Guru
Joined: 13/10/2014
Location: AustraliaPosts: 1845
| Posted: 01:37am 30 May 2023 |
Bad Inverter Loads:
Briefly and simplistically generalized by myself: Going back 7 years in various forum postings, the decision when choosing a Choke was initially around the lowest Idle current, the rational was sound, it was realized that normal inverter loads were around 300 to 1kW 99% of the time and for a number of reasons, most of us went for the lowest idle current.
We still make that choice, but in my case I have proven that it's not really a compromise to get a Choke that virtually stops 99% of the noise, even with bad loads, even loads that in the past would destroy some inverter, obviously "DUH" this can "not" be put down to simply changing a Choke.
The typical Waveform:
ABOVE:
This is what you see with Heatguns that switch a Diode in series with the Heating element on LOW. The same thing happens with the Hair Straighteners, and even the AirCon. Choke value was around 58uH, very high saturation chokes in all cases.
This was with the China inverter in the Cabinet, I never bothered with capturing an image of the New inverter board running this load, but it was quieter, still made you want to turn it of "quickly" though.
These Loads vary in how deep they cause a step into the waveform, other waveform distortions and how much ringing they cause. Almost like hitting something with a hammer, in this case the Toriod, and making it ring.
I've found that one change I can make in the Inverter that has a very noticeable change to the amount of ringing, Toriod noise, and helps reduce the step in, or at least reduce the sharp edge nature of it, is the Choke inductance.
Below
37uH to 40uH Choke:
30A peak DC input and the step around 6A, the AC load is around 400 watts
The ringing has completely gone from what I was seeing the other day, and the step in is less.
There is only a small value of current at the step. This inverter is now very quite running this load. Before it was scary loud, flashing Workshop lights and UPS beeping like crazy.
Idle Current:
Chokes: 37uH to 75uH give virtually the same Idle current in this Inverter.
Bare transformer tested with a Variac, 14 turn primary @ 27.3VAC for 230VAC out @ 15 Watts.
Tested again with 40uH Choke:
The Inverter Idle current is 22 watts running "Wiseguys" Controller board and Inverter power stage, along with LEDS and a small relay.
It raises to 27 watts with two the bigger DC to DC power packs running and the big Contactor engaged.
This is virtually the same as the China Inverter board.
.
Edited 2023-05-30 11:47 by KeepIS