Battery SOC Measurement using Current (Directionality?)

AKExcalibur

New Member
Joined
Feb 28, 2021
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6
Hello, I've setup a remote off-grid cabin monitoring system (using a Pi, PZEM-017 RS485 Power meter, and Shunt). I actually have it working, and using voltage to measure approximate state-of-charge works, however I'd like to log current (watt hours) and use this for a better measurement of the battery's charge and ongoing health.

The problem I've observed is that measuring with a shunt has no "sign" or directionality. The current is just the sum of current-in and current-out, such that the system being used while charging from solar power doesn't lend itself to measurement. Is there a correct way to handle this, such as using two shunts (the other to measure PV current-in to the charge controller*) and subtract? Perhaps there are better meters that actually do measure direction of current flow?

In summary, I'm interested in how other people measure power consumption and battery state, given the lack of directionality of shunt-based measurement.

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* A note on the Charge Controller: The charge controller itself is a Renogy 48v 3500w all-in-one, and seems very locked down, so I'm not bothering with trying to get data just yet. (It also uses voltage to get SoC).
 

rmaddy

Full-time Solar-powered Trailer Life
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Nov 16, 2019
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If you were to use a Victron SmartShunt you could setup Victron's Venus OS on your Raspberry Pi. You would get all of the data you are looking for. If you also setup the RPi with Internet access you can setup a VRM account and see all of the activity remotely.
 

AKExcalibur

New Member
Joined
Feb 28, 2021
Messages
6
If you were to use a Victron SmartShunt you could setup Victron's Venus OS on your Raspberry Pi. You would get all of the data you are looking for. If you also setup the RPi with Internet access you can setup a VRM account and see all of the activity remotely.
Okay, that's excellent to learn about - I was concerned that even with the Smart Shunt I'd need pricey controller hardware. I see that Venus OS is on GitHub, and looks like it'd be easy to get running on a Pi (or even the BeagleBone Black I have laying around unused!)

I'll give that a shot, as the $130 is going to be worth the time saved.
 
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