SS1CC

SS1CC : Self Starting One Coil Circuit

This circuit i use frequently in my projects. I got the circuit from : solarbotics_sunswinger_kit_jan082007.pdf (application/pdf-object) and modified it to work with a Mendocino motor(Magnetic Levitated Rotor - Low friction)

(Modified) Schematic:

PCB pictures:

How does it work ?

The SelfStart part consists of : capacitor 100uF and 47k resistor in combination of resistor 1k and 1000uF capacitor and PNP transistor BC558B. If the rotor of the Mendocino is fully stopped the 1000uF capacitor gets loaded via the 1k resistor. Therefor the voltage slowly going up over 1000uF. The 100uF capacitor and the 47k resistor is now also loading voltage over 100uF. As soon as the voltage over 100uF is about 0.6Volts the PNP transistor starts to open and activates the base of the NPN transistor that activates the coil. At this point the 1000uF capacitor is discharging it's voltage over the coil and starting the magnetic rotor of the mendocino to turn. As soon as the PNP transistor stops conducting the LED light up by the BEMF of the coil (550 tuns, 0.1mm wire). The 100uF capacitor is also a bit discharged over the 47k resistor due to the voltage drop over 1000uF.

This repeats itself until the magnetic rotor has enough speed to induce a voltage in the coil with the moving magnets. This spike goes from the coil through the 100k resistor to the base of the PNP transistor. Opening the PNP and therefore opening the NPN transistor which powers the coil, given the rotor a push in the same direction, therefore speeding up the rotor.

In my projects the LED stops flashing when the normal operation takes over from the starting up. I think this is because of the lower BEMF in the coil while turning fast the rotor. The voltage over the 1000uF is now more or less stabilizing to a 0.8 Volts.

This is because the 1000uF integrates the voltage at higher frequencies (9Hz) making it almost a steady voltage.

The 100pF capacitor can be inserted as the circuit starts to self oscillate, due to changes in the coil and or rotor.

Transistors can be excanged with other regular types (2N2222) etc.

Experiment freely and share with others freely. :-)

The complement of the circuit :

This works just the same. Only now the PNP transistor is driving the coil.

Both circuits work and can be used to make the rotor of the Mendocino turn.

I found that other transistor types work also (eg NPN BC550 and PNP BC560). The coil distance to the rotor is in my project about 2mm. At greater distances the LED keeps on flashing therefore using th SS1CC in startup mode.

Here the PrintedCircuitBoard of the SS1CC can be downloaded.