Variable speed control of
a 3-phase azimuth motor

The following infomation about how to make a variable speed control of a 3-phase azimuth motor was posted in the Moon-Net reflector by Roland ON7RB. I found the subject so interesting that I decided to put it in this page.

On 2-September-1999 ON7RB wrote:
Hello OM,

Some time ago I asked on this reflector if anyone had a solution for the problem of reducing the speed of the 3-phase motor I use for azimuth rotation. The replies were either "the solution is very expensive" or "if you find it, let me know".

Well, I found a solution that is both simple and inexpensive.

In HR Jan 81, WB4EXW published an article on "Pulse-position control of the CDE Tailtwister rotor". I still use such a system on the portable eme array. It uses 2 NE-555 timers, one for pulse rate and another for pulse width. It triggers an electronic switch, a Triac 2N6071 which gives full wave ac control to the rotor motor.

For a 3-phase motor, the simple triac won't do the job. I got 10 Amps Solid State Relays at the fleamarket in Friedrichshafen and set up the system as follows :

• 3 SSR's are mounted instead of the triac
• the output of the pulse control unit is connected to the 3 DC controls of the SSR's
• the 3 phases of the motor are connected to the output of the SSR's
• the 3 phases of the left/right actuators are connected to the input of the SSR's
• the AC for the power supply of the control unit is taken for a small transformer, its primary is connected between two phases at the input of the SSR's (in this way, there is only power on the control unit if the left or right actuator is activated)

There is no more jerking and twisting when I rotate the array now :-)))

C U on the moon and 73's de Roland ON7RB

(Note: I'm not showing any E-Mail address here in order to avoid them from being collected by SpamBots. You can possibly find the E-Mail addresses of the above OM at QRZ.COM.)

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