You can easily design a remote control system without the 5 sec delay
devices. but you have to remember not to switch from up to down (visa versa)
quickly as motors with centrifical start switches have a bad habit of not
changing their direction of rotation. The "glass" delay switches are
easy to find (with short delays) and quite reliable. There are solid state
types, but one has to be careful to make sure the delay relay control circuit
is understood and the control function will work. The control remote control
box consists of a up relay, and a down relay, interlocked with remote limit
switches. In addition there is usually a Main Relay to supply power to the
motor, and the up down relays only control the polarity of the START winding.
A transformer to supply 24vac for relay operation is a must or you will be
running 115vac to the limit switches, (not a good idea). Then you need a main
ON/OFF switch (control the main relay) and a double pole, center off switch
to select the proper relay. And you need to delay the application of voltage
to the UP/DWN relays to assure motor decay and proper direction of rotation.
The thermal activated delay relays (glass) are simplicity at work, apply the
power and 5 seconds later the contact closes, and this SAME power source
also activates the control relay. The solid state relays require a control
and the power line. Many of the solid state devices found in surplus are
Delay on OFF, that is remove "control" voltage and the count down starts.
The other advantage of the "tube" type is the failure mode (heater opens) is
a SAFE mode in that the relay won't operate. That may not be the case with
solid state device unless you think through the control circuit and make
failure mode analysis.
A long winded discussion, but remote control is pretty straight forward yet
has pitfalls. The requirements can be modified depending on how much "fool
proofing" you want to design in.
In a message dated 9/14/2006 4:34:05 P.M. Eastern Daylight Time,
From: "Bill Erickson" firstname.lastname@example.org_ (mailto:email@example.com)
I have a Tri-Ex LM-470 motorized crank up tower. I would like to be able to
remotely control it from my ham shack. The only remote control system that I
have been able to find is the original system that was offered by Tri-Ex. My
concern with that system is that it uses (GASP) vacuum tubes to provide the
delay required when changing directions. Does anyone out there have a
schematic or other information on a more modern design? I have the
facilities to fabricate anything needed, or I would be willing to purchase
an existing system. Any suggestions?
Thanks for your help.
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