Mxx75, Mxx76

[terrydeltasigmacorp.com]

What are the units of Mxx75 and Mxx76? How do I use these values to calculate motor current?

 

Thanks

[curtwilson]

The units are a little abstract, but let's go through the process. We'll call Mxx75 "Iq" and Mxx76 "Id".

 

The vector magnitude of the current in these "field coordinates" is the vector sum of these:

 

Idq = sqrt(Iq^2 +Id^2)

 

In a three-phase motor, this corresponds to a peak ADC current reading on a phase that is 1.15 (1/cos(30)) times larger. (For a 2-phase motor, no conversion is necessary.)

 

For your particular amplifier, you must find out what the maximum phase current reading (which corresponds to a number of 32,768) is.

 

Let's say your Idq is 10,000, so your peak ADC phase current reading is 11,500. On a Turbo Brick AC 5A/10A drive, the maximum phase current reading is 16.26A. So your peak phase amperage is

 

I(peakphase) = 16.26A * (11,500 / 32,768) = 5.70A

 

Now, generally people want to express current in a 3-phase motor as RMS, not peak, and as full motor current, not single phase current.

 

To convert from peak to RMS, multiply by 1/sqrt(2) (0.707). To express as full motor current, multiply by 3/2 (1.5). So in our example, we get:

 

I = 5.70A * 0.707 * 1.5 = 6.05A