I'm attempting to regulate the output voltage of a synchronous motor being used as a generator.

I've hooked up a LM317 along with a high voltage capacitor and some diodes. I decided to attach the diodes to try and isolate the interaction with the LM317. When leaving the load and capacitor unattached I am able to reach 150-200V easily with this motor.

However, as depicted in the diagram, when I attach the load: the voltage of the system drops drastically. Between .3-1.5 Volts.

The LM317 seems to not be doing it's job, as I move the pot's value, change the resistor value, and the overall system voltage is the same. However removing the LM317 does cause the voltage to drop a bit as well.

The two dots on the rectifier bridge are where I am measuring voltage, as well as where the two circuits are connected up to.

I have tested the circuit with the LM317 with both diodes, one or the other diode, and with no diodes. While also swapping out two resistors of 462Ω and 8.17KΩ. The swapping had no affect on voltage.

The removal of one diode (either side) drops the voltage from 1.5V to .95V.

The removal of both diodes gives a voltage of .3V.

Having the load attached to the rectifier be only 2 diodes gives a voltage of 1.25V.

I don't know if this has to do with impediance and current or what. Also am not too sure how to begin testing for those factors.

  • \$\begingroup\$ one simply reads the data sheet of LM317 to ensure input and output voltages are achieved with the correct R range and R ratio mulitplier while not exceeding load current. \$\endgroup\$ – Sunnyskyguy EE75 Sep 5 '17 at 2:57
  • \$\begingroup\$ What voltage do you get with just the rectifier and capacitor? Disconnect the motor and measure its resistance. What do you get? \$\endgroup\$ – Bruce Abbott Sep 5 '17 at 4:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.