Electrical – Calculating electrical contact surface area

contactcurrentresistancetemperature

First off, I am no electrical engineer: I am a mechanical engineer. I am making a saddle (holder for the rack) for contacting to a plating rack for anodizing. We are a small plating shop and I figured I would ask to see if anybody would be willing to help me out. The rack material is made of titanium because it is light and easy for an operator to move around. The saddle can be made out of stainless steel, aluminum, or brass. This is an image of the saddle I am thinking about using. In the two smaller holes I will be adding Ball-Nose Spring Plungers (http://www.mcmaster.com/#3408a551/=13r1zel) to create the pressure and hopefully remove any oxidation that may have formed.

This is an image of the saddle I am thinking about making. In the two smaller holes I will be adding ball-nose spring plungers (http://www.mcmaster.com/#3408a551/=13r1zel) to create the pressure that will hopefully remove any oxidation, when the rack is pushed/slid against the teeth.

Our DC power supply has a max output of 30V at 200 amps. I need to know how much surface area of the saddle will need to be contacting the rack (not shown), in order to get good contact and not overheat the rack. I would like the operator to be able to pick it up with bare hands after 90 minutes of plating. Assuming no heat is generated from the plating process.

So how many square inches will be required to have a good contact at 30V, 200 amps without generating a significant amount of heat?

Any help would be appreciated.

Best Answer

This is a fairly sophisticated contact resistance problem. If I understand, the ball will be making the electrical contact. A sphere has very poor surface mating against a flat. That being said, we make high voltage/high current relays up to several hundred amps and the moving contact is made from rod stock. Similar to a sphere but more contact area.

With a 1" diameter x 1/2" length we get 200A continuous and about 5000A momentary. The spring return is less than 9oz but the contact PSI is probalby very high. I'm not sure how to relate the 2 surfaces.