Voltage drop

mountainmanmountainman Posts: 121Registered Users ✭✭
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.


Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 45.

Comments

  • EstragonEstragon Posts: 2,607Registered Users ✭✭✭✭
    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.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mountainmanmountainman Posts: 121Registered Users ✭✭
      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.
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 45.
  • mike95490mike95490 Posts: 7,790Solar Expert ✭✭✭✭
    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.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • mountainmanmountainman Posts: 121Registered Users ✭✭
    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??
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 45.
  • EstragonEstragon Posts: 2,607Registered Users ✭✭✭✭
    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
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mountainmanmountainman Posts: 121Registered Users ✭✭
    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?
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 45.
  • mcgivormcgivor Posts: 2,052Solar Expert ✭✭✭✭
    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
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • westbranchwestbranch Posts: 5,084Solar Expert ✭✭✭✭
    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.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
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  • mountainmanmountainman Posts: 121Registered Users ✭✭
    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.
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 45.
  • BB.BB. Posts: 27,684Super Moderators admin
    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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