Small Motor Circuit Diagram | AC or Not?

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Discussion Overview

The discussion revolves around identifying the type of motor circuit in a polisher, specifically whether it operates on AC or DC. Participants explore circuit diagrams, motor characteristics, and control methods, including PWM and rectification. The scope includes technical explanations and conceptual clarifications related to motor control and circuit design.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests the circuit may be for a PWM speed-controlled DC motor, seeking confirmation and additional information about the motor's markings.
  • Another participant questions the feasibility of full-wave rectifying the motor circuit if it receives AC and controlling current with a variable resistor, noting potential issues with torque and feedback.
  • A later reply discusses the possibility of using a capacitor to create square wave pulses instead of PWM, while acknowledging the need to rectify AC to DC first.
  • Participants express varying levels of comfort with the technical aspects, with one indicating a desire to expand their electronics knowledge.

Areas of Agreement / Disagreement

Participants express differing views on the motor's operation, with some proposing it is a DC motor while others explore the implications of AC input. The discussion remains unresolved regarding the exact nature of the motor circuit and the best control method.

Contextual Notes

Participants mention the need for additional information about the motor and circuit, such as markings and images, which could influence the discussion. There are also unresolved technical aspects regarding the effectiveness of different control methods.

Who May Find This Useful

Individuals interested in motor control, circuit design, and electronics, particularly those looking to enhance their understanding of PWM and AC/DC motor operations.

Adder_Noir
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Hi,

I've been messing about with my polisher lately as those who read the other thread will know. I decided to open a more relevantly titled thread and here it is. I've acquired what I think is the circuit diagram for the motor. There is nowhere where any AC is rectified by the looks so I think it is an AC circuit. I've scanned it in anyway.

http://i207.photobucket.com/albums/bb281/adder6/circuit001.jpg"

And that's it. Can anyone throw any light on this, is it definitely AC? Also I must point out I'm new to all this and won't be in the least bit offended if someone points out that I'm in over my depth with this one and should stick to more simple stuff :redface:
 
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My initial guess would be that it's a PWM speed controlled DC motor. Do I win a prize if I'm right?

Does the motor have any markings that we/you can google?
 
berkeman said:
My initial guess would be that it's a PWM speed controlled DC motor. Do I win a prize if I'm right?
I think you should for getting so close to the mark. Thanks for that, it helps me even just to know what I'm looking at!

berkeman said:
Does the motor have any markings that we/you can google?
I can get a photo of it if that's any use?

I also noticed there are two toroids and some small windings in the motor circuit occurring after the circuit shown, I wonder what they do. I'll try and get some pictures.
 
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Could I full wave rectify this motor circuit if it's receiving AC at the source? And then control current through it using a variable resistor. I know this wouldn't give any torque/current feedback but would it still work?
 
Adder_Noir said:
Could I full wave rectify this motor circuit if it's receiving AC at the source? And then control current through it using a variable resistor. I know this wouldn't give any torque/current feedback but would it still work?

In general you can't use a resistor to drop voltage to control speed on a motor. The power lost in the resistor takes torque away from the motor, and the motor is generally too weak to operate correctly.

Instead, you want to deliver full power to the motor, and vary what percentage of the time that full power is delivered -- hence the PWM function.
 
Understood. Thanks again, that makes perfect sense.

*Edit*

Out of curiosity could one use a capacitor and other necessities as a timer to deliver square wave pulses of uniform size and separation instead of using PWM to mimic the sine wave input with regards to pulse width?
 
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First in order to use a cap to make a squarewave, you would have to rectify the AC and make it DC. Secondly, a squarewave is the addition of the harmonics of a sinewave. That means that a squarewave will have a lot more power than a sinewave of equal amplitude and frequency. But I believe the answer to you question is ultimately yes, but how involved do you want to get into this project?
 
Not massively. I'm trying to fill out my electronics knowledge as much as anything. If PWM is easier I'd go with that, but whatever solution was found would have to be better than the bad power and torque I get out of it now.
 

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