Guru
Joined: 21/06/2018
Location: AustraliaPosts: 1156
| Posted: 03:58pm 08 Jul 2022 |
Thanks for the info Roger, I have a source now !
Boy have I been having fun today, every time I went to confirm the resonant frequency I was getting different answers and I was getting quite frustrated. I was beginning to doubt my sanity again - some others may have already wondered.....
The remanence in the transformer can apparently change the resonant frequency by nearly 100%.To confirm my findings I ran the nano code with a slow stop. Then I checked my resonant frequency and it was 76 Hz.
Next I turned on a variable source with 1V @ 0.5A and placed it across the mains winding momentarily. Bingo! the resonance peak dropped and after a re-tune the peak was now at 132Hz. I then ran the nano code & soft stop and we're back to 76Hz AT LAST I finally nailed it !! Even 50mA momentarily injected could cause a 20Hz shift in the peak
I was using a signal generator, output 5Vp-p sine and a 15K resistor in series with the 240V winding and parallel capacitor, the CRO was across the winding.
So when checking the resonant frequency, the core should be de-magnetised/de-gaussed or you can end with a misleading answer, this was totally unexpected ! The signal generator was also capable of removing the remanence by shorting the 15K resistor and driving at resonance and reduce the output slowly to zero. Unshort the resistor and resonance is back to its lowest value, for my set up 76 Hz.
I also found that even disconnecting the signal generator whilst running & checking resonance and reconnecting it could temporarily detune the result also. The crux (flux?) of this finding is that the inductance is reduced if there is any remanence still in the core, this will result in an increased resonant frequency value.
Last test, I shorted the transformer/choke connection points on the Power PCB (no power connected to inverter !!) whilst I still had the resonance set-up connected, this enabled the last test to be done, I tuned for the peak which was found for my setup at 760Hz. this is the mains capacitor & choke combination resonance.
Edited 2022-07-09 02:25 by wiseguy