When all the relays are open, is the controller not completely isolated from the positive ground system? That was my intent. If any one of the relays is closed, then the respective resistive divider is switched into the circuit and its scaled output can be safely measured.
Maybe I didn’t abstract the positive ground system correctly in the schematic? I was trying to simulate how one could take the measurements if the controller was a hand held DMM.
I think there are 2 solutions to this:
Can you elaborate on the second option?
Absolutely none. I just stumbled in here looking for a quilting forum.
Write code that just measures the voltage and sends it out on a serial port via an opto-isolator. The connections to the controller would have to be such as to measure voltage with reference to a positive ground and the power supply would have to in independent of and isolated from anything else. The controller would be connected with positive connected as ground. The data would then be read on the other side of the opto-isolator by another controller completely isolated from the first.
More details than that would require more work than I am interested in putting in. I think flying capacitor would be simpler.
Understood. That’s kind of like what I was trying to illustrate.
I have a similar charge controller. When the battery voltage is < 14.6V, the panel voltage is the battery voltage + probably a blocking diode.
We have a solar panel on our RV and it uses a MPPT charge controller. I wasn’t aware that some of the PWM controllers were positive ground hence my interest in this topic.
There is a display remote to the MPPT charge controller that displays panel voltage as well as battery voltage, charge current, load current, etc. and I just assumed that this was common to all types of solar systems. This topic has been educational for me.
MPPT is a pretty sophisticated controller. The cheap one I have just switches the panel between "open" or connected to the battery, and it is positive ground. Really confused me at first! Then I read that it is an economic choice: N MOSFETs are cheaper and easier to use than P MOSFETs in that application.
Yes, I can see the economics of it and I can imagine the confusion. We have a 100W panel and a Morningstar PWM controller, purchased for a project that hasn’t materialized that I’m going to have to dig out and play with.