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February 2005

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Subject:
From:
Dwight Mattix <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dwight Mattix <[log in to unmask]>
Date:
Fri, 11 Feb 2005 09:27:09 -0800
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At 11:27 PM 2/10/2005, Ingemar Hernefjord (KC/EMW) wrote:
Think in terms of PRESSURE!


I concur.  I'd add another term "gas tight joint."   In my past
(un)professional life, :^)  I had a lot of experience working on a high
power airborne radar at sea.  The final stage amplifier (1 megawatt
coaxitron piggybacked tetrode/triode tube) had a filament power supply that
provided 900 amps at 1.64VDC.  The braided cables were terminated with
silver plated metal plates.  It worked well as long the joint was kept
torqued together (gas tight).  However, the silver oxidized rapidly when
cable was off for maintenance and had to be polished before re-assembly or
else there'd be unacceptable volt drop.

a recovering sailor,
dw


At 11:27 PM 2/10/2005, Ingemar Hernefjord (KC/EMW) wrote:
>Think in terms of PRESSURE! I learned a lot about this topic years ago
>when I analysed catastrophic failures on relays and connectors. Railway
>connector makers know all about high current contacts, they need
>connectors for 10,000 amperes! Pressure and correct sliding mechanism is
>alfa & omega. Oftenly, they use copper alloyed pins without any kind of
>plating. When the pin and the female meets, the sliding force removes all
>debris and when the mating is fulfilled, the resulting pressure per
>microscopic contact spot is so high that you have an almost gastight
>connection. This is the secret of a successful high power connector. 80A
>does not seem much, but you still ought to consider basics.
>
>Below is a good example on what I mean. These connectors have a spring
>loaded ring that cause hundreds of reliable high pressure microcontacts on
>the pin.
>http://www.multi-contact-usa.com/products/powerline/1
>
>Good Luck
>
>Ingemar Hernefjord
>Ericsson Microwave Systems
>
>PS. Carbon steel pin, not much used as pin bulk material...
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of - Bogert
>Sent: den 11 februari 2005 00:39
>To: [log in to unmask]
>Subject: [TN] Calculate current capacity for electrical contacts
>
>
>February 10, 2005
>
>How does one determine what current can be carried by electrical connector
>contacts to determine capability to carry about 80 AMPs (RMS), low freq
>AC, or DC.
>
>We have an application that uses a carbon steel base metal pin
>contact.  The contact is given a nickel flash, followed by a copper
>plating (to fill in small voids), followed by another nickel flash,
>followed by silver plating.  Does one calculate current capacity from just
>the carbon steel base metal, or does one need to take the plating into
>account?  What formula or chart is used to support the calculation?  If
>the nickel flash thickness is increased, will it impact current
>capacity?  If plating is changed to gold, does that impact current
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>capacity?
>
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