Connecting Second Battery and Power Sense Module

[bsnow (Benjamin Snow)]

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:

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:

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

[EliotBR (Eliot)]

Hi @bsnow,

@bsnow

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?

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!

[bsnow (Benjamin Snow)]

Hi Eliot,

Thanks very much for confirming, much appreciated!

Ben

[odedezra]

Hello there,

I managed to configure the 2nd battery input in QGC, and now I’m trying to find a way configure Cockpit to do the same, is it possible?

[tony-white]

Hi @odedezra -
Have you setup a second power module to read your second battery, connecting it to the ADC input?
Generally when using two batteries, it is easiest / best to just equally charge them and connect them in parallel. You can set the capacity to reflect the combined batteries as well to track consumption against it.

If you setup the Autopilot Parameters to have the values for a second battery, and then restart the autopilot, it should be possible to add a generic indicator widget to track battery 2 related voltage and current in Cockpit!

[odedezra]

Hi @tony-white

I did manage to solve this matter in QGC showing the two battery sets (I’m using 14.8V for electronics, and 22V for T500 thrusters), it worked well (at least until I started to setup Cockpit which seemed to mess up some parameters in QGC, but that’s a different matter). But in regards to Cockpit I couldn’t find a place to set up similar parameters related to Battery2.

[tony-white]

Hi @odedezra -
As mentioned, you’ll want to edit layout from the Cockpit menu, and select the Very Generic Indicator from the mini widget list. When configuring it, search for Battery, and you’ll want the parameters associated with Battery 1 (with battery 0 being the default that is already displayed in the existing battery widget.)
Let us know if you can’t find those parameters to connect to the widget!