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May 20, 2021, 05:09 PM
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How does motor insulation die?


Making sure to not ruin the magnets from getting them too hot is easy and need not be a problem but the winding’s insulation will be breaking down at some unknown. You could maybe calculate time at different temps and even log the shock temps, but no one does that, instead an eventual short in the winding is an assumed eventuality. Luckily with a plane you likely can glide to a safe landing but I believe the esc can be damaged and maybe destroyed from a motor shorting, no?

Even if the magnet wire insulation were to breakdown from time and repeated high temp, the voltage going through the wires is only going to be a very few volts ( just enough to pass the desired current over the winding resistance). there is still the gap between the wires where the remaining insulation isolates the wires a distance..the thickness of the insulation. And it jumps that gap with such few volts or does the insulation become a conductor?
Last edited by Hummina; May 23, 2021 at 01:53 PM.
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May 21, 2021, 03:04 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by Hummina
How does a motor die?
In the rain. Alone.


Winding wire insulation temperature rating is higher than Neodymium magnet temperature rating.
Magnet and magnetwire info
www.rcgroups.com/forums/showthread.php?240993-Re-winding-and-building-motors-tips-and-tricks-checks-and-tests


Prettig weekend en wees voorzichtig, Ron
• Without a watt-meter you're in the dark ... until something starts to glow •
E-flight calculatorswatt-metersdiy motor tips&tricksCumulus MFC
Last edited by Ron van Sommeren; May 21, 2021 at 07:05 PM.
May 21, 2021, 07:54 PM
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lets say the wire is rated to 200c for i think it was 20,000 hours, and lets say 20,000 hours at that temp happens or maybe the motor repeatedly does a lot higher temps than 200c, and the insulation "dies" and the motor shorts. what happened? does the insulation literally deteriorate to such a point the copper is exposed, or does the insulation become a conductor or what? a chemical transformation?
May 22, 2021, 07:58 AM
Registered User
Remember the windings suffer considerable g forces when running so it is quite possible if the insultation is mechanically degraded for a winding to touch in neighbour or worse a neighbour several turns away. and possibly the iron of the core. The resulting reduced reluctance means the amps in that winding will rise significantly further exacerbating the heat generated problem. Such an event may also take out the ESC.
If a motor smokes in any way it is reasonable to assume the insulation has been compromised.
Water on its own does not effect a brushless motor. They will run submerged but any iron or steel in the motor is of course subject to oxidation.
May 23, 2021, 01:10 PM
Mmm...castor smoke....
Overheat them, let them corrode, mechanical damage from unplanned lithobraking, bad bearings allowing rotor and stator to make contact, and excessive dirt ingestion.
May 23, 2021, 01:10 PM
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dangerdan's Avatar
200 C translates to 392 F.
According to Google
"As soon as the Neodymium Rare Earth Tube Magnets are exposed to temperatures exceeding 212 degrees F, the magnetic strength becomes compromised. On returning to normal operating temperatures below 176 degrees F, there is an irreversible loss in magnetic strength and permanent damage"

According to RcGroups
Depending on ethylene content of the plastic resin, foam melts around 120 C for polyethylene to roughly 145 C for polypropylene.

According to Google
Balsa wood has an ignition point around 392 degrees F

Needless to say if an RC motor windings get to 200 C , nothing will survive UNLESS you meant to say 200 F.
May 23, 2021, 01:44 PM
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Thread OP
Magnets can get to much higher than 200c before being damaged

https://www.kjmagnetics.com/specs.asp



My question is related to the wire insulation alone which leaves me in the dark as to how long till it breaks down and shorts. I could add a temp meter to the winding and compare to the 200c wire chart and get a pretty good idea of when it will expire but baring that it’s a guess. And then HOW does it actually deteriorate, does it convert to becoming a conductor or does it vanish somehow allowing the wires to contact or what?


