Do I need larger battery cables?

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hillside
hillside Registered Users Posts: 148 ✭✭
in Solar Beginners Corner #1
From "Time for New Batteries" posting a couple weeks ago..update--
small, 940 watt back-up system, 24 volt, 3000W inverter, 40A SRNE C/C..using 4- 6V- 208AH golf cart batteries that are getting tired ..I bought 4 Deka 370AH 6 V batteries and I'm wondering if I can use the existing cables.
They are, as far as I can read on them (7 yrs. old) size 4/0 and say T90 nylon or TWN 75 Burden/Kayler, copper strand with a crimped terminal size 1/0.
I read that a crimped AND soldered terminal is best for heat dissipation..so, should I go with a larger cable size and terminal?
The run from the batteries to the inverter is 5 ft.
8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
Honda EU3000W generator for backup.
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  • hillside
    hillside Registered Users Posts: 148 ✭✭
    #2
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    Edit: to clarify, I'm talking about the battery cables that connect each battery in series, not the cables going to the inverter, which came with it and appear to be 10mm.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
    Honda EU3000W generator for backup.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    3,000 Watt 24 volt AC inverter would draw around:
    • 3,000 W * 1/0.85 inverter eff * 1/21.0 volt battery cutoff = 168 Amps
    From a simplified NEC table:
    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    4/0 is good for 195 to 260 Amps depending on insulation type/temperature/etc.

    And from a voltage drop calculator:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.1608&voltage=24&phase=dc&noofconductor=1&distance=10&distanceunit=feet&amperes=168&x=84&y=25

    10' one way run of 4/0 cable at 168 amps has a voltage drop of:

    Voltage drop: 0.16
    Voltage drop percentage: 0.69%
    Voltage at the end: 23.84

    Same thing with 1/0 cable:

    Voltage drop: 0.33
    Voltage drop percentage: 1.38%
    Voltage at the end: 23.67

    Which is well under the 1-2 volts maximum drop I would suggest for 24 VDC battery bus.

    Take a volt meter and measure the DC input voltage for your inverter (no-load, under your "heavy load") and see what DC voltage you read.

    If you have good crimped connections, do not add solder. It will not improve the connections and can make the present connections more fragile (I am not a fan of soldered connections when crimp connections are available).

    So, I don't see any issues with just installing the new batteries...

    You have enough solar panels to keep the batteries "happy"?

    Suggested to 5% to 13% rate of charge... 5% for backup/sunny weather system and 10%+ for full time off grid (and following most FLA battery charging recommendations):
    • 370 AH * 29 volts charging * 1.0.77 panel+controller deratings * 0.05 rate of charge = 697 Watt array minimum
    • 370 AH * 29 volts charging * 1.0.77 panel+controller deratings * 0.10 rate of charge = 1,394 Watt array nominal
    • 370 AH * 29 volts charging * 1.0.77 panel+controller deratings * 0.13 rate of charge = 1,8112 Watt array typical "cost effective" maximum
    So--If you have the ability--I would be suggesting at least a minimum of 1,394 Watt array for best battery life.

    And there is sizing the system for the amount of energy (Watt*Hours/Amp*Hours) per day you want to draw from the battery bank (assuming poor sun/weather) assuming 2 days of "no-sun" (recommended) or 1 days of no-sun (good for emergency systems/RV usage):
    • 370 AH * 24 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max battery discharge (longer battery life) = 1,887 WH daily
    • 370 AH * 24 volts * 0.85 AC inverter eff * 1/1 days storage * 0.50 max battery discharge (longer battery life) = 3,774 WH "emergency" usage
    And there is the amount of sun for your location... Fixed array facing south for Miami FL:
    solarelectricityhandbook.com/solar-irradiance.html

    Miami
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 64° angle:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.61
         		5.25
         		5.54
         		5.88
         		5.58
         		4.90
     
    JulAugSepOctNovDec
    4.94
         		4.86
         		4.69
         		4.96
         		4.56
         		4.43
     

