[TowerTalk] Relay lightening protection

[Michael Tope]

jimlux wrote:

>Kipton Moravec wrote:
>  
>
>>On Fri, 2009-01-30 at 06:53 -0800, jimlux wrote:
>>    
>>
>>>donovanf at starpower.net wrote:
>>>      
>>>
>>>>This discussion of relay reliability and switching speed is
>>>>irrelevant for a relays in a phased array that should never be hot
>>>>switched.
>>>>        
>>>>
>>>The reliability issues in the Tyco ap note aren't tied to whether the 
>>>contacts are carrying current.
>>>
>>>      
>>>
>>Carrying current IS the whole issue. If they were not carrying current
>>then it does not matter how fast the contacts close or open.
>>
>>The goal of the applications note was to minimize the contact arcing,
>>which increases contact life or reliability. It is described in the
>>second paragraph of the second column of the first page. 
>>
>>http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf
>>
>>You do not have arcing if there is no current. So if there is no current
>>then contact speed is not an issue.
>>
>>
>>    
>>
>
>I think they're talking about the "control contacts", while the life 
>issue is the "controlled relay".  i.e. the residual flux making the 
>relay sticky, etc.
>
>
>  
>
Jim,

Did you actually read the app. note? It very clearly indicates that the 
reliability issue is due to contact welding caused when high levels of 
DC current are interrupted in the normally open contacts. It also goes 
on to say:

"Now that we have provided suggested suppression techniques based on 
normally-open contact performance, we must add a qualifying comment 
concerning the normally-closed contacts. When the primary load is on the 
normally-closed contacts (and a small load or none on the 
normally-open), it may be desirable to use a rectifier diode alone as 
the relay suppression (or perhaps a rectifier diode and a lower value of 
series resistor). The retarded armature motion that adversely impacts 
normally-open contact performance will typically improve normally-closed 
contact performance. The improvement results from less contact bounce 
during closure of the normally-closed contacts. This results from the 
lower impact velocity created by the retarded armature motion and has 
been utilized in the past to improve normally-closed contact performance 
on certain relays."

This is a great app. note, but my reading is that the particular 
circumstances for which it applies aren't those found in a RF phased 
array application.

73, Mike W4EF.......