Identifying extra wires from AC induction motor

[bigal_scorpio]

I have been given a motor by a mate, it is a Carpanelli MM63b2 230v AC .25Kw 2820rpm.

It is dated 25/3/09 and looks like new. It works beautifully, smooth and quiet and is just the job for a Woodlathe I am planning to build.

I plan to have speed control on the lathe and maybe a readout of the speed. I have built a previous rpm meter for a machine before using a Pic micro and a light sensor etc but this motor has something which I may be able to use for that! IF I can figure out what the motor has in place?

Inside the motor's connection box beside the normal mains in connectors is a small hole which is plugged with sponge. Two thin wires go through this, one red and one blue. They seem to be going to the bearing end part of the motor. I would usually just split the motor to discover what they go to but I would rather not as the motor is so good!

I have measured across the wires and get 71 ohms whether the motor is spinning or not so I am wondering what they go to and how to test any theories as to what they could go to?

Any ideas would be appreciated as stripping the lotor is a last resort.

Thanks, Al

 

[fernando_g]

A thermistor to monitor bearing temperature?

A very simple test. Attach an ohmeter to the wires and read the resistance at room temp. Then with a hair dryer gun, heat where the wires go... if the resistance starts to change, bingo, you have a thermistor.

 

[alec_t]

Another simple test; see if any output voltage is produced between those wires (preferably using a 'scope) when the motor is running.

 

[scubadog]

6 wires would be normal for an AC motor. It gives the option of wiring in either star or delta. I would expect two ends of the windings tko show continuety.

 

[bigal_scorpio]

A thermistor to monitor bearing temperature?

A very simple test. Attach an ohmeter to the wires and read the resistance at room temp. Then with a hair dryer gun, heat where the wires go... if the resistance starts to change, bingo, you have a thermistor.

Hi Fernando, I'm liking the temperature idea!

Just ran the motor for about 6 minutes and cold the wires gave 72.6r and dropped steadily to 53. It seemed very linear so I should be able to use that in my build. A little overheat protection never hurts but I guess I will have to fall back on the old slot opto for the speed regulation feedback.

Anyway good catch mate!

Al