Motor temperature sensor

The FB1-4001 from Advanced DC motors is far from having all the bells and whistles you'd hope for. In fact the only sensor it has is an on/off over heat sensor that is open until the temperature has risen too high in which case the circuit closes. This is great for a dummy light or buzzer but for those of us who want real numbers all the time you'll have to make your own.

I found a large bolt hole that I think was used to hoist the motor into the crate. It's a 5/16 course thread and looked like a good spot to mount the sensor. I bought a 1" 5/16 bolt, washer and a nut. The reason for the nut is so that I can shorten the bolt and then remove the nut which helps to clean up the threads after cutting them.



After cutting the bolt I drilled a hole down the center of the bolt. The sensor will be installed here later.



The sensor is a LM34 from National Semiconductor. There are quite a few ways to use this little guy depending on the temperature range you need. I'm just using the basic setup which allows for 5-300 degrees Fahrenheit. Each degree will change the output signal by 10mV. Then by using an analog to digital converter (ADC) you can get a nice digital readout of the temperature. Below is the sensor after connecting it to three wires and heat shrinking them so they can't touch.



Next I wrapped the whole thing in another heath shrink layer to hold it all together.


We are now ready to mount the sensor so I mixed up some JB weld.


I filled the hole with JB Weld and then inserted the sensor.


The other side of the sensor after JB Weld.



After it dried I applied a coat of paint. This is a steel bolt and will rust if not protected.

Finally here is a shot of the new sensor installed in the motor. Later when finalizing the wiring during install I will protect the exposed sensor wires in a wiring loom.



Here is the output from my debug terminal. I tried running the motor for awhile but with no load and only 12 volts going through it the temperature didn't rise. I did take the sensor and set it in direct sunlight and it went up 10 degrees in just a few minutes. The picture below is showing the ADC value that is being returned. It's a 12 bit ADC (0-5v) but you could easily go with less accuracy for the sensor.