Dumb Question on DC Motors!

[dave12]

I know this isn't House Electrics, but I thought someone might be able to help.

When checking the resistance between the +ve & -ve Busbars on a large DC Motor, is it right to have a short Circuit?

The DC Motor is a Brush Motor.

Many thanks

 

[plugwash]

Please define what you mean by "short circuit" and tell us some specs for this motor.

The stalled resistance of a DC motor is very low. That is why it is vital to have overload protection on motors. A stalled motor will almost certainly cook itself if there is nothing to stop the current.

 

[GaryMo]

Field winding will probably be high but armature winding may be very low and seem like a short circuit (less than 1ohm).

 

[dave12]

Hi Thanks for the replies!

The Motor is a 550V 1280KW Ansaldo DC Motor. It is fed from an SCR Unit.

The tests I have carried out are accross the in coming + & - (Armature?) the resistance is 0.7ohm.

I have also IR Checked each to ground and got >50Mohm.

Io my mind it seems ok. But my understanding of these systems isn't great. Any thoughts?

 

[tim west]

The unit will limit the current (usually through an H-Bridge) until the motor has gained sufficient speed for the back EMF to counter the supply voltage and current flow drops to an operating level.