WETTING CURRENT IN CONNECTOR

No. Hopefully a high contact force, hermetic bond is "guaranteed" as the pin and socket slide together.

But you need to select the correct connector, correct pins and sockets and correct plating for your application.

This 10mA "minimum" is someone's random rule of thumb.

As currents get smaller, the ability to tolerate contact resistance increases.

If the switch cannot perform adequately for lower currents, it's either badly designed or badly constructed.




TTFN

I'd never heard the term "wetting current", but it seems perfectly appropriate. Last time I checked, and it was a while ago, gold crosspoint switches were rated at "2...20mA". I.e., subtly not guaranteed to be 'closed' at currents below 2mA.

I don't recall seeing minimum currents in connector specs, but they should be buried in there somewhere, at least in the fat connector catalogs that the reps don't like to give away.

Sorry, I don't believe in hermetic bonds made in air at room temperature, especially not in connectors, especially not in pin and socket connectors.

Coupla milliamperes in a benign environment with a short warranty, sure. But putting a high impedance signal through a connector is just asking for trouble, IMHO.






Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

A gas tight connection is quite common. Wire wrap with silver plate still works after significant exterior oxidation.

Lots of in-circuit switches operate at very low currents. A 10k pullup can only source 500 uA.

TTFN

In my application there is a wetting current of 150uA. And I think it could be a lifetime problem but I cannot guarantee.
I'm using a header connector of 0.635mm2.
Do you know if there is any formula or something like that which give you the minimum wetting current depending on the connector or terminal type?
The thing is that the product is already in production. For the next ones we are going to change to gold plated terminals but for the ones that are on the market !!??

Thank you for your help!

I would think that it would have been obvious by now that you are attempting to fix a purely mechanical problem through this "wetting" current"

What if the answer was 1 Amp? Would you seriously redesign or modify your circuit to dump 1 Amp in a microamp circuit?

Bad contacts are either bad mechanical design or bad mechanical fabrication and should be corrected mechanically.

TTFN

150ua into an input impedance of what?
wetting current in a switch and contact resistance of a conector are two different things.
if your input impedance is high enough the contact resistance won't matter unless it becomes somehow contaminated.

(kindof like everything electrical on a ship)

I do know that high current miniature relays with cadmium alloy contacts are unreliable when used as inputs to sensitive low voltage low current electronic circuits because there is insufficient energy in the circuit to burn through oxide coatings or some type of film that developes on the contacts. We found this out the hard way.

Jeff

The real application is an input comming from a switch connected to battery (12v). This switch has enough weetting current. But the input of my module has a 80Kohm pulldown resistor. I cannot decrease the resistor because this would increase the current consumption.
The thing is: Is it really a problem for the connector?
Can the connector become contaminated over the life making the contact resistance to increase because of the low current?

Antonio

Are you asking about connector or switch problem?

A connector's wiping action from the contactor spring load should be enough to clear out most oxides and some contaminants. Again, this is a mechanical problem. If there is a contaminant issue, there should be seals, etc. to reduce or eliminate the contamination.

Once the connector is mated, the contact area should remain electrically conductive. If not, again you have a mechanical problem. The connector should be protected with seals, etc.

TTFN

The real application is still something of a mystery to me.

Is the circuit in question:

- supplying power from your module to charge the battery?

- supplying power from the battery to run your module?

- intended to monitor the battery voltage?

- intended to detect closure of the switch?

What life do you expect the system to demonstrate? How do you define its end of life criterion?

None of that is a problem _for the connector_.

But connectors do change with age, with mate/demate cycles, and in response to their environment. Note especially that 'wiping action' only cleans the connector when its parts are subject to relative motion, and the connector may change over time, independent of mate/demate cycles. Look up 'tin plating'.

Somebody, e.g. you, needs to evaluate/ predict/ analyze how the _system_ behaves as the connector impedance changes.

Then the connector impedance that your system can tolerate over its entire lifetime, minus some cushion for comfort, becomes part of your selection spec for the next generation connector.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

If you have ever worked with old cars (especially those blessed by Lord Lucas, the Prince of Darkness) you will know that the longevity problem is chemical more than mechanical. Oxidation, often helped by galvanic action is the most common problem (followed a long way behind by vibration and contamination.)

Perhaps you can solve the lifetime/longevity problem can be solved by the use of an anti-oxidant conducting lubricant like PFPE or PFPE-urea grease. Hope this helps, derek

The application intends to read the switch state. The switch is connected to two modules (one of them is my module).
The switch has enough weetting current (specified 10mA) because the second module has a pulsed 1Kohm pull-down resistor (10mA pulsed).
Sw
Bat__o/o_____
|
>
< 1Kohm
>
|
-
Q1 |-
-
|
---
But my connection between the connector and the header?? That's the question.
I've asked to the supplier of the connector and they said they had never heard about the words 'weetting current'.
I don't see why the connector scenario should be different than the switch. If a switch needs a weeting current to clean the contacts, why the connector shouldn't?

My input can tolerate switch contact impedances very high (i.e. 10Kohm) but I think it could not be enough.
If there is an oxidation of the contact the process could be exponential. If there is oxidation the current through the contact is lower, as lower the current as more oxidation appears and .....