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[Towertalk] sixpack relay problem

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Subject: [Towertalk] sixpack relay problem
From: (Tom Rauch)
Date: Wed, 19 Jun 2002 17:37:46 -0400
> The problem I experience was that while there was voltage getting to
> the relay it wasn't quite enough to effect closure of the relay - in
> my case you could give the box a whap and that would cause the relay
> to close - or as I mentioned - upon inspection I found that when
> energized it took just the tiniest amount of persuasion for the relay
> arm to make the trip to was on the edge - the spring was
> just more than it could overcome..

First, most people just do not understand how difficult it is to use 
large heavy contacts to switch weak signals with any reliability. 
EVERY manufacturer fights that problem, unless they use very special 
relay designs.

In your case, either the supply voltage is too low or the relay is 

It could be, in an effort to have good connections on a large contact 
used for receiving applications, that tension is being set too high 
and now pull-in is unreliable. Or it could be the supply is simply 
too low in voltage.

If tension is increased from manufacturer's settings, then the surge 
voltage needs to be increased. We should always have significant 
headroom on closure voltage, or we would certainly see unreliable 
operation popping up here and there. It is always necessary to have 
reasonable headroom, that is why 24 volt vacuum relays operate on 14 
volts and 12 volt relays normally work on 8 volts.

It does not hurt to bang a relay coil with two or more times the 
normal steady working voltage. The problem is, if this is a hold-hold 
system where one relay closes immediately as one opens, designing the 
supply is somewhat complex. Things designed for amplifiers will 
generally **not** work, because those systems have a zero-load 
current period that allows charging time to recover charge in an 
energy storage system.

As another suggestion, try rotating the switch *slowly* from one 
position to the next and see if the switch, while in transition, 
grabs two or more relays at once. Does it do that? If so, what is the 
supply voltage when multiple relays are engaged?73, Tom W8JI 

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