Simulating any PMDC motor during Hydraulic Pump testing

A practical problem will be the lead time between specifying and receiving PMDC motor samples, particularly if specifying a custom motor. Custom motors are best specified as slightly modified versions of existing motors which the supplier is tooled up to produce in volume. The motor manufacturer will probably be able to inexpensively produce a custom motor curve by changing the motor stack height and windings. Be aware that changing brush compounds and even the wiring harness can also have a large impact on motor performance.

The motor samples you have access to will likely have dynamometer curves, probably for that specific sample. Recall what was mentioned in the PMDC motor post: the rpm vs. torque curve of a motor can be varied arbitrarily and systematically simply by changing the no-load rpm (by changing supply voltage): the slope of this curve is unchanged, and the current vs. torque curve can be assumed to be unchanged.

Since you have a motor of known performance, you can vary its rpm from baseline and still know its efficiency. This is important since it allows you to divide out the effect of motor efficiency and thus have complete knowledge of the pump input and output parameters: Power In is torque * omega, Power Out is pressure * flow rate.

Better still, by varying the supply voltage, you can make any PMDC motor simulate any other motor, within reason. You will need to use your mathematical model of the motor to determine the rpm as a function of voltage and torque, and to vary the voltage for each data point (use the amps to infer the rpm). You can also put a strobe light on the motor and measure rpm directly a a check.

This simple trick saves you a huge amount of time, particularly if the motor supplier can generate predictive curves of their motor using their own software, thus allowing you and the supplier to work together on a design before a motor sample needs to be built.

Matching of a pump to a motor is easy if you have power to burn, but more challenging if you are on a power budget, which is common for PMDC applications.

You might be tempted to save having to add a relief to your system by stalling the motor at some relatively low pressure. It is OK to do this by deliberately designing a "leaky" pump, which deadheads against a pressure that is safe for your system, but it is definitely not acceptable to stall a motor in order to stall a pump. Depending on the design, damage to the motor  is likely.