# question

## BMV Resolution and measuring small currents

Hello,

I have a remote off grid site, running a Raspberry Pi for monitoring and it is supplied by a 48Volt Battery Bank. Raspberry Pi + 4G Modem consuming together about 4W continuous power. The current measurement resolution shown in Venus is 100mA leading to a 5W resolution on a 48V battery bank. If no load is active except the RPi, I have a flipping DC consumption monitored and shown in Venus. So the VRM charts look like:

With a fully charged battery it gets logically worse, leading to zero consumption for longer periods:

Is there a way to improve this?

Thanks,

Markus

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Hanging my head in shame, this is actually a very well documented setting, I had just overlooked.

07. Current threshold
When the current measured falls below this value it will be considered zero.
The current threshold is used to cancel out very small currents that can negatively affect the long term state-of-charge readout in noisy environments. For example if the actual long term current is 0,0A and due to injected noise or small offsets the battery monitor measures -0,05A, and in the long term the BMV can incorrectly indicate that the battery needs recharging. When the current threshold in this example is set to 0,1A, the BMV calculates with 0,0A so that errors are eliminated.
A value of 0,0A disables this function.

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So, the BMV it's self has a resolution on 10mA (480mW), which is good. The BMV in a Venus environment seems to report a resolution of 100mA (4.8W), which is not a problem.
Now, as I'm sure you are aware, the measurements are taken as snapshots in time. The RaspberryPi is a computer, so its power consumption is contantly changing.
I wonder if the RaspberryPi and its associated components are spiking above the 4.8W threshold just as a reading is being taken?
It's awesome how such low power measurements (0.48W) are even possible over a shunt that is designed to provide readings up to 500A or 24KW!

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Hi WKirby,

thanks for your answer. OK, so the SOC is calculated with 10mA resolution, this is good.

But I did some measurements with a good Fluke, and there were no such spikes.

DC Amp readings were rock solid when RPi was idle

So the reported resolution to Venus is a problem for me, a small one, indeed ;o)

Maybe there is a possibility to fine tune this somewhere in Venus itself.

Or to make a setting for this, in future firmwares...

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