Temporary upgrade to a 12v off-grid system

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cdre
cdre Solar Expert Posts: 78 ✭✭
in Off Grid Solar & Battery Systems #1
I'll likely to start building my off-grid house early next year which will require a brand new system, but in the next few months I expect to be shifting to working off-grid in my 5ver for at least the next year. As such, I'll need to upgrade my system to accommodate my electronics and a split unit A/C. Most of my heavy use is during the day, but I'd like to have the batteries well charged up heading into the evening so the wife can watch TV without running the gen.

Here's what I have now: 300 watts of panels, a Blue Sky controller rated for 25 amps at 12 volts, 4 6v Sam's Club golf cart batteries, a Trimetric 2020 and a Xantrex ProWatt XW.

With most of my heavy use during the day and with the batteries already 2 years old, I'd prefer to not add to the bank. I'll run a Champion 4 stroke 1200w generator as a crutch on cloudy days or as needed. Gas in Belize is currently at US$6/gallon though, so I want to plus up my PV array. None of the components will be common on the new house, as I'll be looking at a 48v system likely with a Flexpower 2. I'd like to limit the cost of my temporary upgrades.

I'd like to add 300w of panels and enough charge controller to carry the full load. The new panels will have roughly the same specs as the old (Vmp ect). Should I combine the array into one big array feeding a larger controller (ie a Xantrex C60) or keep them split and add an additional charge controller (ie a Xantrex C35)? Is it safe to run 2 charge controllers in parallel to the same bank?

Thanks!
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Re: Temporary upgrade to a 12v off-grid system

    It's safe to parallel several quality charge controllers to the same battery bank.

    If you can plan out your realistic load requirements now, then you bcaktrack from that to find your battery need, then your array size. Your array size sets the charge controller, and most of the quality ones (Midnight, Outback, Xantrex, Morningstar) will all operate at the SAME AMPS, at 12V. Your array wattage capacity goes down, as your battery voltage goes down.

    And a early morning run with the genset, will quickly BULK charge the batteries, and let the solar do the slow part the rest of the day.
    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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  • cdre
    cdre Solar Expert Posts: 78 ✭✭
    #3
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    Re: Temporary upgrade to a 12v off-grid system

    Thanks for the initial input. I definitely understand you should build from the loads, but being a pre-existing system, I'm just looking to extend it's usefullness for a year.

    I think I'll adjust the new charge controller to an Outback FM80, as I can use that on my next installation with a Flexpower 2. I'll probably run a higher voltage array there as well.

    So I guess the real question is whether the FM80 and BlueSky 2512i will play well together on the same 12v bank...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Temporary upgrade to a 12v off-grid system
    cdre wrote: »
    Thanks for the initial input. I definitely understand you should build from the loads, but being a pre-existing system, I'm just looking to extend it's usefullness for a year.

    I think I'll adjust the new charge controller to an Outback FM80, as I can use that on my next installation with a Flexpower 2. I'll probably run a higher voltage array there as well.

    So I guess the real question is whether the FM80 and BlueSky 2512i will play well together on the same 12v bank...

    No worries as the FM80 can be programmed to match whatever charge parameters the Blue Sky has.

    I agree with your plan to up the panels to 600 Watts total, as that is a better match for parallel golf cart batteries.

    Unless the new panels are completely different from the old, the FM80 would easily handle all 600 Watts together.

    You probably already know this but ... just be sure when you add on to an existing system that the wire in place is capable of handling the change in current. For example, if all panels are combined at the array then the lead to the controller will have different Voltage/Amperage than before (depending on the configuration) and the output from the FM80 will be in the neighbourhood of 40 Amps which the wires from the Blue Sky never saw.
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  • cdre
    cdre Solar Expert Posts: 78 ✭✭
    #5
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    Re: Temporary upgrade to a 12v off-grid system

    Thanks! The three old panels are 110w at 12v. Would it make sense to run two Kyocera KD235GX-LPB's (max 30v) in series with two of the 12v panels in parallel, all on the FM80? I'm sure I can use the other 110w on another project.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Temporary upgrade to a 12v off-grid system
    cdre wrote: »
    Thanks! The three old panels are 110w at 12v. Would it make sense to run two Kyocera KD235GX-LPB's (max 30v) in series with two of the 12v panels in parallel, all on the FM80? I'm sure I can use the other 110w on another project.

    It all depends on the actual panel specs. When you connect panels in series you want the Imp's to be close. When you connect them in parallel you want the Vmp to be close.

    The Kyocera's you mention have a Vmp of 29.8 and Imp of 7.89.
    If you know the specs on the 110 Watt panels and they come within a few percentage points then there may be a way to connect them all. For instance if the Imp of the small panels is 7.5 to 8.25 they can go in series. But chances are the small panels have specs like "Vmp 17.5, Imp 6.3". In that case the Imp is too far off for a series connection. Likewise two of them in series wouldn't parallel with the 235's (2 * 17.5 = 35, which is too high to parallel to Vmp 29.8 ). Besides you have three of them.

    Confused?
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  • cdre
    cdre Solar Expert Posts: 78 ✭✭
    #7
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    Re: Temporary upgrade to a 12v off-grid system

    Yeaaaaahhh.... Probably best to just run the old boys off the BlueSky and new on the FM80. That gives me the full 800w anyway.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #8
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    Re: Temporary upgrade to a 12v off-grid system

    When you connect the charge controllers (and loads) to the battery bank--Make sure you have heavy/short cable from the batteries to the common +/- bus bars... Then "home run" a dedicated circuit to each charging source (two or more charging source sharing a single cable can confuse each other about the "true state of charge" for the battery bank.

    Also, if you are paralleling batteries, try to keep all wire runs for each "parallel connected battery string" have equal lengths:

    www.smartgauge.co.uk/batt_con.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • cdre
    cdre Solar Expert Posts: 78 ✭✭
    #9
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    Re: Temporary upgrade to a 12v off-grid system

    Thanks for the link. When you say "home run" I assume you mean to connect each charging source with it's own set of cables to the bus bars?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #10
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    Re: Temporary upgrade to a 12v off-grid system

    Correct... Not "daisy chained" where cable goes from Battery to Controller A to Controller B to Controller C... Home Run can also be called "Star Connected" (center of the star is the battery bus, the loads/chargers are the "points" of the star).

    These charge controllers output varying current (DC level, pulsed current, etc.) which can confuse other interconnected charge controllers and may reduce overall charging performance (mixing "noise" with "true" battery voltage).

    Keeping battery cables short and heavy, and using rated fuses/breakers for each positive run that leaves the battery + bus (assuming negative ground) based on the connected load and wiring gauge (fuses/breakers are there to protect the wiring run from overheating/starting a fire, not the device at the end of the branch circuit).

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