Guru
Joined: 13/10/2014
Location: AustraliaPosts: 1688
| Posted: 01:43am 08 Mar 2024 |
Mike, I found that I need the Ferrite Beads.
Using a differential Probe and DSO.
Tested unloaded and loaded to around 250 watts resistive load without the beads fitted.
There was quite a lot of ringing on the waveform across the power board output terminals, on both HI and LO sides of the waveform.
I'm not going to waste time describing the various methods, loads, choke variations, Caps and filtering etc that I tried to narrow it down.
The difference between my Big inverter and this inverter is this:
The FET Drain metal facings are bolted directly to the two separate low side heatsinks. There is some expected ringing, but it's minimal compared to what I'm seeing on this board.
Could bridging the FET Drains (4) on each side, "ever so slightly" change the effect of the short Drain lead connection in that build and help to dampen the ringing that I'm now seeing, (no beads fitted).
The new build in contrast, has the FETS fully isolated on both HI and LO side.
I then fitted the Ferrite beads and retested.
What a massive difference. I also had a very faint very SLOW cycling hum in the Toriod (no load and loaded) a very strange effect that I have not heard before, ear pressed against the toriod. As this faint Hum cycled, the idle current went up and down by around 50mA to 100mA.
The Ferrite beads have completely eliminated 95% of the ringing, and that cycling effect has completely gone.
The beads I used are Electus, from Jaycar - LF1251 or FX1115. They are about 4.2mm diameter x 5mm long the hole in the center is ~ 1.3mm. They seem to change the carried stock form time to time. They have an LF1250 but I don't know the inner dia, it may be suitable?
.
Edited 2024-03-08 13:33 by KeepIS