Friday, June 17, 2011

Choosing a Motor Controller

Before you can think of how to drive your motor, you need to know what kind of motor/actuator you are using. This is because each motor type got different spec especially on the current consumption, rated voltage and torque.
  1. Rated voltage - always check your motor operating voltage. if your motor operates at 12V, you cannot use a motor controller that support output voltage at only 5V or less.
  2. Current requirement - Choose a motor controller that offers output current equal to or above the motor’s continuous current consumption under load. If your motor require 3A current under load, it means that you will need at least 4A motor driver to drive the motor. otherwise you might burn your motor controller. What if we don't know the current requirement for the motor?? - try to attach the motor to laboratory power supply that has digital output display for voltage and current. increase the voltage gradually until the motor running and you can see the current consumption from the current display. try to halt the motor while its running and you'll get the current draw under load.
  3. Control method is another important consideration. Control methods include analogue voltage, I2C, PWM, R/C, UART (a.k.a. serial). If you are using a microcontroller, check to see which pin types you have available and which motors are viable for you to choose. If your microcontroller has serial communication pins, you can choose a serial motor controller; for PWM, you will likely need one PWM channel per motor.
  4. The final consideration is a practical one: Single vs. dual (double) motor controller. A dual DC motor controller can control the speed and direction of two DC motors independently and often saves you money (and time). The motors do not need to be identical, though for a mobile robot, the drive motors should be identical in most cases. You need to choose the dual motor controller based on the more powerful DC motor. Note that dual motor controllers tend to have only one power input, so if you want to control one motor at 6V and the other at 12V, it will not be possible. Note that the current rating provided is almost always per channel.
  5. examples of motor controller or motor driver can be found here

Power window motor require high operating current(>3A)

reference : Read More!

Tuesday, May 17, 2011

how does energy saver works?

We often heard about energy saver or power saver. just plug it in a socket nearest to the meter and the electricity consumption goes down anywhere between 20% to 50%. Is it really works? what is the principle behind it??

In this post, i'll discuss in details the principle behind it and it is open for further discussion. just write down your comment/arguments at the comment part at the bottom of this page.

Do you actually need to install these power saver??- the answer can be YES or NO.
how do i know?
It is a YES if there is an additional sentence about SURCHARGE in the particulars column of your electricity bill.
It is a NO answer if there is no additional surcharge in your electricity bill.
There is a power factor surcharge by TNB when your average monthly power factor falls below 0.85. The lower your power factor, the higher the surcharge. The rates fixed by TNB are as follow:
(a) Below 0.85 to 0.75.....1.5% per unit
(b) Below 0.75..................3.0% per unit
The % total of (a) and (b) will be levied on your electricity consumption for the month.

these power saver helps to increase your power factor anywhere between 0.9 to 1.0. So, no more power factor surcharge you need to pay.

Why do i have such a low power factor?
We usually have a low power factor when there are a lot of inductive loads in our house. Any devices that have coils of wire can be classed as inductive loads. e.g. motors, solenoids and contactor coils, air condition, light bulb, florescent lamps, mixer,blenders,fan etc. In fact, most of our household appliances are inductive loads. These loads need to be balance using capacitive loads. So the power saver gadget is actually some kind of capacitive loads installed to balance the inductive-capacitive loads at our house so as to increase the power factor.

If I don't have any surcharge, why shouldn't i use power saver to save more?
Theoretically, there is no way you can save your electricity using the power saver gadget. Yes, it help to correct/improve the power factor, and this help you by eliminating the surcharge. We are being charge for the amount of real power been use in a month. Have you ever notice the 40Watt label on your florescent lamp when you buy them?- that label tells you the real power requirement for that lamp- and it is a fixed value. Let say you are using 100 lamps, 24hr-7days a much it will cost you?

40watt X 100pcs X 24hr = 96kW per day = 96 X RM0.20 = RM19.20 per day

The only way you can reduce the RM you need to pay is to reduce the amount of lamp been use at a time.Why? because the 40Watt value is fixed and you still need to pay every time you use it.

notice that when you install a power saver gadget, it reduce the current consumption. Why?

consider the following equation

real power = current X volt X power factor

with the real power and volt fixed, improving the power factor(e.g from 0.8 to 1) will actually reduce the current. But still, you need to pay the same amount as TNB charge you for the amount of real power usage.

as a conclusion, you'd better check you bill before you decide to buy such device. in some situation, it might not benefit you, but it benefit the environment for more efficient power transfer to your house. efficient power transfer means, less loses, less fossil fuels use to generate inefficient power, less energy waste. Read More!