Motor Space Heater voltage drop 7

[mikeengurs]

I have a 1187W motor space heater rated at 120V. I'm using 12AWG wire. The cable length is 450ft. I found a table indicating resistance for this size cable is 1.588 for 1000 ft, which means 0.7146 ohms for the 450ft. How is voltage drop calculated in this case, knowing that current will not be constant? Also, would less voltage cause any heater failure? I believe it's just gonna have less heat.

 

[electricpete]

Absolutely. And sometimes it's tricky to navigate the water when you don't have the benefit of looking someone in the eyes to see their reaction to what you're saying. It's the nature of the forum beast.

I was thinking a little more about something you said:

I am more concerned with the iron temperature than the winding temperature.

With the motor shut down, I don't think there is much difference between the two. Winding is in intimate contact with core iron in the slot.

I guess if we assumed air temperature was everywhere uniform (including inside the motor), then we may suspect windings warm up faster than core due to higher ratio of surface area to mass on windings than on core. That would suggest parts of the core could be even a little cooler than was indicated. It’s worth considering, good point.


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(2B)+(2B)' ?

 

[electricpete]

A few last thoughts on comparing winding temp to core temp: the winding temp is measured in the axial center. If the coils were warming up faster than the core due to their large endwinding surface area, then this measurement point (in axial center) would have the smallest temprature differential between winding and core

Also, core may have slight tendency to warm from O.D. inward (assuming majority of heat is transferred from core to frame to ambient), which leaves the measurement point near radial and axial center of stator as one of the coolest parts of the motor during the critical warmup transient. On the other hand, if wind is blowing through an open motor and cooling from inside out where we get the reverse effect.

I’m not quite reaching a conclusion on the question of core vs winding temp, just noting some more aspects to consider (still mulling). But I’ll sign off for now since I'm probably dragging things off track.


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(2B)+(2B)' ?

 

[waross]

I am used to a warm case. The case, the windings core and the space between the core and the case are all raised above ambient temperature. It is hard to quantify the effect at any one place. But, if the case is quite warm, I am happy.

Bill
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"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Guys,

Thank you for that very friendly and informative discussion you shared with us. LPS for both of you.


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If we learn from our mistakes I'm getting a great education!

 

[mikeengurs]

Thanks guys for the Valuable information!