Loose Neg DC Connection

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ForeverHomestead
ForeverHomestead Registered Users Posts: 28 ✭✭
in Off Grid Solar & Battery Systems #1
I have an outback Inverter with a Mate 3 on it.  Back in the summer I was getting a Loose Neg DC connect error and my inverter shut down.  I went through everything.  I have a couple of connections on the battery bank that were a bit corroded.  I cleaned them up and added a anti corrosion gel to them.  Now here I am 5 or 6 months later and I am occasionally getting the same thing.  It happens when my well pump kicks on.  But not every time.  Seems a bit random.

I have checked all cables and cannot find an issue.  What could be causing this?
My system:
Radion 8000w Inverter, Load Center, Mate3, FNDC, Hub 10, Midnight Classic Controller x3, 10 Kw Array, Generac Ecogen, PV Combiner Box x2, Midnight Solar Birdhouse
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    edited December 2021 #2
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    Sounds like you could have a high resistance connection somewhere. Could those funky cables you cleaned have green crud back up under the insulation. Are you using flooded batteries? Acid mist from charging flooded batteries contributes to corrosion on cables/terminals. Be sure all connections are clean and tight

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • checkthisout
    checkthisout Registered Users Posts: 31 ✭✭
    #3
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    ForeverHomestead said:
    I have an outback Inverter with a Mate 3 on it.  Back in the summer I was getting a Loose Neg DC connect error and my inverter shut down.  I went through everything.  I have a couple of connections on the battery bank that were a bit corroded.  I cleaned them up and added a anti corrosion gel to them.  Now here I am 5 or 6 months later and I am occasionally getting the same thing.  It happens when my well pump kicks on.  But not every time.  Seems a bit random.

    I have checked all cables and cannot find an issue.  What could be causing this?
    Assuming it's not a technical issue with the inverter itself. 

    The way to diagnose is to place a voltmeter at the inverter negative connection and then at the battery connection. Load the inverter to it's max output and then see if you get any measure voltage. If you do then wiggle the cable and see if it changes. You can do this throughout the connections. 

    Place your hand on various points of the cables throughout the system and see if you feel an unusually warm/hot spots that would indicate high resistance. 

    How does the inverter know if the negative cable is loose? Does it have smaller voltage sensing leads going to the battery?
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