AC Mains powered motors and their differences in regard to speed control - Page 1
Forum section: electronics / beginners

author: SaleB
author_rank: Contributor
timestamp: May 03, 2022, 05:26:44 am
content: I have not posted (asked questions) for a while now. When I arrived here, wanted to ask the question in the projects section, because I have a particular project in mind, but it turned out that I do not know as much about motors as I thought I knew.My formal education had not had much contact with mains voltage powered machines. Also, there is a language problem that there are substantial differences among 230VAC mains powered motors even if they look similar from the outside. Our education prepared us for differentiation as synchronous and nonsynchronous machines mainly. Many years ago I have found out that a synchronous machine can also be a BLDC or Brushless, and that it is essentially an electronically controlled three-phase AC motor, that sometimes can be a low voltage one.When reading technical content on the sites by industrial speed control device manufacturers I mostly find the information that frequency controlled speed control for a single-phase motor is discouraged and that they recommend exchanging the motor for a three-phase one without going into details. This does not help me much because I have only access to single-phase power. As I understand there are main two ways of controlling the speed of a motor, one that changes the frequency of the sinusoidal signal powering the motor called variable frequency drive or VFD, and the other, a triac based device that cuts off a section of 50Hz sinusoidal halfwave from the moment of zero-crossing and before the next zero-crossing, essentially lowering the mean value of the voltage.I am interested, in what motor design characteristics distinguish if one or the other (or some third) speed control method is applicable or more appropriate?Specifically, I am interested in controlling the speed of four types of 230V mains-powered AC motors. One of those three can be found in kitchen appliances and other household devices (mixers, blenders, ...), most of the time they have only two leads, a capacitor connected across them, and no brushes, so a permanent magnet rotor and a wound stator I assume, power range 50-1200W. The second kind are the motors available in the older washing machines, they have brushes, and usually have two leads from the stator winding and two leads from rotor windings and sometimes even two wires from some kind of rotational speed sensor. The third type are the motors found in electric hand tools and home vacuum cleaners, they have brushes, a wound stator, often a capacitor, power range 200-2400W. And the fourth type are motors attached to bigger pieces of equipment like manual plaster and concrete mixers, various types of pumps, they are usually in a cast-iron case, do not have brushes, some of them can be connected either to a three-phase or one-phase source by rearranging the connection bridges in the interconnect box, mostly have a big capacitor attached to the side, the power range is often presented in horsepower and goes from 375-2200W.I understand that one can measure and assume the positions of motor windings when having access to a motor, but how to choose a control method when a motor is a part of a closed device that cannot be disassembled? Can a motor be damaged if the wrong type of speed control is employed? Ideally, I would be interested to make one type of control device and use it for a few different scenarios. Three scenarios come to my mind, controlling a speed of a DIY project that is powered by a motor from a mixer/blender, controlling the speed of a tool or a device (vacuum cleaner, cooling fan, angle grinder, chop saw, ...) that was factory produced without the speed control potentiometer (with or without switches for different speeds, cooling fans and electric drills have those often) and the third scenario is control of the water pump motor to avoid the loud sounds that accompany starting of the pump.I would like a simple answer if one exists, but I would also like to read/listen more about it if you can recommend a youtube clip, a book, or a source on the web. I have found a few circuits on the web which employ one or the other method of control, so I'll, based on the answers here, later open a topic in projects, to discuss some changes that could/should be made to some of those circuits. I like to experiment with electronics, but my usual projects are low-voltage digital electronics, where one can easily recover from errors and misjudgments. When mains is involved it is good that someone comments on my ideas beforehand.Thank you for your time.

author: Benta
author_rank: Super Contributor
timestamp: May 03, 2022, 11:59:41 am
content: For mains AC, you're looking at two types of motors:Universal (with brushes). An example of controlling one is here:https://www.digchip.com/datasheets/parts/datasheet/343/TDA1085-pdf.phpInduction (no brushes), either three-phase or single-phase, which is actually two-phase, the second phase generated using a capacitor.Use that as your search terms, then you'll find a lot more information.Permanent magnet motors actually run off DC with AC being generated by the electronics.Synchronous motors in a household you'll probably only see in a wall clock.

author: WattsThat
author_rank: Frequent Contributor
timestamp: May 03, 2022, 12:10:38 pm
content: It is now common to find three phase motors in appliances powered by a single phase in, three phase out inverters. These are replacing universal motors in higher end and higher power applications, washing machines and dishwashers are good examples.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 03, 2022, 01:15:38 pm
content: I have worked with many motors and speed control on 230-480VAC single phase or 3 phase power but the motors are either 3 phase or DC although the DC type isn't popular any more. I never know how control the speed of a single phase AC motor. If you only have single phase power you can use an inverter that take single phase power and generate variable voltage/frequency 3 phase power to control a 3 phase motor.

author: Zero999
author_rank: Super Contributor
timestamp: May 03, 2022, 01:45:55 pm
content: To complicate matters, brushed DC motors are also found in mains powered appliances. Quite often the DC is generated with simple, bridge rectifier and PWM (Pulse Width Modulation) speed control is also common.

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 03, 2022, 10:38:32 pm
content: Quote from: Benta on May 03, 2022, 11:59:41 amI would expand single phase induction between the type that use the second phase only for starting and disconnect the winding with a centrifugal switch at operating speed, the "PSC" type that run as a self starting 2 phase motor, and the type that uses both a start and run cap for higher starting torque. AFAIK this is why VFD is not recommended for single phase, the cap start type are not designed for that start winding and cap to be powered for long, and it won't disconnect at all below a certain speed. I'm not sure I've ever seen a general purpose industrial single phase motor with just the run cap, you usually see those in fans, garage door openers, etc.

author: Circlotron
author_rank: Super Contributor
timestamp: May 03, 2022, 11:07:33 pm
content: Single phase induction motors with a permanently connected run capacitor and no starting switch are mostly used for loads with a low starting torque such as a fan or centrifugal pump. At full load those motors run very nicely. Single phase induction motors with a starting switch and no capacitor(s) are rough as guts. Very noisy and often not very efficient. They are the two-stroke of the electric motor world.