Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1440
| Posted: 03:00pm 07 May 2017 |
I hear what you are saying Warpspeed.
Between the excellent primary current sensor, the simple inductor tester using one FET and the LCR meter I have it covered. Maybe if I have a spare afternoon and a few beers in the fridge I might make the 2 FET tester. Gate drive will be via a disposable arduino, then a level shifter.
Today I put the Ecore ferrite in the kitchen oven, baked at 200C to soften the epoxy keeping the two halves together and quiet.
Using the 4" grinder I added an air gap of about 1mm with rounded edges in the middle leg of the E.
Al = 7.9uH/T2 ungapped, with the roughly ground gap I have now, it's 0.56uH/T2
9 turns gives a measured 48uH.
The air gap means saturation will be at much higher currents.
Let's see how it goes.
(yellow is DC bus current, pink is primary current, blue is AC out, light blue PWM%)
this is at idle. not too bad PWM current swing. You can reduce this further with more inductance of course. See some of my previous posts on this subject. The same 7.5W idle power.
This under load. Note very similar PWM current swing with the higher amps.
No saturation now at 435W test load. And a nice looking AC output.
Efficiency now 90% (19.3 A, 27.35V gives 440W RMS)
Getting 9 turns of 50mm2 cable through this core will not be possible.
I found getting 9 turns of 6mm2 earth wire into it hard enough.
The slot dimension is 44 x 12mm
So the search for a simple and cheap 50uH choke good for 100 amps continues.
Time to look at waveform purity. I calculate the THD of this prototype inverter to be about 0.5% (50Hz 70db, 3rd 25db, 4th 25db, 5th 20db, 6th 20db) via the DSO's FFT.
Not too bad at all.
wronger than a phone book full of wrong phone numbers