I don’t know your wiring and devices, but in most cases Gnd is the -side of the circuit.
Like in car battery minus pole is common gnd.
I say in most cases because if you put for example two 12V batteries in series and decide to to make common gnd between two of them, that would result voltage 24V. One side -12 to gnd and other side +12v to gnd.
I get how voltages and grounds work - I manage the electrical and LV component of large data centers. What I’m struggling with is the specific application - I’m just not getting where the three wires I asked about a couple posts above are. It seems you can’t help me with this specific situation.
Edit: and, btw, I have batteries wired in parallel in every vehicle and camper I own - with dc/dc charging, battery isolation, solar, etc. I need help with this specific design. If you’ve ever owned a camper, you know how screwy they wire these things.
I’m not pushing.
Laws of physics don’t change between one application and another.
Good luck with your sensors.
Again, the sketch above shows two wires to each tank. My question above references three different wires identified in @scsowi’s last post. Physics cannot answer that question and it appears you cannot either - although I wish you could as this back and forth is just sucking up screen space on this thread.
I’m really not trying to come off as rude - I really would like your help - can you explain the difference between the two wire config in the sketch above and the three wire config in the last post?
Alright, after the lesson on 12v dc basics (totally kidding), and because of my stubbornness which typically prevents me from ever asking for help on these forums, I decided to open my panel back up and confirm that I only have one wire going to each tank that I can access. I confirmed only one wire per tank at the panel - no common wire from the panel to all three tanks - which does not match what the wiring diagram provided for my panel shows - so as I expected in the terrible camper world, either they wired it different or I was provided the wrong diagram - most likely the former. The wiring diagram I have is similar to the sketch shown in post 19 above. If I did have access to that common wire that goes to all (3) tanks - shown as ground in that sketch, I could see pushing voltage from one buck converter through that common wire and seeing how much voltage comes back through the tank probe/sensor resistance on each of the individual blue/brown/gray wires. This is what I assumed @scsowi did, but still unclear. Based on the black wire shown in that sketch being called a ground (which I believe it is), I would call this back-feeding - as we would be pushing voltage through that wire rather than grounding it - but maybe that’s more of an electrical term than an electronics term.
That said, it appears the way mine is wired is the panel pushes voltage over each of the blue, brown, or gray wires when the corresponding button is pushed. The common tank wire goes to the nearest ground - which I cannot access. The resistance created by the probe based on the tank level is pulling that voltage down relative to the level. Soooo - it seems if I use (3) buck converters - one for each probe wire, I can then read the pulled-down voltage at that buck converter to tank probe wire connection. Of course, that sucks compared to the wiring sketches shown - I will now have (4) buck converters - one for each probe and one to power the esp32. As much as I’d love to use the Uni’s, I am trying to keep the whole camper project under $500 - including a homepod mini. And I’m trying to keep the number of IP addresses/connections on my USB-C travel router (and verizon MiFi) down.
Thanks for the help - and the motivation!
Just want to add this: Assuming most are in the USA here, Most RV camper trailers (bumper pull and 5th wheel), motor homes (not sure about boats though) on the DC side use the standard trailer wiring color code where white is the ground wire and colored wires are the positive leads, black is included as a positive lead in this case.
That said black or green would not be stock negative or ground from the factory.
On the AC side of your power system you follow the standard NEC color code.
Now as for tank sensors, There are different kinds depending on the manufacturer of your RV and what they used on t he model you have (be aware that sometimes same model RV’s can have different parts substituted so you need to make sure what you have and get the manufacturers datasheets on said devices), in this case tank sensors. Different sesor brands output different signal voltages so assuming your RV has a 12vdc DC system which charges at 14.4v and maintains between 12.8 - 13.8vdc you should by default expect a basic tank sensor to output at max 13.8vdc. That said you will need a resistor network of voltage dividers to get your voltages down to 5vdc and lower for Arduino & Wemos and for ESP32 and such 3.3v and lower so you don’t fry the inputs. There are voltage divider calculators online and as phone apps also if you have trouble figuring things manually.
Once you get your voltages where they are safe for your micro, you should have no trouble writing up some code to print those voltages in serial and convert the raw voltage values into a percentage value that makes sense or translate them into a bargraph or whatever.
Of course you could also go totally old school with transistors, or some LM339s or even an LM3914/15/16 ICs, LEDs and some descrete componets to build a set of bargraph meters to display tank levels.
Or go 100% analog with actual analog meters. No joke We tooks a 1997 Excell 5th wheel apart (it had leaks due to poor maintenance from the previous owners, and developed black mold so it had to go) and it had an analog meter very similar to those found in CB radios, that showed battery voltage by default but if you pressed the button under any of the tanks rough level indicators it would reflect that tanks level on that meter in more fine detail. it’s really neat and I kept it because it was so unique.
The sky is literally the limit here and you are not locked into this or that because you can do this in any manner you desire.
I hope some of this helps you all moving forward in this project and even future RV upkeep because god knows when you buy RV parts from an RV shop you pay the VIP tax for something that can be bought at home depot for a fraction.