It seems to be the snubber network doesn't suppress the ringing as I intended. Am I right? I took a shot from mosfet's drain

 

22Ω is a bit high. A good first choice is the same value as the load, about 1Ω.
The drain waveform should be a squarewave, amplitude 24V, if the transformer is correct.

 

22Ω is a bit high. A good first choice is the same value as the load, about 1Ω.
The drain waveform should be a squarewave, amplitude 24V, if the transformer is correct.

Didn't change much.

 

1) You should check the ESR factor of this cap. Thermal flux in Watts is i^2*ESR.
2) You should parallel it with few 0.1 mkF fast caps to avoid the rapid pulses overstressing it by the di/dt

 

With no load on the output, how much current is the circuit taking?

 

With no load on the output, how much current is the circuit taking?

It doesn't take much. Around 0.1~ 0.2 A.

 

1) You should check the ESR factor of this cap. Thermal flux in Watts is i^2*ESR.
2) You should parallel it with few 0.1 mkF fast caps to avoid the rapid pulses overstressing it by the di/dt

Can I also add a choke to avoid back emf to battery?

 

I don’t think it will help. The battery will get rid of the back emf!
the problem is elsewhere. Is the off-load transformer waveform clean?

 

You had the wrong capacitor but that capacitor is gone now. I hope you have an idea of the ripple current so you can select a good replacement.

 

I have applied a snubber network across the mosfets according the steps in the link down below. It reduced the ringing a lot but the amplitude of the peaks still remain the same. Have any idea how to reduce the amplitude as well?

https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/05/05/calculate-an-r-c-snubber-in-seven-steps

 

I have applied a snubber network across the mosfets according the steps in the link down below. It reduced the ringing a lot but the amplitude of the peaks still remain the same. Have any idea how to reduce the amplitude as well?

https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/05/05/calculate-an-r-c-snubber-in-seven-steps

overvoltages are due to a parasitic inductance in the transformer, so it is normal to have these spikes however you must not add more with the layout

to cope you need to oversize the mosfet voltage VDss, (for 24V input a 80V mosfets should be ok)
you can increase the gate resistances but you will have more losses (heat)

using a snuber through the primary mosfets is difficult because the current is high,

the solution is perhaps to put it @ the second.