Due to MOT transformer unloaded saturation significant current is wasted as heat if using the MOT to make a power supply.
My Premise is: If I place a full wave bridge rectifier before the Primary the 120Hz pulsed DC should limit the magnetic saturation. This should then reduce power lost to heat. Power lost to eddy currents is less of a factor.
Sounds good?
Hi there,
That's an interesting idea. To place a full wave rectifier in front of the transformer so it gets driven by some level of 2nd harmonic which would be twice the frequency which would reduce the required number of turns for a given voltage.
There's a problem with that however, and it is a big problem. The problem is that the output of the rectifier has a large DC component as well as the desired 2nd harmonic. That's definitely a no go. An air gap is sometimes introduced to stretch the BH curve and thus make it less susceptible to saturation due to
some DC current, but in this case the DC current would be so high it would not be effective enough. The only way around it then would be to use an AC rated capacitor on the primary. The problem then however is just the opposite: the cap would charge up to the DC peak level and then pass very little current. So for that to work there would have to be significant resistive load on the rectifier, which would kill efficiency.
For low level signals this technique actually works, but for a power supply unless it is very low power it's not effective.
For power applications you'd have to increase the number of primary turns or else reduce the primary voltage. The formula is:
Bmax=E*1e8/(4.44*F*A*N)
where
E is the rms voltage,
F is the frequency,
A is the core cross sectional area in square centimeters,
N is the number of turns.
From that you can see that to reduce Bmax you can either:
1. Reduce E
2. Increase N
3. Increase A
4. Increase F
Those are your choices.
Perhaps you can specify what exactly you are trying to do here. It sounds like you want to use the transformer for some regular power supply yet reduce the heating of the core. Reducing E a small amount can be done by using some series resistance, although the efficiency goes down of course.