Back in the late 1980's when Stuart Hine was technical boffin at Pendon, it was realised that the life of the coreless portescap motors could be shortened drastically with extreme slow running with conventional pulse type controllers. Stuart Hine consulted with the manufacturers of Portescap motors and discovered that the pulse generated by a conventional pulse controller was such that the coreless motor would continually start and stop, iron core motors on the other hand had enough inertia for continual running. It was also discovered that the maximum current a motor was allowed to draw was a problem and also that the non replaceable brushes in the coreless motors lasted only about 200 hours or so before becoming erratic when used with a conventional pulse controller, thought to be mainly due to the number of stop / starts when slow running.
Before we begin, I must mention that I'm no electronics wiz kid, the aim of this project is to make a study of Stuart Hine's Pentroller, an analog controller from the 1990's, learn just enough about electronics to understand the circuit, make an experimental controller and maybe later in another blog, create a new analog controller baised on Pentroller. The idea behind this experimental controller is to have a controller that functions in the same way as Pentroller, but gives a certain amount of control of the back EMF sample time, length of DC period, set current limiting and adjust the amount of feedback so that ideal settings can be found by experimentation through use of the controller, note that although these variables alter the motor speed, actual speed adjustment on the Pentroller is controlled by a variable amplitude DC generated by the SG3527 pulse width modulator control circuit and controlled by the throttle and back EMF circuit. First of all, the new experimental controller replaces the LM393 comparator timing circuit with an alternative NE555 integrated circuit which allows adjustment of the sample time period from 140uSec to 1.8mSec and also allows adjustment of the DC ON period from 2.1mSec to 11.4mSec, the potentiometer positions have been high lighted in one of the illustrations below. The next alteration to the original circuit was to replace the virtually obsolete SG3527 pulse width modulator ic with its more common and extremely cheap SG3525, the only difference between these two chips is that when the SG3527 chip is shut down via pin 10, the outputs are high, were as on the SG3525, outputs are low, for this reason, an LM393 comparator was set up as an inverter and is connected to the PWM outputs of the SG3525.
Testing and trials.
Although the experimental controller was intended to run from a 16VAC supply, the SG3525 pulse width modulation chip got far hot for my liking, therefore the controller was tested from a regulated 12 volts supply under which conditions the chip was warm to the touch. I found that the torque generated by both coreless and iron core motors with the original 2.2ohm resistorto be far to weak for my taste and substituted this resistor for a 0.33ohm 1/2watt value. Under the suggested settings, coreless motors ran cool, had plenty of torque and ran very nice indeed, on the other hand, iron core motors, had a cogging effect that could be controlled to some extend by reducing the current control.
Added 14/04/2019 : It was found that the 2.2ohm resistor mentioned previously was discoloured and should have been a 0.22ohm 1/2watt.
I must thank Stuart Hine for getting in touch and allowing this blog to procede.
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