Why never see metal cast around wound stators?

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Hummina Shadeeba   1 MW

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Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 20 2019 7:46pm

I’ve seen some really high temp magnet wire and with zinc melting at 700f and being a pretty good conductor I’m thinking of giving it a shot. Aluminum melts at 1200f and there’s wire that can sustain that for many hours and maybe even some more standard wire could survive the temp shock of being cast within molten metal. Instead of air encapsulating the heat the vacuumed in metal would transfer better to the stator and if the motor were designed for it could have transit pipes that would go to a heatsink outside the motor.

The cast metal would also hold the wire firm as a winding epoxy does and could replace it.

Maybe there’s expansion rates of the metals that vary and that could lead to failure. Zinc expands more than aluminum and both more than copper. Anyone heard of doing this?https://www.ceramawire.com/technical-in ... chspec.pdf

I was thinking I’d bring the wound stator up to 700f also with a high temp silicone mold and pour molten aluminum or zinc in and maybe would have to vacuum it in for best results.

Maybe eddy currents would be a problem. Wonder if could be simulated well and tempted just to try it.

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Re: Why never see metal cast around wound stators?

Post by KD5ZXG » Feb 20 2019 9:21pm

Eddy? Huge shorted transformer secondary more like it.
Not recommended for stator with an alternating flux.

Shorting ring (or bury in cast metal) might help a DC field
coil or permanent magnet rotor that doesn't change flux.
For fixed flux application, idea may not be entirely daft.

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Re: Why never see metal cast around wound stators?

Post by flat tire » Feb 20 2019 10:35pm

The real question is why we don't see this badass ultra high temp magnet wire used with samarium cobalt already in premium motors like astroflight? A motor that can melt zinc and remain operational would be cool.

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Chalo   100 GW

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Re: Why never see metal cast around wound stators?

Post by Chalo » Feb 21 2019 1:41am

Wouldn't encapsulating a stator with electrically conductive metal squander a huge amount of energy to induction?

Really, you want to encapsulate it with diamond. Excellent thermal conductivity but electrically insulative. Let us know how it goes.
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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 21 2019 1:08pm

Despite strong discouragement about Eddys I’m holding onto the idea given it seems in simulations the field strength is very low in the slot area where the additional metal would be https://m.youtube.com/watch?v=d7wTI2V3gb0
eddy currents are produced in the windings as is and assuming the slot is 75% filled with copper already it doesn’t seem filling the slot that last 25% with zinc would be radical


Or maybe the magnet circuit could be designed for even less field passing the slots.

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Re: Why never see metal cast around wound stators?

Post by maydaverave » Feb 21 2019 1:14pm

Chalo wrote:
Feb 21 2019 1:41am
Wouldn't encapsulating a stator with electrically conductive metal squander a huge amount of energy to induction?

Really, you want to encapsulate it with diamond. Excellent thermal conductivity but electrically insulative. Let us know how it goes.
DLC (diamond like carbon) is getting cheaper and better. Hard as diamond, stronger than steel, slick as Teflon. I can't wait till they start putting it on everything. I would love a quality DLC plated motorcycle chain.
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Re: Why never see metal cast around wound stators?

Post by Chalo » Feb 21 2019 2:16pm

Hummina Shadeeba wrote:
Feb 21 2019 1:08pm
Despite strong discouragement about Eddys I’m holding onto the idea given it seems in simulations the field strength is very low in the slot area where the additional metal would be
Even if you're putting it where the field strength is well below peak, you're still suggesting a heat management method that would actively create heat. Not good.
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Re: Why never see metal cast around wound stators?

Post by billvon » Feb 21 2019 5:59pm

maydaverave wrote:
Feb 21 2019 1:14pm
DLC (diamond like carbon) is getting cheaper and better. [/quote]
Sounds pretty conductive to me.
--bill von

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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 21 2019 7:44pm

If u look at the video it looks like there are practically no flux lines in the slot. The amount of eddy currents generated in the windings of this motor here or any motor of this design and spun at a relatively slow speed I imagine are very small.

