SPWM Output filter design & toroid material help needed

Hello to all.

I have built a pure sine wave inverter from 12v to 230v AC at aproximately 500W.

The DC/DC converter is the usual forward converter with sg3525 and ETD39.

Now my actual problem is the LC filter at the output.

The output is 50HZ sinewave.
The SPWM is 24.3KHZ.

The H bridge driver is the EG8010 + ir2110 board found on ebay with the name EGS002.
The output is a beautiful sine wave, the problem i have is in selecting the core for the output.

I have tried using the toroid core from atx power supply filter, but even with no load the core gets hot.

I do not know, should i use ferrite core at the output or iron powder core?

The chinese people recommend 3.2mh choke and 2.2uf/400v at the output.

I have build a coil on a CM270060 core. It has almost 3mh.

Now I have a beautiful sine output and the core doesn't get warm. I have tested the inverter with 1x21w light bulb, 2x21w light bulb and 2x21w lightbulb and laptop.

The maximum output power I tested was 90w. In this time the rectifier diodes at the output of the DC/DC convertor got extremely warm.
The diodes I use ar by500-800 (800v reverse voltage, 5A, and 200ns).

Why are the diodes overheating with .3A drawn from them?

So I loked at the scope and found that in the primary on the chopper when the fets turn on the tension on the core get way more the 12volts.

So I think that I have some sort of spikes on the primary that generate a lot more then the 400v on the secondary side and that might be why the diodes overheat?

In a cheap 1000W Chinese inverter (a 500w halogen lamp is the max he can power actually) the rectifier diodes are her600( 400v, 5A and 50ns) and they don't get that hot, the inverter doesn't have any heatsink for the diodes.

Does anyone know what is the problem for witch the diodes overheat?