Magnet Wire Current Capacity

[Honduras]

I found a chart, but it was for insulated wire.

It lists the current capacity for AWG 30, at 80 degrees C, as 2 amps. Does that sound reasonable for magnet wire? It also doesn't say if that is Max or Typ.

 

[ChrisP58]

In regards to temperature rise, it largely comes down to two factors.

1) How much heat is generated by current flowing in the wire.
2) How well the heat can be carried away.​

Assuming that you're frequency is comfortably below the point at which the skin effect comes into play, the heat generated is mostly I^2*R.

Getting rid of that heat is a more complex activity. A piece of magnet wire in free air can carry more current than an equivalent thermoplastic insulated wire.

1) The insulation is thinner, so it provides less thermal insulation.
2) The insulation can operate at a higher temperature.​

But that is not the only thing to consider. Magnet wire is seldom used in free air. Instead you wind a bunch of it in inductors and transformers. Now you have changed the thermal situation significantly. Each turn is not in free air, but surrounded by other wires that are also pushing heat out. Figuring the current capacity for the winding of a transformer, is basically looking at how much heat x inches of wire will dissipate, then factoring that into the volume of the finished coil.
But remember:

1) The inner layer will be hotter than the outer layer.
2) The resistance of copper increases about .004% per degree C of temperature rise.
3) In a transformer with multiple windings, the heat will be the sum of the heat in ALL windings.

​

 

[throbscottle]

I looked into this recently. The best guidance I could find was manufacturers ratings, which if you are lucky are given for when the wire is wound into a coil - though they don't tend to say what size. The ampacity given tends to be significantly higher than that given for electrical cables, I was surprised to discover.

HTH

 

[chemelec]

When using Magnet Wire in a Transformer, It is recommended to have 700 Circular Mils per Amp.
(A Circular Mil is 1/1000 of an Inch.)
So a 30 AWG wire is typically good for just 143 mA in a Transformer.

 

[throbscottle]

Circular mil - a rather bizarre unit, is the cross sectional area of a circle of 1/1000 of an inch diameter, so just saying it's 1/1000 of an inch isn't strictly accurate. According to Wikipedia, it's equal to 5.067×10−4 mm². As far as I know only the US and Canada use it. Looks like a convenient way to measure area though - we should have a metric version...

 

[chemelec]

Canada is METRIC.
ONLY the USA is NOT Metric.

And YES, This Info is from a USA Wire Chart.

 

[throbscottle]

Oops, sorry! I put too much faith in Wikipedia there!

 

[chemelec]

Canada Converted to Metric in 1971.

As the Saying Goes: "You can't teach an Old Dog New Tricks".
So most Older Canadian People, Still try to use Pounds.
So most Grocery Stores, List Both Prices in Pounds and Kilograms.

Schools here, basically only teach Metric, so eventually the old Pound prices will disappear.
Gas Stations are Only in Liters.

 

[blueroomelectronics]

I still layout PCBs in imperial, old DIP ICs are 0.1". Metric is better by far though.

 

[KeepItSimpleStupid]

Schools here, basically only teach Metric, so eventually the old Pound prices will disappear.
Gas Stations are Only in Liters.

Darn. Can't use body parts for estimating an inch and a foot.

Kilopascals is a very huge unit.

A supervisor once said numbers have to be withing 1-10, OK 1-100. 16 Fl Oz of ketchup follows that rule.

Hospitals and health care settings have basically gone metric with weight and temperature.
Take 36-24-36 --> 91-53-91 just doesn't have the same effect.
Our state tried to have km based roads rather than miles. It didn't work out.

I like the even power of 10 divisions especially for anything scientific. I worked in a research laboratory. It's hard using an English tool in a milling machine.

 

[throbscottle]

And here in the UK we still use a mixture. I just use whatever units are convenient. We buy fuel in litres, but our cars do miles per gallon, people are weighed in lb's and oz's, food is sold in grams and kilo's, and I drill metric holes in pcb's based on a 0.1" grid. No wonder we're confused...

 

[blueroomelectronics]

I thought they still weighed people in Stone in the UK.

 

[Tony Stewart]

It will take an economic apocalypse before the excited states of america gets with the metric program. Meanwhile if mass production of exported products in non-metric dimensions continues, so will confusion. Even in groceries, cost per pound sounds cheaper than per kg and cost per 100g even less.

Even Canada had an epic story of an Air Canada Pilot who miscalculated the fuel on board shortly after Metric conversion error decades ago.
It ran out of fuel and had to coast and land to a little airport in Gimli.

No matter how much better metric is, there is always a massive cost of conversion and education is lacking as it is.

 

[ronsimpson]

cost of conversion

Converting is hard. Working in any system is simple.
If the sign said 100km to the next town and the car odometer said 100km/hr .....simple.
Gas price is (x)/l and the car holds 100l......simple.
Take away all yard sticks and give back meter sticks.....simple don't ask me to convert.

 

[throbscottle]

I thought they still weighed people in Stone in the UK.

Oh drat, yes, that's what I meant. They weigh us down with stones before before flinging us in the lake. 14lb to a stone. Duh!

 

[Honduras]

When using Magnet Wire in a Transformer, It is recommended to have 700 Circular Mils per Amp.
(A Circular Mil is 1/1000 of an Inch.)
So a 30 AWG wire is typically good for just 143 mA in a Transformer.

I think I will use this one. Nice and conservative.

Oh drat, yes, that's what I meant. They weigh us down with stones before before flinging us in the lake. 14lb to a stone. Duh!

I've always wondered how that was done.

 

[chemelec]

Values between 500 and 1000 Circular Mils per amp Can be used, But 700 Circular Mils is normally recommended.

In free air a 30 AWG wire will probably handle the 2 amps.
But if it is Covered in any way to prevent air circulation, it will than Over Heat.

 

[Honduras]

Values between 500 and 1000 Circular Mils per amp Can be used, But 700 Circular Mils is normally recommended.

In free air a 30 AWG wire will probably handle the 2 amps.
But if it is Covered in any way to prevent air circulation, it will than Over Heat.

Which means coated magnet wire, especially when wound multi layer. I think I'll go with 1000 mil for 30 AWG.

 

[Tony Stewart]

AWG30 is around 100 mΩ per foot so 2A is 400mW per foot , which in free air is warm but not smoking hot.
I use this for up to 6W LED all the time using 2A. If you are using it on an array of LEDs in parallel. The series resistance is useful to know of the load and the wire.

A tightly wrapped coil would get hot.

 

[Honduras]

AWG30 is around 100 mΩ per foot so 2A is 400mW per foot , which in free air is warm but not smoking hot.
I use this for up to 3W LED all the time using 2A. If you are using it on an array of LEDs in parallel. The series resistance is useful to know of the load and the wire.

A tightly wrapped coil would get hot.

Good information. Thanks.