Gerry48:
I don't think you need a common ground when measuring differential. Use a ADS1115. It's a 16 bit a/d with internal programmable op-amp. You'll need 2 ADS1115 modules to measure 4 differential voltages. I've used them with 100A shunts. Check ebay for parts.
Look at the common mode specs of the A/D or opamp.
The voltage you want to measure usually has to be within the extremes of ground and supply.
Read the datasheets. There are exceptions.
e.g. the INA169, mentioned in post#4.
Leo..
When measuring differential, there is no ground reference. Ground of the a/d and the circuit you want to measure are not connected. The measured differential voltage is down in the millivolts. There's no issue exceeding supply voltage.
Wawa:
The voltage you want to measure usually has to be within the extremes of ground and supply.
Read the datasheets. There are exceptions.
e.g. the INA169, mentioned in post#4.
Leo..
Gerry48:
When measuring differential, there is no ground reference. Ground of the a/d and the circuit you want to measure are not connected. The measured differential voltage is down in the millivolts. There's no issue exceeding supply voltage.
Really?
I should try that.
On second thoughts, you better try it first.
Leo..
This line is in the ADS1555's datasheet "electrical characteristics" table.
Analog input voltage | AINp or AINn to GND | GND | VDD V
Leo..
The shunts should be located at the LO side of the circuit. In other words the "N" side. Use one Arduino and ADS1115 for each shunt. Measure shunt current differential and voltage (with resistor divider) using the ADS1115. Very simple.
rafael-b:
Here is the circuit.Thanks, Tom !
Another thing to consider is shunt voltage for max A/D range.
AFAIK 256mV at max PGA gain for the ADS1115.
25watt shunt loss at 100A.
Leo..
The shunt voltage will be around 40mV, since the current will be around 100A, so it's okay for the ADS1115. But won't the resolution be low? At max gain I'll have 0,96V input to the Arduino.
Gerry48:
The shunts should be located at the LO side of the circuit. In other words the "N" side. Use one Arduino and ADS1115 for each shunt. Measure shunt current differential and voltage (with resistor divider) using the ADS1115. Very simple.
You are thinking DC. In a three phase AC system there is very little current in the neutral line. Look at the overhead lines in your area. They are in groups of three. The neutral line doesn't even go back to the power station.
This does seem like a common problem. There must be commercial units out there which do this. I suspect they use a Hall Effect or Current Transformer which is wrapped around each phase and is completely isolated from the mains voltage. Shunts are more useful for DC.
MorganS:
You are thinking DC. In a three phase AC system there is very little current in the neutral line. Look at the overhead lines in your area. They are in groups of three. The neutral line doesn't even go back to the power station.This does seem like a common problem. There must be commercial units out there which do this. I suspect they use a Hall Effect or Current Transformer which is wrapped around each phase and is completely isolated from the mains voltage. Shunts are more useful for DC.
But the point of this circuit is to rectify the current, so the output is DC.
I'm thinking the ADS1115 will work, but the resolution won't be great.
Also, won't there be to much current going to the ADS1115?
Here's an appropriate hall effect sensor that isolates the voltage being sensed: Sparkfun ACS712 Breakout Works on AC and DC. (Copy the circuit in "application 4" on the datasheet if you want to measure AC with an Arduino.)
They do admit to to their mistake in the PCB layout in the description: "not designed for that type of voltage." I would have expected the datasheet to show a recommended PCB layout that you could copy. If you just deleted the ground-pour polygon from the Sparkfun board (download their Eagle files) then you would have something good for at least 500v isolation, probably a lot more.
I use the ads1115 the circuit that I provided using the op-amp using a 100amp 75mv shunt. This operates in the differential mode boosting the voltage from 0-75mv to 0-3.75v then the other Chanel to read the voltage upto 50v can easily add another for the temp. If you are going use an Arduino for each phase then this is the way I would go if it's DC voltage.
MorganS:
Here's an appropriate hall effect sensor that isolates the voltage being sensed: Sparkfun ACS712 Breakout Works on AC and DC. (Copy the circuit in "application 4" on the datasheet if you want to measure AC with an Arduino.)They do admit to to their mistake in the PCB layout in the description: "not designed for that type of voltage." I would have expected the datasheet to show a recommended PCB layout that you could copy. If you just deleted the ground-pour polygon from the Sparkfun board (download their Eagle files) then you would have something good for at least 500v isolation, probably a lot more.
But I can't input 100A to it, it operates on 30A max. Right?
Steveiboy:
I use the ads1115 the circuit that I provided using the op-amp using a 100amp 75mv shunt. This operates in the differential mode boosting the voltage from 0-75mv to 0-3.75v then the other Chanel to read the voltage upto 50v can easily add another for the temp. If you are going use an Arduino for each phase then this is the way I would go if it's DC voltage.
