DC motor housing

[markyli]

I am a product engineer in a home appliance firm. I have the following questions:

1) How is motor housing affect the performance of the DC motor?

2)If the thickness of housing reduced as a result of cost reduction, what kind of problem will be induced into the DC motor?

 

[GusD]

Hi and Good day.I will take a stab at it .
Because of DC MOTOR commutation,the frame plays a large part on the motor magnectics and may impair proper commutation.Depending on the motor type,it may have shims under the poles, they may be required to be made of magnectic material or non magnectic t depending on the motor design.All of this may affect commutation.
As for the motor Frame thickness ,I don't know of any requirement other than it has to be strong enough to withstand maximum torque developed by the drive.
My stat. GusD

 

[UKpete]

GusD, sorry to contradict but the housing thickness is very important to the performance of the DC motor as it carries all the main pole flux. Because this flux is DC it is not necessary to use a laminated frame (except in special circumstances e.g. in a variable speed motor where you want to change the torque quickly). Incidentally the main poles are laminated only because the slotting effect of the armature would cause eddy current losses in the pole faces.

This is why DC motors are often so heavy, for example a DC traction motor (ok, not exactly a domestic applicance application but the principle is the same) can require a solid steel housing 25-35mm thick - and not because it is needed for physical strength. If you thin them down they will be running "weak field" i.e. at a particular voltage they will want to run at a higher speed but with less torque available. This applies whether the motor is series, shunt, compound or sepex. And the lower the number of poles, the thicker the frame needs to be. For the housing you need to use a high permeability steel and the required thickness is a simple calculation based on the main pole flux.

markyli, this all assumes that you do mean a DC motor and not a universal motor - these need to have laminated stators because they are required to run on AC, and any outer housing may not be part of the magnetic circuit so its thickness is simply determined by mechanical requirements (I only mention this because they are common in domestic appliances).

 

[GusD]

UK Pete.

You are right Pete.I was focusing on the mechanical aspects of the frame,and forgot to mention the magnectic concerns which you so well described.
Thank you Pete
GusD

 

[markyli]

Thanks guys. This have been very useful, it enlighten me a lot.

 

[induction]

Field cases are very important As pete describe even cleaning the case such as sanding can change the motor power output.