Voltase hobby: speed

Tuesday, September 9, 2014

Two Basic Motor Speed Controllers

Here are two simple 12V DC motor speed controllers that can be built for just a few dollars. They exploit the fact that the rotational speed of a DC motor is directly proportional to the mean value of its supply voltage. The first schema shows how variable voltage speed control can be obtained via a potentiometer (VR1) and compound emitter follower (Q1 & Q2). With this arrangement, the motor’s DC voltage can be varied from 0V to about 12V. This type of schema gives good speed control and self-regulation at medium to high speeds but very poor low-speed control and slow starts. The second schema uses a switchmode technique to vary motor speed.

Circuit diagram:

basic-motor-speed-controller-schema-diagram1

Fig.1: a very simple motor speed controller based on a compound emitter follower (Q1 & Q2).

Here a quad NOR gate (IC1) acts as a 50Hz astable multivibrator that generates a rectangular output. The mark-space ratio of the rectangular waveform is fully variable from 20:1 to 1:20 via potentiometer VR1. The output from the multivibrator drives the base of Q1, which in turn drives Q2 and the motor. The motor’s mean supply voltage (integrated over a 50Hz period) is thus fully variable with VR1 but is applied in the form of high-energy "pulses" with peak values of about 12V.

Two Basic Motor Speed Controllers Circuit diagram:

basic-motor-speed-controllers-schema-diagram2

Fig.2: this slightly more complicated schema gives better low speed control and higher torque.

This type of schema gives excellent full-range speed control and gives high motor torque, even at very low speeds. Its degree of speed self-regulation is proportional to the mean value of the applied voltage. Note that for most applications, the power transistor (Q2) in both diagram will need to be mounted on an appropriate heatsink.

Author: Ravi Sumithraarachchi - Copyright: Silicon Chip Electronics

Thursday, September 4, 2014

3 φ Full Wave Controlled Rectifier circuit to control DC Motor Speed

In the given Block and schema diagram of a 3 φ Full Wave Controlled Rectifier schema to control DC shunt motor is shown.

In this schema diagram the field and armature diagram are connected through three phase full wave Controlled rectifier schema.

In three phase supply, each phase is different form other one in 120°, therefore at each out put terminal a, b, & c give the following Sine wave voltage.

Through the three phase controlled rectifier, the three phase supply is converted to a DC and provided to the armature and field of the DC shunt motor.

Through the 3φ full wave Controlled Rectifier, the 3φ AC supply converted to a DC voltage and provide to the armature and field of the DC motor, which flow in shape of T_A (Armature Current) through the ckt (DC motor) due to this controlled Dc the motor start in low speed.

If the DC motor start through ordinary way, then an external resistance is connected in the armature ckt, these resistors in armature ckt controlled the speed of the motor, (Gradually decreases the resistance form the armature ckt) and when total resistance (Resistors) remove form the armature ckt, the motor is rotate at its full speed (RPM). The main purpose of the resistance with the armature ckt is that, to match armature current with internal current (emf) to decreased value.

In case of the controlled rectifiers the resistors are not connected because at motor starting time the SCR connected in armature ckt set the delay angle value ,that the armature resistance controlled the voltage drop in the armature. The armature controlled method is mostly used as compare to the field controlled method,

In armature controlled method the field voltage is kept constant, while the armatures voltages changes.

In the given ckt rectifier converted to the in put DC supply (Full wave) , the rectifier is consistof SCRs , the out put of the SCR is Directly apply to the Armature in a variable shape. The applied voltage can be change form the changing the firing angle of the SCR.

Sunday, August 31, 2014

12V Speed Controller Dimmer

This handy schema can be used as a speed controller for a 12V motor rated up to 5A (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W. It varies the power to the load (motor or lamp) using pulse width modulation (PWM) at a pulse frequency of around 220Hz. SILICON CHIP has produced a number of DC speed controllers over the years, the most recent being our high-power 24V 40A design featured in the March & April 2008 issues. Another very popular design is our 12V/24V 20A design featured in the June 1997 issue and we have also featured a number of reversible 12V designs.

Project Image :

12V Speed Controller/Dimmer Project Image

For many applications though, most of these designs are over-kill and a much simpler schema will suffice. Which is why we are presenting this basic design which uses a 7555 timer IC, a Mosfet and not much else. Being a simple design, it does not monitor motor back-EMF to provide improved speed regulation and nor does it have any fancy overload protection apart from a fuse. However, it is a very efficient schema and the kit cost is quite low.

Parts layout:

Connection diagram:

There are many applications for this schema which will all be based on 12V motors, fans or lamps. You can use it in cars, boats, and recreational vehicles, in model boats and model railways and so on. Want to control a 12V fan in a car, caravan or computer? This schema will do it for you. The schema uses a 7555 timer (IC1) to generate variable width pulses at about 210Hz. This drives Mosfet Q3 (via transistors Q1 & Q2) to control the speed of a motor or to dim an incandescent lamp.

Circuit diagram :

12V Speed Controller/Dimmer Circuit Diagram

While the schema can dim 12V halogen lamps, we should point out that dimming halogen lamps is very wasteful. In situations where you need dimmable 12V lamps, you will be much better off substituting 12V LED lamps which are now readily available in standard bayonet, miniature Edison screw (MES) and MR16 halogen bases. Not only are these LED replacement lamps much more efficient than halogen lamps, they do not get anywhere near as hot and will also last a great deal longer.

Source : Silicon Chip

Monday, August 25, 2014

Wiper Speed Control

A continuously working wiper in a car may prove to be a nuisance, especially when it is not raining heavily. By using the schema described here one can vary sweeping rate of the wiper from once a second to once in ten seconds

http://www.electronic-diagram-diagrams.com/carsimages/2.gif

The schema comprises two timer NE555 ICs, one CD4017 decade counter, one TIP32 driver transistor, a 2N3055 power transistor (or TIP3055) and a few other discrete components. Timer IC1 is configured as a mono- stable multivibrator which produces a pulse when one presses switch S1 momentarily. This pulse acts as a clock pulse for the decade counter (IC2) which advances by one count on each successive clock pulse or the push of switch S1. Ten presets (VR1 through VR10), set for different values by trial and error, are used at the ten outputs of IC2. But since only one output of IC2 is high at a time, only one preset (at selected output) effectively comes in series with timing resistors R4 and R5 connected in the schema of timer IC3 which functions in astable mode. As presets VR1 through VR10 are set for different values, different time periods (or frequencies) for astable multivibrator IC3 can be selected. The output of IC3 is applied to pnp driver transistor T1 (TIP32) for driving the final power transistor T2 (2N3055) which in turn drives the wiper motor at the selected sweep speed. The power supply for the wiper motor as well as the schema is tapped from the vehicle’s battery itself. The duration of monostable multivibrator IC1 is set for a nearly one second period.