Baird motor control ascesory

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Baird motor control ascesory

Postby McGee2021 » Fri Oct 16, 2015 12:07 pm

I have been planning a while to build a televisor, and am getting the parts assembled, which is why i have so many topics lately. I found a schematic for a televisor and i plan to copy that circuit and integrate it into my own model. Originally, for the resistor connected to the wandering lead, i was planning to use resistors connected in a series. while at radio-shack during there closing sale, i planned to purchase some various resistors. But, before i could find the resistors, i came across a in-wall volume control, which had a maximum wattage of 100 watts. It also had a maximum voltage of 450 volts. So, instead of using the resistors, i plan to use the volume control, which has an off position and 12 other positions. I would connect that to an extra rheostat, as the circuit has. On the receiver i would have an extra knob though.

The control:
Image



The schematic:
http://www.earlytelevision.org/pdf/baird_svc_manual.pdf
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Re: Baird motor control ascesory

Postby Klaas Robers » Fri Oct 16, 2015 6:32 pm

It depends heavily what type of motor you have. The Baird motor control is for a motor that runs on the AC mains voltage, but it will run by far too fast if you connect it directly. Therefore the resistor is placed in series, devided into a variable resistor (potentiometer) and a fixed resistor with taps. By changing the wandering lead you can come to the situation where the motor with large Nipkow disc runs the correct speed with the varable resistor somewhere in the middle position. The variable resistor gives only a limited variation in the speed.

If you have a motor that prefers to, or can only run on DC (most motors do that) you should preferably use a different circuit. The latest ideas on this are that you should run the motor on a certain variable CURRENT, not VOLTAGE. This current defines directly the torque of the motor, while the air friction on the turning disc then limites the speed. The advantage is that when the motor rises in temperature and the resistance of the copper wires increases, the torque of the motor doesn't change (as long as the CURRENT is kept constant), while if the voltage is kept constant (a situation that you normally strive for) the motor is slowing down when the copper resistance increases.

What is the kind of motor that you are planning to use?
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Re: Baird motor control ascesory

Postby Steve Anderson » Fri Oct 16, 2015 9:22 pm

I have to agree with Klaas, but this device appears to be a pair of transformers which of course will only work on AC not DC. If you run DC through the windings there's a chance you'll simply end up saturating the core.

What it appears to be is a volume control for a PA system or background music (Musak) for a shopping mall or similar. These generally run on a 100V (nominal) line and a local transformer at each ceiling loudspeaker converts that to suit the coil winding. It may handle 450V and 100W but I somehow doubt at 50 or 60 Hz at 100W, maybe 10. PA systems don't need a response to go that low.

If the transformers are less than a 3" (7,5cm) cube, as an approximation, they won't handle 50/60Hz, certainly not at 100W. Two transformers that size will weigh a couple of kg at least...each...

I suggest you DO NOT apply mains power (either 110V or 220V) to them.

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