uController ADC Solar pannel voltage input for either a common GND or common Positive Solar Charge Controller

Thread Starter

gkeep

Joined Oct 21, 2017
63
Hi Guys,

I've been racking my brain for ages and this is the best i can figure for dividing (up to a 65V) solar pannel voltage to a useable uController ADC voltage.

Only problem is, there must be a better/cheaper way of doing it as this requires a 65V opamp and I cant find any. In fact this one is only 35V.

This needs to work for a uC running off a 12V battery on the 'battery terminal' of either a common positive or common negative Solar charge controller.

GND in this schematic is battery 12V GND.

Any help would be appreciated.


1628818336018.png
 
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michael8

Joined Jan 11, 2015
205
I'm guessing that somewhere there needs to be a connection from your battery ground to the solar panel. It would help if you would show the battery & solar panel connections.

Let's assume that the battery negative & the solar panel negative are connected and call that ground. This may
not be the best choice, but lets go with it...

You have announced two problems:

a. attenuate the 65 volt solar panel voltage to what the uADC can handle. A simple resistive divider can do this
depending on the input impedance of the uADC.

b. how to power your opamp (if needed). Check out single supply opamps. With a single supply opamp
you only need one voltage which can be regulated off the battery 12 volt (and/or the solar 65 volts).
 

Thread Starter

gkeep

Joined Oct 21, 2017
63
Hi Michael,

I don't need to show the connections. This system just needs to work with either common + or common - solar charge controllers.

You can assume there is a common Gnd... but the schematic needs to work for common + as well.
 

Papabravo

Joined Feb 24, 2006
17,030
Hi Michael,

I don't need to show the connections. This system just needs to work with either common + or common - solar charge controllers.

You can assume there is a common Gnd... but the schematic needs to work for common + as well.
You come here to ask for help and then cop an attitude when someone politely asks for more information to help them understand the problem. Nobody in their right mind would operate an opamp directly off of the solar panel. They would reduce the voltage that supplies the opamp to comply with the stated requirements on the opamps's datasheet.
The thing you want to use so the polarity of the panel does not matter is a bridge rectifier.
 

michael8

Joined Jan 11, 2015
205
This system just needs to work with either common + or common - solar charge controllers.

OK. So there are at least 3 systems possibly with separate not-connected grounds:

A. solar panel
B. 12v batter
C. micro with uADC

Are any of these grounds connected? Where does the micro & uADC get it's power from?

What about:

D. output of the solar charge controller(s)?

Measuring voltage between "x" and "y" takes two inputs to the measurement instrument. A lot of the time
"y" is some common point to the circut and is called ground. The measurement still takes two inputs.

Since your solar panel doesn't have a common ground with the uADC you will need a floating
measurment using two wires...

Something, but not this:

float1.png
 

Thread Starter

gkeep

Joined Oct 21, 2017
63
Hi Michael,

I didnt mean to give off that i was "copping an attitude". I just meant the solar charge controllers switch on the high or low side to buck their voltage. Unless i didn't understand what you are asking.

Batteries 12V GND is common with uC GND.

Sorry to be more clear, the uC is powered through a 5V buck with common GND straight from the battery. Not through the SSC power out.

Your idea of a DPDT relay is interesting tho.
 
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Thread Starter

gkeep

Joined Oct 21, 2017
63
Papabravo, a bridge rectifier would help prevent damage due to reverse polarity. Which ill implement. Thanks for the advice. But it doesn't help me with my main problem.
 

Thread Starter

gkeep

Joined Oct 21, 2017
63
...Nobody in their right mind would operate an opamp directly off of the solar panel. They would reduce the voltage that supplies the opamp to comply with the stated requirements on the opamps's datasheet.
Hi Papabravo, Thanks for recommending i get in my "right mind"...

So I'm pretty sure reducing the voltage with a voltage divider won't help because you'll have to choose how to reduce the voltage. Common Gnd or Common +ve. Either way wont work in both scenarios.

I was hoping for a mathematical / logical solution to output the correct voltage in either the scenario, where the battery 12V + is common with Sol+, or 12V GND is common with Sol-.
 

LowQCab

Joined Nov 6, 2012
1,189
This is an absolutely hilarious Thread.
The Thread Starter has already been given the incredibly simple, and effective solution,
and then just blows it off,
and then insists on telling everyone trying to help how to accomplish the end result,
and what information / specs are important or not important.
I can't believe it's still going ...........:p
.
.
.
 

Thread Starter

gkeep

Joined Oct 21, 2017
63
This is an absolutely hilarious Thread.
The Thread Starter has already been given the incredibly simple, and effective solution,
and then just blows it off,
and then insists on telling everyone trying to help how to accomplish the end result,
and what information / specs are important or not important.
I can't believe it's still going ...........:p
.
.
.
What's with all the hostility in here?

The solution is simple, but it involves a dpdt relay to measure a voltage. I can't say it's the most elegant solution. But im asking if it's possible to solve it with something cheaper and simpler. I didn't ask for a simple and effective solution i wanted a specific solution. Cheap and easy. I could have just gone with some opto isolator circuit. If you think its not possible, explain why. Otherwise, if you don't have anything constructive to say just move on.
 

Ian0

Joined Aug 7, 2020
3,525
Why the insistence that it has to work both with common ground and common V+?
The power conversion certainly won’t!
 

Papabravo

Joined Feb 24, 2006
17,030
Hi Papabravo, Thanks for recommending i get in my "right mind"...

So I'm pretty sure reducing the voltage with a voltage divider won't help because you'll have to choose how to reduce the voltage. Common Gnd or Common +ve. Either way wont work in both scenarios.

I was hoping for a mathematical / logical solution to output the correct voltage in either the scenario, where the battery 12V + is common with Sol+, or 12V GND is common with Sol-.
You have multiple problems going on simultaneously and I never suggested that you use a voltage divider to create a power connection for the opamp. There are several possible approaches I might consider and none of them involve using a voltage divider for anything except a reference voltage, but they all involve using an active circuit to reduce the available voltage to a safe and useful level compatible with the datasheets of the other parts you intend to use.

One more thing. Not being able to find an opamp that would work on +65 volts should have been a clue that you were looking in the wrong place for a solution. We are 74 years into the semiconductor era and we've managed all this time without a +65 volt opamp.
 

Ian0

Joined Aug 7, 2020
3,525
We are 74 years into the semiconductor era and we've managed all this time without a +65 volt opamp.
LM143?
±40V supplies.
But one could argue that if there had never been such a high voltage part engineers would have found a workaround. The fact that there was such a part and it has been discontinued is actually rather better proof that it really isn’t that useful!
 

Thread Starter

gkeep

Joined Oct 21, 2017
63
Thanks Eric,

You are missing one thing though. Testing the circuit with the 12V supply gnd connected to sol- and then undoing that and having 12V supply 12V+ connected to sol+
 

ericgibbs

Joined Jan 29, 2010
13,881
hi gk,
So we are saying that the first condition is being met in that circuit.?
Testing the circuit with the 12V supply gnd connected to sol-

ESP_ 670 Aug. 13 13.34.png
 
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