I have 12VDC 7Ah Battery
I want a 220AC inverter which can run my laptop and other low powered devices....my laptop charger is of 65watts 13.6VDC needs input of 220ac.

 

Is this an assignment?

 

If you don't need much power (<500W), you can try this circuit:

http://www.aaroncake.net/circuits/inverter.asp

The capacitor selection is vital - you will probably have to go through several sets before you find the right one.

For 230Vac, just change the transformer.

If you are only powering a laptop charger you can get away with using 115Vac most of the time because most laptop chargers are universal models, they will work on a wide range of voltages.

Beware that my laptop charger is a Dell charger and it never worked off a modified square wave inverter, so I find it unlikely that a purely square wave inverter would work better. It *could* have been overloading the inverter, it was a 150W inverter and I had a 95W charger. I find it unusual why it didn't work, but it could have just been that the charger wasn't that efficient, and was consuming more than 150 watts.

You will want a battery monitor circuit or you could discharge your battery too much which can damage it. I also suggest putting a large value high ripple current capacitor across the battery terminals to improve the output.

 

yea i also have a dell laptop..65w dell charger..

 

I reckon you should buy a cheap 150W inverter and see if that works. If it doesn't you don't have much chance.

If you're only wanting to charge a Dell laptop (and run nothing else) consider a DC-DC converter to step the 12 volts to the 13.6 volts the laptop requires.

 

A commercial unit is much cheaper in the long run. I see where you got that design for the other thread now. I remember seeing something very similar over 20 years ago. Nowdays we can do a lot better.