Electrical contacts for moving components - Page 1
Forum section: electronics / projects

author: mbless
author_rank: Regular Contributor
timestamp: May 24, 2023, 03:30:20 pm
content: I have a mechanical linkage system that moves and requires electrical contact at 2 positions. I haven't been able to find an off-the-shelf switch (rotary, rocker, etc.) that will do the job in the space constraint, so I'm working on my own implementation. The movement involves linear and rotary motion, and the electrical requirements are max 50V and 5A for 1 second durations.The current concept uses a ball-nose spring-loaded pogo pin and a flat target. With that, the simulations show I can make contact and there are pogo pins with the current ratings, but my concern is the pogo pin contact area. I can't get perfect alignment where I can use a concave target for more surface area contact, so right now it's a sphere touching a flat surface. That also means I can't use a flat pogo pin since only an edge would touch. (Imagine the pin coming in at an angle due to linear and rotary motion). Does anyone foresee problems with point contact with 5A transmission? Datasheets don't specify the contact area for the current ratings.An alternative that is looking attractive is using rotary switch contacts. The attached images are what I have in mind (sourced fromElectroswitch). They would allow the contact to enter at odd angles and would have a good contact area. I haven't been able to find the actual contacts themselves, so I'm wondering if anyone knows where to source them? Electroswitch calls them of knife switches – double-sided, double-wiping, spring-wiper blades.Thanks for the help!

author: ajb
author_rank: Super Contributor
timestamp: May 24, 2023, 04:25:12 pm
content: Contact resistance between pogo pin and target will depend on a number of factors including head shape, spring force/deflection, target contact material, platings, surface cleanliness/oxidation. Most of those are out of the control of the pogo pin manufacturer, which is why you don't see much in the way of resistance specs for them. This is also why you want different head styles: a single needle-point pin will have higher point pressure and will therefore better punch through surface contamination/oxides on the surface, so are a better choice for boards where the target surface is questionable. But the point tends to leave a small conical divot, which may be objectionable, especially if you're making contact with the same pad repeatedly. At that point, you might be better off with a spherical tip pin and a gold-plated metal target pad, which will be less tolerant of surface contamination but won't damage the pad nearly as much. So it's a bit of a tricky question.I don't think you're going to find a pogo pin good for 5A, mostly they top out at 1-2A each. You can of course cluster the pins for higher currents, but that means more force (all of those springs add up). You might find SMT spring terminal blocks for batteries with more suitable per-contact ratings.Do you really need to handle all of the current via the one contact? Or could you not use the contact/switch to control a relay or transistor to handle the load current?

author: mbless
author_rank: Regular Contributor
timestamp: May 24, 2023, 05:00:31 pm
content: Quote from: ajb on May 24, 2023, 04:25:12 pmIt's not desirable to leave indentations like that. My thought was to use a target designed for pogo pins for durability. And agreed, the current concept specs a spherical tip with flat target.Quote from: ajb on May 24, 2023, 04:25:12 pmThere are plenty of pogo pins rated for 5A+. Mill-max makes them such asthis one #0853rated for 12A with 30oC rise. That one lists a contact resistance of 20mOhm, but that may just be internal to the contact and not contact to target.Unfortunately, I need a mechanical disconnect, and size constraints won't allow for a relay.

author: Gribo
author_rank: Frequent Contributor
timestamp: May 24, 2023, 06:00:25 pm
content: There are high power spring loaded pins, rated for 100A, from QA tech and Ingun. You might want to consider a slip ring.

author: jbb
author_rank: Super Contributor
timestamp: May 25, 2023, 12:55:32 am
content: Err. Do you really need to be making contact? Could you instead run a flexible cable along the moving part of the mechanism?

author: mbless
author_rank: Regular Contributor
timestamp: May 25, 2023, 01:28:19 am
content: Quote from: jbb on May 25, 2023, 12:55:32 amYes it has to also function as an electrical disconnect as well.