Previous in Forum: DC motor tripping on Over & under excitation simultaneously Next in Forum: home inverter
Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30

# minimum input to an inverter

06/13/2009 5:34 AM

Hi, I am stuck while conducting an experiment, can anyone tell me what must be the input given to an 600VA inverter to obtain rated output of 220V, if i'm not using a battery to operate the inverter or UPS. In other words, i want to run inverter or UPS without battery insted i will connect battery terminals to a DC supply using somehow method. It uses 12v, 7.2amph battery. . . . .what must be the value of current along with 12v D.C. supply to get a rated 220v output. NOTE-- i'll not be using any battery but a 12volt dc supply. Is there any effect of current on the o/p frequency. help me!

Interested in this topic? By joining CR4 you can "subscribe" to

Guru

Join Date: Oct 2007
Location: Sour Lake, TX 30°08'59.68"N 94°19'42.81"W
Posts: 671
#1

### Re: minimum input to an inverter

06/13/2009 11:05 AM

Your 600VA inverter will require some 56 amp from a 12 V power supply - as an average. My guess is that your 12 V dc power supply has to be able to provide that kind of current with the overcurrent protection set somewhere higher that 60 amp. I bet that a large battery would be more economical than such power supply.

__________________
Bridge rule #1: Nobody is as good as he thinks about himself nor as dumb, as his partner thinks...
Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30
#2

### Re: minimum input to an inverter

06/13/2009 11:17 AM

THANX INDEL, well we are using some conventional energy resources so thats why we have kept battery aside, one thing you can help me out with is that can i convert 3 ampere to 30 ampere usuable current values using darlington amplifier or any other method you suggest or IS IT NOT POSSIBLE

2
Guru

Join Date: Oct 2007
Location: Sour Lake, TX 30°08'59.68"N 94°19'42.81"W
Posts: 671
#3

### Re: minimum input to an inverter

06/13/2009 11:48 AM

Well, you are not very familiar with electricity, so I could say a simply NO to end the discussion.

But you have to understand why, so I try to explain in a few words:

Your requirement at the place where the battery should be is some 670W. That is obtained from multiplying the voltage of the battery (12 V) and the current from the battery (about 56 amp). I understand that you have a electricity source (and I assume that are some photovoltaic cells) that provides you with 24, 36 or whatever voltage but only 3 amp of current. That's it, your source can provide only 3 amp. To get more current (you wanted 30 amp), you need to put in parallel 10 such devices that yield 3 amp each. Of coarse some precautions have to be taken. You asked if using Darlington configuration can get 30 amp. You need the source that can provide 30 amp, the Darlington can only make it variable from 30 amp to lower value.

With a switching power supply if you consider the efficiency, the output power would be input power (600 VA) multiplied with efficiency (90% or 0.9). Let's say that we have the right switching power supply, and your photovoltaic panels give you 120 V with a 3 amp maximum. That would be 360 W. Still not enough to get a 12 V with 56 amp what you need for the inverter. And we come to the old saying that what it's all about is power and money...

__________________
Bridge rule #1: Nobody is as good as he thinks about himself nor as dumb, as his partner thinks...
Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30
#4

### Re: minimum input to an inverter

06/13/2009 1:24 PM

Well hw cn u say i dont know about electricity ? i agree may be i don't know as much as you bt as a student of electronics i can guess you haven't performed any such experiment yourself. . . . .any ways thanks INDEL . . . . . and yup money is honey :-)

Guru

Join Date: May 2007
Location: Harlow England
Posts: 16498
#5

### Re: minimum input to an inverter

06/13/2009 3:45 PM

Indel has kindly taken the time and trouble to write a very lucid explanation....
The fact that you needed the explanation proves his assertion that you don't know much about electricity.

