# What is the heat dissipation for enameled wire?

#### ballsystemlord

Joined Nov 19, 2018
37
Hello,
One of the (many) things I've never done in electronics is windings. I wanted to do a couple to gain experience. The problem is that although I can calculate the resistance of the copper wire and the amount of power that will be dissipated I'm uncertain how much of the heat the wire can dissipate.
This is totally a learning experiment. I intend to try a few different designs and will have to rewind a few times I'm sure. I'm in the concept stage so I don't have any specifics nailed down outside of:
1: One is going to be a generator and the other a motor.
2: They will be about 3in in diameter by 4in deep.
3: They're going to be low voltage DC. Depending on what the trade-offs are 3v - 24v.

I tried looking online at some listings for enameled wire, but the sellers don't list the values and it will of course vary depending on if I have a fan built into the motor which I'm not planning on, but I might end up doing. I'm also aware that if you pack the wire closer together then it will have to conduct the heat to the outer layers.

If there's a book (not in the $100s please), you'd recommend, I'm listening. What is the heat dissipation for enameled wire? How do I calculate the correct wire size for a motor/generator? Thanks #### dl324 Joined Mar 30, 2015 9,332 Heat dissipation shouldn't be a factor. You size the wire for the current so it doesn't heat significantly. #### shortbus Joined Sep 30, 2009 7,245 Not all "magnet wire" is the same. Many motors are wound with high temp double insulated type wire. By double insulated, I mean they have a second layer of varnish, or what ever is used on it. Most magnet wire is only single layer. http://www.magnetwire.biz/motor_wire.html #### AlbertHall Joined Jun 4, 2014 8,818 I seem to remember a figure of 1000A per square inch cross section for wire in a coil. #### oz93666 Joined Sep 7, 2010 701 This is a complex issue ... a big factor is air temperature ...also some of the heat will be conducted away in the iron core , so the configuration of this is important ...good air flow helps a lot ... so many factors I think it has to come down to experiment .... then again if something works OK for 10 hrs , perhaps the varnish will decay at that temp and after 20hrs a short will occur Thread Starter #### ballsystemlord Joined Nov 19, 2018 37 Heat dissipation shouldn't be a factor. You size the wire for the current so it doesn't heat significantly. Heat dissipation is always a factor AFAIK. Look at any professional motor, say 1HP. There's a fan built into the motor. For dissipating the heat. Unless it's a submersible motor in which case it's cooled by the water around it. (EDIT: Fan motors don't have a motor built into a fan in all cases). Now I can derive values for the resistance from the wires size. I can estimate the length depending on my design. I can guess how much current I'll be running through it. But I don't know how much heat the wire dissipates. As for the temperature, in my area it gets up to 44C. I was hoping to try all combinations: Electromagnet armature and magnetic stator. Electromagnetic stator and magnetic armature. Electromagnetic stator and armature. #### MaxHeadRoom Joined Jul 18, 2013 19,449 When I did my stint in the motor winding dept, we used hi-temp enamel wire and after a re-wind, the stator was dipped in varnish and then oven baked. Any motor winding shop should be able to supply you. Max. #### dl324 Joined Mar 30, 2015 9,332 #### Janis59 Joined Aug 21, 2017 906 No one is doing like that. It is equi-uninteresting to know what a resistance have Your winding and what is the area except the CERN - level machinery. Normal average trafo uses the normal average FACTOR alrady containing all those thermal impacts plus minus 20%. Thus apply the wire cross section = i(Amps max) / J. Where current density J (A/mm2) is for 5 minutes work and hour cooling the 5 A/mm2; for around 200C work 4 A/mm3, for about 120C will be 3 A/mm2 and for just not ever heating at all conditions the 2 A/mm2. Thats all one have need to know. Thread Starter #### ballsystemlord Joined Nov 19, 2018 37 @Janis59 Thanks! As others explained (2x because I'm hard of hearing ), its about sizing according to amperage. You provided the equation to size by amperage. EDIT: You should reformat your reply though, it's a bit confusing the way you wrote it. I consider this question answered. #### KL7AJ Joined Nov 4, 2008 2,224 Hello, One of the (many) things I've never done in electronics is windings. I wanted to do a couple to gain experience. The problem is that although I can calculate the resistance of the copper wire and the amount of power that will be dissipated I'm uncertain how much of the heat the wire can dissipate. This is totally a learning experiment. I intend to try a few different designs and will have to rewind a few times I'm sure. I'm in the concept stage so I don't have any specifics nailed down outside of: 1: One is going to be a generator and the other a motor. 2: They will be about 3in in diameter by 4in deep. 3: They're going to be low voltage DC. Depending on what the trade-offs are 3v - 24v. I tried looking online at some listings for enameled wire, but the sellers don't list the values and it will of course vary depending on if I have a fan built into the motor which I'm not planning on, but I might end up doing. I'm also aware that if you pack the wire closer together then it will have to conduct the heat to the outer layers. If there's a book (not in the$100s please), you'd recommend, I'm listening.
What is the heat dissipation for enameled wire? How do I calculate the correct wire size for a motor/generator?
Thanks
MWS has very detailed specifications for all their magnet wire products.
https://mwswire.com/

#### Janis59

Joined Aug 21, 2017
906
@Janis59 EDIT: You should reformat your reply though, it's a bit confusing the way you wrote it.
Sorry, I am speaking only at 7 languages, and English yet is one of my most used it isnt the mother tongue. When I write rapid and not overread it, I may apply the wrong sequence of words or mistyping of some letter. And my keyboard is sure too old thus some letters are not jumping out after been pushed. Try to show me with finger.

