gotoluc

the ferrite core works on the principles as per faraday laws
v = N d B/dt
means voltage is directly proportional to rate of change of flux 42 KHz means in other words/ mechanical analogy
a generator working on 2520000 RPM

now in this case the benefit is you need less number of turns , higher current, less spikes low value of capacitor to provide dc conversion notch filing gaps of wave form. The ferrite core can lose its value of B very quickly or its BH curve is very steep and vertical. so you cannot get the fly wheel effect
for example mechanical analogy
if you use a 250 gram wheel on a motor top you will get low momentum but if you use 2 kg wheel you will get high momentum and that will store more kinetic energy then light weight one.
some times it is desired to use light weight wheel and some times it is required to use heavy weight wheel it depends on requirement.

now 99% percent books will say that the CRGO( cold roll grain oriented ) core is not siutable for high frequency such as 20KHz they are siutable for 50 hz to 100 hz or some times 400HZ thats all

here this is misunderstanding and this is the biggest advantage when they refer 50 to 400 hZ means core cannot return to neutral position faster then this frequency so any attempt to get it back or reversing the polarity faster then the prescribed values will heat the core and do nothing but loses.

Now understand what we are doing we switch the magnetic field in one direction and then with in mill seconds turn it off, the flux retains there the output will get the same effect but you have turned off your supply now before the core starts going back you pushed it again so you are getting the fly wheel effect but the out put is same and with each and every switching you will get BEMF going into battery again.

in ferrite core you do switch the frequency in reverse direction every time or if you have single direction switching you tend to reverse the magnetic flux to min during off period so you didn't get any advantage.
SMPS were designed to reduce the size of supply and they are complex circuits and serving there purpose very well otherwise you can imagine a computer power supply can be bigger then the computer itself. due to high current requirement.

the above technique will increase the time of your inverter twice and very use full for solar panel or windmills.
if you need one unit i can send you the normal weight of a UPS for a 1000VA is 12KG.

the technique of BEMF collection involve smart switching and turns off the main supply during BEMF collection.

i was continuously switching t on and off there was not at all any effect on the speed with or without load  there is a key in my setup i have shield the south pole in north pole and even you move the disc by hand they keep on moving like a flywheel and produce output till it stops and never exerted any braking force  i am posting the pictures it might help you.