wiring a 24 volt system

alcatel99alcatel99 Registered Users Posts: 31 ✭✭
I am about to start wiring my second solar system which will contain 4 x 6 volt batteries wired in series to give me 24 volts i have read on this forum that to have wire /cable connections  the same length to avoid resistance issues is the best plan  my question is do i use first and last batteries for both my charge controller and inverter by wiring to positive and negative for each component the batteries and components will be within 6 feet of each other, i hope this is understandable.
Thanks

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    edited November 2020 #2
    Having the same cable lengths only matters if you have 2 or more parallel strings. A single series connected string of batteries, there is no reason to "match" battery to battery cable lengths.

    This website does a good job of showing some paralleling options:

    http://www.smartgauge.co.uk/batt_con.html

    If you live in an area with lightning, and/or use radio/TV and want to keep interference down... Then you should parallel cable runs (+/-, etc.). And even twisting cables can help too... Running +/- cables (and AC cable pairs) "separately" ends up make a better "antenna" to "receive and transmit" radio frequency energy.

    Another suggestion is to keep AC and DC wiring separated (I.e., Romex and plastic conduit wiring for AC) to keep crosstalk between AC and DC to a minimum. And, ideally, cross AC/DC wiring at 90 degree angle.

    The other issues are wire AWG--Heavy enough to carry the current... And low enough resistance to keep voltage drop low (for charger to battery bus, around 0.1-0.2 volts max drop at max current from charger to battery, and around 1.0 volt or less maximum drop from battery to loads/AC inverter input--These suggested voltage drops are for a 24 VDC system).

    Using the NEC table for current ratings--Conservative:

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    And a simple voltage drop calculator:

    https://www.calculator.net/voltage-drop-calculator.html

    With wiring, there are usually two calculations to be made, and sometimes more... Current->Wire AWG/Diameter; Current+length+AWG->voltage drop... And parallel connections for battery banks (and sometimes for very heavy loads)--Wire run lengths/resistance to be the same between parallel paths to keep battery charging/discharging "balanced"...

    If you need more help, please feel free to give us some information about your setup (desired loads, lengths of wiring, solar array+charge controller setups, etc.). After you do it once or twice with help, then doing the rest on your own is much easier.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • alcatel99alcatel99 Registered Users Posts: 31 ✭✭
    As always thank you Bill
  • offgridcabin2015offgridcabin2015 Registered Users Posts: 57 ✭✭
    Bill is super helpful. I love that.  :)
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