Mystery voltage

PassnThru
PassnThru Registered Users Posts: 2
in Solar Beginners Corner #1
Full time in rv. Short info: 240 watt panel, Blue Sky 3024 controller, Exeltech 1100 watt inv. and a Bogart TM-2025rv recorder. I went to change a fixture and started pulling fuses to shut the circuit off. Couldn't get the voltmeter to zero out. And the voltage increased when the solar panel got more sun. Got it to zero when I shut the emergency shut off.
Any ideas?
· Share on Twitter

Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Re: Mystery voltage

    Welcome to the forum!
    Would need to see a schematic drawing of your wiring of the panels, controller, battery bank and inverter to see how it's all wired together, otherwise we'd be making only wild guesses, and that's about as useful as taking a long walk along the edge of a cliff on a cold and windy day.:D
    Oh, and what voltage were you referring to, DC from the panels, Battery voltage, or AC voltage from the inverter?
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Mystery voltage
    PassnThru wrote: »
    Full time in rv. Short info: 240 watt panel, Blue Sky 3024 controller, Exeltech 1100 watt inv. and a Bogart TM-2025rv recorder. I went to change a fixture and started pulling fuses to shut the circuit off. Couldn't get the voltmeter to zero out. And the voltage increased when the solar panel got more sun. Got it to zero when I shut the emergency shut off.
    Any ideas?

    What voltage wouldn't go to zero? AC or DC? Was the voltage between chassis and neutral? Were you on shore power?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Mystery voltage

    Without knowing in advance what the residual voltage was, several options some to mind, all assuming that the voltage was low relative to normal voltage, and this was a 12V DC fixture:

    1. Fuses were in negative wire, not positive. That would leave the full 12V though.
    2. The charging current into the battery is flowing through a negative wire which is also part of the 12V DC circuit to the lights or some other loads.
    The voltage on the return (negative) wire is going through some loads which are turned on and thus getting to the + on the far side of the fuses. If you are measuring + to ground at the fixture, that explains the whole thing. If you are measuring voltage from + to - at the fixture, then that fixture's - lead is connected closer to the battery -, leading to a difference in the - voltages when current is flowing.
    SMA SB 3000, old BP panels.
    · Share on Twitter
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
    Re: Mystery voltage

    I once was changing a out Inverter in a boat that had a 12v voltage issue. I had disconnected the DC battery leads and was disconnecting the 120v leads. As I disconnected the Neg / Ground I got a spark, I was like what the heck, I checked it and sure enough 12v. It took me forever to find it, it was in a set of 2 way switches in a hallway that had been wired wrong and had a negative crossed over in a 12v /120v light fixture. The funny thing it all seemed to work, but the guy told me that the battery for the 12v lights would go dead without a charger on it 24/7. I wasn't in on the fix because it was all buttoned up behind the paneling, I'd guess they never fixed it.
    · Share on Twitter
  • PassnThru
    PassnThru Registered Users Posts: 2
    #6
    Re: Mystery voltage

    Guess I need to add some info:
    1. I was plugged in to "shore power". Football and Nascar......
    2. Pulled all the fuses from the service panel. Thought that would kill the volts to my leads.
    Tested the wire leads to the 12 volt fixture leads and had 8.58 volts. This number changed up/down with the sun hitting the panel (clouds). The Blue Sky controller said it was "making" 2.3 amps (varied with voltage). What happens when system makes 18 amps????
    3. Was talked into buying a Bogart Engineering TM2025rv which has a shunt on the neg side of the battery bank. Was a help when I had wet cells not so good with AGM.
    4. I have since reinstalled the light fixture and everything is as it was RV wise. But where is this "bleed thru" voltage coming from? And why is it not 12 volt?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: Mystery voltage

    Sounds like you may have pulled the battery fuses--But left the solar array/charge controller and some of the DC load fuses still connected... That could supply current from the solar array to your DC load circuits.

    In general, solar charge controllers are not really designed to operate in that mode (batteryless mode)--Sort of like disconnecting your car battery with the engine running--Your "12 volt" DC voltage will be all over the map (including high enough to kill your car's DC Electronics/Lights from alternator over voltaging).

    The battery bank is really the "voltage" regulator for DC power systems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Mystery voltage
    BB. wrote: »
    Sounds like you may have pulled the battery fuses--But left the solar array/charge controller and some of the DC load fuses still connected... That could supply current from the solar array to your DC load circuits.

    Another possibility is grounding... I wonder what's connected to what... shore power ground to chassis? Is PV or battery floating? It sounds a bit like the situation when a DC GFP trips and leaves the DC fixtures floating at PV voltages above or below ground.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Mystery voltage

    It's pretty easy to screw up the wiring on an RV because most of them start out screwed up from the factory.

    Does it by any chance have a converter built in? Many do: it's basically a big DC power supply meant to take over DC loads and charge battery when shore power is connected. If there is one and the battery is pulled/disconnected while shore power is attached you will see lower than normal Voltage from the converter 'leaking' to 12 Volt load connections.
    · Share on Twitter
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #10
    Re: Mystery voltage
    BB. wrote: »
    Sounds like you may have pulled the battery fuses--But left the solar array/charge controller and some of the DC load fuses still connected... That could supply current from the solar array to your DC load circuits.

    That was my first thought also. Of course if this is the case, the best thing the op can do after pulling fuses and whatnot and returning to service, is to make sure the battery is inline with the controller FIRST, and then activate the panels last, otherwise some controllers may not act properly, or stay in a permanent float or some other sort of safety state.
    · Share on Twitter

Categories