Hello,
I have to find a way to measure voltages up to 120V and currents up to 100A DC (over long periods of time and on 3 different points on the circuit) with Arduino for a project in my University. Is it feasible? How do I proceed?
I have found out about the ACS758 to measure the current. Is it the best option? How to implement it?
Thank you very much !
How accurate do the readings need to be?
If you have 120v connected to the Arduino in any way, EG, voltage divider, you should treat the the whole circuit as live. This may not happen but if there is a problem such as R breakdown, it could be so. It is safe only when the voltage is removed.
How do you intend to use the date, store it, send it or only read it as required?
Weedpharma
For AC circuits, use a current transformer to sense current. That way you are electrically isolated from the circuit, and do not have to insert anything into the primary wiring, which is not the case for the ACS758.
Use a small wall transformer to isolate the primary circuit and reduce the line voltage to an easily measurable range.
Both options are discussed at openenergymonitor.org
weedpharma:
How accurate do the readings need to be?If you have 120v connected to the Arduino in any way, EG, voltage divider, you should treat the the whole circuit as live. This may not happen but if there is a problem such as R breakdown, it could be so. It is safe only when the voltage is removed.
How do you intend to use the date, store it, send it or only read it as required?
Weedpharma
Thank you.
At first, I just need to be able to read it. Maybe in the future I'll have to store it, cause I'll also have to measure temperature with a thermocouple, but that's all after I can implement the basic readings of voltage and current.
jremington:
For AC circuits, use a current transformer to sense current. That way you are electrically isolated from the circuit, and do not have to insert anything into the primary wiring, which is not the case for the ACS758.Use a small wall transformer to isolate the primary circuit and reduce the line voltage to an easily measurable range.
Both options are discussed at openenergymonitor.org
Thanks for the answer. In my case, I'll be measuring a DC circuit.
I would use a voltage divider ( make sure you use high voltage rated R's), ACS758 and LCD in an insulated box so you cannot contact any of the electronics.
Weedpharma
weedpharma:
I would use a voltage divider ( make sure you use high voltage rated R's), ACS758 and LCD in an insulated box so you cannot contact any of the electronics.Weedpharma
Could you recommend me some resistors? I searched for high voltage ones and all I find is resistors ranging from 6kV to 96kV, but I'll only get to 120V !
I'm ordering three ACS758, and already have the LCDs.
almost any resistor you can buy will work with 120 VAC. as you found most will be rated for kv .
in a few rare occasions, Neon light transformers and microwave transformers, we run into voltages high enough to break down the resistor and jump the circuit.
3 of the 1k resistors will divide the voltage into 3rds. each would see about 40 volts.
using a 10k ohm and a 500 ohm should get you into a decent range for an analog input.
how do you get DC voltage ?
if you are using AC to create the DC, can you measure AC amps ? it is much easier.
The OP looks to be doing some circuit analysis in 3 places so probably does require DC Amps.
Weedpharma
dave-in-nj:
3 of the 1k resistors will divide the voltage into 3rds. each would see about 40 volts.
Mmmhh, 120 Volt and 3 1k resistor will result in 120/3000=0.04 , 40 mA . At 40 Volt 40 mA will result in 40x0.04= 1.6 Watt, so you'll need a 3/5 Watt resistors to dissipate the power. Better use higher values...
Cheers, Ale.
ilguargua:
Mmmhh, 120 Volt and 3 1k resistor will result in 120/3000=0.04 , 40 mA . At 40 Volt 40 mA will result in 40x0.04= 1.6 Watt, so you'll need a 3/5 Watt resistors to dissipate the power. Better use higher values...Cheers, Ale.
It is normal practice to use much higher higher resistance values when measuring voltages, so that the measuring circuit doesn't load the circuit under test.
For example, most digital multimeters have a 10MΩ input resistance, and oscilloscopes are 1MΩ, (or 10MΩ if a x10 probe is used).