The permanently attached Barco ICP battery

[Harold Hallikainen]

The issue is contact fretting. I had a large page on the USL Engineering Wiki devoted to the issue. There was a graph showing contact resistance versus time for several types of contacts. Nickle on nickle was among the worst while gold on gold was the best. Contact fretting is an issue when a contact carries very low current. It is why switches and relays have minimum contact current ratings. It is why telephone companies run "sealing current" on local loops even if DC is not required on the loop (Plain Old Telephone Service uses DC to power the telephone and detect on-hook, off-hook, and dial pulses. DSL does not need the DC, but telcos still run DC as a sealing current to maintain the quality of splices). The CMS and similar products have a battery current of about 10 uA. That is not high enough to eliminate fretting, which is why I suggest gold on gold contacts. That 10 uA powers the security chip that holds the private key, runs the real time clock, and detects tamper switches and temperature extremes. The tamper switches also have a contact fretting issue. In the latest CMS design, we increased the tamper switch current to several mA when main power was available to "seal" the switches, then drop to a couple uA when main power was not available. Contact fretting was also the cause of the "white screen" issue on the JSD-100. Though gold contact connectors were specified, one run used a connector on the front panel cable that did not have gold. Unplugging it and plugging it back in would solve the issue for several months. Coating the contacts with Cramolin or Deoxit ( https://caig.com/ ) makes the contacts last even longer, but not as long as gold on gold. Finally, the CCH-100 has a cable between the power supply and the glasses that has 2.5 mm TRS connectors on each end. In the prototypes, we used tin plated connectors. They very quickly became intermittent. We switched to gold and had no problems.

It does not take much gold to solve contact fretting problems.

Harold

[Mark Gulbrandsen]

Nothing a little De-Oxit treatment wouldn't cure. All the contacts I have treated with it in the past in the past have never had to be re-treated again.

[Randy Stankey]

At Airborn, if a customer is concerned about fretting and/or oxidation, they can order their connectors with silicone interfacial seals.

The seals keep out oxygen and moisture but they also reduce vibration which can cause fretting and other problems.

If a customer wants to use De-Oxit or some other lubricant/protectant, they can do that, themselves. We don't supply connectors that way. It's not mil-spec and we have to go by the book.

You should see some of the contacts that we use. Most of them are standard pin-in-socket types but there are a few that are just crazy looking.
I wish I could show you pictures but I'd be fired in a heartbeat if I did that.

Yes, I understand that current plays a large part in this issue. My job is to put things together. I only get into discussions like this at work when people start saying things crazy things such as "Gold is the most conductive metal." No, it's NOT! It's only the THIRD most conductive metal behind silver and copper.

Where gold has something like 40E6 S/m conductivity (in standard conditions), copper has something in the high 50's range and silver has approx. 60.