Ideas for 120 VAC fan motor failure detector.

[Rulemob]

Im trying to figure out what the best way to detect a failure of a 120 Vac fan motor. Mainly a burnt open windings situation. I was thinking about maybe having a light thats on to indicate fan is still running and it goes off when motor fails. This motor is inside an enclosed oven measuring 7.5" x 7.5" the temperature in ove reaches 100 to 140 degrees celcius. i have acces to the wires for line and nuetral wires on outside of oven box. i was thinking maybe putting a bridge rectifier circuit in series with line voltage to power a LED so if windings burn open dc voltage to LED quits thus shutting off LED. Also maybe a relay type sensor in line? Im not sure looking for advice or insight from people with experience. thanks for replying.

 

[Gryd3]

Im trying to figure out what the best way to detect a failure of a 120 Vac fan motor. Mainly a burnt open windings situation. I was thinking about maybe having a light thats on to indicate fan is still running and it goes off when motor fails. This motor is inside an enclosed oven measuring 7.5" x 7.5" the temperature in ove reaches 100 to 140 degrees celcius. i have acces to the wires for line and nuetral wires on outside of oven box. i was thinking maybe putting a bridge rectifier circuit in series with line voltage to power a LED so if windings burn open dc voltage to LED quits thus shutting off LED. Also maybe a relay type sensor in line? Im not sure looking for advice or insight from people with experience. thanks for replying.

Do you know the current draw of the motor?
If you used a 'shunt' resistor, you could measure the current through the fan.
The voltage across this 'shunt' will be high under a heavy load, and low under a low load... it will be 0 when the fan fails in an 'open' condition.

 

[Rulemob]

yes i know the current draw is .08 amps, ill look into shunt resistor. thanks for input.

 

[Gryd3]

yes i know the current draw is .08 amps, ill look into shunt resistor. thanks for input.

Because you are dealing with a high voltage, please observe as many safety rules as you can.
Don't work on it alone, don't work on it while it's live, please post the drawing of the circuit you wish to use, and don't leave it unattended.
There is lot's more of course, but I'm not familiar with your current expertise in the subject

 

[Minder]

An ideal device such as Honeywell CSDA current sensor works on a non invasive method, but I am not sure if they go that low.
M.

 

[Rulemob]

yes i know the current draw is 128ma, ill look into shunt resistor. But dont shunt resistors only work on dc circuits.

 

[Rulemob]

An ideal device such as Honeywell CSDA current sensor works on a non invasive method, but I am not sure if they go that low.
M.

They only go as low as .25A but thanks.

 

[Gryd3]

yes i know the current draw is 128ma, ill look into shunt resistor. But dont shunt resistors only work on dc circuits.

Depends on your installation/circuit.
A shunt resistor simply sits in-line with the device being powered. If you are using AC, then the shunt resistor will have an AC voltage drop across it.
You measure the voltage drop across the shunt resistor to determine the current draw.

You only have 3 options:
- Invasive device in series with the fan. (The Shunt Resistor)
- Non-invasive current sense. (A Split Core Current Transformer)
- Non-invasive / Invasive sensor on the fan itself to detect rotation. (Hall sensor, optical sensors, etc... May not be viable based on the location of the fan)

 

[Minder]

They only go as low as .25A but thanks.

You should be able to increase the sensitivity by use a couple of repeated turns instead of single conductor.
M.