Greetings and Off-grid advice requested!

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  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Re: Greetings and Off-grid advice requested!

    It is OK--Blue Sea makes some nice marine bus bar+Fuse combination holders.. As well as a very nice two fuse holder (unfortunately, the smallest fuse is still 30 amps--May be too large for your charge controller wiring):
    Attachment not found.
    Back to the DC switch in the negative lead--Still not my favorite location--And you may have some devices that are frame grounded (such as an AM/FM car radio--if mounted in a grounded sheet metal enclosure) and such.

    There are some conditions where you could over current the "return" wire in this type of setup if there was a short (in a DC light fixture, for example).

    Is there some reason you cannot put the switch in the positive leads (you could even put it in the cable that links the two 6 volt batteries together in series)? Less than perfect, but better than switching the negative power bus).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RossmanRossman Solar Expert Posts: 178 ✭✭
    Re: Greetings and Off-grid advice requested!
    BB. wrote: »
    Is there some reason you cannot put the switch in the positive leads (you could even put it in the cable that links the two 6 volt batteries together in series)? Less than perfect, but better than switching the negative power bus).

    -Bill

    There is no reason I cannot place the DC on/off switch anywhere you suggest, as this is a planning exercise to get ready for Spring 2013! I hope to get everything together so that when I open up the RV I can install the whole system and be ready for the summer there. Where is the ideal location for the on/off switch?
  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Re: Greetings and Off-grid advice requested!

    Here is one diagram from poster "2manytoyz" and his website:

    http://2manytoyz.com/altdiagram.html

    He is missing a fuse from the Battery bus + to the Iota charger--But otherwise this is one way to wire up a system (his is for a home backup power system--But similar in design to an RV system).

    You have to decide your needs--A master load switch so you can turn off all your loads when RV is in storage is usually a good idea (one thing left on--and there goes your battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RossmanRossman Solar Expert Posts: 178 ✭✭
    Re: Greetings and Off-grid advice requested!

    Thanks again Bill, great diagram!

    Agreed, purpose of the DC switch is to keep the batteries from getting drained without having to actually disconnect wires. Pretty sure that happened at least once so far to these poor interstates :)


    Just to confirm, you'd advise moving the switch to the positive instead of the negative side of the battery bank?

    Cheers!
  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Re: Greetings and Off-grid advice requested!

    Yes. Battery plus to switch. From switch, one wire through fuse/breaker to load. Repeat for each separate load circuit.

    -BILL
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RossmanRossman Solar Expert Posts: 178 ✭✭
    Re: Greetings and Off-grid advice requested!

    Thanks again Bill! Much appreciated!
  • RossmanRossman Solar Expert Posts: 178 ✭✭
    Re: Greetings and Off-grid advice requested!

    I managed to find some time to get up to the property today with the charged Interstate house batteries, and got some good readings with my DC clamp meter!
    I also installed the DC on/off switch on the positive side of the battery bank!

    Seems like the core RV power systems draw around 2A.
    When I turned on three lights (2 fixtures contain 1 bulb, another contains 3 bulbs), I got a draw of about 6.5A...five crappy 12V bulbs draw 4.5A?? Seems excessive, perhaps I should replace these with LED bulbs?
    With the furnace on, blowers going, I was seeing a draw of 9.5A, and 14.5A with the furnace and the above three light fixtures on.

    I guess what I should plan for, at a minimum, would be to replace the constant power drained by the RV while I'm not there.

    170Ah battery bank
    25% allowable usage = 42.5A (25% gives me two days of power?)
    Basic RV function = 2A * 24hr = 48Ah


    So this means I really need a higher Ah bank to meet my needs, as this doesn't even take into consideration any additional load, right?

    If we add in light usage, which I'll figure @ five hrs a day for those three fixtures:
    4.5A * 5hr = 22.5A

    TOTAL: 70.5Ah / day
    Resulting battery bank size = 352.5Ah ??

    Seems like no way I can do that with batteries of the same physical dimensions as the ones I have :(

    Could anyone kindly confirm that my numbers above make some kind of sense?

    Thanks!
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