240c is the highest rated wire I can find and will last the longest but even this will eventually short through too and maybe when doing only 100c or less after years and will be a surprise.

http://www.baewire.com/HEAVY-ALLEX-H...mwhml150cn.htm


I’m also curious how a coil varnish will effect the wire’s insulation ability and on the phone they say they don’t know. I vacuum in a thin one-part epoxy more so to keep things solid.

https://www.epicresins.com/


(I changed the thread title to be more specific)

Its not ideal going to such high temp but necessary due to motor size constraints

https://us.megger.com/blog/december-...megger-a-motor

https://megger.widen.net/s/9qkpsjwcwp
Last edited by Hummina; May 23, 2021 at 02:17 PM.
May 23, 2021, 02:21 PM
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https://gadgets-reviews.com/review/8...n-testers.html
May 23, 2021, 02:33 PM
If it flies, I can crash it.
rocketsled666's Avatar
Quote:
In the rain. Alone.
Poetic. But far from the truth. Usually, they die in an alley or gutter, with the broken end of a needle sticking out of a vein in their arm. It's quite sad, but not poetic.
May 23, 2021, 04:29 PM
Registered User
Hi Hummina,
i allways use Polyimide enamel coating. This is resistant up to 420 Degree Celsius.
Most of the time, the windings are destroyed by longer intervals at high temperatures. The insulation slowly charred and becomes electrically conductive. If that happens at one point it is too late and the temperature continues to rise, more and more charred until everything ends in a total short circuit.
The insulation can also be damaged when winding the coils, the smallest cracks can appear at the bends or the insulation is scratched through and damaged by the iron sheet of the stator. Polyimide enamelled wires are very expensive. The higher the temperature resistance of the do the more expensive. But there is also a method for a high temperature-resistant insulation that is not that expensive. To do this, a copper wire is covered with a thin layer of aluminum. This is done by pulling the copper wire through an aluminum melt. The wire coated in this way is then loosely wound in the form of a coil and anodized in a pre-bent form in an eloxal bath. The anodized layer is aluminum oxide. This is then a ceramic material that can withstand very high temperatures. I have z. B. in quartz glass drawing yards for optical fiber so the connections for a graphite heating element made of aluminum that was only isolated by elexizing. There the heating power was at 24 volts and 5000 amps 120 kw power. Other insulations consist of ceramic fibers that are applied with ceramic mass. Another source of error are tiny iron particles or iron powder that are drawn into the motor by the magnets. There these iron powder particles remain on the windings. But due to the alternating magnetic field of the motor, they rotate or vibrate like small motors and work like small drills or handcraft files and saws. They destroy the insulation mechanically. Later the insulation must be removed and a new insulation applied. B. have no cracks or other defects.

https://www.qiwenwire.com/fiberglass...re&matchtype=e

Happy Amps Christian
May 28, 2021, 10:43 AM
Retired Electronics Specialist
vollrathd's Avatar

Damaged Insulation?


If the insulation on several adjacent turns of the motor winding fails, you have what is called a "Shorted turn" or Shorted turns in the windings. Those shorted turns become a "generator" inside of the winding that generates very low voltage at very high currents.

Those turns are a dead short, resulting in those turns getting very hot, very quickly. It won't take long before that winding completely burns up.

One way to visualize this is to take all three motor wires, and dead short them together at the lead wires them selves. Then, try to spin the motor rotor.
May 31, 2021, 01:29 PM
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FLOEY's Avatar
Quote:
Originally Posted by rocketsled666
Poetic. But far from the truth. Usually, they die in an alley or gutter, with the broken end of a needle sticking out of a vein in their arm. It's quite sad, but not poetic.
Peculiar mine usually expires in a puff of smoke
Jun 08, 2021, 03:13 PM
Registered User
Quote:
Originally Posted by rocketsled666
Poetic. But far from the truth. Usually, they die in an alley or gutter, with the broken end of a needle sticking out of a vein in their arm. It's quite sad, but not poetic.
A back alley in L.A. Among the rats, garbage and human offal.
Jun 13, 2021, 08:14 PM
Registered User
Thread OP
Quote:
Originally Posted by vollrathd
If the insulation on several adjacent turns of the motor winding fails, you have what is called a "Shorted turn" or Shorted turns in the windings. Those shorted turns become a "generator" inside of the winding that generates very low voltage at very high currents.

Those turns are a dead short, resulting in those turns getting very hot, very quickly. It won't take long before that winding completely burns up.

One way to visualize this is to take all three motor wires, and dead short them together at the lead wires them selves. Then, try to spin the motor rotor.
What can you do to increase the lifespan of the winding and have it fail in as least spectacular way? Higher insulation temp of course, and vacuumed epoxy into the windings to secure and transfer heat, .. but maybe LRK winding isolating the windings, or anything else?


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