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high current DIY inductors

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NiHaoMike:
I'm working on a large power inverter, for a DIY solar power system. I have found fairly cheap sources for the power semiconductors and capacitors, but the inductors seem to only be available at crazy prices.

I found this old thread on DIYing large inductors:
https://www.eevblog.com/forum/projects/big-inductors-diy-style/
My requirements, however, are quite a bit more reasonable - on the order of 500uH-1mH at up to 60A or so. (2 of them, one per phase, along with a bunch of much smaller inductors elsewhere in the unit.) The switching frequency is 15-20kHz and size and weight are not that important, low losses and low cost are.

Thus far, it seems like rewinding a few big transformers would be the most economical route. Or is there a reasonably cheap source of magnetic cores?

BravoV:
Bought this from local re-cycler, it was salvaged from a big telecom big rectifier (AC to DC converter).

Measured using LCR meter, DCR=0.04Ohm, inductance 502uH@100 Hz and 460uH@100 kHz.

Shot with TO-220 chip as size comparison.

T3sl4co1l:
A pile of T300-52D's would do.

Tim

jbb:
A stack of E65 ferrite cores can get huge core areas with common parts.

For this application frequency range, nanocrystalline / amorphous iron materials can be quite good. They have the high saturation flux density of iron with much lower core loss. But they will be very noisy acoustically.

What topology are you looking at? Moving from 2 level to 3 level can be very beneficial; it reduces switching losses (may allow higher frequency) and can straight up halve the inductor value required.

NiHaoMike:

--- Quote from: jbb on January 03, 2020, 07:44:27 am ---For this application frequency range, nanocrystalline / amorphous iron materials can be quite good. They have the high saturation flux density of iron with much lower core loss. But they will be very noisy acoustically.

What topology are you looking at? Moving from 2 level to 3 level can be very beneficial; it reduces switching losses (may allow higher frequency) and can straight up halve the inductor value required.

--- End quote ---
I did a lot of reading about amorphous iron cores and they do appear to be the perfect kind of core for my application. Is there a guide for how to select the size of core and what turn count/gap size to use? I also read that those cores are fragile, is that really true or it that only in comparison to the conventional iron cores that are very rugged? All the amorphous iron cores I could find available in small quantities are horseshoe shaped (sold in pairs) and since the bigger ones are somewhat cheaper per pound, I had the idea to buy a single large pair, wind each phase on each horseshoe, then put them together with a piece of ceramic in between to set the gap and keep the two sides isolated, as well as keep the windings away from the gap area. Would that cause undesirable interaction between the phases if they're running at the same switching frequency but the output currents are not the same?

I don't think it would be very easy to do 3 level switching for a split phase design. The power module I'm planning to use (3rd gen Prius inverter, goes for fairly cheap) has 2 3 phase bridges. One I will use as a 3 phase variable frequency output for a thermal storage compressor (only needs light filtering to avoid EMI and standing wave problems) and the other I will use 2 phases for interfacing to the mains (via a 240V plug to a dedicated circuit) and 1 phase for a 120V UPS output. The neutral is connected to the center tap of the DC bus capacitor bank, so each phase is more or less switching at +-200V or so. (There's a control system that senses the current drawn from the grid and commands the inverter to source a current to mostly offset it without netting an export, so it's not a grid tie inverter in the conventional sense.)

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