It can be dangerous to think you understand more than you actually do.
Del

__________________
health warning: These posts may contain traces of nut.
Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30
#7

### Re: minimum input to an inverter

06/13/2009 4:03 PM

the guest post is by me. . . .i 4gt to re-login. :)

Score 2 for Off Topic
Active Contributor

Join Date: Jun 2009
Location: Atlanta
Posts: 15
#14

### Re: minimum input to an inverter

06/15/2009 8:17 PM
• I can see I'm in the right place to get some good answers to some doozie questions!
• Thanks guys
__________________
Everthing changes or becomes extict
Off Topic (Score 5)
Guru

Join Date: Feb 2008
Posts: 1357
#12

### Re: minimum input to an inverter

06/14/2009 8:42 AM

That is true in linear mode but not in switching mode.

You can increase the current at the output IF you have a higher input voltage. In this case, you need at least 30VDC at 30A to produce the 56A DC at 12V. Using a step-down switcher configuration, you will get the equivalent of a high frequency step-down transformer. All you need is a power transistor and heatsink, an inductor and a control circuit.

This is not a simple circuit and you will needs some expert's help if you go ahead with it. Find a local engineer with power electronics knowhow.

If your source is already AC, simply use a step-down transformer + rectifier.

__________________
Experienced is earned, common sense is taught, both are rare essentials of life.
Anonymous Poster
#6

### Re: minimum input to an inverter

06/13/2009 3:57 PM

THANX GURU for proving that i don't know much, if i have known that much i mÃ¬ght have solved my problem myself rather than asking on the forum. I DON'T HAVE KINDA RESOURCES TO PERFORM EVERY EXPERIMENT SO IF YOU CAN HELP ME PLEASE PROCEED.

Guru

Join Date: May 2007
Location: Harlow England
Posts: 16498
#8

### Re: minimum input to an inverter

06/13/2009 4:19 PM

I think we have a language/communication problem.
So forgive me if I state something which you may already know.

If your power souce can only supply say 3 amps...
(E.G you connect a current meter from the + to the - terminal and it reads 3 amps)
There is no way you can increase this current, it's as simple as that.
You could add more power souces in parallell so two power sources give 6 amps, three give 9 etc.
As an example, a PP3 battery when new will give say 9volts off load and a short circuit current of say 1amp (I'm guessing here) limited by it's internal resistance... You can do nothing to increase the 1 amp figure, although I s'pose you could place it in liquid Nitrogen, that might help a little.
But no ammount of circuitry or experimentation will increase the current capability.
And yes we have all tried it, I'm sure we've had situations where the ultimate limiting factor of our circuit was the power supply.
You are quite right to experiment yourself and discover these things...but once you have discovered them, then accept them and start learning more...don't waste your efforts trying to change the fundamentals laws, they are fixed.
Del

__________________
health warning: These posts may contain traces of nut.
Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30
#9

### Re: minimum input to an inverter

06/13/2009 4:30 PM

thanks guru. . . . .

Power-User

Join Date: Jan 2007
Location: Berlin (Germany)
Posts: 333
#10

### Re: minimum input to an inverter

06/14/2009 4:59 AM

The only way to make 30A DC at Uout out of 3 A DC at Uin is to take a DCDC-Converter. But, assumed your converter has an efficiency of about 90%, the output voltage Uout will be only somewhat like 1/11 Uin.

__________________
The sum of intelligence on earth is a constant. And the population grows and grows and .....
Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30
#11

### Re: minimum input to an inverter

06/14/2009 5:12 AM

UWEKA thanks . . . . i havn't given a second thought to converters rather i was stuck to amplifiers. . . . but due to so much confusion now i have to perform expt. myself. . . .

Anonymous Poster
#13

### Re: minimum input to an inverter

06/15/2009 11:08 AM

shocked at the ignorance level. fundamental laws have been forgotten and also forgetting to show courtesy of being in communication with experts.

Associate

Join Date: Jul 2008
Location: New Delhi,India
Posts: 30
#15

### Re: minimum input to an inverter

06/16/2009 3:44 AM

this guest getting crazy . . . . lol :-) . . .well no 1 is expert may be one knows more than other. . . .

Interested in this topic? By joining CR4 you can "subscribe" to