Good day, I have an ACS712 Current Sensor that has an operating current of 20A. I only intend to measure less than 15A but I have a circuit that sometimes exceeds the 20A operating current, giving more than 50A.
I'm planning to use a relay switch to turn off the ACS712 Current Sensor when it reaches 20A to prevent any damages to the sensor.
Does the current sensor still has limit even if it's off? And if not, what is the best approach for this set up?
The limit is defined by the internal resistor that can be burnt by a too high current.
The chip can withstand pulses of 500A for 100 ms, perhaps (not specified) 50A for 1 s. But how do you want to detect currents above 20A so that you can short circuit the sensor in time?
A 50A relay is a big one, too. What are you planning to use? Why not just add a shunt resistor?
As I said, I don't wanna detect current above 20A, I only need to measure less than 15A. But unfortunately my power supply exceeds 20A and goes over to 50A, this could damage the sensor. So I want to know, will the 50A can still damage the 20A current sensor even if the sensor is off?
So how else do you know when to turn the sensor on and off?
That does not prevent damage.
If the current sensor measures more than 15A, I plan to use a relay to turn the sensor off and manually turn it on. But I guess even if the sensor is off, the current always passes and it can still damage the sensor.
May I ask how can I apply the shunt resistor to ACS712?
Not for the 'faint of heart', but here's an app note on measuring higher currents with the ACS712:
It's a fairly old device, so you might look around to see if there's something more in line with what you need to do.
But if you stick with the ACS712, remember, you cannot recover based on what you cannot measure. Even if your ACS712 could handle infinite current, and had a method of being turned off/on such as what you suggest, how could you know to turn it back on when the current drops to measurable range again, given that you've 'shut it off'? Or will you require some form of manual intervention to resume measurement?
C
All shunt resistors are parallel resistances.
Unfortunately the internal resistance is not specified, and the data sheet warns about different temperature coefficients of internal and external resistors. If it's only about extended range then I'd look for a 50A module.
Sure, although in this application it's just sensing a "trip point" that might not be required to be very accurate. But it would have to be tested/calibrated for those reasons.
We never asked if the galvanic isolation is really required. If not, an amplified voltage reading across a commercial shunt would work.
Actually I don't see where we were told whether it is DC or AC. If it's AC then a current transformer circuit can work.
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