#### ballsystemlord

Joined Nov 19, 2018
37
@Janis59 Permit me then, to do it for you for posterity. Please read over what I've typed below to ensure it's correct.
Utilize the normal average FACTOR already containing all those thermal impacts plus an additional -20%.
Wire cross section = i(Amps max) / J
Where current density: J == (Amps at given run time/mm2)
For 5 minutes duty cycle and an hour cooling it's 5A/mm2.
For around 200C work continuous duty cycle 4A/mm3.
For about 120C continuous duty cycle it will be 3A/mm2.
And for just not ever heating under all conditions; 2A/mm2.

As a bonus, here's an example for future readers:
Code:
5 (5min run with 1 hour cooling)

__________________________ == 5

1mm2

10 (i is some arbitrary number of amps you chose)

________________________________________ == 2

5 (This is J)

2 (This is the FACTOR) * 0.8 (The plus an additional -20%) == 1.6mm2
So, your cross section in mm2 would be 1.6.

#### Janis59

Joined Aug 21, 2017
906
Agree!
Or other words - never try overstep the 3.0...3.5 A/mm2 but better keep into 2,5...3.0 A/mm2.
Here mm2 means pure copper cross section A=pi()/4*D^2.

When wire is laying in bobbin there happens one another important factor, the Pack Factor.
It is far less accurate but anyway - in idealistic scenario with no gap no crossing obstacles it will be "bobbin area filling with copper" factor of 0,78 (=pi()/4). But at practice it never is higher as 0,5...0,6 for very thick wires (1 mm and above); 0.35-0.45 for average wire diameters like 0.4...0.5...0.6 mm and is so bad as 0,2-0,25 for wires 0,1...0.25 mm.

Surplus to said, the insulation layers paper thickness must be added, but not a wire isolation what lays into this factor.
My experience is that every layer paper isolation is completely unneeded except the multiple kilovolt constructions. Normal mains trafo may apply isolation layer once at each 50 Volts (about), as the lack isolation have limitation around this figure. Thus, 220V bobbin will have a 4 or 5 sections separated by thin paper or film.

Then roughly estimating the max possible power obtained from certain steel core, the thumb-rule may be applied turns / Volt=50/A(cm^2) what is true only for 50 Hz and 0,8 Tesla. Therefore for another f just apply the anti-proporcion factor (60 Hz will be (50/60)=0.833 less turns, and for more qualitative cores the up-line figure 50 may be substituted with 45 for sure, sometimes 42-43, and in very few cases with even 38, however then will happen the abnormally high stand-still current i(0).

Reversing this factor feets-up&head-down (ie Volts per turn), multiply it with core window area half (but in mm2), apply the packing factor and current density factor in wires J (A/mm2), so get coming out the maximum power of this core.

For example, core area 50 cm2, core window 10 cm2. Then turns pe volt=50/50=1 --> 220 V=220 turns. And Volts per turn =1/1=1 Volt per turn, therefore Power=10 cm2=1 V/turn*(1/2)*1000 mm2*0.35 (=packing factor)*3.0 (=J factor)= 1 kW

#### shortbus

Joined Sep 30, 2009
7,245
Surplus to said, the insulation layers paper thickness must be added, but not a wire isolation what lays into this factor.
My experience is that every layer paper isolation is completely unneeded except the multiple kilovolt constructions. Normal mains trafo may apply isolation layer once at each 50 Volts (about), as the lack isolation have limitation around this figure. Thus, 220V bobbin will have a 4 or 5 sections separated by thin paper or film.
Since this is for winding a motor or generator, how is a paper or film layer added in the windings? Never saw that done before.

Joined Jul 18, 2013
19,449
When I did my motor winding stint, we Always used Presspahn paper insulation it was folded and fed into the slot before the coil winding was added.
Max.

#### Janis59

Joined Aug 21, 2017
906
Yeppsk, I wrote about transformers. However, anyway, it is rather dangerous to fill into window channel a coils, having more than 50 V between wires. Thus, if there is one phase cap motor with one coil, it are winded like transformers, older soviet gramophones had it so, whilst younger having 4 coils automatically has 55 V only. Larger motors of squirrel cage have undoubtly more channels than 4, thus even in the case of 3 phases all is OK. But when more sophisticated windings are takking the place, like many popular varipole motors applied in most of turner benches, grinding machines and even some high-end drilling machines, then in each channel is inevitable to have more than one coil, and those varipole circuitry may produce more than 380 V difference in one channel. Then I seen a multiple U-shape coil separator envelopes staying into steel channel, otherhow the motor lifetime will be too short.

#### Janis59

Joined Aug 21, 2017
906
Wow, presspahn? You use a German terminology, actually spread over many laguages including russian (špan, španner = to press, to squeeze, to hit). However my nation use another term = press-paper or paraffin-paper.

#### shortbus

Joined Sep 30, 2009
7,245
When I did my motor winding stint, we Always used Presspahn paper insulation it was folded and fed into the slot before the coil winding was added.
Max.
But it wasn't used between each layer. And used more to prevent rubbing the wire "varnish" off when winding and from vibration when running than actual insulation.