Best way to hook up eight 12 volt batteries for 48 volt system...

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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,165 ✭✭✭✭
    #32
    At the risk of being overly repetitive:
    If you are concerned about resistance/conductivity, go basic. Measure the voltage drop and current draw on each cable segment with the largest load that you can muster. Isn't that the whole point?
    I always have more questions than answers. That's the nature of life.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,165 ✭✭✭✭
    edited July 2017 #33
    Everything you want to know about your blue batteries: http://centexbatteries.com/fullriver/OandM.pdf

     
    I always have more questions than answers. That's the nature of life.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #34
    Dynamic testing with a load, using a DVM set to milli voltage scale, lug terminal, would reveal if there is a volt drop, volt drop would  mean resistance. As @bill von novak stated contact resistance renders them unsuitable for trouble shooting, the ohms per volt of the meter is also a consideration, when tracing ground faults on fire alarm systems, I would use an analog meter as the DVM would read all over the map, insulation testers are useful for that purpose too, with extreme caution.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #35
    The way to measure for bad lugs/crimps/attachments is  fire up the charger in the morning and send 20-40A through the system.  Then you start looking for VOLTAGE.  When you find voltage between 2 points, that's the high resistance point. 
    I've used similar technique to find Vcc - Gnd shorts in wire wrap planes, and multi layer PCBs
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #36
    softdown said:

    Still might be useful for finding a bad connection with the lugs?
    Generally not; it's hard to detect a .1 ohm difference with a meter, even though a .1 ohm increase will result in 250 watts of heat in the connection if you are drawing 50 amps.  (And 250 watts will quickly make the problem worse.)

    If you really need to measure resistances down that low, then get a 4-wire meter.  They are much more accurate.  You can also use two cheapo meters and a lab supply to do the same thing - send 1 amp through the wire via the lab supply and one meter, then use the other meter to measure millivolts on the WIRE ITSELF (i.e. lab supply and second meter connect to different points.)  Then it becomes easy - 1 millivolt on the second meter is 1 milliohm of resistance.
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  • softdown
    softdown Solar Expert Posts: 3,885 ✭✭✭✭
    #37

    3/4" copper tubing is about the best battery bus bar.

    Just spent 1/2 hour trying to upload the 3/4" copper bus bar battery connections. Having downloaded all Microsoft updates, my laptop now works at a veritable snails pace. Including not recognizing the smartphone that it recognized 15 minutes ago. Oh well.

    Edit: Can you believe the laptop decided to recognize the phone after five minutes? Newer technology = state of the art nirvana!

    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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