Homemade Inverter and Battery Charger (chopper based)

ASSALAMUALIKUM to all WP members . This is my first post on WP . I design and build final year projects for university mainly quadcopters (rcpak member kkashif2009) . I wanted to share some pictures of my ups project , which i have been working on almost an year .

The purpose of this project is to design a ups which is lowcost and reliable , and also easy to repair . All the components used in this project are easily available and are of through hole type ( no smd parts ) . The reason for posting here is that i want your feedback that what features home user wants in ups . I will try to implement these features , if possible . It is microcontroller based ( atmege8) .

Currently images shown are of 200 watts inverter and 14.5 volt 10a charger . Charger is cc/cv type (constant current/constant voltage) . I am working on new pcb which will able to handle 600 watts .

Thankyou for reading my post and your feedback will be greatly appreciated .

Regard Kashif khan .



Welcome to the forum.

If you look at the various threads in this Board, you will find a lot about batteries and the associated failures/short lifetimes. This is essentially because of use of car batteries for UPS service in Pakistan - something for which the automotive battery is not designed.

So my recommendation would be to build a very robust battery management system into your design. A simple cc/cv charging may not be enough. In my opinion you must spend more time and effort in having a sophisticated battery management system in your design. I was working on one as you can see in the following thread.

I have finalized part of the design, for measuring current, but unfortunately due to paucity of time I am not able to move forward. I can share my work with you, particularly the ISIS files which should help save your time. As such your project offers a good opportunity to collaborate and take this forward.

Having a u-controller would certainly help in achieving the project goals. Someone should be able to help write firmware so that we can take the project forward rapidly.



ASSALAMUALIKUM to all WP members . Thank you for your reply Aurangzeb . Charger is currently in prototype stage , the purpose of it was to check what winding ratio should be used and what type of results can be achieved . I have some ideas in my mind about charging system like three stage charger design and also measurement of ambient temperature to adjust the top off charge accordingly .

For 24 volts system i am thinking of charger which will have a separate connection for the center tap of the battery to monitor the voltage , which will charge both batteries in balance with each other . This type of charger is used in Radio control model aircraft lipo batteries and give it excellent results .

Can anybody shed some light on how chinese chopper based ups handle short circuit ? I mean does these ups really have short circuit protection as advertised . I dont have any other ups except my own designed one but i am still working on short circuit protection .

Thank you and Regards .

Kashif khan

Do you have oscilloscope plots of the output waveform? What protections does this circuit afford on the input and output?


How will you measure current?


ASSALAMUALIKUM to all WP members . @Asad, I will try to upload the ups output waveform soon . As for the protection used ,it is all standard stuff used by Chinese brands like short circuit and overload . Also will use over temperature shutdown .What you guys suggest ,should I use frequency monitoring or not ?@ Aurangzeb I am using CT ( current transformer ) to measure the output current of ups . CT is used in charger also ,on chopper primary side to regulate the DC current .


Kashif khan

Frequency monitoring is a good idea!

ASSALAMUALIKUM to all WP members .

Here are the few scope images of ups waveform .

Two of the images are 2ms and 5ms waveforms . Last one is 2ms per division with pedestal fan load .