anshulkumar1234
Branch Unspecified
25 Jan 2008

# significance of back e.m.f. in d.c. motors

can any one plz write to me the significance of "back emf" in came of d.c. motors....plz write to me at " anshulkr123@rediffmail.com " ....
11 years ago
anshulkumar1234
can any one plz write to me the significance of "back emf" in came of d.c. motors....plz write to me at " anshulkr123@rediffmail.com " ....
Hi Anshulkumar,

I think this post should better be placed in Electronics & Electrical Engineering section.

[Moving the thread to Electrical /Electronics engineering section]

anshulkumar1234

Branch Unspecified
11 years ago
can any one plz say me the significance of " back e.m.f. " in case of d.c. generators....plzzz do reply to me at " anshulkr123@rediffmail.com "

litjo

Branch Unspecified
11 years ago
Back emf in a DC Motor plays a role of a regulator,We know the basic equation V=IaRa+Eb,where Ia,Ra are is the current through and resistance of the armature coil,Eb is the back emf and V is the Pd applied.Consider,
Ia=V-Eb/Ra,The value of Ra is really small, just a few ohms and V would generally be around 240-220V(Indian conditions),assuming Eb to be zero(at the time of starting),it shows that Ia comes to be a really large value that the motor coil can barely handle,thats why we use a 3,2 POINT Starter that avoids large starting current,Now in the running condition of the motor Back emf would naturally be produced(say around 200V) this tends to reduce the value of(V-Eb), thus stopping a large current from entering the coil.But as the Load applied to the motor increases , Back emf would naturally come down to allow more current to enter the coil upto its rated value,to deliver the load requirement.thus Eb acts as a regulator.(Eb opposes the applied voltage)

just2rock

Branch Unspecified
11 years ago
well to be very simple back electro motive force...itself describes wat it means.. d.c motors itself generate an force equivalent to V=I*R+Eb,whre Eb is the BACK E.M.F gereated by armature COIL of motor,actin as an Feedback OPAMP in my ELECTRONICS or as an REGULATOR in electrical terms

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