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Dual Rotor Toroid Core PMA build

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CraigM:
MagnetJuice,

Thank you for the recommendations. I believe I lucked out with the molding I used. According to the manufacturer this material is a "special formula" polyurethane material with a maximum structural working temperature of 300F.

I did an oven test to see what would happen.


* Placed six inch piece of material on aluminum foil, put this in cold oven and set temp to 300F.
* Examined material when oven temp reached 300F. No change in material characteristics.

* Set over timer to 10 minutes, left temperature at 300F.
* Examined material after 10 minutes. Very hot to hold in bare hands. Material was not sticky, pull test and compression test (pinching) did not notice a change in material characteristics. No outgassing.

* Set over timer to 10 minutes, raised temperature to 350F.
* Examined material after 10 minutes. Could not hold material in bare hands. Material was not sticky, characteristics unchanged, only difference was slight discoloration (darkening). No outgassing.

I've based my temperature considerations on the use of polyester resin by Hugh Piggot. Polyester has a maximum service temperature of around 300F. As long as I stay in this range or above I'm hoping to not have a material failure due to excessive heat.

I'm going to roll the dice and continue on with this material. This however was just a short test, how it will hold up in the long run is anyone's guess. It's all experimental at this point and lessons will need to be learned along the way.

...kind of how I like it... keeps the journey interesting.

Thanks again,
CM

MagnetJuice:
That is good news; it saves you some work and gives you peace of mind.

Can you tell us where you got that molding and what is called? Just in case that someone else needs to use something like that.

Ed

CraigM:
MagnetJuice,

I purchased the material through Amazon. Here is the manufactures web site https://flexiblemouldingconcepts.com/

Thanks,
CM

CraigM:
Found this on Temco Industrial web site concerning magnet wire insulation types. I feel better about the Polyurethane molding I'm using since it's also used as magnet wire insulation.

https://temcoindustrial.com/product-guides/wire-cable-and-accessories/magnet-wire/magnet-wire-faq

Here are some common types of insulation and their specifications:

Insulation Type            Thermal Class                    AWG Wire Size Range
Polyurethane            120°C, 130°C, or 155°C    20-18
Polyester                    >155°C                            20-14
Polyester-imide            180°C                               38-18
Polyamideimide            220°C                               38-14

I've seen photos of burned out coils in axial flux type stators. Does the burn out happen when the coil temperature exceeds the insulation temp rating, which in turn breaks down the insulation and causes a short within the coil?

Thanks
CM

SparWeb:
Basically, yes, that is the reason the lacquer on "magnet" wire has a temperature rating.
That's not the only possible cause of burn-out, but certainly a common one.

(...wonder how he knows...?)

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