Calculating Air Gap of feritte cores

[BADFLOPPY]

Hi,
I found various Gaps filled with small chip or Insulators between two ferrittee pieces removing which the performance reduces. For example, in mosquito Trap (A Batminton racket type with three net with supply of 2.5KV, while I check spark in HV winding, just opened and rewind with proper insulation, I just peel off the small plastic piece and after fixing, found the frequency reduces and comes in audible range. As it is a self resonating Transformer (Heartley Osc.) surely the inductance increases.
I have observed this in several other devices too. Now my question, I am going to make an SMPS of 500VA to supply 75A at least at 5 volt for chemical synthesis. Now what air gap I should have to maintain, or how I can calculate? Using E50 or E65 cores, or if the had to go higher size as the freq reduces.

Moreover, if we put air gap or simply gap, then the magnitizing power required would be higher and the power loss may be higher?

Thanks in advance.

 

[rajudp]

for 500VA you better go for full bridge , there is no need of gap, you can make the pwm with sg3525 and IR2110 as mosfet/Igbt Driver

 

[karesz]

Hi,
The air gaps are used to adjust a tolerated Al value of your core, that has otherwise lot of scattering...
Typically you can order the most cores airgap less too_ so your Al is nice higher, but the tolerances toooo.
If you need some calculated/tolerated inductance: for me you must have air gap in the cores.
K.

 

[rajudp]

yes air gap is needed for fly back, but it is not a good idea to make a smps with output about 500VA in fly back