current sensing

hi. I'm using a 12v permanent magnet DC Motor with a overheat protection. it draws 10-15A current when blocked and I would like to count how many times the thermal protector switches on and off when Motor is in blocked condition. anyone can help?

darshana_hegdeb:
hi. I'm using a 12v permanent magnet DC Motor with a overheat protection. it draws 10-15A current when blocked and I would like to count how many times the thermal protector switches on and off when Motor is in blocked condition. anyone can help?

You will need both a temperature sensor for the motor and a current sensor for the power. You need to be able to determine why the power was interrupted so you are not counting normal on-off of the motor. Temperature range needs to be determined before a proper sensor is chosen.

Paul

The voltage across the motor will drop to zero when the switch opens.
Sample the voltage via a resistive divider once per second and count the number of times it transitions from high to low voltage.

mikb55:
The voltage across the motor will drop to zero when the switch opens.
Sample the voltage via a resistive divider once per second and count the number of times it transitions from high to low voltage.

Quite doable if the temp switch is external. Most motors monitor the winding temperature with a sensor in bedded within the windings, because that part gets hot first.

Would help to know what the motor actually has.

Paul

Isn't it the motor power wires that you'd watch the temperature switch act on? Temp high, cut power till it cools. OP knows the motor will overheat when stalled, no need to get at the sensor, just watch the results on PWR and GND.

Motor being inductive, won't there be a backsurge (through the protection diode you're supposed to have in your motor circuit) every time it's switched off?

Thanks for the suggestions. My problem was not regarding the sensor however it was regarding the number of times it switches on and off. Anyway I did it using ACS712 Current sensor. I monitored the current passing through ACS and when it gets back to zero I use it for counting. Works perfectly. 8)

The temperature sensor won’t sense a problem until heat builds up while using the current sensor to turn power off prevents the excess heat and waste. Question is, how often do you check to see if it’s unblocked and what does this blocking?