It would be great to have 100% copper in the slot at lower temps but if the motor is run hot and 80% of the slot is conductor and the remaining 20% is able to rid of heat enough to keep it at a lower temp it could be more efficient even, but more so the benefit being hit a max power possibly, possibly, way higher. It would be adding a metal heatsink directly to the worst heat source. The best possible passive cooling second to maybe having a natural spring running through. Who doesn’t like cooling. I love cooling https://m.youtube.com/watch?v=N60utqXf5HQ

How many Eddys in the windings?

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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 22 2019 12:22pm

I’m impatiently waiting for one of you to bring evidence of eddy currents generated in the windings being significant! I’m sure they are there to some extent but in my looking at research papers related to Eddys in bldc machines’ windings I haven’t even found anything. I imagine for a very high electrical switching frequency machine then it would be an issue with any design but the motor I’d pot in zinc would only hit maybe 10,000 erpm

Any naysayers please speak up

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Re: Why never see metal cast around wound stators?

Post by Chalo » Feb 22 2019 1:32pm

You're the one suggesting that you, without data, can do better than a development cycle that's now close to 200 years old, by using a method that would have been available for most of that time (but which has obvious foreseeable problems).

I'd say the burden is on you to try to demonstrate the advantage you're talking about-- if only so the rest of us can remind you that we told you in advance what would happen.
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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 22 2019 1:42pm

I read from people eddy currents will ruin performance. I can’t find any info supporting that. At this point having searched all over I can’t find evidence that eddies would be much. Of course would depend on frequency and magnetic design but even w a standard 12x14 outrunner as above...where’s some evidence of much eddy currents? It’s the difference in eddies between 100% copper fill and 80% pretty much just without the increase in conductance.

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Re: Why never see metal cast around wound stators?

Post by APL » Feb 22 2019 2:00pm

I think your idea has merit, I always encourage out of box thinking, theres slow headway made in mainstream thought.
But the initial wall of failure will most likely be high, and we need to prep for that.

I don't see any problems with eddy heat, more intense in steels, rather than alloys, and if you kept the coating thin,
it would be even less.

The devils in the details though, and being able to draw the heat away from the windings is good, but at a certain rate
is a problem, lest it serves to hinder rather than help.

As I understand it, heat in the standard model is transferred from the copper through the lamination stack and into the
stator structure. Hardly a heat sink, as once it absorbs the initial heat load, there is nothing to take away the excess.

The way in which you get rid of the heat will be important,.. it has to go somewhere. :?: Perhaps shape the zinc into
a lattice work of finn's, and provide cooling holes or scoops in the side covers?

Have any ideas on how to remove heat from the coating to the outside of the motor?

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Re: Why never see metal cast around wound stators?

Post by e-beach » Feb 22 2019 2:06pm

Hummina Shadeeba wrote:
Feb 22 2019 1:42pm
I read from people eddy currents will ruin performance. I can’t find any info supporting that. At this point having searched all over I can’t find evidence that eddies would be much. Of course would depend on frequency and magnetic design but even w a standard 12x14 outrunner as above...where’s some evidence of much eddy currents? It’s the difference in eddies between 100% copper fill and 80% pretty much just without the increase in conductance.
The flux happens primarily inside the coil not outside the coil. You are correct about that. However if you encapsulate the coils, thereby encapsulating the heat, now you have the the job of trying to cool a large mass of metal instead of cooling an air gap. An airflow around the stator is a more practical idea. Although, I could see pre-cast covers bolted around a stator that encapsulates and allows a forced air flow around the stator as way to cool the stator.



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Re: Why never see metal cast around wound stators?

Post by Punx0r » Feb 22 2019 2:22pm

This thread badly needs a diagram explaining the idea...

