Hi All,
So I am slowly getting closer to having my big OLTC coil running.
I have been running low power tests with input voltages upto about 350v
DC, and already getting 600mm sparks.
I have two problems:
First, I am not used to tuning using a scope.
The secondary with top load shows self resonance at 28khz.
The Tank cuircuit (28uF capacitor and a single turn of copper sheet
500mm diameter) tests up at 26khz.
When I put the secondary into the primary, the secondary seems to jump
up to 30khz and the Primary drops to 25khz.
Whatever is happening, it seems that the tuning is off, because when I
run the coil and add or subtract capacitance from the tank to tune it,
there is very little difference between "good tune" and "bad tune".
It seems to be working more as an induction coil than something with a
clear point of self resonance...
Secondly, Because the coil opperates at such a low self resonant
frequency of 28khz, the inductor designed to double the DC bus voltage,
and give the IGBT time to fire, is not blocking the HF properly from
getting back into the PSU.
I was wondering if I could put a capacitor across the inductor, creating
a parallel resonant circuit tuned to 28khz.
In theory it would have high impedance to the HF and low impedance to
the incoming DC, but I am not sure how it would effect it as a charging
reactor...