Guru
Joined: 13/10/2014
Location: AustraliaPosts: 1845
| Posted: 09:59am 29 May 2023 |
Chasing the elusive Choke inductance
There is nothing like high power sustained running to show up any weakness in your inverter. There are a few reasons for doing this at 7kW to 8kW, which I reached today, but 8kW was for only 1 minute as the large Inverter input Fuse holders big cable connecting blocks were boiling and evaporating fluid on the moisture test.
Wiseguy did not design the power board to run this hard for any length of time. I believe his power board was designed with the idea of easily using two or more power stages in parallel to run unstressed at high continuous power.
So, 7kW to 8kW gives me an idea of the limits of the boards power and Toriod connections, these can be increased / complemented by using the Heat sink for some power connections, in my case the FETS are connected directly to the very thick Heat transfer Bars, so that's easy to do.
It also tests the dual sided thick copper power tracks capacity on the PCB for up to 10 minutes, and at a higher power then I'm sure they were really designed for, Mike may elaborate on that, and it also allows me to push a little harder to test the FET heatsink coupling design that I used.
The elusive Choke Inductance: This has been the best test I have had for absolutely selecting the Inductance value for my Choke, and the effect it has on nasty loads.
I am fortunate to have FIVE Toriod ringing / prodding loads, and was able to compare the initial changes to the Choke value and the difference changes as small as 5uH in a Choke can make to the inverter.
My Wife informs me that the Hair curler is a Hair straightener, horrid devices for Toriod noise and I have access to an old and new unit.
I have Two Heatguns, one has variable Heat on High and LOW which BTW still appears to have a Diode in series on low, the other is just HI-Low heat with a diode in series on Low, finally the Reverse cycle AirCon on Heat at Full output.
RECAP:
LOAD: Hair straightener.
Choke inductance 73uH:
Sounds like a bucket full of bolts rattling, very loud and causing the UPS to beep like crazy and the lights to flash like a disco dance floor.
Choke inductance 37uH:
The noise now a slight background buzz and nothing else, no Disco or UPS beeps.
Choke inductance 46uH:
The noise still a slight background buzz and nothing else, no Disco or UPS beeps.
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LOAD: Reverse Cycle Inverter AirCon on High heat drawing 2.2kW.
Choke inductance 73uH:
Extremely LOUD BUZZ, the UPS beeping like crazy and the lights flashing madly.
Choke inductance 37uH:
Total Silence.
Choke inductance 46uH:
Total Silence.
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LOAD: Heatguns on Low.
Choke inductance 73uH:
LOUD HUM, I would NEVER leave it running.
Choke inductance 37uH:
Subdued Hum, you could leave it on and not worry.
Choke inductance 46uH:
Subdued Hum, you could leave it on and not worry.
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Rewound Chokes:
I removed one Blue toriod and got the inductance down to 20uH from 23uH.
Total inductance is now 40uH down from 46uH.
Below:
Saturation curve for One 20uH Choke, there are two Chokes in the Primary.
V-scale: 250A per division:
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Today: Before changing from 46uH to 40uH, I re-tested the Inverter with the Hair straighteners plugged in very close to the Inverter.
All other loads are always near the inverter.
Hair straightener.
46uH Choke
The UPS started to beep, but noise was still not "to" bad.
Choke 40uH
The UPS is silent - buzz is just in the background.
Everything else was silent at 40uH.
Final result: 40uH is close to the sweet spot.
The Inverter is now running with two 20uH chokes, one 20uH choke in each side of the Toriod Primary.
I have some DSO Screen shots of the Hair straightener waveforms to follow, and the startup waveforms and current using the 40uH choke, which show that 40uH is better then 46uH at extremely high demanding 3Hp Induction motor loads.
I'll do that tomorrow.
.
Edited 2023-05-30 08:46 by KeepIS