Incidentally, U.S. Tower runs 110VAC to their tower raising motors, which
are attached to the lowest section about ten feet off the ground. If you
have one of these towers, make sure it is is well grounded and turn off the
AC before doing any work on it. A GFI circuit breaker would be advisable,
too.
Incredibly, U.S. Tower also uses 110VAC control signals in its remote
control package. The remote control box simply sends 110VAC signals down the
multiwire control cable (like rotor cable) to enable the main motor relay,
switch the tower-mounted relays to raise or lower the tower, and from the
limit switches to turn on the "full up" and "full down" control box neon
lights. That means that the cables running up the lowest section to the
limit switches carry 110VAC. These cables are rather exposed to damage
during shipping, installation, and maintenance, so check them carefully.
I ran the control cable for the tower in a 250' conduit before I knew that
it would have to carry 110VAC. That's undoubtedly a major code violation and
a dangerous situation. My top priority winter project this year is to build
a remote relay board that will allow me to send 12VDC or 24VDC down the
cable instead. I've roughed out the schematic and it's very simple to do.
The relay board goes in the weather-proof electrical box on the tower. A
control box with switches and LEDs replaces the U.S. Tower control box in
the shack. The control box sends low voltage signals to the relays on the
board, which switch 110VAC available in the box to the stock relays. A pair
of 110VAC relays controlled by the limit switch signals will switch low
voltage relays to light LEDs at the shack end. In all, it takes six relays.
An auxilliary project is to mate a small DC motor with the new control box
to run a mechanical counter that keeps track of the current tower height.
While we're on the subject, I'm still pondering whether to use 12VDC or
24VDC to control the relays. 12VDC would be much easier, because I can just
tap into the shack 12VDC power supply. My Ameritron RCSV-8 coax switch works
just fine at 12VDC on the 250' run to the tower. Would 24VDC be any better?
I might have to build a power supply for that unless the combined current
draw can be handled by a wall cube. Since there's a certain amount of drop
at either voltage, it seems to me that it's just a matter of the sensitivity
of the relays. How do I determine the sensitivity of the relays that I need
to buy for this application?
73, Dick, WC1M
-----Original Message-----
From: K7LXC@aol.com <K7LXC@aol.com>
To: ddjones@nas.com <ddjones@nas.com>; towertalk@contesting.com
<towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Tuesday, December 02, 1997 9:40 AM
Subject: Re: [TowerTalk] 110 Vac up a tower
>In a message dated 97-12-02 04:35:26 EST, ddjones@nas.com writes:
>
>> In responding to the querry about what type of coax to use, KC5UOO
>> suggested running 110 Vac to the top of a tower to operate an antenna
>> switch. Please note that this is potentially LETHAL unless industrial
>> grade installation guidelines are used throughout the project. That
>> means running metal-type conduit up the tower for the AC power line.
>>
>> It is far safer to run 12 Volts ac or dc to the top of a tower to
>> operate switches, so long as the relay coils are consistent with
>> that voltage.
>>
>> Just a word of caution........Avoid running 110 Vac up to the top of
>> a tower if at all possible, or if you EVER intend to climb that tower
>> with the AC power on!!
--
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