Garage solar system size requirements?

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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #32
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    Re: Garage solar system size requirements?

    gotcha .. i guess i will wipe the lugs with some 80 grit and scuff the batt terminals with a wire brush and go for it .. seemed to always work out good on automotive using regular grease i just wanted to make sure i wasnt screwing myself here . i want to do it right.
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #33
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    More questions :)

    sorry im so unlearned when it comes to this stuff guys, especially charging a battery bank and understanding the relationship of bank size to current/ voltage requirements for charging ..
    so given:
    -i have a 8 cell bank of 215AH golf cart batts i wired to 12V, i know there are better options for a system now but thats pretty much what im locked into, and already have the charger, inverter ect for 12V so '24 or 48 is better' isnt in the equation at this point .. I used 4/0 to wire the bank and have access to some nice thick stuff for the panel side as well ..

    -i wired the bank today, played with the inverter with a drill press and skill saw and all is well there and works flawlessly. I took the bank down to 12.6 resting voltage.

    - i put my shop charger on the bank at ~40 amps and got a rise to 13.80 in an hour or so (its still going) and its slowed now to 35 or so amps.

    -so now, at this relatively low (as i understand it) charge rate for this 8 cell bank:
    1) what voltage would i pull the charger off at? Still around 14.2? Turn it to low and let it baste for awhile at a lower charge rate?
    2) assuming my 7/ 140 watt panels produce a real world 40 or so amps in full sun can i expect about the same charge characteristics as im getting on the shop charger at 40?

    i really am sorry for my ignorance on the matter guys and i thank you for your time :)

    -Brad
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #34
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    Re: Garage solar system size requirements?

    Brad;

    We're all ignorant about something. I for one know next to nothing about brain surgery. Nor can I speak Japanese! :p

    Your panels will probably manage 50-55 Amps. But the main difference is in the control of the charge: standard battery chargers do not do the 3-stage charging we want for deep cycle batteries. So you'll be able to bring the batteries up to 14.2 Volts, but you won't be able to hold that level for the Absorb cycle. The battery charger is going to try and push the Voltage up, up, up - and that's not good.

    The best you can do is watch the Volts and Amps carefully; if the Voltage goes up to 15, shut it down. If the Amperage drops to less than 2-3, shut it down. Look out for the batteries getting very warm and/or bubbling a lot. It's going to be a bit touchy keeping them properly charged without the help of a charge controller.
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #35
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    Re: Garage solar system size requirements?

    Ok, i really dont have a problem baby-sitting them, im actually quite adept at that messing with hobby type rc things with nicads and lipos for years heh.

    So this is a point i would like to get down in my brain .. if i 'switch off' a panel or two at a time and drop amperage, will that not then drop the voltage across the bank? Can i use this manual approach to charge controlling as the bank peaks out?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #36
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    Re: Garage solar system size requirements?

    Look at it like this:

    All seven panels have a Vmp of 17.5 Volts and an Imp of 8 Amps (may not be exact; just for example).
    All seven panels wired in parallel have a Vmp of 17.5 Volts and an Imp of 56 Amps.
    Take out one panel, the Vmp remains 17.5 and the Vmp drops to 48 Amps.
    Take out three panels, the Vmp remains 17.5 and the Vmp drops to 32 Amps.
    And so forth.

    Not the best system in the world because it is still not Voltage regulated but you should be able to "switch out" panels and decrease the total Amperage potential.

    Charge controllers are wonderful things.
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #37
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    Re: Garage solar system size requirements?

    i agree, i wish i had one of those big mppt controllers, my list is long and the paychecks small though .. i want to increase my panel count to at least 12 over the coming months and maybe 18 eventually .. from everything ive seen i would need pretty deep pockets to work a controller in that could handle all that, but in the end i'll do what i have to if i absolutely cant make the system work right without one .. thanks for your input Cariboocoot ...
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #38
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    Re: Garage solar system size requirements?

    Hello everyone
    .. so my scheme is 'manual' charge controlling via switching individual panels at this point. What i would appreciate is if you could look at my vid of charging in action and tell me specifically if you wouldnt mind,

    - what voltages i should look for when bulk charging for peak , floating, and absorb because im not 100% sure.
    - how long should i float and how long for absorb .. any other strategies i should utilize with this approach .. i know its odd, i may be alittle off :p

    .. thanks in advance

    the system is (12) ~140watt panels (~19V@~8A short test)
    in parallel to (8 ) 6V 210AH wired to 12V

    http://www.youtube.com/watch?v=a9PGUgvYgmg
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #39
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    Re: Garage solar system size requirements?

    I can't view video on my primitive netbook, so I'll give you the "generic" 12 Volt charge procedure:

    Bulk: push as much current as possible up to the limit of 13% of the total Amp hours until battery Voltage reaches 14.2 to 14.4 Volts.
    Absorb: hold at this Voltage for either as long as it took to reach the Voltage from start of charging or until the charge current drops to <3% (or so - some variation possible) of total Amp hours.
    Float: Maintain 13.8 Volts as long as possible.

    See why charge controllers are so good? :p
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #40
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    Re: Garage solar system size requirements?
    Cariboocoot wrote: »
    I can't view video on my primitive netbook, so I'll give you the "generic" 12 Volt charge procedure:

    Bulk: push as much current as possible up to the limit of 13% of the total Amp hours until battery Voltage reaches 14.2 to 14.4 Volts.
    Absorb: hold at this Voltage for either as long as it took to reach the Voltage from start of charging or until the charge current drops to <3% (or so - some variation possible) of total Amp hours.
    Float: Maintain 13.8 Volts as long as possible.

