Motor analysis in Heat Pump - Page 1
Forum section: electronics / projects

author: kevinateev
author_rank: Regular Contributor
timestamp: December 30, 2017, 05:50:39 pm
content: Hi all,Got my new scope here and want to document how this motor and controller are working. Firstly, the motor is for a fan application. The part code is WZDK58-38G and for the life of me, I could not find any specs on this motor!Here is the overall rig. On the furnace is the internal control board to a Senville Heat Pump. I’ve replaced the one it came with with an A style coil that is in the ductwork now.(img 1498)Here is a closer look at the control board. I’ve made an intercepting cable that is in my breadboard here and the motor is off to the right.(img 1497)A closer look at the wiring setup shows this: the wires from top down are Red (Vm), Black (Gnd), White (Vcc), Yellow (Vsp), and Blue (PS). By checking with a multi-meter, the Black wire is at -120VDC relative to Earth ground so I put a 10Meg Ohm resistor between that and the Earth Ground lead of the Oscilloscope probe. The probes are set to 10Meg Ohm themselves. I know this is going to screw with accuracy but this circuit is hooked up to my Heat Pump, not to easy to isolate that etc.(IMG 1496)Here is my first measurement. CH1 is Vsp and CH2 is PS. Red is the difference between them. The scope is DC coupled here, it looks like my power supply is full wave rectified and not much else for this motor. The difference shows very clearly a return pulse from the motor’s PS line.(PRINT 05)So, I crank up the speed of the motor and sure enough, the pulse gets shorter in time. Given knowledge of how fast the motor is spinning approximately, it looks like the feedback pulse is a result of a flip-flop circuit hooked up to a single hall sensor internally to the motor. That is, the signal flips between Vcc and GND references once for every revolution. Cool, hadn’t seen that before.(PRINT 10)In comparing ground to Vsp, all I got was this (below) — I’m now looking for the driving signal to the motor. I don’t trust it however because I don’t see any change from one speed to the next and it’s frequency is suspiciously close to line frequency.(PRINT 11)The only other signal information I could find was between Vcc and Vsp. This pulse also looks suspicious as it didn’t change with motor speed changes either. Also it is close to line frequency also.Anybody got any ideas? The RPM of the motor is between 250-600 RPM (I don’t think it went over 500 in the above screen shots) so, the frequencies measured close to 120Hz may be realistic. Also, there is no load on the motor so this may also have an effect. I did load the motor with my finger a bit, pinching the shaft, and did see phase changes on PS signal but that was it.(PRINT 20)

author: kevinateev
author_rank: Regular Contributor
timestamp: December 30, 2017, 05:57:00 pm
content: The remaining photos here.(PRINT 05)(PRINT 10)(PRINT 11)(PRINT 20)

author: kevinateev
author_rank: Regular Contributor
timestamp: December 30, 2017, 06:05:17 pm
content: Here is a link to my first video into this subject. Sorry for the annoying qualities of this video, I'm such a newb. Next one will be better..Provides some context to task anyhow.https://youtu.be/fpdHFLBdKP0