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Wetting current and CW paddles

What is wetting current and why worry about that when using a CW paddle ?

Do you sometimes have hard time to get your paddle to follow your fingers or do you need to clean your paddle contacts often to get a prober CW.

Wetting current can be your problem.

 

During my work with programming a new keyer, I did found a very interesting issue.

The base for the new keyer was a stm32 board, and I did use one of the input pins and the internal pull up resistor.

After some minor problems with debouncing a schurr paddle I did found my good old bencher, and put it on my keyer project..

IT DID NOT WORK AT ALL .....

After some thinking I did measure the resistance over the contact set on the 2 paddles and there was a "big" difference - The bencher was higher than the schurr.

After some more thinking I did realize that the current over the contact had to play a role and google was my friend.

https://en.wikipedia.org/wiki/Wetting_current

After reading this I did mount ekstern pull ups on 200 ohms in my new keyer and BOTH PADDLES WORK LIKE A CHARM !!!!!!!

NO CLEANING NO NOTHING ....JUST PULLUPS ON 200 OHM ...

It means that the current over the contact set is very important.

I did try to find information on google but nothing say what the "right" current is and how to calculate.

But if we do look in one omron data sheet https://omronfs.omron.com/en_US/ecb/products/pdf/en-d3v-01.pdf we do find very good and useful information

They say that even for GOLD contact you do need to have at least 5V and 1mA

On my new keyer I did measure the current over the contact and it was 16 mA ..

That explain the problem because a internal pull up is typically 50k and then the current with 3,3 V are very limited...

Now it was very interesting to see which current different rigs did use.

It is very easy ...just plug in a jack and key with a mA meter ...on the picture you can see I do measure the FTDX101D FRONT jack...

 

As you can see in this table I get some VERY interesting results and compared to OMRON specification there is a issue here.

For sure I will never use the internal keyer again because of the way they did construct the rigs - even my GOLD contacts from Mr. Bengali are not good enough for this limited current ;o)

My new keyer do work VERY well and you can find all information here ...link will come in short time

If you measure the wetting current on your rig OR your keyer please do send me a mail on hjh@skovholm.com and I will put your measuring in the table you see here.

Thanks to my good old friend Jørn Olav OZ8RW for some good inspiration regarding this topic.

Links with good futher reading

https://pickercomponents.com/pdf/application%20note/Relay_Contact_Life.pdf

https://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1988/in88098.html

Here you will find some of the mails I did get ..Thanks 

 

 

 

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