WTS/WTT: T520-2 - Micrometals core, MO, USA

[coilerer]

Hey,

I know I'm new here, but I figured I would offer this in case someone else is building a buck qcw and needs a core capable of handling hundreds of amps. Not selling the whole inductor, just the bare core.

Ordering from micrometals has a minimum of two for this part number, hence my spare. I'm only looking for what I paid for one. $45+shipping.

I am also down for cool trades. Let me know if you have anything you want to swap.

Datasheet: https://datasheets.micrometals.com/T520-2-DataSheet.pdf

[flyingperson23]

I'd like to buy it. I PMed you about it.

[flyingperson23]

NVM it's too small sorry. If I'm not misreading the datasheet, it looks like with enough turns for a few hundred uH, it saturates at under a hundred amps.

[klugesmith]

Welcome to the forum!

...If I'm not misreading the datasheet, it looks like with enough turns for a few hundred uH, it saturates at under a hundred amps.

Sounds about right.  In an unsolicited design review:
120 turns would give you 287 uH. 
Then 100 A would put H at 457 Oe (36400 A/m), where permeability is down to 88% of nominal.
B would be 4020 gausses instead of 4570 gausses; L would be down to 256 uH.
There are applications where that might be a reasonable operating point.
The core is big enough for 120 turns of AWG 6 or even AWG 5 wire, presumably stranded with very thin insulation.

I think this material (Mix-02) approaches the maximum energy anyone could store in a core that size. (order of 1 joule)
There's so much distributed air gap, that the nominal relative permeability is only 10.  I hadn't known that catalog parts went that low.
With same winding on higher permeability core material, L would go up and I_sat go down in same proportion, so energy would go down.

[edit] Actually we could get more DC energy in similar size inductor using a laminated steel core with air gap, able to handle more than 15000 gausses before saturation.  Not practical for a switching converter!

[davekni]

[edit] Actually we could get more DC energy in similar size inductor using a laminated steel core with air gap, able to handle more than 15000 gausses before saturation.  Not practical for a switching converter!

Tape-wound amorphous steel cores are used at 20kHz.  Haven't seen any such cores available surplus.

If I'm not misreading the datasheet, it looks like with enough turns for a few hundred uH, it saturates at under a hundred amps.

I'm curious about this QCW coil that requires such large buck inductance.  My QCW buck uses a 40uH 400A inductor, switching at 40kHz.

[klugesmith]

Tape-wound amorphous steel cores are used at 20kHz.  Haven't seen any such cores available surplus.

Good point.   And some vacuum-tube audio output transformers and microphone transformers with punched laminations are characterized up to 20 kHz, where operating power will be low and losses may be high.

I just answered my own question about air gap availability. Mentioned for example in this datasheet:
 https://www.magneticmetals.com/products-materials/tape-wound-cut-cores/
For the application in today's discussion, high flux density and low loss at 20 kHz to 40 kHz are useful, even if gapped design has no use for  high permeability and low magnetizing current.

[Anders Mikkelsen]

Saturation with powder cores does not happen abruptly like with ferrite, but across a very wide range of currents. It's perfectly fine to operate the core with less than 20 % remaining permeability, as long as your design can handle the resulting ripple current.

As mentioned by Dave, it sounds like you are aiming for a lot of inductance for this application and current, and very little drop in inductance. That will require a very large and expensive inductor. As a point of reference, I've done a 16 kW continous buck using a core that cost less than 5 dollars, with over 99 % efficiency. This was using SiC, but at frequencies where IGBTs work well aside from having higher switching losses.

[flyingperson23]

I'm making a boost converter, hopefully at least 30kW. Switch is a cm300, for 20khz I'd like at least 400uH 200A. A few of these cores stacked would probably work, but toyota prius hybrids used to have buck/boost converters with beefy inductors, getting a few of those seems like my best bet. Sorry to hijack your thread a little coilerer.

[davekni]

Sorry to hijack your thread a little coilerer.

I'm the one who should apologize for hijacking this thread.  You're just answering my question.

I'm making a boost converter, hopefully at least 30kW. Switch is a cm300, for 20khz I'd like at least 400uH 200A. A few of these cores stacked would probably work, but toyota prius hybrids used to have buck/boost converters with beefy inductors, getting a few of those seems like my best bet.

