This is for a single-phase motor(fan).
I have been thinking about voltage doubler directly at the mains but I don't know math good enough to be able to actually calculate the current that such a circuit could be made to supply, but from what I have read the current are very low.
I don't consider isolation to be a criteria since the original circuit isn't isolated, but still I wouldn't mind winding a SMPS transformer and I must say that I got very intrigued by the smijesh linked to an article about, the
LT3751.
It appears to be very suitable, except for one thing which might be a problem of sorts.
This fan isn't used all day, it gets turned on in intervals determined by temperature and other factors so it spends much of a day off, I'm not sure but when reading about AC-DC converters and in regards to efficiency it is clear that converters generally have lower efficiency the lower the current you draw from the output... Now I can't recall what I thought might be a problem but it had to do with the fact that the circuit will often be in a state with no output load at all.
I have made a circuit layout of a high-voltage H-bridge and I will begin by simply rectifying the output from an isolation transformer that converts 230Vrms into 250Vrms, and see what kind of amplitude that will allow me to create. Then I can asses how high of an output in DC voltage I actually need.
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I have decided that I will make it an priority to actually calculate what a mains voltage doubler would be capable of in terms of delivering output current, I know that the equations for the energy stored in a capacitor or coil are really simple equations but I have some problems with how it fits together and what different equations actually imply apart from the numbers actually calculated(I can get numbers and I know they represent for example a value in Henry's that a coil need to be but I can't see deeper into the equation to understand more than the amount of the output value) but this is not the place to go through this but I will for sure need to open a thread about this when I have made the most I can my self.
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In any case, the LT3751 might be called as a "High Voltage Capacitor Charger Controller with Regulation", the regulation it refers to is that the IC can function as an ordinary voltage regulator and there are configurations supplied in the datasheet for using it as a offline high-voltage input, high-voltage output flyback converter which I will look into more also.
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The fact that the LT3751 is a capacitor charger seams suitable since that is an application which is only intermittently operating, or it can be.