Senior Member
Joined: 11/12/2020
Location: CanadaPosts: 138
| Posted: 04:04am 03 Jul 2024 |
So I hooked the revised inverter board to my new wound transformer/inductor and the standby current draw was 60w! What was going on? I temporarily moved the inverter back to the old transformer/inductor setup and rather than drawing 6.6w it drew ~11w. Increasing the dead time to 1.5uS, reduced standby to about 7w or so.
Placing the revised inverter back into my new transformer/inductor the standby power was now 55w!
This was where my inductor education began. First off, I didn't consider that putting inductors in parallel would reduce the overall inductance. I had 11 scavenged 52uH/8a inductors in parallel, yielding 5uH. I moved the inductor from my previous setup and tested a bunch of other values and ended up with these numbers.
Ind Stdby Power
5uH 55w
26uH 20.2w
52uH 13.7w
78uH 12.9w
104uH 12.1w
156uH 12.1w
So I figured, I needed to build a 100uH inductor with the largest wire possible.
I ended up buying some large iron powder toroidal cores off ebay(fortunately I have another use for them). I managed to stuff 4awg wire on 4 stacked cores and ended up with the inductor in the foreground which measured about 110uH.
I connected it up and the idle power was now 16w! Grrr.
So I unwound one of the inductor core sets I had used with the previous inverter and the cores were Kool Mu MS-157060-2 (stacks of 3). I signed up to use the Micrometals inductor calculator and was surprised to find that the calculator came up with the exact same results as I had measured for saturation when I first got these cores 3 years ago. So I played with the inductor calculator looking for a better solution at a reasonable price. Ultimately, having something in hand will always be far cheaper than buying something.
So I added additional windings to the inductors I already had, and decided to put 3 of these completed inductors in parallel (each one individually measured 340uH).
The base inductor had 36 turns of 14awg wire.
I added 3 parallel 18awg windings of 36 turns to each core.
Calculated inductance for these 3 inductors in parallel and the 5uH (11 in parallel) is 90uH at 45A and 45uH at 86A. DC resistance was measured to be .0055ohms.
Not fantastic, but should be good enough.
However when doing some initial power/efficiency testing, the inductors were running hotter than I would have expected.