Frequency effect in the operation of a MOT.
Posted: Fri Oct 12, 2018 10:51 am
Hi:
I recently became the happy owner of an old MOT. I have been perusing the FAQs and found this post (viewtopic.php?f=29&t=4843) where it is stated that fusor demo operation is normally located in the 3-10 kV range. Considering that the output of such a transformer is around 2,2kV with plenty of current (0,5 amps, according to the Internet), it seemed like the construction of a power supply consisting of the MOT and a Cockroft multiplier is a viable option.
However, I pretend to control the voltage being supplied to the chamber, which is difficult taking into account that I have no Variac, and buying one is completely out of question (money problems). I started thinking about different options of electronic control, but then I decided to search for "Microwave Oven Transformers" in this forums and found several interesting threats, such as this ones:
viewtopic.php?t=4422
viewtopic.php?f=11&t=4566
Apparently, not only could the voltage be increased by increasing the frequency, but also control it with a VFO. However, I was not able to find a definite range of frequencies on which the transformer could be operated. I decided to do a little experiment. I hooked up a function generator creating a 6,2 V RMS sinewave to the primary and recorded the voltage depending on the frequency. The results are presented above.
It seems like the maximun output voltage is reached at 4,6 KHz, which seems to be way up of the suggested in the previous posts. I pretend to do different tests and post the results, but right now I am intrigued to why does this peak appear. ¿Is it the resonant frequency of the transformer? ¿Can this results be extrapolated to higher voltages?
I would be extremely grateful if someone could help me with this.
I recently became the happy owner of an old MOT. I have been perusing the FAQs and found this post (viewtopic.php?f=29&t=4843) where it is stated that fusor demo operation is normally located in the 3-10 kV range. Considering that the output of such a transformer is around 2,2kV with plenty of current (0,5 amps, according to the Internet), it seemed like the construction of a power supply consisting of the MOT and a Cockroft multiplier is a viable option.
However, I pretend to control the voltage being supplied to the chamber, which is difficult taking into account that I have no Variac, and buying one is completely out of question (money problems). I started thinking about different options of electronic control, but then I decided to search for "Microwave Oven Transformers" in this forums and found several interesting threats, such as this ones:
viewtopic.php?t=4422
viewtopic.php?f=11&t=4566
Apparently, not only could the voltage be increased by increasing the frequency, but also control it with a VFO. However, I was not able to find a definite range of frequencies on which the transformer could be operated. I decided to do a little experiment. I hooked up a function generator creating a 6,2 V RMS sinewave to the primary and recorded the voltage depending on the frequency. The results are presented above.
It seems like the maximun output voltage is reached at 4,6 KHz, which seems to be way up of the suggested in the previous posts. I pretend to do different tests and post the results, but right now I am intrigued to why does this peak appear. ¿Is it the resonant frequency of the transformer? ¿Can this results be extrapolated to higher voltages?
I would be extremely grateful if someone could help me with this.