R: [AMPS] Relays hanging up

[measures]

>
>Actually, magnetical histeresis causes the core to temporary become a
>magnet.
>In good relays this time is generally a short one and a permanent retention
>is only a matter of mechanical problems or arc soldering between realy
>contacts.
>Concerning the lack of receive and relays this is really caused in most
>cases by high resistance in  the contacts.
>Altought looking strange, which is missing here is the lack of a
>micro-arcing between contacts that serves to remove oxidization.
>Once I saw a tricky method where a limited DC current was set to flow  into
>a receiver relay contacts to overcome the oxidization problem.
>
The Matsushita RF reed relay that we sell uses rhodium-gold contacts.

cheers,  Mauri
>
>----- Original Message -----
>From: Tom Rauch <w8ji@contesting.com>
>To: <amps@contesting.com>
>Sent: Saturday, August 12, 2000 12:03 AM
>Subject: [AMPS] Relays hanging up
>
>
>>
>> I've never seen a DC relay hang up from residual magnetism.
>>
>> The reason is the core material is intentionally a type that does not
>> retain magnetism. If it is magnetized, it will simply magnetize again.
>>
>> The reason most relays hang-up is because they weld into position
>> from hot switching.
>>
>> Lack of receive is more commonly caused by high resistance in
>> the contacts, which is generally caused because the contacts are
>> high current contacts designed to wipe when normal current
>> passes through the contact. Running a 20 ampere relay at nearly
>> zero amperes will almost certainly insure the relay will become
>> unreliable over a period of time.
>>
>> That is a constant fight when using conventional high current relays
>> to switch receiving lines.
>>
>>
>> 73, Tom W8JI
>> w8ji@contesting.com
>>
>> --
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>
>
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>


-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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