To continue hijacking I'm still puzzled as to why 400uH is needed.  I'd think 50-100uH would be sufficient.  However, no requirement to answer.
For example (ignoring losses), if 30kW is boosting 240V at 125A to 600V at 50A, duty cycle is 60%, 30us at 20kHz.  100uH would ramp by 72A (= 240V * 30us / 100uH).  To average 125A, inductor current is 125A +-36A (89A to 161A).  50uH would ramp twice as much, 144A total or +-72A, so 53A to 197A.  That still fits within 200A maximum.

[flyingperson23]

Ah I see, I was misunderstanding how boost converters worked. I may still be misunderstanding, but It'll be boosting max to 1200v 25A which should be 80% duty cycle so 185A max with 100uH. That's 15% permeability loss with 75 turns, which hopefully is fine. To unhijack your thread coilerer, I would once again like to buy the extra core.

[klugesmith]

... It'll be boosting max to 1200v 25A which should be 80% duty cycle so 185A max with 100uH.

That suggests your current is 125 A +/- 60 A. Consistent with 100 uH, 240 V, 80% duty cycle, 16 kHz. 

I was going to ask the experts about derating the ampacity of thick wires, to account for skin effect and proximity effect.   Then realized it's not that bad here.   The DC current (125 A) sees full wire area.   The superimposed AC current, which is concentrated away from conductor center, is only 35 amps RMS.

[edit] also, at 30 kW, if we need active cooling for semiconductors we can actively cool the coils and cores.

[davekni]

Ah I see, I was misunderstanding how boost converters worked. I may still be misunderstanding, but It'll be boosting max to 1200v 25A which should be 80% duty cycle so 185A max with 100uH.

Using 1200V rated IGBT for 1200V output will be problematic.  There is no margin for parasitic inductance.  That is why gate charge etc. for 1200V IGBTs are specified for 600V.  That is typical use voltage, 600V nominal + 600V for spikes and tolerance.  Some list use to 800V.  Beyond that has a high probability of failure.  Given your 200A rather than nominal 600A, perhaps you could bet 1000V output.  Would require good low-inductance interconnect.

If 240V is rectified and unfiltered 240Vac, then calculate at 340Vpeak.  Ripple current will be a little higher than at 240V, but still fine presuming 20kHz.

[flyingperson23]

The boost converter is thoroughly actively cooled, and the primary and secondary will be as well. I'm using 1700v bridge igbts, and all the boost converter parts except the switch are rated for at least 1600v. I'll try up to like 1000-1100v out and if the spikes are too much for the cm300, I already have mounting holes for 2 of them in series or more likely just replace it with a single 1700v switch. I'm just using cm300s as that's what I have on hand. Inductor(s) will probably be actively cooled so I'm not worried about wire temperature. Wouldn't the only inductance to worry about be the internal inductance of the igbt and the connection from emitter to bus negative, as all other inductance is effectively in series with the main inductor?

It probably won't be run at more than like 800-900v very often for power draw reasons, I'm just interested to see what happens

[davekni]

Wouldn't the only inductance to worry about be the internal inductance of the igbt and the connection from emitter to bus negative, as all other inductance is effectively in series with the main inductor?

Inductance that matters is the loop through IGBT, diode, and output capacitor.  If using diode internal to CM300, there is relatively small inductance between IGBT collector and diode, perhaps 10-20nH.  Output cap from emitter back to diode anode (unused high-side collector terminal) is where layout will matter most.

[coilerer]

Wow. This thread really took off with some great information! Honestly, most of this is above my head.

@flyingperson23 - The other guy hasn't responded to my reply, so it's yours if you still want it. I'll send you a PM too.

I'm curious about this QCW coil that requires such large buck inductance.  My QCW buck uses a 40uH 400A inductor, switching at 40kHz.

@davekni - The inductor you see would in the OP is ~100mH. I haven't properly measured it, but I don't think its exact value is super important. I have no formal electronics training (I'm a biologist), so I am basing my design heavily around Loneoceans QCW1.5.

[davekni]

@davekni - The inductor you see would in the OP is ~100mH. I haven't properly measured it, but I don't think its exact value is super important. I have no formal electronics training (I'm a biologist), so I am basing my design heavily around Loneoceans QCW1.5.

That makes sense and is probably a reasonable size for your needs.  My question was about flyingperson23's need for several hundered uH and several hundred amps (which this core would not support).  I think that question is reasonably settled now.

Have fun building your QCW coil!