    So--For an "average" poor day, the harvest from a 940 Watt array and 1,394 Watt 10% array:
    • 940 Watt array * 0.52 average off grid system eff * 4.43 (December) hours of sun avg day = 2,165 WH avg December harvest
    • 1,394 Watt array * 0.52 average off grid system eff * 4.43 (December) hours of sun avg day = 3,211 WH avg December harvest
    Anyway, some math and $$$ to ponder.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • hillside
    hillside Registered Users Posts: 148 ✭✭
    #4
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    Thanks, Bill. I'm in the central Caribbean and we get a lot of sun, averaging 6 hours p/ day in May and June.
    As for keeping the batteries happy, we will often go 2 or more days without using the system at all and the inverter is off.
    In the earlier post I measured voltage at the C/C at 11:30AM at 52.5 volts. Is that what you're referring to? (Moderate cloud cover at the moment)
    As I learned here, keeping the system under 1000 watts kept things simpler in that I wouldn't need a larger charge controller, more panels, bigger wire, etc., and I'm just leery of a bigger investment when with the amount of lightning strikes we have in summer it could all turn to ashes in a second.
    And though I wanted to take the solar panels down before the hurricane it arrived too soon and luckily they stayed in place. So we have that to consider every year.
    My neighbor had a small lightning strike go into an open window and take out the TV and sat. receiver while he was sitting in the recliner watching it.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
    Honda EU3000W generator for backup.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    edited June 2019 #5
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    BB. said:
    10' one way run of 4/0 cable at 168 amps has a voltage drop of:


    -Bill
    Bill The OP said the interconnects are 4/0 wire with lugs that have 1/0 stamped on them. 
    The inverter cables are 10MM squared. What is that in USA wire gauge?

    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #6
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    I am not sure "measured voltage at the change controller at 52.5 volts) means...

    If you you mean at the solar panel input... It sounds like you have Vmp-array ~ 60 volts under standard conditions (aka nameplate 2xVmp~30 volt panels in series--plus some stuff in parallel). Which is all fine for a 24 volt battery bus system.

    Generally, batteries seem to be relatively immune to nearby lightning strikes (of course, a direct strike will take out everything).

    Typically, besides satellite dish LNB (receivers at the antenna) which are very easy to fry with a strike a few miles away if the antenna is facing the strike (from stories I have read), your AC inverter's AC output tends to be the most susceptible to nearby AC strikes.

    So--If you have issues with lightning, then Surge Suppressors would be a good thing... One AC one at the main panel or output of the AC inverter. And at least one at where the solar array +/- enter the side of the home (and run the ground wire from the suppressor down the outside wall to a ground rod/plate directly below (and the rest of the grounding recommendations of running a 6 AWG cable between the "new ground rod" and your existing building ground--This is to provide a safe green wire grounding path for 120 VAC between all of your ground points).

    http://www.midnitesolar.com/doc_prod_list.php?menuItem=products&productCat_ID=23&productCatName=Surge%20Protection%20Devices

    http://www.midnitesolar.com/pdfs/howLightningProtectionWorks.pdf

    Midnite's Videos on surge suppression (they have a lot of other product videos too:

    SPD (Surge Protection Devices)
    Midnite surge suppressor pricing (our host, Northern Arizona Wind & Sun):

    https://www.solar-electric.com/search/?q=midnite+surge

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • hillside
    hillside Registered Users Posts: 148 ✭✭
    #7
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    Thanks and I was referring to your sentence,
    "Take a volt meter and measure the DC input voltage for your inverter (no-load, under your "heavy load") and see what DC voltage you read."
    Being a total novice at this I'm not sure what you meant.
    But I did read 26.6volts at the C/C and 26.2 at the inverter this afternoon. If that matters.. :)  (with the old batts. still)
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
    Honda EU3000W generator for backup.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    That sounds good (battery bank under a little bit of charging (or running a low float voltage)... Just wanted to make sure your cabling and connections were all OK... I.e., 26.3 volts at the battery bus and 26.2 volts at the inverter (very little voltage drop) under load.

    Also, understand what your battery bank condition--I.e., after you run the system overnight, what is the battery bank voltage before the sun hits/crank up genset (if used).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    #9
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    I'm curious about the lugs on your 4/0 interconnects. Do you know who made them?  It seems odd that the lugs are 1/0. Were the cable strands trimmed off till the 4/0 cable fit the lugs?

    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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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited June 2019 #10
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    hillside said: ......I read that a crimped AND soldered terminal is best for heat dissipation......
    Maybe, but it's also a recipe for mechanical stress fracture of the entire cable thickness, if it does not self-immolate as half the strands break.

    When cable is soldered, solder wicks up inside the insulation some distance.  Where it stops wicking, the cable abruptly changes from "solid" to "stranded" and all the flex force (movement, thermal expansion, vibration) gets focused on that small section of cable. The distance of wicking is un-predictable, and the time to failure is random.

    The other failure mode for soldered connections, is that under heavy current, solder (tin & lead) has a higher electrical resistance than copper and can begin to self heat.  When it gets hot enough, it can slip out of the lug and you now have a DC arc welder spraying sparks and copper plasma around your battery caps.  If you are lucky, it's just a mess.  Unlucky and a battery goes BOOM.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • hillside
    hillside Registered Users Posts: 148 ✭✭
    #11
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    littleharbor2 said:
    I'm curious about the lugs on your 4/0 interconnects. Do you know who made them?  It seems odd that the lugs are 1/0. Were the cable strands trimmed off till the 4/0 cable fit the lugs?
    These were crimped at a commercial electric store and they were not trimmed. They appear to be a perfect match.
    But I'll take a second look at them today because you've got me wondering..

