Archive for September 2011
The Difference Between DC and AC Driven Electric Motors
September 30, 2011 | 
Author The Difference Between DC and AC Driven Electric Motors
When it comes to electric motors, many people do not know the difference between AC and DC electric motors. In order to understand the difference, one must first be made aware of the fact that an electric motor is a machine that is used to convert electrical energy into mechanical energy. Our modern society depends upon these motors as we use them in our computer printers, machine tools, automobiles, vacuum cleaners, water pumping stations and much, much more.
Electrical motors fall into two broad categories: direct current and alternating current motors. Direct current or DC motors are those that work for situations where speed must be controlled. Direct current motors were the first and earliest motors in use. However, they were found not to be so good to use when power was required for long periods of time. Early on, electric utility companies discovered that using DC motors to generate electricity did not work because the power was lost as the electricity was being transmitted. There are both brush and brushless direct current motors in use today. The brush DC motor uses rings to conduct the current and which form the magnetic drive that turns the rotor. A brushless direct current motor uses a switch to produce the magnetic drive that turns the rotor. Many common household appliances make use of direct current motors.
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Even though the majority of electric motor manufacturers are moving away from direct current motors, DC machines are still powering a lot of machinery in heavy industrial settings. DC motors are still being used to power surface mining excavators, mine hoists, massive metal rolling mills and many more types of industrial applications and direct current is expected to continue delivering the power in many types of production work for many years into the future.
Alternating current or AC motors work well in many different types of situations. This type of motor was first made back in 1882 when a two phase induction motor was designed. There are two basic types of alternating current motors, depending upon the type of rotor employed. One is the synchronous motor and the second is the induction motor. With the first type, the motor rotates exactly at the supply frequency and with the induction AC motor, it runs slightly slower than the supply frequency. Alternating current motors are ideal for use with equipment that is difficult to start because this type of motor is tremendously powerful. The name ‘alternating power’ was assigned to this type of motor because AC motors alternate in power. In other words, the amount of power expended by an alternating motor is determined by the amount of power required to run the given machine or equipment.
AC electric motors are used the world over in homes, businesses and industrial settings. An alternating current motor can be a part of a fan or a pump or it can be connected to some other form of mechanical equipment such as a conveyor belt or a mixer. Some mechanical applications require just one AC motor while others may need several motors in order to operate. The torque capabilities of an AC motor are taken into consideration to determine whether it can meet the torque requirements of the application’s load when deciding on what size of motor to use.
The Difference Between DC and AC Driven Electric Motors
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Acquiring a car in Singapore
Acquiring a car in Singapore
Driving in Singapore is so convenient and can save you a lot of time. This article discusses some ideas for acquiring a car in Singapore.
Buy or rent? 3 years or less : Don’t even think about buying a car. Certificate of Entitlement (COE) premiums have already increased across the board.
Above 3 years : It will most definitely be better to buy or lease a car.
Tips for renting in Singapore
Who can rent?
You can rent a car in Singapore if:
You are a holder of a valid Singapore Class 3 or approved foreign license.
Some vehicle hire companies require the driver to be over the age of 24 and has a minimum driving experience of 2 years. Other companies have lower minimum age or experience requirements, such as age 18 or 21, and may require a large surcharge, and reduced insurance.
Features to look for
Air conditioning (it is safe to assume that all reputable rental companies will have airconditioning fitted in Singapore).
Manual or Auto. Most of the cheaper and older cars come with Manual transmission.
What insurance included in the price?
Is the Goods and Services Tax (GST) included in the price?
Can the car be driven across the border to Malaysia? Most major car rental companies allow their cars to be driven in Malaysia. A surcharge will require.
Is there a mileage limitation? Cars rented for driving in Singapore commonly have unlimited mileage. Cars rented for driving into Malaysia rarely do.
Is 24-hour Roadside assistance offered?
Safety features
Fuel economy
Maps or GPS navigation system. You may need to pay a small amount of fee to rent a GPS navigation system.
Pick up and drop off points. Some rental companies offer these service island-wide in Singapore free of charge.
Is cash card provided? You need one to pay for the toll fee (ERP gantry) in Singapore. Most rental companies offer cash card for sale.
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Saving Money
Understand the full insurance cost. Often travel insurance can work out cheaper than paying the excess reduction insurance at the time of rental. If you already have travel insurance, make sure you don’t pay for extra insurance that your travel insurance already offers.
Pickup or returning cars to airport or other locations often incurs an additional charge. Look for rental companies that provide these service free of charge.
Tips for buying
Many of these tips are true regardless of where you are looking to buy a car, but there are a concern specific to cars in Singapore that you should be aware of.
The Certificate of Entitlement (COE), instituted by the government of Singapore, is a program designed to limit car ownership, and hence, the number of vehicles on the country’s roads. An restriction on car ownership is the requirement that motor vehicles more than ten years old, known as ‘time expired’ vehicles, must either be scrapped, or exported from Singapore, usually to neighbouring countries. So don’t buy a car with only a few years left on it’s COE!
Don’t buy a car you have not test driven yourself for at least around the block. If you are too scared to drive it, ask the seller to take you on a short ride and tell him what you would like him to do: brake sharp, accelerate fast, etc.
Don’t buy a car (from a private person) if you do not have at least some basic knowledge of cars and know what to look for.
Don’t buy a car from a dealer unless he has a good reputation (ask him for feedback from his customers and check the Internet).
Don’t buy a car that is leaking any fluid (black=engine oil/brake fluid, brown=engine oil/brake fluid, red=gearbox, green=radiator or other.), has an oily looking engine head or rust on important parts of the chassis such as the door areas, or near the suspensions.
Don’t buy a car that has problems with the gearbox (automatic or manual) – this type of repair can be very expensive. Don’t buy the argument that you will have to use overdrive or use neutral position when parking.
Don’t buy a car that doesn’t stop (SHARP!) when you want it to stop. Check all the car lights with the help of a friend.
Send the car for inspection.
Acquiring a car in Singapore