[Amps] Automotive Relays,bad eng.

[Jim Thomson]

Date: Sun, 08 Aug 2010 10:44:45 -0400
From: "Joe Subich, W4TV" <lists at subich.com>
Subject: Re: [Amps] Automotive Relays


 > Currently using an RCS-10, which can have up to 7 relays in the
 > RF path.  Will be interesting to see how it holds up.

Since the relays are arranged in a "tree" (one feeding two, each
of which feeds two more) there are always three relays in line to
each antenna.  See: http://ameritron.com/man/pdf/RCS-10.pdf

73,

    ... Joe, W4TV

## per the manual, there is exactly 3 x relays, nose to tail,  in the  circuit for any given ant.
That means BOTH the RX + TX  on some ports,  is passing through NC contacts....that's a no-no..esp
with mech relay's in an outdoor environment.  Strike-1    

## the RCS-10  will handle 8 [eight] ants.  They used a total of 7  relays do accomplish this. 

## NONE of the 8 ants have their center conductor's grnded, when not in use !  More fubar.  Strike-2 

##  A better technique would be to use 8   DPDT  relays.  Parallel all the contact's.  Now you have some redundancy. 
Each ant port goes to the COM of it's own, dedicated relay.  NC contact goes to grnd buss.  NO contact goes to 
hot kw  TX/RX  main input buss.  

## Ok, now with the above config,   ALL DE-energized relay/ant port's have their center conductor's  grnded...and right
at the top of the tower.   NO ant port ever gets connected to the input  via NC contact's !   For added measure, you could
add one extra SPDT-NC  relay, and wire it between grnd + INPUT connector.  Then during any thunderstorm activity, and 
all  9  relay's  DE-energized, not only are all 8  ants  grnded at top of tower, but the input is also grnded..at top of tower.  A gas
discharge tube on the input side of the box should also be used. 

##  the above box is how my Array solutions 20 kw rat pack  came wired.  They used DPDT-20A relays, with 20A contacts,
and all contacts in parallel.  10 kv between any contacts, or contacts to armature/grnd.   The 7-16 Din connector's  I asked for,
have a 4.5 mm gap between OD of the 7mm  female inner tube and  the 16mm  ID of the outer tube. [16-7= 9mm.  9/2=4.5mm]
4.5mm = aprx 6300 v  break down.    You can get em in up to 12 positions.  This box I have has no pc board traces at all.  They
used 3/4"  wide Cu strap for both the NC  grnd buss, and also the NO  hot buss... and  5/16"  spacing between em.  This results
in a  50 ohm strip line.  Flat swr from 160-6m.   Mine came in a die-cast al box.

##  I added up what 7 connector's + 6  relays would cost, box, etc, and decided this was one item I was not going to hb  for a change.
There is no reason why you couldn't hb one of these things. I have also seen them using P+B  DPDT power relays, with 30A contacts,
again, with all contacts in parallel.  To eliminate/minimize any contact  issues,  I re- silver plated all the contacts with the cool-amp goop.
I then apply a thin coat of ..'conducto-lube'  to all contacts.   That stuff is just pure silver powder, suspended in grease.
    http://www.cool-amp.com/    I also had all the cu strap inside the box  silver plated.   

I use 2  resistor's in parallel, to add heat inside the box. [ gold/metal finned dale type], again for redundancy, and also installed a bag
of desiccant [silica gel].  The  resistor/silica gel  idea is also used on my nema box's, used for other stuff.   This is as good as I could
get it to my liking.   Another method is to use  SPDT  vac relays..instead of DPDT mech relays... like  Gigavac GH-1  G-2... or 
Jennings's  RJ-1A / RJ-2B / C. ..or kilovac eq.    I use  vac relay's  for all the BIP/BOP  box's I design for friends.  Then they are
110% bullet proof.  There is no reason a SPDT relay [with all contacts in parallel] would not work  for a simple BIP/BOP box. 
We gave up on the top/bottom/BIP/BOP circuit..and just use the BIP/BOP  config.  The BIP/BOP box's  I cooked up use a 
simple  LC config,with just a mess of NPO caps to grnd on the input... and a series CU tubing coil to output.  The LC box is used
for  any 2 stacked yagi  set up.[25 ohms output]... and also the  3 x yagi setup [16.67 ohms output].   This is for monoband ant's only.
 BIP/BOP box's  used only on 40m and 6m..in most cases. 

later...... Jim   VE7RF