    About crimped and soldered connections--it was while researching cables and lugs that I came upon the pictures on a Trojan site that showed infra-red photos of crimped fittings glowing red hot (hotter than the rest of the cable) and then ones showing both crimped and soldered showing even heat distribution.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
    Honda EU3000W generator for backup.
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  • hillside
    hillside Registered Users Posts: 148 ✭✭
    #12
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    And my unofficial measurement (don't have calipers) is that the battery cables are between 7/16-1/2" thick with the insulation.
    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
    Honda EU3000W generator for backup.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #13
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    Really need the copper diameter. Insulation can be of variable thickness.

    Littleharbor2,

    Here is a chart for AWG to metric conversions:

    https://www.rapidtables.com/calc/wire/awg-to-mm.html

    AWG to mm conversion chart

    AWG #Diameter
    (mm)    		Diameter
    (inch)    		Area
    (mm2)
    0000 (4/0)11.68400.4600107.2193
    000 (3/0)10.40490.409685.0288
    00 (2/0)9.26580.364867.4309
    0 (1/0)8.25150.324953.4751
    17.34810.289342.4077
    26.54370.257633.6308
    35.82730.229426.6705
    45.18940.204321.1506
    54.62130.181916.7732
    64.11540.162013.3018
    73.66490.144310.5488
    83.26360.12858.3656
    92.90640.11446.6342
    102.58820.10195.2612
    112.30480.09074.1723
    122.05250.08083.3088
    131.82780.07202.6240
    141.62770.06412.0809
    151.44950.05711.6502
    161.29080.05081.3087
    171.14950.04531.0378
    181.02370.04030.8230
    190.91160.03590.6527
    200.81180.03200.5176
    210.72290.02850.4105
    220.64380.02530.3255
    230.57330.02260.2582
    240.51060.02010.2047
    250.45470.01790.1624
    260.40490.01590.1288
    270.36060.01420.1021
    280.32110.01260.0810
    290.28590.01130.0642
    300.25460.01000.0509
    310.22680.00890.0404
    320.20190.00800.0320
    330.17980.00710.0254
    340.16010.00630.0201
    350.14260.00560.0160
    360.12700.00500.0127
    370.11310.00450.0100
    380.10070.00400.0080
    390.08970.00350.0063
    400.07990.00310.0050

    Just to confirm, the cable is 10 mm^2 (area of cross section) and not 10 mm diameter? I am always a bit careful with metric--Different countries/regions seem to use different units (area vs diameter). And they can be "close enough" for some sizes that it is not obvious which system is in use.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    #14
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    Bill, After my 1st post on this thread I realized I should have just looked this up myself.  I am the one who added "squared" to the equation. Probably shouldn't have. My bigger concern was the 1/0 lugs on the 4/0 battery interconnects. 

    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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  • softdown
    softdown Solar Expert Posts: 3,821 ✭✭✭✭
    edited July 2019 #15
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    hillside said:
    littleharbor2 said:
    I'm curious about the lugs on your 4/0 interconnects. Do you know who made them?  It seems odd that the lugs are 1/0. Were the cable strands trimmed off till the 4/0 cable fit the lugs?
    These were crimped at a commercial electric store and they were not trimmed. They appear to be a perfect match.
    But I'll take a second look at them today because you've got me wondering..

    About crimped and soldered connections--it was while researching cables and lugs that I came upon the pictures on a Trojan site that showed infra-red photos of crimped fittings glowing red hot (hotter than the rest of the cable) and then ones showing both crimped and soldered showing even heat distribution.
    1/0 lugs will not be any sort of match for 4/0 cable. The tolerances are so tight that lugs made for normally stranded cable will not accept the much more multi stranded and finer "welding cable" - which is just slightly thicker in overall O.D.  
    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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  • hillside
    hillside Registered Users Posts: 148 ✭✭
    #16
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    Major correction..the cable is size 1/0 and the lug is size 1/0..
    I found a cable that am no longer using from the first set of 12v. batteries that does not have faded print on it.
    Batteries have been installed now for 3 days and no problems.
    I know I don't have enough panel wattage (940) to fully charge these 370AH batts. in one day but this is not a problem as the usage is periodic and we are able to reduce our electric bill substantially by selective use.

    8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller &  40 Amp Renogy controller, 24 Volt system.
    5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
    4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
    Honda EU3000W generator for backup.
    · Share on Twitter

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