Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1424
| Posted: 08:04pm 06 Nov 2017 |
Part 17: That Powerjack I bought. It has a primary choke.
I bought this a while back when the Victron poo’d it’s pants.
The primary choke is 2 turns through a Green ring of unknown provenance.
Two turns measures as 28uH at 1KHz via the LCR meter.
OK, maybe the PJ people know what they are doing. For sure, their powerboards are
very strong. Do they know much about primary chokes?
Since I have no interest in horse racing (my view is that the jockeys are drugged up on speed and the horses drugged up on whatever passes the urine test this year) today I got busy instrumenting the PJ 6000W LF.
First we see the primary winding current waveform at idle, in light Blue and AC output in dark Blue. Primary current equates to 10.6mV/Amp and the DSO gain is 1v/div. This means these are sharp peaks +/- 100 Amps. The time period where the bottom trace is zoomed into is just before zero cross of the output AC.
At the top of the AC output cycle, the primary current drops back to something more sensible.
But I estimate that 2/3 of the time, the primary current is peaking at 100A.
Just What The Actual F@#k?
This shows the primary current under a load. (The 3 speed brushless DC motor pool pump with it’s poor power factor.) Primary current is much more than the sensor can handle so we see it clipping. Still the huge current spikes can be seen.
I next retain the 2 turn choke and add in series a nice E core ferrite, 6 turns 47uH, wound with 6mm2 wire. Idle - no load.
Now this looks more like it.
And for completeness sake, under load.
I now tested both inductors using the di/dt pulse test method. This is useful in that it gives an indication of saturation current for the device under test.
E core, 47uH gave me 112us, 29.6A, 12V supply, so L = 12 x 122E-6/29.6 = 45uH
Saturation starts at about 35A
Ring, 28uH gives me 7.7us, 10.2A, 12 so L = 12 x 7.7E-6/10.2 = 9uH
The LCR meter gave me 28uH but the pulse testing is 9uH!
Saturation started at about 15A.
DC supply current during idle improves using the E core choke,
from 1.0A to 0.4A (50W to 20W..)
These E core chokes are the way to go. The one I used is RS part no. 6479389
E70/33/32 N87. It has no gap so I ground down about 0.5mm on the belt sander.
Cost was $14
wronger than a phone book full of wrong phone numbers