Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1432
| Posted: 01:13am 07 May 2017 |
The inductor test circuit I used was based on that linked by Solar Mike.
http://www.thebackshed.com/forum/forum_posts.asp?TID=9409&PN=1&TPN=1
Instead of using a 555 based drive, I used an arduino.
I liked having complete control over the pulse width and repetition rate.
No fiddling with time constants and such.
I found that you can't ever have enough capacitor bulk charge. Small amounts of voltage sag during the ON pulse mean the calcs are not quite right. They require a constant voltage.
But saturation is a reality.
I tested today the large E core ferrite with 5 turns.
This adds up to about 182 uH
At idle we see a very smooth primary winding current. The 182uH smooths things out really well. Idle current is .27A (at 27.3V power is about 7W)
Yellow DC bus current, pink primary winding current (41mV/Amp both scales)
Blue is AC output, light blue is PWM duty %
its when a proper load appears we see the E core ferrite find it's all too much
and saturate.
This also has the output AC waveform fairly well distorted too.
The PWM current swing during peak AC voltage is about 700mV or 17 Amps.
Once a decent amount of current pre-exists in the inductor, any transient current sees a much less inductance.
The E core is a TDK E 65/32/27 RS part no. 840-7727. The spec sheet from RS weebsite shows A(L) value is 7200nH
i.e. 7.2uH per turn2, so 5 turns means 5x5x7.2 = about 180uH
Just as the LCR meter confirms.
wronger than a phone book full of wrong phone numbers