Electronics > Projects, Designs, and Technical Stuff
high current DIY inductors
MagicSmoker:
--- Quote from: NiHaoMike on January 08, 2020, 01:03:59 am ---What source would you recommend for getting a few of the Kool Mu cores? Searching Digikey or Mouser doesn't give any results for cores, just (small) complete inductors.
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Pretty much anything involved with magnetic components - wire, cores, bobbins, tapes, etc. - is still operating in the pre-internet era, with all pricing done by RFQ and with oppressive minimum order quantities. The one partial-exception to this is Dexter Magnetics - they do have an actual web shop but quantities rarely seem to be accurate and the search function is terminally stupid. Still, you can probably, eventually, maybe find some Kool Mu cores to order from them.
Otherwise, a somewhat close competitor to Magnetics, Inc.'s powder materials can be had from CWS Bytemark. I've used them for one-off (and not "state of the art") type applications with good results.
EDIT - it looks like Mouser carries a few sizes of Hitachi FineMet amorphous/nanocrystalline cores now... sit down before you look at the price, though.
NiHaoMike:
Is fringing losses with amorphous cores really a big deal at 15-20kHz? The following shows a gapped amorphous toroid for PFC and inverter applications.
https://www.nanoamor.com/pfc_choke_cores
As a guideline, at 15-20kHz, what would be reasonable J/kg values for amorphous, iron powder, and Kool Mu cores, assuming the core geometry makes efficient use of materials as most do? I'm starting to get the impression that for small hobby quantities, amorphous cores might actually end up the cheapest option.
Someone suggested salvaging the stators out of the hybrids as well (as in where the transmission casing is damaged but the stator itself is still usable) but I'd prefer to not do that since it sounds messy and time consuming, plus probably would not be cheaper after factoring in buying the entire transmission and then selling it minus the stators. (Of which, from the pictures, the stators appear to be made from laminations, how do they keep the losses down?)
MagicSmoker:
--- Quote from: NiHaoMike on January 11, 2020, 05:09:23 am ---Is fringing losses with amorphous cores really a big deal at 15-20kHz?
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Fringing effect is proportional to gap gap length and current to the first degree. The fringing field from the gap induces eddy currents in the windings closest to the gap (roughly out to a distance equal to the gap length) and those losses go up with frequency, of course, but a counterbalancing effect is that wire diameter (or foil thickness) have to be reduced with increasing frequency which limits the magnitude of the eddy currents in each wire/foil.
--- Quote from: NiHaoMike on January 11, 2020, 05:09:23 am ---As a guideline, at 15-20kHz, what would be reasonable J/kg values for amorphous, iron powder, and Kool Mu cores, assuming the core geometry makes efficient use of materials as most do? I'm starting to get the impression that for small hobby quantities, amorphous cores might actually end up the cheapest option.
--- End quote ---
The amount of energy stored in the core is almost irrelevant; most of the energy is stored in the gap (whether discrete or distributed).
--- Quote from: NiHaoMike on January 11, 2020, 05:09:23 am ---Someone suggested salvaging the stators out of the hybrids as well (as in where the transmission casing is damaged but the stator itself is still usable)...
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That doesn't sound practical at all. IIRC, early Prius models used a bidirectional buck/boost converter in between the battery and inverter which would have a rather beefy choke (or 3?) that would be better suited to your use.
NiHaoMike:
--- Quote from: MagicSmoker on January 11, 2020, 12:35:13 pm ---Fringing effect is proportional to gap gap length and current to the first degree. The fringing field from the gap induces eddy currents in the windings closest to the gap (roughly out to a distance equal to the gap length) and those losses go up with frequency, of course, but a counterbalancing effect is that wire diameter (or foil thickness) have to be reduced with increasing frequency which limits the magnitude of the eddy currents in each wire/foil.
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There was a reference to fringing losses in the core material itself, is that a problem at the low frequencies I'm working with? I'm thinking the fringing losses in the windings could be solved by sectioning the windings so that they're away from the gap area.
--- Quote ---The amount of energy stored in the core is almost irrelevant; most of the energy is stored in the gap (whether discrete or distributed).
--- End quote ---
The iron powder and Kool Mu cores have the air gaps integrated so there should be a value for the maximum energy that can practically be stored in them. For the horseshoe amorphous cores, the gap is chosen by the designer but in the end, there's still going to be a value for how much energy an inductor made from that core can practically store.
--- Quote ---IIRC, early Prius models used a bidirectional buck/boost converter in between the battery and inverter which would have a rather beefy choke (or 3?) that would be better suited to your use.
--- End quote ---
Those are only on the order of 250uH, which is fine for DC but for AC, the large filter capacitor (about 300uF) would pull a lot of reactive power.
T3sl4co1l:
--- Quote from: NiHaoMike on January 11, 2020, 05:09:23 am ---Is fringing losses with amorphous cores really a big deal at 15-20kHz? The following shows a gapped amorphous toroid for PFC and inverter applications.
https://www.nanoamor.com/pfc_choke_cores
--- End quote ---
They don't give losses. :-// Impossible to tell.
Tim
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