[ARC5] ARC5 CW Question

[John Watkins via ARC5]

I still have a few of the crystal can relays from the Apollo program, 28 and also some 12V.  Very reliable relays.  Collins also used the double anode zeners on them.

John WD5ENU
Sent from my iPad

On Jun 23, 2014, at 11:27, Mike Hanz <aaf-radio-1 at aafradio.org> wrote:

> On 6/23/2014 11:46 AM, w4thq at cox.net wrote:
>> The Apollo program during the 1960's and 1970's had complex relay logic in the control systems of both the launch vehicle and ground support equipment.  Because of RFI-EMI problems, NASA required double-anode zeners across all 28 volt crystal-can relays.  We found this approach was effective.  We also discovered that the back-emf would "ring" and was not just one spike.  The drop out time was not significant in our application so I don't remember what it was exactly.
> 
> Yup, we also used them on the relays that were installed in nuclear weapons back in the 1960s, and for the same reason.  Like your Apollo app, they were not used in circuits where drop-out time was critical either, and cost was no object.  I designed a couple of automated relay testers for the nuke folks that examined every aspect of a relay - coil inductance, coil and contact resistance, pull-in time, drop out time, contact bounce time of every pair of contacts, etc.  They found that once these relays had been hermetically sealed, variations of more than 5% indicated higher probability of failure in life testing, so those were rejected.  I still have a couple of those around here somewhere - they worked fine in my little home projects for years, but there are some places where you don't want to gamble.
> 
> - Mike  KC4TOS
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