acs712 current sensor for protection purposes - Page 1
Forum section: electronics / projects

author: vis5254
author_rank: Contributor
timestamp: February 04, 2019, 02:53:08 pm
content: Technically speaking i'm a noobie in this field . But i did search a lot and made some research to gather some info regarding my college work .idea is to use a current sensor ACS712 current sensor for a three phase line application , so to use the current sensor to read the optimal current value in three phase line say 30 A , once that optimal value crosses beyond its limit due to some fault , acs712 should detect it , inform to an arduino , and arduino opens the contactor relay to disconnect the power supply towards the '3 phase' motor .acs712 has just 2 input terminals , i'm planning to incorporate this unit into this particular work . will be really helpful is someone really helped me in what way things should be interconnected . i meant the wiring .

author: Jeroen3
author_rank: Super Contributor
timestamp: February 04, 2019, 03:38:13 pm
content: You can use three of these type of sensors for such application. But you must also consider some other factors with applications like this.The ACS712 is NRND since June 2017 and it cannot handle the short circuit current of a 32A three phase mains connection.You can use current transformers with ACS712 or similar chips as secondary. Current transformers have a much higher current surge rating.But with transformers you could also use shunts.LEM also has similar modules suitable for current measuring that may be able to handle the short circuit current.However, in the scope of a college project the ACS712 might be fine for a demonstration behind a transformer or low voltage supply. With the remark that for industrial applications the front end should use current transformers instead of direct pass-trough.

author: wraper
author_rank: Unknown
timestamp: February 04, 2019, 03:51:19 pm
content: There are much beefier sensors than ACS712, for example, ACS758. But still, ACS712 is rated for 100A surge current for 100ms.

author: IDEngineer
author_rank: Super Contributor
timestamp: February 04, 2019, 07:02:20 pm
content: I've used the ACS series of current sensors in many designs, they're excellent as long as you understand what they are and their limitations.In this application, are you sure your overall design will work fast enough to provide the protection you seek? The ACS parts have a raw bandwidth around 80KHz IIRC, so by definition there is a delay between an overcurrent event and seeing it at the output. Then you say you're feeding it into an Arduino, which implies firmware in the loop, which will introduce further (possibly variable) delays. Depending upon what you're trying to protect, will this overall system react fast enough?

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 04, 2019, 07:12:44 pm
content: If you mean the wiring....The current sensors, whichever you choose, should be placed in series with the wires leading to the motor itself.Now, the Arduino or whatever you are using to detect an abnormal condition, should drive an extra relay not shown in your diagram. Let's call it KC.You should wire KC'sNormally Opencontact in series with the stop switch.Some people may argue that a Normally Closed contact could be used. They are also correct.But I like to use Normally Open contacts because that way you ensure that the contact will close only if the protection circuitry is operating correctly.