[TowerTalk] Re: Motorized Crankup Towers- shack control project. K0FF

[K0FF]

The station here includes 4 motorized crankup towers and I am building a
remote control panel for them, so that I can raise and lower them from the
shack. Two of the towers were bought new from US Towers, and already include
the limit switch package. The Triex's were purchased used, and have no limit
switches yet, so they will be the last  to be remoted.

The peculiar thing about AC motors that are reversed electrically, is that
if they are still moving in the initial direction, and the reverse switch is
thrown, they continue to go in the initial direction, and don't reverse.
Part of the reverse switch also brings in the limit switch for the opposite
direction. You can see that if you reverse the switch too soon, the tower
will continue in the wrong direction, and won't stop when the limit is
reached. Ouch.
The simple answer to make the remote relay control system work safely is to
build in a delay.

Digital Delay relays are perfect for this function, but can be very
expensive, and that's one reason that the remote boxes from the tower mfg.
is so costly.

Fortunately I ran across some new surplus 24V Potter Brumfield delay relays
at an affordable price. The dealer only had a limited number of theses, so I
bought them all, and will keep a few for my own needs, and pass the others
along to anyone who NEEDS them.
It will takes 2 per system, and also 2 3PDT relays. These are 24 volt DC.
(most commercial relays are).

The PB relays have the flat blade type pins of .165 width, and require an
external resistor to set the delay value. These are rated at .1-10 secs, but
have been tested at 20 seconds with good repeatability. 1-3/8 by 1-/12 inch
cube and 2" tall.    $6.00 ea w/ socket. (83.00 in current ALLIED catalog)

The motor control relay is made by Aromat. 24VDC coil, 3 sets of very heavy
contacts for switching the motor current. Rated at 3/4 HP at 125V( very
conservative), and 2HP at 250V. Relay case is 1-3/8 by 2" and 2-1/4" tall.
No sockets yet, but the flat blade pins of .250" will accept a std. female
FASTON appliance connector. These cost me $5.00 ea.

There is another type of digital delay relay available made by Amperite. It
has a built-in pot, but therefore only goes from .1-10 seconds. Much
bigger - stands 3-1/2" above the socket. Works FB but would require a deeper
outdoor box. It has an octal tube base and costs $6.00.

Both the digital delay relays have 2 form "C" contacts, and work by throwing
those contacts X-seconds after voltage is applied. They them release
immediately upon removal of the control voltage.



I AM LOOKING for a wind-up 10 minute electrical timer, that can be set to
5min
accurately, or a reliable 5 min digital timer(cheap). This will be to
provide a choice of final levels when lowering the tower level during winds.
Also looking for ideas on height readouts, and overcurrent trip for the
motor if something jams the tower during raising/lowering.

Geo> K0FF
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