[TowerTalk] cleaning relay contacts ?

[Leeson]

I think the limited DC arc is the cleaning mechanism, but it would be 
good to give AC a try. A typical rig relay failure point is the RX side 
of the TX-RX relay, which is often available from the external connectors

Dave.

On 2/17/26 10:04 AM, Richard (Rick) Karlquist wrote:
> I am wondering if it makes sense to use 60Hz AC for the wetting current, 
> to avoid pulling an arc when the relay opens.  With AC the ARC is 
> extinguished in at most 8.3 msec.
> 
> 73
> Rick N6RK
> 
> On 2/17/2026 9:10 AM, Leeson wrote:
>> Many years ago, Dave Pruett, K8CC (SK) was working for Chrysler-Jeep, 
>> and he mentioned to me that auto manufacturers specified a minimum 
>> current to maintain the contacts in every switch, relay or connector, 
>> typically 10 mA. Without this current, there is potential for surface 
>> oxide or sulfide to develop on the contacts, resulting in a failure 
>> and safety risk.
>>
>> He told me those with a maintaining current level were termed “wet 
>> contacts” while those with too little (or no) current were called “dry 
>> contacts.” This came back to mind as I’ve recently experienced a spate 
>> of relay and connector failures, all of which were situations without 
>> a “wetting current” (also termed “fritting current”).
>>
>> I refurbished my old IC-730 for my grandson who recently upgraded, and 
>> both the T/R relay and the preamp relay weren’t working on receive. 
>> ICOM’s bulletin shows how to add resistors to provide a wetting 
>> current for the preamp relay, and I made a similar fix for the T/R 
>> relay. Then I had a failure in my remote antenna rotating system, 
>> which I finally traced to a dry contact failure in the RJ45 connector 
>> on the cable that included a wire to the solid-state relay that 
>> controls the rotator primary power. With the dominance today of CMOS 
>> circuits that don’t need input current, it seems this problem has 
>> become more common with control circuits, as well.
>>
>> Cleaning the contacts with contact cleaner or a mild abrasive can 
>> temporarily fix things, but the problem can return without a real 
>> wetting current. In addition to providing this small current through 
>> resistors, there is a suggestion to discharge a capacitor through 
>> relay contacts on closing. Some relays have wiping contacts, which can 
>> help remove surface contamination. Apparently, even 1 mA is enough to 
>> do the job. I hope this info can be useful.
>>
>> Online references include these:
>> “Wetting current,” https://en.wikipedia.org/wiki/Wetting_current;
>> P-T de Boer, PA3FWM, “Relay contacts and ‘fritting’"
>> https://www.pa3fwm.nl/technotes/tn17a.html;
>> “Wetting Current,” 
>> https://resources.pcb.cadence.com/blog/2023-wetting- current;
>> D. McCarty, “Wetting or Sealing Current,” https://www.isemag.com/ 
>> columnist/article/14266765/wetting-or-sealing-current.
>>
>> For the ICOM upgrades, see A. Copland, GM1SXX, “IC-730_relay_fix.txt, 
>> “ www.f6hoy.com/wp-content/uploads/2022/01/IC-730_relay_fix.pdf and 
>> "Preamp Relay Circuit Modification for IC-730" on mods.dk.
>>
>> Dave, W6NL/HC8L
>>
>>
>> On 2/17/26 6:40 AM, Jamie WW3S via TowerTalk wrote:
>>> I seem to recall someone mentioning a way to clean relay contacts by 
>>> applying voltage ? Looking for a way to try to clean up some sealed 
>>> relays in a 2x6 antenna switch
>>>
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