Connecting Second Battery and Power Sense Module

Blue Robotics Products Sensors
1

Hello,

We are working on adding a second battery to our BlueROV2, we have two 18Ah batteries, of a similar age, more or less equal cell voltages that we plan to connect in parallel.

We have two BlueRobotics Power Sense Modules installed, one is connected to Battery 1 (shows as Battery 0 in QGC) and onto the designated port for the BlueRobotics power sense module (6 pin port near the top edge of the Navigator). This once works as expected, no issues.

The second power sense module is connected to Battery 2 (shows as Battery 1 in QGC). It has its 6 pin cable coming from the Power Sense Module end split into two, and we’ve soldered on 3-pin connectors to interface with the ports labelled ‘ADC 6.6V’ and ‘ADC 3.3V’ on the Navigator, as detailed in this post: How to connect 2 power sensor - #2 by EliotBR. Only the ground pin (-) and the sense (‘S’) pins are connected to these two ports, the positive pin (+) has been left disconnected.

When have gone in and selected this power sense module as ‘Analog Voltage and Current’ in the QGC Vehicle Setup for power, and have edited the parameters for “BATT2” in QGC, as shown below:

power setup
power setup1343×830 100 KB

We have also set the following parameters for BATT2

BATT2 VOLT PIN: 2
BATT2 CURRNET PIN: 3
BATT2 VOLT MULT: 22

This seems to give the correct voltage reading, but I believe from reading the specs for the Power Sense Module that the voltage multiplier should be 11V rather than 22V? However, setting the BATT VOLT MULT parameter to 11V give a voltage of ~8.2V for Batt2 at full charge, while setting is 22V gives ~16.3 or so. Perhaps more important, both batteries show the same voltage at full charge when we use the 22V scalar:

battery voltages and consumption
battery voltages and consumption1918×1033 118 KB

I guess we are just looking for a sanity check? Is it OK to be using 22V, and is the reason we are not getting the expected results with a 11V scaler due to the fact that we are feeding a 0-3.3V signal into an ADC port with a full scale range of 0-6.6.V, or something like that?

With regard to the analog current, that all appears to be working fine without needing any non-standard parameters.

Thanks very much,

Ben

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2

Hi @bsnow,

Yeah, I just took another look, and it looks like my original “11.0 V (or maybe 5.5 V?)” was doing the conversion backwards.

If you look at the Navigator schematic (page 3) you can see that the 6.6 V ADC input gets halved onboard by a voltage divider so that it can be measured by the same 3.3 V ADC chip as the other inputs, so the normal ratio of 11.0 V of battery input per 1 V of power sensor output needs to be doubled to account for that internal halving.

I’ve corrected the number in my table in the original post, and added a note about it there as well. Thanks for raising this, and hopefully your double battery monitoring goes well! :slight_smile:

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3

Hi Eliot,

Thanks very much for confirming, much appreciated!

Ben

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