|Rotator Brake Delay
for the hy-gain rotators
In the standard circuit, the primary of the 'power' transformer is energised by depressing the Brake switch lever, operating a microswitch. The secondary side energises the brake solenoid directly, releasing the brake. Additional switches on the secondary feed the clockwise or counterclockwise mode of rotation for the motor. From this you will realise that it is not possible to energise the motor without first or simultaneously releasing the brake. Of course rotation should be stopped by first releasing the selected motor switch and pausing before applying the brake, as the momentum of the antenna is obviously considerable. It is very easy to forget the pause.
Several schemes have been published for a delay to prevent the brake from being applied to the still-rotating antenna but they tend to be elaborate. Mine is simpler than others I have seen.
So here are the modification details. ( Schematic )
Another microswitch driven by the brake switch lever is interposed on the secondary side before the motor switches and a relay is also fed from this point. The relay drive circuit includes a diode to provide DC and a capacitor and resistor to delay the drop-off. Relay pick-up is immediate, however. Note that the brake is still energised as soon as the switch is depressed as in the original design. However, a normally-open contact of the relay is in parallel with the original primary-side microswitch and hence when the brake switch is released the brake remains energised for the drop-off period, in my case 3 seconds. But the motor circuits are de-energised by the second microswitch as soon as the brake switch is released.
The relay and the microswitch contacts should be rated 10 amps AC or more as the brake and and motor currents are of this order. I chose a common octal-based relay which has a coil requirement of 12 volts 100 mA DC. The voltage at the capacitor exceeds 40 VDC so it needs to be good for 50 V . The resistor must be capable of 2 W but I suggest more as that is close in my case, resistor and capacitor values need trial and error according to the relay; the diode and resistor were mounted on a scrap of Veroboard with a small bolt securing it to the control box chassis. The capacitor, relay and microswitch are silicone-glued in place, saving time and effort!
The motor cannot be energised without the brake nor during the brake delay period.
Incidentally, I would have liked to have put two more switches, with normally-closed contacts, each in series with a motor switch, to provide a directional "cross-interlock". As the circuit is and was, it is possible to select both motor directions at once, and I don't suppose that would do the motor a good turn! But there is not room to do this as other components intrude on the space required.
73 de KEN WOOD ZS2ACB
By Ken Wood ZS2ACB
Click the image for a full size schematic
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