Different people seem to be imagining different configurations from the description. I assume the idea is to fill the voids in a stator winding with cast metal to improve the thermal path from the winding to the stator. This would work, but as mentioned above, eddy currents would be a problem: you're casting a big lump of conductive metal (a shorted half turn) inside a object that is made from laminated steel for a reason!

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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 22 2019 2:34pm

"The flux happens primarily inside the coil not outside the coil." does it? looking at the simulation I posted from youtube a couple posts back it seems the magnetic field strength is very small in the windings and much greater in the air gap. We're looking where the strongest switching magnetic field is in search of the eddies no? the only strong magnetic field outside of the air gap is in the ferromagnetic stator and that makes sense it would use lams but the only time I've ever heard mention of eddy currents produced in the slots/windings is with a very high frequency machine and then they would use litz wire and that's more so even to reduce skin effect and not eddies.
my evidence that eddies aren't produced much is based on what I read and in the simulation I posted. Looking at that...the field strength is very small in the windings. I challenge any of you to find evidence of anything beyond negligible eddies in the windings with such a design going at only 10,000erpm. I challenge you because I haven't found the evidence and it would go against how I understand eddies are produced. Solid zinc is conductive but the field strength in the windings where it would be seems minute.
Last edited by Hummina Shadeeba on Feb 22 2019 2:36pm, edited 1 time in total.

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Re: Why never see metal cast around wound stators?

Post by e-beach » Feb 22 2019 2:35pm

Could also use a thermal gap filler to wick heat away from the stator into a chamber that can then be cooled.



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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 22 2019 2:41pm

I think I have that stuff in the video If it's their thermally conductive silicone.(can't hear). I told them was thinking of making thermally conductive silicone lead wires and they sent me a gallon (get all kinds of samples easily stating Im a business looking for stuff I could potentially use) but after casting it I found its tear strength is very low.
https://www.stockwell.com/thermal-mater ... ta-sheets/ all their stuff is also far from as thermally conductive as zinc. the only concern with casting zinc in the windings seems possible eddies, which I don't think are an issue, and possible difference in thermal expansion rate of the copper windings and the zinc cast around it and this possibly leading to a breakdown of the copper insulation and a short. I could vacuum in some winding resin as a first layer maybe to offer some protection. no?

with the zinc you could cast it around the stator and with the addition of routes for transfer right out of the motor to a sink of different types. It would depend on the motor design as far as how you can do it or how well it could possibly go but at least with a standard bldc outrunner there's a side of the motor where the shaft comes out which is almost always stationary aluminum and right beside the stator and could be cast to or through with the zinc.
still waiting to hear some evidence that it won't work well before doing it.

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Re: Why never see metal cast around wound stators?

Post by Punx0r » Feb 23 2019 6:38am

Take a look at induction heaters to see what happens if you place lump of metal in a high-current coil!

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Re: Why never see metal cast around wound stators?

Post by TilmanBaumann » Feb 23 2019 8:17am

Exactly right.
Try this perhaps for explanation.
https://youtu.be/u7Rg0TcHQ4Y

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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 23 2019 11:28am

If an ac current were being fed through the coils at a fast enough frequency to produce eddy currents the iron teeth would be heating up especially as it’s feromagnetic and would be heating through hysteresis as well as Eddys. But they don’t heat through these and the frequency is not fast enough. Why? I’m thinking while the esc has a switching frequency within the range of an induction heater its just pwm and not true ac and this switching doesn’t get past the inductance of the coils anyway before smoothened. the commutation frequency is still not fast enough but if it were able to be sped up a lot then maybe it would be an induction heater no? . None the less the motor hasn’t shown to be an induction heater thus far and theres no reason to believe this would change with an added 20% material within the slots

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Re: Why never see metal cast around wound stators?

