Gold plated contacts in salt water

Live? For how long?

DC current will electroplate off the gold, or practically anything else.

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John Larkin Highland Technology Inc

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators

I used to design marine radios in the 1970's and 1980's. I have plenty of experience doing it wrong.

Yes. As John Larkin mentioned, it's dependent on what manner of signal you shove through the connections. The assumption with gold is that you have a "dry" contact, which means no DC. That includes AC signals sitting on top of a DC voltage. For example, one of my less brilliant ideas was to combine the +15v power and signals on the AN/SRD-22 VHF direction finder antenna. There was no immersion test for antennas, but it barely passed the salt fog and salt spray tests due to the DC. In order for it to work, we had to use 50 millionths gold plating. Any less would just disappear. Inside the radio were the usual (now ancient) 0.156" gold PCB edge connectors. The PCB connectors did well, but they too had to be 50 millionths gold plated. It was correctly decided to concentrate on sealing the radio and antenna, rather than trying to make it corrosion proof. There just wasn't anything better than gold.

You didn't specify which ASTM or MIL test you were running. In my never humble opinion, the real problems are how long an immersion test, and whether it is cyclic (dip-dry-dip-dry-dip-dry-etc). Short term immersion is probably not a big challenge. Long term and cyclic, where little things like changes in internal air pressure can pump salt water into the unit under test, are far more difficult. Salt crystals can also creep into cracks in the PCB, under paint, inside devices, and then expand when heated. You may not have a problem during immersion, but when the device is powered on and the crystals expand, you may see some very strange problems.

Good luck.

A gold-plated AK47?

Cheers

Phil Hobbs

I think they took that requirement out of the new NATO carbine spec.

You get what the committee's willing to pay for.....

RL

"Raving Looney"

Salt water conducts electricity so nothing electrical can be immersed in it.

... Phil

Waterproof connector. ITT Cannon makes MIL spec connectors.

Cheers

Careful what you ask for:

The spec says half the test samples should have exposed connectors

When specified batteries shall be tested as follows. Weigh batteries and record their weight. The test samples shall be configured as follows: half in operating configuration (with sealed mating connector attached) and half in with dust cap removed. Immerse the batteries to a depth of not less than 3 feet in salt water substitute conforming to ASTM D - 1141 for not less than 2 hours.

All bets are off then since the battery will generate free chlorine at the anode and gold chloride is moderately soluble once it is formed.

Tell them that to meet their specifications only solid platinum connectors will be good enough (and academic since the batteries are likely to be ruined after 2 hours aggressive discharge in brine anyway).

;)

Reminds me of "Snoopy and the Red Baron".

"He challenged the German to a real dog fight/while the Baron was laughing, he got him in his sights."

_Not_ what you want if you're trying to get guerilla street cred.

Cheers

Phil Hobbs

Or use a sealed connector with an internal switch which cannot be closed without the sealed external connector in place, so there is no power applied to any pin when the external connector is removed, as is commonly done on ship shore power connectors for example. These have mechanical interlocks which prevent the switch being closed without the connector in place and also prevent the connector being removed without the switch being open; the same sort of mechanical interlock could automatically close the switch when the connector was seated if desired. There exist connector manufacturers with experience in this area, but I have long forgotten who they are. An electrical interlock is also a possibility, preferably with power to close the switch provided from the external connector, allowing the use of standard connectors.

What spec? Names and numbers are better than vague descriptions.

How long do you have for the UIT to dry out? Most of the intermittent connections occur after drying.

Kinda looks like an immersion test in fake salt water with maybe DC power through gold connectors. Some clue at to the type and size of the battery and current drain would be helpful.

It probably won't work without additional protection. You don't want to run too much DC through gold or it will electroplate itself to the negative terminal. I've welded gold PCB connectors in place doing that at fairly high currents (about 20A DC).

In fake sea water, the battery current is going to break down the salt water into sodium and chlorine ions, forming various soluble gold salts. If your gold battery terminals turn black, you have a problem. If in a battery holder, the gold salts make a marvelous intermittent connection when dried.

If the battery had bolt on terminals, you can probably survive a 2+ hr immersion test by coating the terminals and lugs with some type of grease, goo, gum, crud, or yuck. Anything to keep the fake salt water from touching the gold. You will still have problems with condensation in any voids (screw threads, washers, bolt holes) as well as capillary action along the interfaces. I suspect that your chosen battery manufacturer will have some experience in such matters. Of course, that won't work with a battery holder.

Good luck.

I helped design and build a prototype VHF marine radio, that operated immersed in salt water. The trick was to use all low impedance circuits. At 12VDC maximum, there isn't going to be much conduction. The most difficult part was that crystal filters of the day (about

To be fair, getting it to work in a tank of salt water was easy compared to keeping it working after it dried out. Of course, that wasn't demonstrated at a boat show. When dry, the salts would crystalize and jam up everything. Potentiometers and switch shafts froze. Turning tuning caps was impossible. PCB's could be removed from their sockets, but were intermittent when reinserted. Dissimilar metals would try to weld themselves together. We won't talk about stainless screws into aluminum PEM nuts. I could hose off the radio in clean water, and after drying, most of the problems might go away.

How about glassy carbon contacts...

Cheers

You're correct of course, but I based my answer in the OP's statement: "When specified batteries shall be tested as follows." Unless he has invented an AC battery, I would think that the DC definition would be adequate. In any case, a dry contact does not switch power, either AC or DC.

Now you've done it. Tonight, I'll probably be re-living my past nightmares and horrors working with pressurized environmental radio enclosures. Visualize painting a NEMA enclosure, with kids bubble liquid, on top of an 80ft radio tower, in a 30 kt wind, looking for leaks.

While pressurized products do work, at least on paper, they are a pain in the posterior to repair, maintain, test and keep things sealed. Putting a battery INSIDE a sealed and pressurized enclosure is really a bad idea if the battery is expected to be charged. Even a gel cell or AGM battery belches a small amount of acid, sufficient to rot everything inside the box. Desiccants help, but not forever. Some radio sites have pressurized Heliax coax and pressurized tower top NEMA boxes for TMA's (tower mounted amplifiers). There's nothing better than climbing a tower with a heavy pressure bottle of dry air to repressurize a leaky enclosure.

Much as I hate it, the de facto field service and automotive method of battery connection corrosion mitigation is to slop copious amounts for grease all over the terminals. Unless someone adds solvents or boiling hot water to the fake salt water, grease should be sufficient for a 2 hr immersion test.

Even dogs deserve to have dreams...

And some dreamers actually do deserve to be called dogs.

Define "survive"; one could almost use metallic sodium..