12V 600VA inverter project using a transformer salvaged from UPS

In this inverter I have opted to use a SG 3525 as the main oscillator. This IC is specially made for use with pulse width power supplies. R5, Preset P2 and C1 set the oscillator output frequency. By adjusting Preset P2 you will be able to vary the output frequency of the inverter. This IC also contains complementary driver transistors internally and therefore the output MOSFETs can be driven directly from it s outputs. Preset P1 adjusts the pulse width of the digital wave. This way you will be able to adjust the output voltage of the inverter. You can also convert this inverter to supply a constant voltage even when loaded simply by applying a small voltage feedback from the output of the inverter to pin1 of SG3525.

Diodes D1 and D2 protect the main oscillator from damage in case the MOSFETs blow. Feel free to use output MOSFETs of your choice as long as their rating is not less than 50 amps.

UPS transformers often give an ac output of about 7.5 volts across the center tap terminal and the outers. With this circuit you will be able to make use of Transformers salvaged from UPSs as they are without any need for modifications.

10uf / 25V

Construction Tips

Secure a nice housing for your project or you could even use the UPS housing as it is. Having done that you can now proceed to mount your transformer in place.

Next get 2 L shaped aluminum sheets of at least 6cm by 4 cm and mount them on a wooden block. The aim of the wooden block is to insulate the heat sinks from one another and also from the housing.

L shaped Aluminum

Mounting screw

Wooden block

Now mount three MOSFETs on each of the aluminum sheets after which Mount your heat sink assembly into the housing. Connect the two outer windings of the UPS transformer to each of the L shaped aluminum sheets. Use cable clamps if possible.

For initial testing remember to use an adjustable power supply.

Good luck!!!

Pictures from this project

Oscillator circuit (using SG3525)

Everything after initial setup

Inset is the circuit at work (loading 100W Philips bulb)

Design by Wafula Emmanuel