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Topic: Using an Allegro ACS713 as a sensor for over current protection (Read 142 times) previous topic - next topic

schmarduino

Hi all: I want to build a DIY, latching over-current circuit using an ACS713 type current sensor (12-page data sheet: https://www.allegromicro.com/~/media/Files/Datasheets/ACS713-Datasheet.ashx)

The sensor's output would go to a Nano acting as the supervisory element.  I want to use it because I think it might act faster than a fuse and this would be for use in my power supplies feeding prototyping circuits. When it trips, it will energize a relay that interrupts the current and is reset with a push of a button.  Not saying that I ever make mistakes.....:)

herbschwarz

A "crow-bar" circuit is commonly used for over-current protection.

Ron_Blain

Well fast acting fuse and crowbar circuit aside you can use an ACS 713 as you mentioned. The down side is the ACS 713 with 0 Amp current outputs about 0.5 VDC. It comes in a 20 and 30 amp version. The 20 amp flavor outputs a nominal 185 mV/A so 0 to 20 amps becomes 0.5 to 4.2 VDC out which isn't bad. Now if you want 20 Amps that is fine but 20 Amps is a pretty large chunk of current. Really depends on what your projects are I guess.

Another possible would be an ACS 712 which includes a 5 amp flavor for lower current. The x05B PERFORMANCE CHARACTERISTICS give you an output of 190 mV/A with a 0 Amp output of 2.5 volts (1/2 VCC). The ACS712ELCTR-05B-T Interfacing with Arduino Uno is easily done and the chip offered on a modular board making life easy. Here is an example with Arduino interface. Just a matter of modifying the linked code to give a latch from a DIO port. Could also add a display to display current if your source PSU doesn't.

So yes, any number of ways to do what you are looking to do.  :)

Ron

schmarduino

Thank you Ron!  The attached links with Arduino code are especially useful!  I owe ya a car wash!

Semtex9

Hall probes are inacurate at low current, and get more accurate at the top of their range, but you can do it.

If you need a cutting edge response, you can swap out that relay with a mosfet or igbt, and drive the gate with a flip-flop and antiparalel diode to gate resistor, so the gate gets grounded immediately at signal loss. Select a double power rating transistor then your circuit.

If you want even better speed eliminate the arduino for this, and make a voltage comparator for probe and reference to disengage the circuit like herbschwarz mentioned.

You can still tap the probe with arduino if you want measurement, or you can tap the relay or error line if you want your arduino to know when your protection activates, thus less work for arduino, and way better speed protection. If arduino needs to operate the relay(mosfet), then you will need dual control, so the protection circuit can override the arduino.

IMHO always better to have independent protection, and its not very complicated.

schmarduino

Thanks semtex9!  I really like the dual monitoring method you mentioned and I didn't know about the HE sensors being more accurate at higher current levels. 

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