I wanted to be able to run a Dual CS505 turntable off-grid. This turntable has a 2-phase synchronous motor "SM 100-1". Its relatively easy to open up and there's a box with phasing capacitors in it, and a resistor that is known for overheating in the 240V version.
The phasing is 120 degrees so its self-starting.
I wanted to avoid extra boxes, excessive power draw and decided rewinding the motor and driving it at 12V would be better than using an inverter. Note the above picture is an intact motor (the original - I bought a spare from eBay to play with, the wire is from one of the windings on the modified motor.
Taking the motor apart was a bit of grinding to extract the poles and remove the bobbins, and I created an adapter to hold the bobbin on a hand-winding machine with turns counter, removing the find wire laboriously. Then rewound for 1/20th of the voltage and rebuilt the motor. Sorry no photos on that.
The old caps and resistor were stripped off the board and a new PCB glued onto it with the new driver:
The driver is an Arduino-compatible ATmega328 microcontroller generating PWM to two MOSFET H bridges, with quartz timing accuracy.
The output devices are ZXMHC3F381N8TC SOIC8 H-bridges which are 2 N-channel and 2 P-channel devices pre-connected for a 12V H-bridge. Less than an amp is needed to drive this small motor (its probably an underpowered design to be honest).
The phasing is 120 degrees so its self-starting.
I wanted to avoid extra boxes, excessive power draw and decided rewinding the motor and driving it at 12V would be better than using an inverter. Note the above picture is an intact motor (the original - I bought a spare from eBay to play with, the wire is from one of the windings on the modified motor.
Taking the motor apart was a bit of grinding to extract the poles and remove the bobbins, and I created an adapter to hold the bobbin on a hand-winding machine with turns counter, removing the find wire laboriously. Then rewound for 1/20th of the voltage and rebuilt the motor. Sorry no photos on that.
The old caps and resistor were stripped off the board and a new PCB glued onto it with the new driver:
The driver is an Arduino-compatible ATmega328 microcontroller generating PWM to two MOSFET H bridges, with quartz timing accuracy.
The output devices are ZXMHC3F381N8TC SOIC8 H-bridges which are 2 N-channel and 2 P-channel devices pre-connected for a 12V H-bridge. Less than an amp is needed to drive this small motor (its probably an underpowered design to be honest).
Because its integral with the pulley and pulley adjust mechanism, and already mounts to the turntable straightforwardly - besides this way I know the performance isn't going to change.
Yes, sorry about lack of pics, I did this last year and have only recently started properly frequenting here. There should be no difference as the turns ratio was chosen to match the voltage ratio.
It wasn't the easiest motor to get apart, but I'm sure it wasn't the hardest. Since the coils were on removable bobbins the actual winding was easy.
Mains voltage 240 rms, new driver gives about 12V peak, so ratio new turns to old about 1:30, with wire of 30 times the CSA. Same mass of copper, same amp-turns total, motor knows no difference... Plenty of inductance to smooth out the PWM drive to sinusoidal current waveforms.
Are you sure? The pulley is a stepped, bulged one (for two speeds) that is cut into six segments, isn't it? Speed adjustment is done by a cone that is more or less pushed into the center to spread those segments? I've never seen a Dual TT motor with the shaft and the pulley as a single unit. There has to be a clamp screw somewhere.
Yes, these big black WW resistors are prone to fail. The motor winding was laid out for 110 Vac. For 220 Vac operation the resistor simply was put in series. This was a poor, cost-cutting solution! On top of that, the 505 motor had very low torque.
Your mod is a very cool one, though!
Best regards!
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