Dear Reader,

Recently Eric posted an educational entry on Power Factor. To demonstrate some of the AC measurement capabilities of the Mooshimeter, I set up a quick demo to measure power factor and harmonic distortion in a kitchen blender.

Like many blenders of a certain era, it has two “Major” settings – Low and High – and three “Minor” settings, which give it a total of 6 speeds.  There are some “Pulse” buttons in there too, but we’ll ignore those for now.

Since I was only interested in the power factor and not the absolute value of the current being drawn, I decided not to run the current directly through the meter.  Instead I would simply set up the high voltage channel to measure the AC voltage at the wall, and use the precision voltage channel to measure voltage drop along a section of the wire supplying the blender.  Since the two voltage channels share a common port, this is a 3-lead measurement.

The high voltage channel is connected to the voltage outlet at the wall.

The precision voltage input is attached to the AC neutral line to pick up resistive drop in the power cable

The two voltage channels share a common line.

The power factor can then be easily diagnosed from the Mooshimeter using XY capture mode.  In the captures below, wall voltage is shown on the X axis and voltage drop in the wire (proportional to current) is shown in the Y axis.

Here are three power factor graph screenshots from the three “low” settings of the blender: “Puree”, “Crumb” and “Chop”.

There are a few interesting things to notice.  First is the fact that the current is only flowing in one direction.  It seems that the blender’s “low” settings simply shut off half of a rectifier, so for half the AC cycle negligible current is flowing to the wall.  Also notice that as the setting is increased, the amount of current drawn is increased and the shape of the graph becomes less round and more elongated… speaking roughly, an XY power factor diagram that’s more rounded has a greater reactive component than a diagram that is more linear.  As the setting on the blender is turned up, the resistive components of the system (winding resistance, motor friction) increase in proportion to the reactive components (winding inductance, motor inertia).

Here are three power factor graph screenshots from the three “high” settings of the blender: “Beat”, “Blend” and “Liquify”.

Notice that the current flows in both directions in all 3 of the above diagrams.  Also notice that as the setting is increased, the shape of the diagram changes in the same way as before, with the profile becoming more resistive and less reactive.

Just for fun, let’s try to change the shape of the diagram by changing the operating conditions of the motor.  All the profiles above were taken with the blender empty.  How does the power factor diagram change if we fill the blender and in doing so change the load of the motor?

High setting 1, blender empty

High setting 1, blender full of water

The blender drew about 50% more current, but not much change to the basic shape.  I need to find a more exciting electrical load…

Thanks for reading, comment with ideas for the next thing to analyze.