DC Motor Winding Selection

Learn how to select the optimum motor winding with Dr. Urs Kafader from the maxon academy. The starting point is a given motor type that has been selected previously according to the speed, torque, and service life considerations.

Transcript

00:00:01 [Music] this tutorial shows you how you can find the optimum winding for a Maximo tur starting point is a given motor type that has been selected previously according to speed torque and service life considerations please refer to the corresponding max and selection videos for more details for a given motor type you can choose

00:00:29 between different windings the purpose of the winding selection is to match the available electrical power current and voltage to the required mechanical output power of the motor it is torque and speed the different windings of a motor type are listed in columns the resistance increasing from left to right the first winding on the left is made with a wire of the largest diameter

00:00:53 accordingly it's resistance is low when the currents needed are high however at the low voltage the last winding on the right is made with the thinnest wire the resistance and the needed voltages are high but there is only a low current flow looking at the mechanical output of the different bindings we observed the following the mechanical motor limits

00:01:18 are almost identical over the winding series the maximum speed remains the same the nominal torque is the border of the continuous operating range is almost identical for all the windings the speed torque line describing the mechanical behavior is almost identical to it's about 175 rpm per million Newton meter in this example the particular nominal voltage of each winding is selected to

00:01:44 give a similar no-load speed for all the windings essentially this means that from a mechanical point of view there's hardly any difference between the windings each one can do the job the difference lies in the electrical characteristics here is a graphical representation of the findings of the previous slide the operating range diagram of one winding

00:02:10 can stand for the full winding series the speed torque lines lie in a narrow band and start at similar no-load speed this is how the nominal voltage is assigned to each winding for a particular application however the available voltage is given and the objective is to reach all the operation points with this voltage usually the most demanding operation occurs at the

00:02:36 end of the acceleration it is the one at maximum speed and maximum torque all the other operation points can easily be reached by reducing the voltage a task usually done by the controller therefore let's concentrate on the extreme operation point and see how the different windings can reach it with the available voltage selecting the winding with 24 volt nominal voltage similar to

00:03:04 the available voltage may not be the right choice here the acceleration cannot be fully achieved the winding to the left in the catalog with a higher speed constant of 705 rpm per volt and the nominal voltage of 18 volt covers all operation points easily when operated a 24 volt speed or position controller will adjust the motor voltage to the lower values needed however the

00:03:32 current to reach a particular torque is higher the windings with 12 or 9 volt nominal voltage won't make good use of the 24 volts available and the currents needed are even higher the remaining two windings with higher nominal voltage cannot reach the required speed because the speed constant is too low in other words the winding selection is a matter of calculating the minimum speed

00:04:01 constant required to reach the speed on the load given the peak torque and maximum speed of the application as well as the available motor voltage we calculate the speed constant that theoretically can just fulfill the task the formula uses the speed and torque of the extreme operation point and Delta in our Delta M the typical or average speed torque

00:04:26 gradient of this motor type from a graphical point of view the formula calculates the no load speed associated with this operation point and divides it with the available voltage at the motor selecting the optimum winding is now a question of comparing the speed constant of the different windings with this minimum value what we need is a speed constant larger than the calculated one

00:04:54 let's illustrate this with an example assuming that the extreme operation occurs at 10,000 rpm at 19 million Newton meter with 175 rpm per milli Newton meter speed torque gradient and 24 volt supply voltage we end up with the speed constant of at least 555 rpm per volt a glance at the catalog page shows in line 13 that the first three windings

00:05:23 fulfill this condition the winding with 24 volt nominal voltage is just a little short selecting the winding with 18 volt nominal voltage gives us a nice speed Reserve the speed torque line lies above all operation points optimally the selected speed constant should be about 20% higher than the calculated one this gives us some Headroom for proper

00:05:50 control and to account for all kinds of tolerances however do not select a speed constant that is too large because this means that the available voltage is not used well and that you need a lot of current from power supply in controller a remark just to make things clear do not refer to the nominal voltage for the winding selection the nominal voltage is just the reference voltage for

00:06:16 specifying modes it's irrelevant for the motor selection that's it a short introduction on winding selection in conclusion the optimum winding uses the available voltage well and requires the lowest possible current and don't forget you have to know the extreme load operation to make a proper winding selection good luck

00:06:46 [Music]