Post by Ianhill » Feb 23 2019 12:02pm

Hummina Shadeeba wrote:
Feb 23 2019 11:28am
If an ac current were being fed through the coils at a fast enough frequency to produce eddy currents the iron teeth would be heating up especially as it’s feromagnetic and would be heating through hysteresis as well as Eddys. But they don’t heat through these and the frequency is not fast enough. Why? I’m thinking while the esc has a switching frequency within the range of an induction heater its just pwm and not true ac and this switching doesn’t get past the inductance of the coils anyway before smoothened. the commutation frequency is still not fast enough but if it were able to be sped up a lot then maybe it would be an induction heater no? . None the less the motor hasn’t shown to be an induction heater thus far and theres no reason to believe this would change with an added 20% material within the slots
Heating through hysteresis?
Hysteresis is the left over magnetism in the core it takes energy from the opposing magnetic field to neutralise it, it is not the cause of heat but rather the reminants of the field.

Any frequency creates eddy currents they happen in a changing magnetic field any metal will induce a current how much will flow is based on it resistance thats why magnetic steel has has high resistance less current flows across it so less eddy are induced we then chop that eddy into many a small piece with lamination to limit the circulation within the core to keep the losses small as possible.

If you use a solid material these eddy will circulate more freely into larger ones and as more current flows things get hotter, the material would need high resistance and good magnetic properties to allow the field lines to flow through it and not around it.

If a laminate could be laser printed to the windings it would increase the contact area and pressure to the winding and is more secure in operation as strong fields will move stray windings easily and thermally the path will have less resistance to move heat away but all of this can be done by using a none circular winding wire.

Look at industry and research the latest released motors as some of the latest patents may blow your mind like the dual halbach effect ironless bldc motor with direct winding cooling that can be run like a traditional dc motor no need for encoders or hall effect sensors and has around 4× a traditional bldc commercial motors throughput for any given size/weight.

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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 23 2019 12:32pm

“ eddy currents flowing through the resistance of the material heat it by Joule heating. In ferromagnetic (and ferrimagnetic) materials like iron, heat may also be generated by magnetic hysteresis losses.”
-Wiki induction heating
Given the motor doesn’t heat much from eddies and hysteresis and surely the large majority of heat produced is from copper losses as with most hub motors we use. even if eddies were formed in the zinc in the slot it seems safe to assume they would be a small loss. The motor already uses either 16 or 17awg wire and I’ve never heard of fat wire being a detriment unless the motor frequency is much faster. The zinc cast in the slot likely wouldnt be any thicker than maybe 16awg anyway.

I don’t see the “dual hallbach” in my search but I’m looking for passive cooling methods.

Was thinking standard magnet wire temp ratings need not be an obstacle and could wind with any rated magnet wire and then vacuum in some high temp resin that would be able to not breakdown from the 700f of molten zinc or maybe even 1200f and aluminum

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Re: Why never see metal cast around wound stators?

Post by Ianhill » Feb 23 2019 2:11pm

Hysteresis
The phenomenon in which the value of a physical property lags behind changes in the effect causing it, as for instance when magnetic induction lags behind the magnetizing force.

it's the magnetism in the core that lags behind the changing field it's the induction thats causing the heat same as a induction loop or hob.

Ideally we would have no iron at all in a motor but it's there's to guide the field lines if we use flemings law and line up the torque vector angles of the windings to the magnets then theres no guiding needed and the use of an extreme small air gap will give a large opposing torque in the rotor with zero iron and thus meet the dual halbach array ironless motor.

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Re: Why never see metal cast around wound stators?

Post by Hummina Shadeeba » Feb 23 2019 2:35pm

I think iron will be needed in this motor at least for the great increase in magnetic strength it brings. But the casted zinc? I’ll be seeing what resin I can find that could be vacuumed into the winding first and hopefully not breakdown w the heat of the casting.

650c. Almost heat resilient enough to cast aluminum around
https://www.cotronics.com/vo/cotr/pdf/4703.pdf


Even better possibly
http://www.flexibleceramics.net/high-temp-resin.html


Maybe best to not have any lower temp enamel on the wire which would maybe transform badly with the heat.

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