronic systems go - all of them rectify the AC input first into DC, and usually the input harmonics don't matter for such systems.



UPS vs. inverter wise - if there is a power cut and you lose the tubelight for a second nobody cares. But if you lose the supply to the desktop computer for a second - that's a useless UPS. Usually the latter application require really fast reaction times (of the order of 50ms) and the cheapest way is to implement a system where the battery side is the one that always supplies power the the computer. To my knowledge most inverters are not designed that way (the method is inefficient if fast reaction time isn't required) therefor AFAIK UPS systems of similar capacity are almost always more expensive than inverters.

Last edited by vina : 1st October 2011 at 23:41.
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Old 2nd October 2011, 12:14   #461
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several kHz in harmonics ??? 1kHz is 20th harmonic of the 50Hz. You can't possibly get it unless the guy designing the UPS/inverter messed up royally - and I mean royally - he would have bought more expensive components than he needed to to get the switching speeds needed for this.
The hum/noise can certainly be eliminated by filtering, but aside from the filtering the motor like components already have, any filtering will be prohibitively bulky or very expensive (solid state emulation of filters) - not practical for the application in question. However usually the hum is due to high order harmonics - 200Hz and above - these harmonics are easier to get rid of but better not to have them - they will not damage the coils that easily but they will overheat the capacitor choke.

UPS vs. inverter wise - if there is a power cut and you lose the tubelight for a second nobody cares. But if you lose the supply to the desktop computer for a second - that's a useless UPS. Usually the latter application require really fast reaction times (of the order of 50ms) and the cheapest way is to implement a system where the battery side is the one that always supplies power the the computer. To my knowledge most inverters are not designed that way (the method is inefficient if fast reaction time isn't required) therefor AFAIK UPS systems of similar capacity are almost always more expensive than inverters.
The first point is valid. Higher order Harmonics decay pretty fast, especially in long lines of house hold wiring (quite some inductance in them), so we should be bothered about the first three or four only.

The APC UPS I have is a "Line Interactive" type, that is it switches the UPS when power goes. As it takes at least two cycles to "realise" that power is gone the desktop power supply has to sustain power for that much time. On the other hand the Inverter switching is at least 10 cycles, good enough for appliances, but doubtful in case of computers (unless the power supply has capacitors large enough to sustain the outage). An interesting case is of disk power supply of the older mainframes. They had a large capacitor banks to ensure that the heads could be parked safely in case of power outage. (Disk of 50-100MB cost at least $250K in those days and the removable packs a few tens)
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Old 3rd October 2011, 10:38   #462
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Default Re: Inverter or generator?

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Also changing of impedance doesn't mean equipment will fail - high impedance for inductive components is almost a given, and that is also desirable (that's what is filtering) while lower impedance of capacitors will cause the driver (UPS or inverter) to get current-saturated, increase the rise/fall times and reduce the amplitude of the fast harmonics in voltage.
Apparently the Usha fan's windings had developed short. It must have passed more current when fed through a UPS. As Aroy says, some Usha fans seem to show problems handling square waves.

Quote:
I would have thought the opposite, at least leaving aside the cheapest end of the UPS market. A computer UPS may be running for many (if not 24) hours a day. It may be trimming over-voltage or boosting low voltage regularly. In the current "electrical climate" here (and it looks bleak for TN at the moment) my UPS is likely to be giving two hours powering my PC (after that, I save the remaining capacity for the 5w desk lamp as emergency light) every day.
True Thad. But the UPS is not supplying power to the computer all the time when there is mains supply. The line interactive UPS supplies power only when the mains supply fails. They deliberately use a smaller capacity battery so that the inverter is not forced to work longer hours. They skimp on larger heatsinks and forced air cooling.
As you are not so kindly disposed to fan noises, the simple UPS doesn't have one built in.
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Old 4th October 2011, 03:46   #463
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Default Re: Inverter or generator?

Mine does have a fan, which comes on when the battery cuts in. Yes, it is noisy!
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Old 19th January 2012, 07:45   #464
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I thought of getting inverter for my home. I have few queries which experts could answer.
I just read about inverters coming in single and three phase designs.
My home has 3 phase supply - where the entire power outlets of my home is divided into three groups each group getting power from each phase provided by EB.
Now, is there a difference in getting single / three phase inverter?

My logical thinking is: If I get single phase inverter, it would cater to only one particular phase. Only those electrical items that are connected to that phase alone gets served by the inverter. Is my thinking correct?

On the other hand, if I get 3 phase inverter, and if power supply is not available in only one phase, will the inverter cater to only that phase alone from battery and other two phases directly from EB? or all three phases are supplied with power from inverter batteries?

Last edited by iamswift : 19th January 2012 at 07:48.
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Old 19th January 2012, 09:55   #465
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My logical thinking is: If I get single phase inverter, it would cater to only one particular phase. Only those electrical items that are connected to that phase alone gets served by the inverter. Is my thinking correct?

On the other hand, if I get 3 phase inverter, and if power supply is not available in only one phase, will the inverter cater to only that phase alone from battery and other two phases directly from EB? or all three phases are supplied with power from inverter batteries?
Inverter have two parts
. Charging circuit
. Inverter circuit

Normally there are two types of 3-phase inverters.
. Those that use 3 phases for charging, but have a single DC output
. Those that use 3 phases for charging and 3 separate DC outputs

The difference between the second one and 3 single phase inverters is that the 3 phase inverter has a common battery bank, while the later has 3 separate battery banks.

The best option is to get 3 single phase inverters, one for each phase,, even though you may have to spend more on batteries.

Before you install an inverter, you have to make sure that "Power" devices (refrigerator, AC, heaters, microwave etc) are on a separate circuit, else your inverter will be overloaded.
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