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high volt EV battery reading ADC on Arduino pro mini using differential powered by isolated power supply.

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Mar 21, 2023
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Hello team,
As our battery & Arduino don't have common ground as we using flyback topology for isolated ground, & isolated 5v output of our flyback supply will power opam LM324, we are using as differential opam to get ADC reading on arduino.

Screenshot 2023-03-21 at 15.03.25
Screenshot 2023-03-21 at 15.03.25763×568 135 KB

so my main doubt is, do we directly need to feed battery volt to opam to use this differential circuit , can opam handle it, as i read, lm324 can handle 32 volt only.

if not, then after voltage divider only, i need to feed divider volt to this opam circuit will be the way ?

As we were suggested to use a differential amplifier by our senior mentor sir to safely give this 88v to ADC of Arduino mini. (please check in above image about the gain formula I was suggested to use, now I need help to calculate gain & hence to get a safe ADC to read this high voltage)

can you please help to give some references for calculating gain?

Gain looks correct, I've seen this used a lot in PFCs to measure the line voltage. See the attached spice file.

Multiple high resistance resistors (usually size 1206 or greater I believe) are used for safety and single fault tolerance.


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so my main doubt is, do we directly need to feed battery volt to opam to use this differential circuit , can opam handle it

As the picture shows the battery voltage is not fed to the Opamp at all, it is fed to resistors.
For the Opamp the battery voltage it is not relevant at all, only the voltage directly at the Opamp pins is relevant.

The existing resistors already act as voltage divider.

In an industrial application I use a similar circuit to measure 2500V AC. For sure no 1206 resistors, but two high ohmic, high voltage resistors.


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