Minimum Voltage Level Monitoring

Hi Folks, I am building a 390W 3 130W panel (maybe 520W, 4 panel) system with all parallel panels into an MPPT charger for a 12V RV system. I will be building a custom breaker panel with one breaker for each panel, and one for all four in parallel. Since this will be a small strip panel above the refrigerator (close to the ceiling, and hence, close to the panels) with pushbutton breakers, I was thinking of putting a low voltage level sensing circuit on each module. Basically using a voltage activated switch circuit on each module, at the push of a button, if the modules are above a preset level, a Green LED will light. This will basically tell me at a glance if I have a shaded / failed module. I am doing this because my modules will be mounted flush on my roof, but the roof of the trailer is curved, so one or more modules may be out of ideal inclination at any given time. I would like to know this, so I can perhaps redesign the mounts accordingly, for example, and also use this for a "health check" on the panels. ALso the potential panel # 4 may be a hinged deal, where it hinges closed over #3 when not in use/transit, and parked in my driveway, and only deployed while camping. I'll only get half the charge current when parked at home, but have weeks between trips to top the battery bank up.

Before I delve into this either with a transistor or even Arduino project, is there such a commercial beast available (To save me time)? It would be like the tank level monitor in an RV. "Press to test" would activate all channels and give me all greens, for example, or perhaps three voltage levels... I may even adapt one of those things, as they work on different voltage levels from the sensors in the tank.

I will be using diode isolation to ensure each switch/sensor only reads it's respective panel.

I'm NOT looking for a computer solution. Just want KISS method.


  • BB.
    BB. Super Moderators, Administrators Posts: 33,530 admin
    Re: Minimum Voltage Level Monitoring

    Personally, if I understand your plans, I don't think it will tell you much. One of the solar panel failure modes is a "high resistance" connection. I.e., the panel will develop voltage, but very little output current. Unless you put a "test load" on the panel, you cannot detect this failure.

    Plus you are adding series diodes on each string--More points of failures (open/shorted diodes), more loses (voltage drop across diodes).

    Best method. Put a series breaker on each string and for testing, turn off one string at a time and see that power/current is dropped by proportional amount.

    Or make each string + lead accessible by a DC Current Meter and measure the current once a month or if output seems low.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Minimum Voltage Level Monitoring

    There's no point to doing this. System put together and working stays working until something goes wrong. Exercising your OCD by checking that each panel has output over and over again is futile. You can't read them individually while they are connected up anyway, and a drop in expected power output (as seen by the charge controller) will show there's a problem causing you to disconnect and diagnose.
  • ZoNiE
    ZoNiE Solar Expert Posts: 100 ✭✭
    Re: Minimum Voltage Level Monitoring

    Crap, Hit the wrong button. Hate that! Retyping now...

    This is only a hobby for me, not a lifestyle (yet), and not something I will depend on to live. It is also a Trailer, and trailers bounce and move, so these panels will be subject to some stress, and being in different places, subject to differing conditions, including large trees and larger RV's nearby (hopefully not THAT close). It gives me something to tinker with.

    I didn't think about just looking at the production data from the Kid and popping each breaker off one at a time to see which one makes little or no change. Makes sense just to do that.

    It is also easy enough for me to put in test points so I can test current/voltage easily. I will forget the diodes, even though 3mV is negligible in an over panel system anyway (at rated wattage, that is) if I go with four.