Arduino clamp ammeter

Question

I am using an Arduino Uno as a watch dog for a project I a doing; its job is to monitor what is happening in the system and shut down the system if it is not operating within spec.

One of the parameters I need the Uno to watch for is voltage and amps. The system has a combination of 24V, 12V, and 5V components so it is essential that the voltage is monitored. I was planning on using this DC Current Sensor for reading the voltage. But I am at a loss on what to use for measuring the current.

I need the max I need to measure is 130 amps at 24V. Do I need a clamp for this? Sears makes this AC Clamp-on Adaptor; could this be repurposed for my project? It says AC amps, what is the difference between AC amp clamps and DC amp clamps? I have a clamp-on multimeter that does both AC and DC amps could I modify it to work? If so how? Could I create a circuit that allows the Arduino to measure the amps?

Answer 1

An AC clamp meter won't read DC.

The ACS758KCB-150U is a Hall effect current sensor rated for 150A. It has a sensitivity of 26.7mV/A, which equates to 3.5V at 130A. Most A/D converters should be able to measure this voltage without amplification.

The advantages of a Hall effect sensor over a shunt resistor are galvanic isolation and very low insertion loss. A 50mV current shunt dissipates 5 Watts at 100A. The ACS758KCB-150U has a resistance of 0.0001 Ohms, so it only drops 10mV and dissipates 1W at 100A.

However it does have one disadvantage - magnetic hysteresis. After passing a current of 150A, lower current readings may be out by 0.2A. If you are just checking for overloads and don't need high accuracy at low current then this shouldn't be a problem.

Answer 2

I would recommend using a gigantic current shunt and a differential amplifier built for current sense applications. A shunt is rated some number of millivolts at some current, say a 50 mV 100 A shunt will produce a drop of 50 mV when 100 amps flows through it. Then attach a differential amplifier that can deal with a very large common mode voltage to measure the voltage across the shunt. See

http://www.linear.com/parametric/current_sense_amplifiers

for some amplifiers designed for this purpose. For measuring the voltage, just hang a voltage divider off of one of the sense wires from the current shunt.

Actually, what you could do is buy one of those INA219 based boards like you linked to, remove the built-in shunt resistor, and then connect the sense leads from a monster external shunt to the terminal block on the INA219 board.