When used properly, the limit switches are an additional 2 sets of
contacts. Any additional sets of contacts do serve as additional
safety. Mine are Microswitches which are widely used in industry. If
you are not satisfied with the reliability, purchase SPDT Microswitches
and the enclosures for exterior use. They are very reliable. The
companies I worked for over the years all used Microswitch limit
switches as do most of my machine tools.
There are no relays in my control box, nor is there a key switch. The
power comes from an extension cord which is only hooked up when raising,
or lowering the tower. Emergency shutoff is simply pulling the plug.
I thought about copying the original setup and decided on simple.
Operation is a simple DPDT, spring return, center off 10A 120 VAC bat
handle, toggle switch.
73
Roger (K8RI)
On 7/23/2016 Saturday 7:41 PM, Richard (Rick) Karlquist wrote:
On 7/23/2016 3:25 PM, Roger (K8RI) on TT wrote:
I'd definitely want limit switches. They are good insurance.
73
Roger (K8RI)
Actually, limit switches are NOT good insurance. They
don't protect against the contactor sticking. The
contactor used is the same kind that air conditioners
use, and air conditioner contactors are famous for
sticking. Read about that on the internet.
What you need for insurance is a local (on the box)
power switch that cuts the power to the MOTOR. The
power switch built into the control box only cuts
the power to the coil of a relay that in turn cuts
the power off to the COIL of the contactor. I had
to add a real power cutoff switch to the box.
I have had a contactor stick twice. Fortunately, I
was standing next to the control box monitoring
when it happened and was able to pull the big switch.
Rick N6RK
--
73
Roger (K8RI)
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