Non-Copper Ampacity

[Eltron]

O.K. I've been all over Hell's creation on the web looking for a straight forward equation for this, but either I'm inept or impatient (I could also be both if you ask my wife...)

I am trying to determine the ampacity of a titanium current collector. I know the ballpark for copper is ~2A/mm^2, and there is a plethora of other info out there for copper and aluminum conductors. I just can't find anything for other metals.

The electrical conductivity of Ti (.0234) is about 1/30th that of Cu (.596). Something doesn't feel right about just doing a ratio to compare the two.

So, can someone lead me down the path to enlightenment. I'm looking for some equations or general "rules-of-thumb" for this type of calculation.

Dan

http://www.eltronresearch.com

 

[dpc]

You have to determine how hot you will allow the titanium to get and its heat transfer characteristics. Obviously you have to stay below the melting point. If this is insulated, you have to consider the temperature limits of the insulation.

The ampacity of a copper or aluminum conductor is directly related to whether or not it is a bare conductor, ambient air temperature and how it is installed. The ampacity tables are a combination of the physical properties, thermodynamics and practical experience. It won't be quite a simple when dealing with a non-standard conductors. But the heat generated is directly related to the resistance, so that can be calculated. The rest is not so simple.

 

[Clyde38]

Good advice dpc... There is much more to the "ampacity" of a conductor than just the conductor material itself. There is some help in "The Standard Handbook for Electrical Engineers" I've attached a spread sheet that may be of help.

 

[Clyde38]

sorry, the equations will not show unless you have ExcelCalcs. Here is version that will display....

 

[Eltron]

Thanks, guys. I know that the temperature of the insulator matters. So does the shape of the conductor, melting point and the skin effect. My application will essentially be a bare bus bar that is in constant contact with coolant. I don't need to be too fancy about it, either.

I'm just looking for some equations that I can plug the specs for my material into and churn out an approximate current that I can pump through the bar before it destroys my system. I'm just not finding them for anything except copper.

Clyde, it looks like that spreadsheet is for copper only. Am I reading it wrong?

Dan

http://www.eltronresearch.com

 

[Clyde38]

Yes, mainly for copper. However, constants (a) for Copper, Aluminum, Platinum, German Silver, Platinoid, Iron, Tin, Alloy (2Pb-1Sn),and Lead were developed by W.H. Preece for the formula I=ad^3/2. The upper left formula by I.M. Onderdonk is for the fusing current-time for copper. You may be able to substitute the melting point for other materials for the melting point for copper (Tm). I've never investigated.

 

[Eltron]

I've figured out a semi-non-convoluted way to determine what I'm looking for.

1. First calculate the resistance based in your geometry and the resistivity of the conductor material.
2. Then you can determine the power you're dumping in based on the resistance and the square of the current.
3. Then you can determine the heat added from the mass, specific heat of the material, and delta T. This will give you an output of Joules, and you've already got power (watts=J/s).
4. This will let you calculate the time it takes to to raise the temp by delta T.
5. If I do the heat-added calc on my coolant and set the two equal, I should be able to get in the ballpark of an equilibrium temp with some fudging here and there.

I just don't know why there isn't more info available on other metals besides the two big hitters. Anyway, I think I got the info that I needed. Thanks for the input, guys.

Dan

http://www.eltronresearch.com