[Towertalk] sixpack relay problem

[Tom Rauch]

> Privately, I observed that the most likely problem was
> IR drop, or a bad relay. Let me repeat it publicly:

The most common problem (by far) seen at Ameritron and other 
companies that use relays in hard-wired applications is flux 
contamination of contacts.

It's pretty tough to get a high-resistance connection via separate 
control cables. I often just twist wires out in the field, and have 
thousands of feet of control wire! In 12 volt systems, you can 
usually tolerate dozens of ohms of loop resistance in control lines. 
I have systems switching multiple parallel relays reliably at 2500 
feet, just using thin telephone-type wire. I can't imagine a case 
where a 3-foot wire would have enough resistance to cause unreliable 
or "soft" switching. 

Personally, I'd check and clean the contacts. Hopefully they are gold 
flashed, or at least silver plated. You do NOT ever want a high 
current relay designed for switching operating loads, because the 
contacts will make bad connections after time.

Clean the contacts by taking a hard paper like thin smooth semi-gloss 
cardboard (sometime on matchbook covers) and soak it in WD-40 or some 
other cleaner and rub it between the contacts. When you are done 
clean it with 100% pure alcohol or a very light cleaner like Toluene, 
Methyl Ethyl Ketone (MEK), or Xylene.

Tension should be set so the relay pulls in at about 50-70% of rated 
voltage.

Virtually any relay that is working at all, and has not had the 
contacts ate up by switching during high-power operation or arcing 
from lightning, will be 100% repairable using the above methods.

Even brand new relays are subject to flux contamination, so 
replacement should be as a last resort.

I don't know how Jay does the ground return, but I always make the 
ground common with coaxial cable grounds so the shields augment or 
entirely can replace the ground wire.73, Tom W8JI
W8JI@contesting.com