How Do I Modify A Small Blower Motor To Be Variable Speed?

The speed controller shown is to vary the average power/voltage to the motor. Split Phase Induction Motor – Motors that can generate more starting torque by using a centrifugal switch combined with a special startup winding. Some other application considerations: The full-load speed of high-efficiency motors is usually somewhat higher than standard efficiency models. In order to comply with UL and CE requirements, the AC Motor system must be grounded in a grounded conducive enclosure offering protection as defined in standard EN 60529 (IEC 529) to IP55 such that they are not accessible to the operator or unskilled person.

The winding voltages, Va, Vb, and Vc, should be controlled to achieve the phase difference between the effective voltages across the main and starting windings, in order to have a 90-degree phase shift to each other. Central to the answer of this question is the principle of a rotating magnetic field and how rotor speed is primarily a function of line frequency.

The number of separate electric currents energizing the coils independently, out of step, is known as the phase of the motor, so the design shown above is a two-phase motor (with two currents energizing four coils that operate out of step in two pairs). The exact motor performance curve for a given fixed-speed NEMA design B motor for operation on an AFD varies and should be supplied by the motor manufacturer.

I found this handy source that explained how capacitor-start motors designed for single-speed operation will typically have an auxiliary starter winding which shuts off when the motor reaches near the rated RPM. This, in conjunction with the short duration of pulses to the motor (50 nsec to 1 msec), can result in excessive overvoltage transients at the motor. The phase angle is varied using DIAC and TRIAC only but DIAC and TRIAC are triggered by digital means using 8051 microcontroller The speed variation is displayed on LED bar graph display. The higher output speed may also increase overall output by allowing a piece of machinery to finish its job faster.

In order to control the motor’s rotational speed, a Variable Frequency Drive controls the frequency of the electrical power supplied to it. Adding a Variable Frequency Drive to an application allows the motor speed to be adjusted in accordance with the motor’s load, ultimately saving energy. They match the control signals (voltage and power levels) as well as the signal type (analog or digital).

The key to understanding the purpose of an overload heater is found by examining the single-phase (L1 / L2) control circuit, where a normally-closed switch contact by the same name (ÖL”) is connected in series with the motor relay coil. One simple and easy way to control the speed of a motor is to regulate the amount of voltage across its terminals and this can be achieved using Pulse Width Modulation” or PWM.

Many modern VFDs also have a set point control function called PID (Proportional-Integral-Derivative) and it is very important to many HVAC and pump users. Fixed losses occur whenever the motor is energized and remain constant for any given voltage and speed. A Current Source Inverter (CSI) is a type of variable frequency drive (VFD) which converts incoming AC voltage and varies the frequency and voltage supplied to the AC Induction Motor. It is defined as the actual rotor speed at rated voltage, rated hertz, and rated load.


In the simplest drives or applications, the speed reference is simply a set-point; however, in more complex applications, the speed reference comes from a process controller such as a Programmable Logic Controller (PLC) or a tachometer. Generally, the less voltage on the stator winding of AC, the less current (it concerns, first of all, the no-load mode (it is not clear if your AC motor has any load) because the value of AC motor current under load depends mostly on value of the load torque). Optimizing motor control systems by installing or upgrading to VFDs can reduce energy consumption in your facility by as much as 70%.

The ac motor’s rotor speed is just slow enough to cause the proper amount of rotor current to flow, so that the resulting torque is sufficient to overcome windage and friction losses, and drive the load. Thus, when using motors under large power voltage fluctuations, it is important to remember that the generated torque will vary. I am wondering if possible to add a speed control to a single phase motor, similar to how a VFD is commonly used to control a 3-phase motor. Although the heater” elements are connected in series with the motor lines as fuses would be, they are not fuses! An AC Controller (Sometimes reffered to as a Driver) is known as the device that controls the speed of the AC Motor.

It also has an influence on electric motor pull-in and pull-out torques because the unexcited salient-pole rotor tends to align itself with the stator electric motor magnetic field to maintain minimum magnetic reluctance. When there is no mechanical load on the motor shaft (no-load condition), the rotor almost manages to keep up with the synchronous speed of the rotating magnetic field in the stator coils. Also, when applying an AFD with a motor, keep in mind that the available torque for starting and peak loads is different using an AFD compared to across-the-line motor operation.

There are several ways to control the speed, such as changing the number of poles in very small increments, changing the slip of the motor, and changing the frequency of the AC signal. Some adjustable speed driven applications use less energy than fixed-speed operated loads, variable-torque centrifugal fan and pump loads are the world’s most energy-intensive. Three speed fans are simmilar, built with three speeds depending on which coils receve power. A particular drive, if you find one, may not be compatible with your type of motor.

A: Gearheads reduce the motor speed anywhere from 1/3 to 1/180 (For AC Induction Motors.) This speed reduction is a result of multiple gears; the number of gears depending on the amount of speed reduction. WARNING – Dangerous voltages capable of causing injury or death, may be present in the AC Motor system. Ac motors use readily available power, are lower in cost, have improved life, and do not generate RFI.

This method of speed control is used when drop in speed is required only for a short duration of time for e.g. in overhead cranes. Don’t make extreme adjustments or changes to the AC Motor system parameters, which can cause mechanical vibration and result in failure and/or loss. A: Power supply frequency determines the speed of single-phase (AC) induction and reversible motors. Some light dimmers will work with some motors : ) sorry, that’s what i’ve found experimentaly when trying to control the speed of a blower.

Since greater levels of current will trip the heater in a shorter time, they actually heat up the motor less during that brief on” time than a sustained overcurrent of lesser magnitude. The converter part of the CSI uses silicon-controlled rectifiers (SCRs), gate-commutated thyristors (GCTs) or symmetrical gate-commutated thyristors (SGCTs) to convert the incoming AC voltage to a variable DC voltage. The use of pulse width modulation to control a small motor has the advantage in that the power loss in the switching transistor is small because the transistor is either fully ON” or fully OFF”.

For vfd’s to make sense as speed control, it either has to be a system like a conveyor where hp will drop as speed drops, or it has to be sufficiently overrated that the performance degradation isn’t an issue. For example, in a dish-washer, if the drive is blocked due to accumulated waste, it could prevent the motor from rotating. The direction reversing circuit shown is a H bridge, which reverses a DC permanent magnet motor.

Describe one application where using a fuse as a current-indicating shunt would yield trustworthy information about the current. There is no other method of AC electric motor control that allows you to accomplish this. We see the results of power usage all around us. Every day, the generation and usage of energy produces more pollution than any other single industry. Guys who have a 2hp mill, cut the speed by 75% via vfd and say its fine, are really saying 1/2hp is all they need at those speeds…..and they for sure don’t have 2hp at 1/4 the speed. If the motor is running, the current will be roughly proportional to the torque required by the load.