WR8K wrote: Are diodes across the relay coils necessary? And if so, how
can I detect a failed diode (a short, correct?) before turning on the
power?
I answered the first part of that with my first post. Here is the
answer to the second part.
Every situation is a little different. I will tell you how I do it.
When I use remote DC relays, inside the control box in the shack I use a
regulator IC to obtain the voltage to drive them (a three terminal TO-3
device). These have built in short circuit protection and over-temp
protection. When a diode shorts it is likely that there will be lots of
current drawn. The regulator survives this on a short term basis.
However things (like the power transformer) may burn up long term, so I
have another method to tell if something is wrong. The power light on
the box (powered from the regulator IC) will either go out or be very
dim. That tells me there is a problem. You could also add a fuse if
you wanted but I don't find this necessary.
I also have a method of debugging the remote antenna from the shack for
things like a failing relay. The problem is usually first noticed by
the antenna not performing properly. In my system there are a different
number of relays engaged for each position of the antenna. (Yours may
be different.) I simple step thru all the positions and measure the
current drawn for each position and compare that with my standard data
for a good system. I can then tell where the problem is in the
antenna. That doesn't cover all the problems that can happen but it
gets the high failure rate items.
Jerry, K4SAV
Wolfert, William R. wrote:
> Gentlemen
>
>
>
> I'm putting together a switchbox for a phased array. I had many spdt relays
> on hand so I'm using them. 2 relays per antenna will work fine. The array is
> an 8 circle
>
> (for 80m, hung off the top of the 160 Vertical) and I've used ON4UN's
> switching scheme (on page 11-65 of latest edition of LBDX). I'm located in
> central Ohio, with moderate thunderstorm activity in the summer. Since unused
> antennas must float, the relay contacts are spoken for. The 160 Vertical has
> a spark gap and I intend to put a spark gap at the base of each wire. The 160
> antenna has 120 ¼wl radials and each 80 m element will have 64. Control wires
> are underground from the shack to the towers. I have bypassed the control
> wires at the phase box. The feed coax is grounded when not in use. Adding a
> third relay per element would allow me to ground the system when not in use,
> but I'd rather not have 3 relays per element. Are diodes across the relay
> coils necessary? And if so, how can I detect a failed diode (a short,
> correct?) before turning on the power? The entire system (house, towers,
> shack, etc) is properly grounded by SPG. Your input is appreciated.
>
>
>
> 73, Bill WR8K
>
>
>
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