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48V 5000W Oil cooled inverter build
#61
More nice work :-)
How are the 23kHz traces looking at the fets? Are you seeing ringing there? Might be a source of higher losses, eg cross conduction pulses?
Are the traces different on the fet side with the T400 ferrite vs the side direct to the transformer?

The hum you're chasing, could this be "magneto-stricting" of the core, eg at peak of 50Hz current it "tightens" & when current = min, it "relaxes", result = hum?
Wondering if supporting the transformer on the edge per the pic leads to hum coupled to timber box?
If transformer was supported at centre would that be better?
Running off solar, DIY & electronics fan :-)
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#62
Thanks, I had thought about hooking the scope up and was a bit lazy / tired and just plugged the wind grid inverter in as one screen shows a waveform output. At that point I was just interested in seeing the right shape and no shape horrors. When I get around to it I will hook up the scope again because I am now a bit more curious. It's nice and relatively silent now though,

The hum can also be the build up of the flux in the transformer due to resonance as the L(winding)/C(output cap) approaches 50Hz, which eventually pushes to saturation and the excess/additional field strength starts to push/pull on the windings more, so if any have room to move they will and then hum.

After researching magnetics for a few weeks for the build I'm quite amazed at the dual magic of a magnetic field. What amazes me most is a coil can take a bit of energy just to create the magnetic field and then that very same field can be reversed and thrown around at 50Hz with near zero additional energy input. That is what seems like a magic trick in some ways.

I did think I should just dump it into a tub of oil and then up-rate it to 1500W. When the battery has a bit more charge and the input voltage is around 52V I will see how the 2kW fan heater performs in terms of sag on the output voltage as it may have been partly due to the low input voltage on the battery pack at the time, or just due to the 200% loading of the transformer, or the different winding ratio.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#63
(10-01-2019, 09:10 AM)completelycharged Wrote: The hum can also be the build up of the flux in the transformer due to resonance as the L(winding)/C(output cap) approaches 50Hz, which eventually pushes to saturation and the excess/additional field strength starts to push/pull on the windings more, so if any have room to move they will and then hum.

Well there's your problem!! You should be running it at 60Hz! Crazy EU power systems trying to be different Tongue
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#64
Yeah, oscillating low loss coil+cap circuits are weird. Exactly what a magnetic field is, is fun too (know what it does, but not what it is!).
It's almost like you need the gap an E core transformer has for a bit of loss - ie what a torroidal one basically doesn't have.

Maybe some of the sag under the 2kW load might be resistive losses in the primary side wiring? Wire doesn't look that thick for ~40A (average) operation?
Bit hard to tell your actual wire sizes from the pics!

I'm a 50Hz'er too - each time I've visited the USA, I really noticed the 60Hz buzz - funny what the brain "tunes out" after a while ;-)
Running off solar, DIY & electronics fan :-)
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