starting of motors

[chetanerande 0]

hi! can anybody tell me methods & hardware used to start electrical motors(e.g. star-delta starters etc) thanxs

[santiago 0]

there are basically 3 ways , Inverters , Soft starters , and the old star-delta with contactors, Inverters and soft stareters are SCR devices with electronics and processors . It all depends in what you need for an application , like speed controll , the frequency of starts , energy controll and others , if you dont need them then the best way to start a motor is straight to the power line , if you have the transformer to take the transient power, for small motors if you dont need speed controll , just use a contactor if you have a powerfull and stable power supply.

[crying_baby 0]

hi santiago, is it possible to control the speed of of a motor using a PWM? PWM = pulse width modulator i presume PWM is a type of inverter corrrect me if i m wwrong. btw i need some words of advices if its feasible to control a motor's speed, thru a pwm, using PLC. thanks buddy :Respect:

[KinK 0]

OK it is technically possible but would probably end up costing as much or more than just buying the inverter... that is what they are there for.

[larry818 0]

For single phase motors, as long as they are shaded pole or permanent split capacitor (psc), you can control them with a chopping type light dimmer. Most dimmers these days are choppers. For three phase motors, you can use a three phase chopper. They exist for controlling heaters, but aren't significantly cheaper than VFDs. Choppers are useful if you want to GFCI protect the motor circuit. VFDs are so noisy that it takes a GFCI with active filtering to protect the circuit. There's only one manufacturer in the US that does that, and they are expensive. Inverter is a terrible term. It actually refers to that buzzing mechanical oscillator used in old car radios to make AC power for the tubes. Ever since then, anything that modifys power has been called an "Inverter".

[crying_baby 0]

ok the cost is not a matter at the moment but.. this control of induction motor had already existed in the past. in my thesis, i m to control the speed, position, started and brake of teh motor bvy means of pLC. according to wat i came /r3ead acrosss in books, this method is cabpabpel to be very accurate and economical. and fast as well this project thesis is using PLC theory and dealing with induction motor -inverter fed control in 1 package design. the project is on hardware programming and implementation just to obtain a simple outcome result of speed, position and fast breake control for the induction drive. task 1) programming the PLC on PC to give the right and the wanted signal to the inverter 2)implement the hardware drive action for the motr control any1 please offer some advice on how should i start and where should i start plz thank a milliona :respect:

[Sleepy Wombat 27]

What books have you read...and more to the point how throughly have you read them past the point that Posistion...what posistion are you referring to ????? Positional data as fed back from an encoder mounted on the motor to aid in the firing of the transistors to obtain your control, or for posistioning of a table, or belt that is driven by the motor ????? Finally have you ever typed in google "induction motor PWM control circuits"..... Students of today have what i consider a wonderful recource in the internet, that i or neither did a lot of others have at our finger tips when learning, we either purchased books or went to a library or asked some one of experience after we had made an initial effort and had come to a halt and needed pointing in the right direction, we never ( well i never got or expected the whole solution from them ) .... So my point being is that make a little effort and a number of people will be willing to help, if you are lazy then expect lazy answers as well.

[crying_baby 0]

thanks for your useful advice. i m now at a holiday and i plan to start finding resources now rather than wait till my semsester starts,. btw the possition i will double confirm from my prof. thanks again for your advice and the books u recommend , man Respect

[santiago 0]

it all depends in the motor you choose , if you chhose DC or Step , then PWM (pulse width modulation) will be OK , provided you have a PLC with a fast transistor output. If you are using asynchonus AC motors the simple way is to controll speed with an inverter and a PLC with an analog output. For the price it all depends on the size of the motor, you can get quite cheap inverters today , if you use a 0.12KW motor a small inverter (single phase input ) should be around $150, and you can get a small PLC ( smart relay type) with an analog output for around the same price.

[crying_baby 0]

ok thank santiago i will figure something out at the moment. will reply again when i got prob thanks man :))