Voltage drop

mountainman
mountainman Registered Users Posts: 439 ✭✭
edited July 2018 in Caravan, Recreational Vehicle, and Marine Power Systems #1
I have a couple  questions about voltage drop. I have My vabs at 14.8 but at the battery I see 14.4 checked at cc connector screws 14.8. I only see a  v drop with higher amps like in  bulk or absorb. In float at 13.2 very low amps battery posts and cc give the same reading.  7 feet from battery to cc on  4 awg copper.  Could it be a bad cable??  Next problem  came home at the end of the day and checked my  sg. 1st batt 1.280 2nd 1.265. Voltage at battery post 12.72. Came in turned on gas hwh .8 amp gas valve. I then checked Mt 50 12.2 volts?? Went back out checked at  battery posts 12.2. So I cut the hwh off. back to 12.7 volts. Thinking the hwh was shorted I turned on various other loads and the same voltage drop 12.2 with a 3 amp or a 10 amp load. I checked all connections. Then turned on every thing in the rv. After about 15 mins voltage dropped from 12.2 to 12.1. Within 2 mins after turning everything off. Back to 12.7. Batterys are only  5 months old.


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 6 230ah GC @36 volts 
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Comments

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
    Depending on current involved, IMHO it could be either a loose crimp or other problem with the cable, or possibly even the size of cable. I have a short piece of 4ga from controller to buss bars, and larger stuff (2/0 or 4/0, don't recall offhand) from buss to bank. It would be best to find and solve the problem, but in the meantime some controllers can have a small sense wire with little current to adjust for drop and/or an offset setting to adjust for the drop so the controller can charge at proper voltages.

    What was the charging stage when you came home? If "fully charged" and resting, dropping to ~12.2v with relatively small loads isn't great. SGs seem ok though. If actively charging, some of the drop might be a surface charge coming off with loads.
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #3
      I'm thinking a loose crimp from cc to battery. Ill replace them and see if that is the problem.  When dropping to 12.2 battery was fully charged and resting.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    a handheld IR thermometer from harbor freight or somewhere will quickly show your bad connection, unless they are all bad and all read the same.   Run a still load or charging power >20A through the cables, let them heat up a couple minutes, and then use the thermal reader gun, and find the bad one.
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #5
    Problem solved I had a bad ground cable. All of the copper in the cable had turned black? Replaced the cable all is well again. Any ideas on what could have caused that to happen??
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #6
    Copper sulfide can make wire look black (with sulfur from battery mist). Or maybe arcing :#
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #7
    Checked the positive cable it was still shiny inside. I stripped the coating from the negitive it was black the entire lenght. would copper sulfide cause voltage drop?
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #8
    The black is copper oxide the common causes are salt and sulphur, lthe latter is most likely when near lead acid  batteries since they contain sulphur, sulfuric acid, this creeps up the copper even inside the insulation jacket. Tinned copper is commonly used to prevent these issues,  battery terminal spray is also quite effective as it is almost like a paint sometimes grease, being liquid on application allows it to creep between strands before drying. The integrity of the copper is not greatly affected by the surface oxidation , the termination ends can be cleaned, not easy on fine stranded,  then reused, but better to replace either with tinned copper and or terminal spray.
    https://eshop.wuerth.co.th/Battery-terminal-protector-BTRYTRMLGRSE-PROTECTOR-150ML/0890104.sku/en/US/THB/
    https://www.crcindustries.com.au/products/corrosion-protection-and-inhibitors/battery-terminal-protector
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #9
    did you give it a coat of grease, Vaseline or No-Alox?  any of these will minimize the formation of oxidation on copper or Aluminum.
     
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #10
    I just put them on dry. I have seen corroded battery cables on cars but wasn't aware it could travel up the cable. And I thought no-alox was just for aluminum. Very informative thanks all.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #11
    A little copper oxide is generally not a big problem (as long as the connections are clean and have good pressures from screw/crimp/etc.).

    Environmental issues can cause the oxides to form... Heat, carbon monoxide, moisture, oxygen/age, etc.... As well has "cheaper" copper (contamination, poor refining).

    Finer strands (vs thick strands or solid cables), more surface area, possibly more corrosion/shorter life.

    Finer strands, better flexing life (thick strands/solid conductors when flexing will work harden sooner).

    Using some greases on some cables--Not all insulation types are grease/solvent resistant.

    Engineering your system is a balancing act.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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