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Forum Index : Electronics : Another Inverter Build
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| analog8484 Senior Member  Joined: 11/11/2021 Location: United StatesPosts: 138 |
I remember that from your posts. The difference I see is the lack of the very sharp and deep divots. I think that's because your inverter is so beefy compared others. That's why I was wondering if and how the very sharp and deep but single per half cycle divots actually show in the VFB. |
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KeepIS Guru  Joined: 13/10/2014 Location: AustraliaPosts: 1858 |
Although the screen capture was from a 3 stack toroid, I have tested a single toroid as well and the results are almost the same. The only thing that shows up at the VFB input to the ADC is a DC voltage. Because the VFB circuit and the ACV display on the Nano cannot calculate True and Apparent power (LOW % PF) and not being true RMS detectors, they will respond the same to any load that introduces high harmonic distortion, results will be out by a few volts, AC might be 236v instead of 230v, or 224v instead of 230v, and the AC voltage display will be also be slightly out. 99% of the time it's all good, that 1% of very low PF garbage loads are not an issue, and those voltage margins have never been an issue. Not knowing the bandwidth and sampling limitations of the small DSO means the previous waveforms "may" appear completely different on a higher spec DSO. IMHO if that waveform with divots was being presented to the VFB Input terminal at the controller PCB, I doubt it would make much or any difference to AC regulation . Edited 2025-05-19 09:09 by KeepIS NANO Inverter: Full download - Only Hex Ver 8.1Ks |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1138 |
@ analog8484 The sharp divot is just a product of the scr speed controller, I haven't seen anyone else use one regardless of the type or size of inverter, hope that helps explain it, I have added a footnote on the other page. Thanks Mike, I do like the way that this inverter just keeps going well, even when throwing this crap at it, my other HF inverters will shut off with a fault (high voltage on DC Buss) when using the heatgun on low. Will be running an Air fryer shortly.  Cheers Aaron Off The Grid |
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| analog8484 Senior Member Joined: 11/11/2021 Location: United StatesPosts: 138 |
That's a good point. SCR can start the phase cut anywhere in the mains cycle while the diode half wave rectifier can only start the phase cut at zero crossings. I wonder if you had adjusted the SCR to start the phase cut at/near zero crossing you would have seen a similar waveform as KeepIS did. |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1138 |
Ok, so you made me dig a little deeper....and my curiosity joined the party , after looking at the difference between the signwaves with either a diode (heatgun) on the low power settings and the speed controller running at different power levels while watching the DSO,  I suspected the speed controller is a bit more than just an ordinary SCR and a few bits, after some stuffing around I could just make out half of the part number and it turns out to be a Triac bta100-800b so it now makes more sense the way the is shows on the DSO and is easy for the inverter to run and not as hash as a diode or single SCR.The first photo is the speed controller running a restive load at 200w the second photo is at 1700w the divot moved from one side over the peak of the wave to the other side, the inverter runs this just fine, no change in sound from the toroid and no other loads running, turn the controller all the way up and the divot is gone.  Keep in mind that some appliances have filter caps, and others have very little, with so many variables (different DSO) its a bit much to expect it to look identical to the signewave on other builds although it can look quite close. Busy with other work lately. Been thinking about making some terminal covers for the terminals on the bottom of the inverter.  Cheers Aaron Off The Grid |
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| KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1858 |
The variable speed heatgun is pulling power from both halves of each AC cycle so the Toroid does not complain much, if at all, but those garbage heatguns that use a Diode in series for low speed, pull power from only half of each AC cycle, causing higher harmonic distortion and unbalance the AC waveform which causes the Toroid to growl. NANO Inverter: Full download - Only Hex Ver 8.1Ks |
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| analog8484 Senior Member Joined: 11/11/2021 Location: United StatesPosts: 138 |
Thanks @Revlac for doing the test. It's interesting that low and high speed controller loads caused divots with similar magnitudes. I had expected the magnitude to be proportional to overall load. But now it looks like the rate of load current change and voltage magnitude at the sine wave position likely play a bigger role. |
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