Brushless motor current


Thread Starter


I am interested in measuring the no load and load current (20.0 in-lb) of two brushless motors. (I do not have much experience in brushless motors), I tried already with an oscilloscope, but with no load the rms current changes to much. since this is totally different to induction motors, I would like to know what the best way to measure it would be, Where can I find aditional information?, and what devices can I find in the market (No to expensive).
Thank You.
Some servo drives can record the current curve and you can use a PC to retrieve and save in files.
What are you interested in - RMS or waveform only? Either way, first you need to accurately capture the waveform. Unless it is a slow fixed speed application with sinusoidal commutation, those current clamp type devices may not read accurately because of the higher frequencies in complex waveforms, typical of brushless motor apps. One method used to evaluate any kind of waveform is: Hall isolated current probe with digital scope that has RMS measurement function. The newer scopes e.g. Tek phosphor TDS3000 series
have built-in current probe amplifier/converter stage. You simply plug the current probe into the scope and away you go. Capture a time slice of the
current waveform and apply the RMS function over any section of the waveform.