I think that's what I'll do. One Arduino and two ADS1115 for each phase. The firts ADS1115 will measure (differential) and amplify the voltage on the shunt (40mV), and also measure the voltage on the capacitor (30V). The second will measure the voltage on a thermocouple.
rafael-b:
I think that's what I'll do. One Arduino and two ADS1115 for each phase. The firts ADS1115 will measure (differential) and amplify the voltage on the shunt (40mV), and also measure the voltage on the capacitor (30V). The second will measure the voltage on a thermocouple.
AFAIK shunt voltages have to be witin the ADS1115 supply range (see datasheet).
Draw a diagram showing how you are going to do that.
I don't see why you have to use differential A/D.
Leo..
Steveiboy:
I use the ads1115 the circuit that I provided using the op-amp using a 100amp 75mv shunt. This operates in the differential mode boosting the voltage from 0-75mv to 0-3.75v then the other Chanel to read the voltage upto 50v can easily add another for the temp. If you are going use an Arduino for each phase then this is the way I would go if it's DC voltage.
I was reading your posts again and I didn't understand some details.
You're getting the voltage on the shunt to another op-amp and then to the ads1115?
The ADS1115 as Wawa said has a minimum input range of 256mV but you used a 75mV.
Can you show me the full circuit? Diagrams including the shunt and every part connected to the Arduino would be awesome!
Thanks.
rafael-b:
The ADS1115 as Wawa said has a minimum input range of 256mV but you used a 75mV.
Not minimum.
If.... you want to use the full range of the ADS1115, you have to provide 256mV.
75mV is only ~30% of the A/D range , but it might be enough for the resolution you want.
It might be harder to build an opamp circuit that is better than just using 30% of the ADS1115.
Leo..
I will see about getting it drawn up, The opamp boosts the voltage from 75mv depending on the current be drawn
Do the maths.
100Amp is 50mv across the shunt OP has.
OP wants a resolution of 10 nanovolt (post#0).
Compare the opamps temp drift and other gremlins against a straight A/D.
Building that opamp circuit adds even more gremlins.
I would start experimenting with one INA169 board from Adafruit (post#2) across the existing high side shunt, some small Arduino compatible with inbuild 16-bit A/D, and a Pololu 5volt micro buck converter (if those supplies don't drop below 5volt). Optical serial links could connect it all.
What is the expected ripple on that analogue? supply.
30volt (AC? DC?) @100+Amp requires several soda-can sized caps.
Curious why you want to make a 3x ~30volt, ~10KW supply.
Leo..
Wawa:
Do the maths.
100Amp is 50mv across the shunt OP has.
OP wants a resolution of 10 nanovolt (post#0).
Compare the opamps temp drift and other gremlins against a straight A/D.
Building that opamp circuit adds even more gremlins.I would start experimenting with one INA169 board from Adafruit (post#2) across the existing high side shunt, some small Arduino compatible with inbuild 16-bit A/D, and a Pololu 5volt micro buck converter (if those supplies don't drop below 5volt). Optical serial links could connect it all.
What is the expected ripple on that analogue? supply.
30volt (AC? DC?) @100+Amp requires several soda-can sized caps.
Curious why you want to make a 3x ~30volt, ~10KW supply.
Leo..
Thanks.
Then I'll try this INA169 board from Adafruit with the Arduino and then later I'll see if I need the Teensy for better resolution. Also I don't see why I'd need this micro buck converter.
But what do you mean with optical serial links? What would need to be connected that way?
rafael-b:
Also I don't see why I'd need this micro buck converter.But what do you mean with optical serial links? What would need to be connected that way?
I understand that you want to measure voltage and current of a variable supply.
If the supply does not dip under 5volt, you can use that to supply the INA169/Arduino.
You will need a switching regulator for the large variation (5-30volt).
You could also supply the INA169/Arduino from a separate 5volt plugpack (e.g. 5volt USB phone charger).
I understand you want to measure THREE separate regulated supplies (grounds not connected).
If you want the current and voltage data to a single display, you have to keep them galvanically isolated.
Optical is one way. Protocol is up to you. Or Wifi, bluetooth, etc.
Leo..
Edit: ! The INA169 needs a minimum voltage to work. See datasheet.
Wawa:
I understand that you want to measure voltage and current of a variable supply.
If the supply does not dip under 5volt, you can use that to supply the INA169/Arduino.
You will need a switching regulator for the large variation (5-30volt).
You could also supply the INA169/Arduino from a separate 5volt plugpack (e.g. 5volt USB phone charger).I understand you want to measure THREE separate regulated supplies (grounds not connected).
If you want the current and voltage data to a single display, you have to keep them galvanically isolated.
Optical is one way. Protocol is up to you. Or Wifi, bluetooth, etc.
Leo..Edit: ! The INA169 needs a minimum voltage to work. See datasheet.
The voltage is ok. It will be around 30VDC.
I'll just have to remove the R100 that comes with it and hook the Vin+ and Vin- of the Adafruit INA169 breakout board to my shunt.
Then solder a 50k load resistor for a gain of 50.