    See why charge controllers are so good? :p

    thats good news and clear info cariboocoot, i think i got it now. I had the absorb/float kindof backwards in my head and didnt realize the goal was to hold the 13.8 for an extended period .. i assume this applies whether the system is at a no-load state or in use? In other words, if i have a solar water pump pulling off the bank a few amps and the inverter on and running a pc only during the day/charge hours, i try to hold the voltage to 13.8?
    .. and final question (sure right :) ) - on a day to day basis not fully running 'off grid' and pulling the bank way down like in overnight use, should i try to keep it at 13.8 at all times and avoid peaking it off daily? Or is it better to 'cycle' the bank somewhat and take it down to say in the 11's and go through a full charge cycle occasionally?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #41
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    Re: Garage solar system size requirements?
    bsolar wrote: »
    ... didnt realize the goal was to hold the 13.8 for an extended period .. i assume this applies whether the system is at a no-load state or in use?..

    If you have sufficient solar, then even with loads, the batteries will still be presented with 13.8V. If it does not have enough solar, then the batteries will discharge and voltage will drop. Controller will sense this, and re initiate BULK till it recovers, and then restarts the timer for ABSORB.

    Also, different battery mfg's will have slightly different specs for "their" batteries.
    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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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #42
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    Re: Garage solar system size requirements?
    mike90045 wrote: »
    If you have sufficient solar, then even with loads, the batteries will still be presented with 13.8V. If it does not have enough solar, then the batteries will discharge and voltage will drop. Controller will sense this, and re initiate BULK till it recovers, and then restarts the timer for ABSORB.

    Also, different battery mfg's will have slightly different specs for "their" batteries.


    thanks Mike, i was testing the system today off-grid in full sun and it keeps up pretty well .. i roughly guess-stimated that in full sun my panels can keep it at 13.8 with a full size fridge running, a desktop pc w/sound system, various wall-warts for phone internet and router, an aquarium pump, and a few lights .. im enjoying having the main grid breaker off this is cool stuff, now all i need is my 12V well pump system installed and i'll be ready to rumble off grid whenever i can put up with no ac, cloths dryer, or hot water :p during most day hours anyway ..

    ... thanks so much for all the input guys its helped immensly make this operational, albeit somewhat unconventional solar system of mine come to fruition ...

    heres a vid of some initial testing of the system if you get bored :roll:
    http://www.youtube.com/watch?v=vcnKWQdnKGg
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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #43
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    Re: Garage solar system size requirements?

    I'm watching the video, and have to admit, I did not read pages 2-4 of this thread, but it does not seem like your running a charge controller.... that would make your panel flipping on and off to "maintain" 13.8v a heck of a lot easier... not to mention automated.. Just a thought, tho I'm sure that has already been covered. However, nice setup.

    JP
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #44
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    Re: Garage solar system size requirements?

    My cheapie controller maintains my power pak at 13.3 volts. It's automatic with no user-adjustable points. It is the one part from my beginner's parts that I have not yet upgraded. Is 13.3 volts an incorrect float charge? Thank you.
    TheBackRoads wrote: »
    I'm watching the video, and have to admit, I did not read pages 2-4 of this thread, but it does not seem like your running a charge controller.... that would make your panel flipping on and off to "maintain" 13.8v a heck of a lot easier... not to mention automated.. Just a thought, tho I'm sure that has already been covered. However, nice setup.

    JP
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #45
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    Re: Garage solar system size requirements?

    13.3 volts is too low for anything other than, possibly, long term float/storage charging.

    For automotive charging, they typically use around 13.8 to 14.2 volts... And 13.8 is pretty low (very near a high float charge set point).

    For Deep Cycle Batteries that are charged with solar--you pretty much want to dump all the energy from the sun you can into the battery bank until it is full--then have the controller back off. You only have a few hours during the day to recharge the bank for next use. At 13.3 volts (assuming the regulator is current/voltage limiting at that point), you are throwing away a lot of energy during the solar day that should be used to get your battery at 90%+ state of charge.

    So, you are probably looking at 14.2 to 14.5 volt volts--and some even recommend closer to 15.0 volts even for "normal" charging.

    Check the specifications for your battery... AGM, Gel, Flooded Cell all respond somewhat differently to charging. Flooded cell typically being the most forgiving (you can always add distilled water). And Gel being the most unforgiving.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ronc89021
    ronc89021 Registered Users Posts: 9 ✭
    #46
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    Re: Garage solar system size requirements?

    I have really enjoyed reading this whole thread! I am just getting started with the solar/wind power thought process and this was very educational....thanks to all!:D
    I went on you-tube and watched most of your postings there ... very educational!
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #47
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    Re: Garage solar system size requirements?

    Sorry, didn't intend to hijack the thread. I ordered the SunSaver 10 amp controller. With my panel averaging between 3-4 amps on a sunny day, I'm hoping for a little higher float voltage.
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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #48
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    Re: Garage solar system size requirements?

    bsolar, how is this system working for you so far?:D
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    edited April 2017 #49
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    wow, its been 6 years i hope everyone is good .. so i dug up this thread for an update - my system of 12 ~144W home built panels is still working great, all the panels are still working .. i finally killed my batteries and have never had a charge controller i manually flipped panels on-off to charge, which im sick of, and i finally decided to move into the 90's so to speak and bought a C60 controller along with a 4 new batts ...the bank 'was' 8 210ah 6v batts, 4 were toast, the other 4 are marginal so i figured i'd wait awhile to replace those and use them for a backup bank in the time being .. but ... my system has seen me through several power outages and storms, one was a serious 3 day outage, love the system, and many thanks to those that got me started with great info here :)
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