Sunday, August 24, 2008

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.


Anonymous said...

Would it be possible to share more details on the debugging software that you are using and how you are connecting it to your laptop? I need to get my tach working as well.


Brian said...

The debugging software is a free download from It of course is required that you have one of their microcontrollers.

Here is a link to the kit I bought from them years ago. It's been great to finally find a real project to use this on :)

So basically you can write some simple code that tells the microcontroller how to read different types of sensors and then for debugging I'm just writing some information to the debug window.