Based on our new-age technology, is it possbile to build up tis kind of convertor? What aspect should i focus on? thx for ur recommendation...

If a transformer can step up the ac voltage from 12v to 110v, does it mean tat it also can be stepped up to 240v by using the same transformer?

 

Of coarse. But what sort of power output (watts) are we talking.
Using 5 Volts with high wattage would be impractical (VERY lossy and high cost, High current devices required).
Thats why most high power inverters are often 24/36/48 volt designs and not 12 volt.

 

It's possible to make an inverter. http://www.mdsbattery.co.uk/shop/productprofile.asp?ProductGroupID=574

Here's an article on how to do 12vdc to 120vac and gives tips on making one do 12vdc to 240vac
http://www.technology.niagarac.on.ca/people/mcsele/i2k.htm

 

OK, you've edited from 5 volts to 12 volts.....
Now don't I look stupid....
Thats OK, yep...12DC to 240AC inverter is easy enough but there are lots of ready made solutions out there that might be an easier and cheaper approach.
What you might want to decide is Power rating (continuous and Surge) Sinewave or Modified sinewave (practically a squarewave).
A 12 volt AC to 110 volt AC transformer will have a turns ratio of 1:9.2 and will output a voltage 9.2 times it's input.
A 12 volt DC to 110 VAC inverter will have internal circuitry and a transformer optimised for both these values (transformer turns ratio, and feedback voltage monitor to regulate the output voltage).

Local stores here are selling 12 volt to 230volt (our local voltage) 300 watt inverters for around $60 NZ (probably about $35 - $40 US)

 

I've changed from 5v to 12v due to its high losses tat might b occured during the conversion. 5v input become impractical and unstable if the output power rating is high.

Is it any latest experiment result shows tat how long actually can a 12VDC supports if the output connect to a device which is 240VAC, 50W, and 50Hz.
If we change the input become rechargeable car battery 12v dc, then how long is the battery lifetime?

Anyway, thx for Gadget & mrmeval Ur supports will oways b in my mind

 

Most inverters are around 85 to 90 % efficient, so if your supplying 50 watts from a low to medium powered inverter, then you are probably drawing around 60 watts (5Amps) from your battery. Use that along with the Amp hour rating of your battery to work out an approx lifetime.