ACS72981LLRATR-050U3 Current Sensor Large Carrier 0A to 50A, 3.3V (POLOLU-5272)

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This is a placeholder topic for “ACS72981LLRATR-050U3 Current Sensor Large Carrier 0A to 50A, 3.3V” comments.

This is the large version of a simple carrier for Allegro’s ACS72981LLRATR-050U3 Hall effect-based, electrically isolated current sensor, which offers a…

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The “ACS72981LLRATR-050U3 Current Sensor Large Carrier 0A to 50A, 3.3V
SKU: POLOLU-5272 Brand: Pololu” looks like a good fit for the current side of my application, which is monitoring the voltage and current of a nominally 12VDC and 30A appliance. However I haven’t found a good fit the the voltage sensor: I need one that is isolated and outputs an analog voltage that is in a ratio with the input voltage.

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Hi Timothy,

Welcome to the forum!

What was your application?

Unfortunately, I don’t think we stock an isolated DC voltage sensor - but would a voltage divider with undershoot and overshoot protection work?

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This configuration using Zener diodes ought to protect the input of whatever device you are using (current is limited through the resistors).

Otherwise, there are bare IC’s available for the sensors on Digikey, Mouser and the like that you could add to your project with an SMT adapter: SMT Breakout PCB for SOIC-14 or TSSOP-14 - 6 Pack! | Buy in Australia | ADA1210 | Adafruit | Core Electronics

EDIT: I found this: Gravity: Analog Signal Isolator | Buy in Australia | DFR0504 | DFRobot | Core Electronics

Liam

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Hi Timothy

I don’t think you can “isolate” a voltage measurement. The current is OK as the Hall effect device provides separation between the active element and the measuring system. But a voltage measurement requires some sort of connection between positive and negative. The negative or ground being the common point or the positive can be common depending on how everything is configured

A circuit or schematic of what you have and what you intend would be helpful.
Cheers Bob

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I don’t think that you will find it as a hobbyist item, but the component distributors have the components available, with example circuits. See, for instance:
ACPL-C870/A/B Optically Isolated Voltage Sensors - Broadcom | Mouser
Note that the suggested applications include “Isolated DC-bus voltage sensing in solar inverters, wind turbine inverters” which seems similar to your requirement.

There is some good discussion here:
Isolated Voltage Sensing in AC Motor Drives

If you are prepared to build it from scratch a good option would be to use a coil and a hall effect sensor, where the magnetic effect of the voltage through the coil generates a proportionate reading in the sensor.

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Hi Liam
Regarding your circuit above

There are NO Zener diodes in this circuit. The 1N4148 is a small signal device. Used here to clamp the input to 5V+0.7V or Gnd-0.7V. Normally would use schottky diodes here to limit to 0.3V or so above and below extremities.

On another note thank you Liam and Jeff for enlightening me regarding liner opto isolator availability. Due to my late wife’s illness I have not worked full time since about year 2000 and unfortunately have failed to keep up with developments.
Your links jogged the old memory a bit and I recall coming across such a beast in the 1990’s. I did question this at the time by asking (the right engineer) how come you are trying to transfer a varying voltage with a current operated non linear diode (LED in Opto Coupler). Turns out ths unit ws a linear opto coupler and could actually be used for video!!!. It came up in the circuit as a pretty normal opto coupler and not the fancy units linked. At the time this unit was pretty rare and correspondingly expensive. This was the only one I ever came across and I forget now which project I was involved with at the time.
Cheers Bob

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Jeff,

Thanks for that. The Broadcom ACPL device looks good. It has very high input impedance so I can use a simple resistor voltage divider to reduce my input voltage to its 0-2V range. It has 1-1 gain, so the output voltage at 0-2V is friendly with ADCs in 3V3 MCUs. Whilst it has differential output, as far as I can see neither output ever goes negative (wrt output-side ground GND2) so I think that means I can just connect Vout- to GND2 and use Vout+ as if it was a single-sided output.

I had looked at some similar devices but they had complexities like very low input voltage (mV), and/or very low voltage outputs so you must add the op amp, etc. But this one looks good (even better if it were in a PDIP8 package but as Liam said, there are solutions to that).

Regards,
-Tim.

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Liam,

I had a look at the specs for the DFRobot Analog Signal Isolator. It all seems perfect except for the bits about “This module consumes relatively large current during operation” and “It is normal for the isolator generates heat while working”. I am interpreting “operation” as applying a voltage to the input. In my application (voltage sensing) there will always be a voltage applied to the input, so I am concerned that it will cook. But I haven’t found data on duty cycle, temperatures, etc. or explicit reasons for high current/heat during “operation”.

Looking at the photo and data sheets, it appears to consists of a high speed opto-coupler, an MCU, an isolated power supply and a dual op amp. My best guess is that the MCU gets hot during operation because it is in a tight loop (e..g constantly digitising the analog input and transmitting the bits over the opto-coupler) but cools off by powering down when the input voltage is zero. But it’s just a theory - others are welcome!

So, at the moment bench testing one to possible destruction seems the way to go. If it is suitable, it has all the bits needed on one little board, as compared to the ACPL-C870, which needs added an isolated power supply, a few caps and a SOIC mount.

Regards,
-Tim.