d.c. motors

We have a portainer crane,it has 12 d.c.motors to drive the crane in a longtitudual direction.The motor armatures are connected in parallel,with a load sharing resistor in series with each armature.The motors are supplied by a a.c. /d.c. converter.My question being how does the load share accross the motors if one takes more load i.e.due to a tight gearbox om one drive.
Thanks micky beard

If one motor has more load than the others, it draws more current. The larger current produces a larger voltage drop across the load sharing resistor and hence a lower voltage on the motor. The lower motor voltage tries to make the motor run slower resulting in less load on that motor. The motor does not actually run slower since all the motors are coupled together through the wheels but the load on that motor is reduced.

If one motor has a large additional load such as a tight gearbox, that motor will probably end up freewheeling and the other motors will be driving it through its wheels and gearbox.

I have seen DC motors where the series field of motor A is connected in series with the armature of B and vis versa. Thats another way of sharing the load
Roy

Thanks Vic