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Starting Resistance (1 Viewer)
- Thread starter Cheezy-G
- Start date
zenger69
Bok Choyer
when motors start-up the back emf is really low as it isn't really doing any work. Therefore the current needs to be put into series to keep the current as low as possible to reduce risks of surges or overheating.
when motors start doing work, thats when back emf builds up and this resists the applied emf. Then the current is put in parallel (as the back emf becomes to resistor) to make sure there is enough current to overcome the back emf and power the motor.
hope it helps.
when motors start doing work, thats when back emf builds up and this resists the applied emf. Then the current is put in parallel (as the back emf becomes to resistor) to make sure there is enough current to overcome the back emf and power the motor.
hope it helps.
m_isk
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once a motor is rotating, it is, in essence, behaving as a generator. Why? because you have a moving conductor (the rotating coil) in the presence of a magnetic field, and thus there will be an induced current. According to Lenz, the direction of the induced current should be in such a way to oppose the cause which created, which, in this case, is the rotation of the rotor. Therefore, there is an induced EMF which opposes the supply EMF, hence the term "back" EMF.
When the motor is starting, there is no back EMF, because there is no induced currnet due to the absence of relative motion between the rotor and the magnetic field. Using Ohms' V=IR, a very large voltage will result in a very large current which will blow your motor to smithereens.
TO counteract this, we use a starting resistance, which limits the potential difference (voltage) and thus the currnet flowing through the circuit. Why do they call it a STARTING resistance?? Because once the motor is rotating, the BAACK EMF will limit the voltage for us, and we turn off the starting resistance...
if i'm being ambiguous in any way, let me know... :uhhuh: :uhhuh: :uhhuh:
When the motor is starting, there is no back EMF, because there is no induced currnet due to the absence of relative motion between the rotor and the magnetic field. Using Ohms' V=IR, a very large voltage will result in a very large current which will blow your motor to smithereens.
TO counteract this, we use a starting resistance, which limits the potential difference (voltage) and thus the currnet flowing through the circuit. Why do they call it a STARTING resistance?? Because once the motor is rotating, the BAACK EMF will limit the voltage for us, and we turn off the starting resistance...
if i'm being ambiguous in any way, let me know... :uhhuh: :uhhuh: :uhhuh: