Charger controller to Inverter and Batteries

bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
I read a thread about someone considering connecting their charge controller to a inverter and piggy backing on the DC wiring to the batteries. I can't find that thread so please, my apologies for the question.

Two different motorhome installs. One is straightforward with easy access to the battery bank from the charge controller. The other is a nightmare as the charge controller is isolated from the battery bank by a sealed under-carriage floor. Due to where the cables from the battery go into that sealed area on their way to the inverter/charger it is extremely difficult to get to.

The idea is to connect the charge controller to the inverter/charger DC separated by a breaker. The cables running from the inverter are OO in size and approx. 7' in length.

Is this permissible or prohibitive for safety reasons?

TIA

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charger controller to Inverter and Batteries

    It's possible. The tricky bit is getting the circuit protection in the right places.

    You have to think of the heavy wires coming from the battery as an extension of the battery posts. Once they are where you can get at them you can split off to the controller and inverter and put the appropriate fuse or breaker for each on those lines. The only down side is you now have a long run of always live wire which may be passing through some area that just might have something sharp enough to break the insulation and ground out the positive. That's when the sparks fly, and why you try to keep circuit protection as close to the source of power as possible.

    Is it legal to do this? I have no idea. If you can add a separate battery fuse at the battery to protect all the wires (like you would with multiple parallel banks).
  • bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    Re: Charger controller to Inverter and Batteries

    Thanks, got it. This is what is envisioned (graphic attached.) I'm not a drawing expert by any means so please excuse the rudimentary attempt.

    While I could possibly get wire to from the battery bank as #8 wire (total run approx 20 feet from PV to battery), I wouldn't be able to get OO wire from the controller to batteries without cutting through the steel container separating the batt bank from other areas. That is a weather tight seal and the wire path is sized exactly for what is already going through from inverter to batteries. There will eventually be 800 watts of PV in this system.
  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: Charger controller to Inverter and Batteries

    You are doing it exactly as I would, given the wire run constraints, except that I would install a fuse between the solar panels and the controller instead of a switch (or in addition to).

    Phil
  • bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    Re: Charger controller to Inverter and Batteries
    PhilS wrote: »
    You are doing it exactly as I would, given the wire run constraints, except that I would install a fuse between the solar panels and the controller instead of a switch (or in addition to).

    Phil

    Thanks for that and easy enough to do since this is all before and not trying to clean up after.

    I have fuses between each panel (10 amp) and I'll add one between the panels and controller.
  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: Charger controller to Inverter and Batteries
    Thanks for that and easy enough to do since this is all before and not trying to clean up after.

    I have fuses between each panel (10 amp) and I'll add one between the panels and controller.

    Although technically it'd be safer, I wouldn't add another fuse since you have the panels fused.

    You have a fuse at the battery. IF the charge controller shorted out (unlikely), that fuse would deenergize the circuit.

    Each fuse adds a little resistance and a corresponding voltage drop.

    On my RV, I have only the CC fused, not the panels. I also, of course, have the inverter fused.

    Phil
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charger controller to Inverter and Batteries

    Technically you do not need to fuse panels unless you have more than two parallel connections, then each panel (or string of) needs its own fuse. Anything beyond that is redundant. Panels won't put out more than their Isc, and all wiring should be sized accordingly. Thus they can feed a dead short indefinitely. The only trouble spot is if a panel itself is shorted, because two or more in parallel with that can feed the bad panel multiples of its maximum current rating.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Charger controller to Inverter and Batteries

    i trust the fuse is going to be close to the battery as a short across the battery wires needs to pop something to keep the huge current surge from going through the wires.
  • bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    Re: Charger controller to Inverter and Batteries
    niel wrote: »
    i trust the fuse is going to be close to the battery as a short across the battery wires needs to pop something to keep the huge current surge from going through the wires.

    The battery bank is already fused for that. So it will look like so:

    battery bank - fuse (within 12 inches)- manual disconnect - inverter - breaker - charge controller - breaker - combiner - panels (individually fused).
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Charger controller to Inverter and Batteries

    Your + wiring should look something like (I think this is what you intended--fuse/breaker values are just examples--fuses/breakers need to be sized to the wire going to loads):
    [FONT=Fixedsys]
    +Battery==300 amp fuse===175 amp brkr inverter----
                           +====80 amp brkr charge controller---
                           +====15 amp brkr 14 awg wire to lights---
    [/FONT]
    
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charger controller to Inverter and Batteries

    Okay it's not easy to do "word pictures" but what you want is:

    Battery - Fuse - "Long Lead" - then branch to: Fuse - Inverter; separate branch to: Fuse - Charge controller

    You can have your battery disconnect either at the battery (preferable) or at the end of the "Long Lead". The charge controller may have its own disconnect independent of the main one.

    The array to charge controller is a separate circuit:

    Panel - Fuse - (X4) - combiner - disconnect - controller

    (If only the vBulletin has some built-in drawing software like devArt's Muro.)
  • bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    Re: Charger controller to Inverter and Batteries
    BB. wrote: »
    Your + wiring should look something like (I think this is what you intended--fuse/breaker values are just examples--fuses/breakers need to be sized to the wire going to loads):
    [FONT=Fixedsys]
    +Battery==300 amp fuse===175 amp brkr inverter----
                           +====80 amp brkr charge controller---
                           +====15 amp brkr 14 awg wire to lights---
    [/FONT]
    
    -Bill

    Yup, just like that. See? I'm starting to get all of this.

    Thanks as always.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Charger controller to Inverter and Batteries

    Note--I see you are using a DC battery switch.

    Note that the "Rotary" boat A/B A+B switches--you should probably avoid switching them under heavy loads. They will probably draw pretty large arcs and burn the contacts. Only switch under load in an emergency. Otherwise, turn off inverter AC loads before switching DC power.

    If you need to switch on/off large DC loads -- You need to find snap action switches / relays / DC Circuit Breakers rated for that activity (for long life and no burned/welded contacts).

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