Negative DC voltage to positive. Solar monitor

Thread Starter

juan3211

Joined Aug 30, 2012
8
Hi,

I am working on a solar monitor. I will use Arduino/esp8266 and INAXXX shunt current (optional with voltage and power) monitors from Texas instruments.

My problem is the solar charger controller.

It has 6 inputs/outputs. Three pairs of negative and positive wires from solar panel, battery and output to loads

The solar charger controller has the three positive ones joined, so it works with positive common rail.

So I can't join negative ones as I would expect by using 3 INAXXX monitors and Arduino, as all these chips need to be joined by ground

Arduuno can measure negative voltages with resistor divider, no problem here, and also some shunt current monitor support little negative shunt voltage.

The problem here is how could I power my Arduino and other ICs.

Options:
1. Another power supply with output ground joined with positive rail of the solar charger controller. I don't like it, as I need another power supply not only batteries of the solar system.

2. Use a isolated dc-dc converter, input pins will be the battery (aprox 13 VDC), and join her output ground with positive rail. Arduino will see 3.3v or 5v (depends on converter). Here, the problem is that dc-dc converters can use almost 30 or 40mA with no load (for example, while I sleep Arduino), and my solar system is "little"
3. Here is where I ask you for help?

Is there any other option?

Thanks a lot.
 

wayneh

Joined Sep 9, 2010
16,398
Do you not have a battery integral to the solar system? I don't see why you wouldn't power everything off that main battery.

A schematic or at least identification of the controller might help folks understand your system.
 

Thread Starter

juan3211

Joined Aug 30, 2012
8
Do you not have a battery integral to the solar system? I don't see why you wouldn't power everything off that main battery.

A schematic or at least identification of the controller might help folks understand your system.
Hi, yes, I have a battery in my solar system.

But I can't use battery's ground. Why?:

1. I need to measure both solar panel's voltage and current, battery's voltage and current and load's voltage and current I need to put a common monitor's ground between these three points and an Arduino.

2. The solar charger controller (and lots and lots of them), use a common positive rail between battery, solar panel and load. It works with MOSFET/transistor by opening or closing "negative wire" of each item (panel, battery or load)

If I use my "monitor's ground" connected to battery's ground, I will be connecting also solar panel's ground and load's ground (as my "monitor's ground does it"), so the solar charger controller will by by-passed.

The only way to mantain solar charger controller away this problem is to connect my "monitor's ground" to the positive common rail of the solar charger controller.

This way I have to measure negative voltages of solar panel, battery and load. But this is not a problem

Also, I could measure current (by shunt resistor) in the three cases without problem

The problem is to get +5 or +3.3Vdc from a -10.5 to -14.8Vdc from the solar system battery.

May be I have explained it better, haven't I ?

Thanks a lot for your help.
 

Thread Starter

juan3211

Joined Aug 30, 2012
8
Hi, see attached schema. In this schema, Arduino power is from an external power source of 9v. (Also, acs712 could be replaced by INAXXX ICs)

I want to power it from the -12vdc of the main battery255L0.png
 
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