1
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ Could you ask a specific question? With a question mark? Its kind of hard to figure out what your asking. Also is this a thermal or electrical resistance question? Because it seems like a thermal question which means it should be asked somewhere else. \$\endgroup\$ – Voltage Spike Aug 16 '16 at 16:50
  • \$\begingroup\$ If you think about 200A car jump leads and that they are not rated for continuous use, might you want to revise your design? Maybe engineering.stackexchange.com would be a better place for your question, as there are several other non-electronic considerations I would bring up. \$\endgroup\$ – Andrew Morton Aug 16 '16 at 18:34
  • \$\begingroup\$ Sorry about any confusion. So how many square inches will be required to have a good contact at 30v, 200 amps without generating a significant amount of heat? \$\endgroup\$ – R Mck Aug 16 '16 at 19:37
  • \$\begingroup\$ Unless someone has relevant experience it's going to be hard to answer this without either testing mock-ups or some pretty involved simulation. Ti is high resistivity and low thermal conductivity (it's actually used as a thermal insulator in some contexts), so examples using copper are not particularly relevant. My initial thought would be a toggle clamp and some copper bars to spread the contact area and heat. \$\endgroup\$ – Spehro Pefhany Aug 16 '16 at 19:47
  • \$\begingroup\$ So the contacts between the rack and the saddle will be your ball-nose spring plungers and the saddle's teeth? Fair warning If you're pushing 30V @ 200A you have a lot to look out for. What if the connection isn't great? Pushing that much current you stand the chance of welding the saddle to the rack. \$\endgroup\$ – jfri2 Aug 16 '16 at 23:14
1
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ Thanks for the info, the sphere/ ball is spring loaded and will be pushing against the opposite side that has more of a teeth appearance. I can adjust the surface area in order to get good current transfer. \$\endgroup\$ – R Mck Aug 17 '16 at 12:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.