Single-battery system design, sanity check?

IneffableIneffable Posts: 2Registered Users
I've searched extensively online and not found detailed answers on this, just hints here and there that I've pieced together.  So, I'm seeking a sanity check on the design.

My goal is to have a small solar system in my vehicle without a separate house battery.  The reasons for not wanting a house battery are mostly not wanting to keep a battery inside the vehicle or have to find another place to put it, as well as simplicity.

Estimated load is < 80W for 6-8 hours, centered around peak daylight hours.

So, my thought is:
  • Replace my current starting battery with a dual-purpose battery like the Exide Edge Marine Dual-Purpose AGM .  This battery is the correct group size for my vehicle.
  • 100-200W 18V panels that can be tilted and rotated (IOW, not mounted to the vehicle).
  • 20A PWM charge controller: https://www.amazon.com/gp/product/B06XWTKYDC/
  • Run most of my load through the "load" circuit of the controller, to take advantage of the LVD feature (staying well within the 20A limit of the controller, of course).
I'm aware that this battery won't give me much reserve for cloudy or short days. I plan to work around this limitation by finding a plug when needed.

Am I missing anything important in this design?  If you can point me to any posts or discussions on a single-battery system, I thank you in advance.

Comments

  • PhotowhitPhotowhit Posts: 4,606Solar Expert ✭✭✭✭
    If you have a small economy model car, just replace with a deep cycle battery if you battery box is large enough. Dual use are not really designed for deep cycling nd will die rather quickly. If you have a larger car/truck you should just get a battery isolator and run a pair of golf cart batteries for best long term cost, in my opinion.

    Loads aren't well defined, and it would seem odd that you will mainly have daytime loads? No lights at night? No music/phone charging etc at night... With a cheap square wave inverter a 8x80= 640 watt load will quickly become 800+ watt load. at 12 volts that's 800/12= 67 amps, a higher regular drain that we would normally recommend for a pair of 6 volt golf cart batteries in series with a storage capacity of 215 amps...

    Just to replace the 67 amps, assuming optimal 1 time positioning of your solar panels each day, and an average solar isolation of 4 hours (more in summer less and perhaps much less in winter) You would want about 400 watts of array on a PWM charge controller. 400 watt array will normally produce about 15 - 18 amps on a PWM charge controller per hour for the 4 average hours during the day.

    Lvd are generally not recommended to use in conjunction with an inverter are your loads all 12 volt?


    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • BB.BB. Posts: 27,575Super Moderators admin
    edited July 8 #3
    Understand the issue of not wanting a second battery and all of its complications... However, if you do run the battery "dead" (or it fails in 1-2 years do to deep cycling) and the vehicle won't start--Does that leave in in a bad/dangerous situation? Or just call a  friend/autoclub for a jump start and buy a new battery at the autoparts store?

    80 Watts * 8 hours * 1/12 volt battery bank = 53 AH

    That most smaller car batteries are not much more than 50-70 AH of capacity.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Posts: 2,453Registered Users ✭✭✭✭
    The LVD value is generally set to protect the controller, not the battery. Running the battery down to LVD (~10.5v?) will be hard on it, and prevent starting the engine to charge or move. You may want to consider getting a lithium booster pack to enable starting in case this happens.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490mike95490 Posts: 7,712Solar Expert ✭✭✭✭
    Yeah, what they say.  Battery goes dead in your location, no solar to charge with, how to get a jump start ??
    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 ,

  • IneffableIneffable Posts: 2Registered Users
    Thank you for the replies.

    Here are some clarifications.

    If you have a small economy model car, just replace with a deep cycle battery if you battery box is large enough. Dual use are not really designed for deep cycling nd will die rather quickly. If you have a larger car/truck you should just get a battery isolator and run a pair of golf cart batteries for best long term cost, in my opinion.
    My thought is that I wouldn't do a lot of true "deep cycling".  I expect to shuffle my load around according to available sunlight, and that the battery will be mostly backup for fringe periods.

    It's a Toyota Sienna, 3.3L engine.  I think Toyota recommends 585 CCA min.  The BCI is 24F / 34R.  Based on your rec, I'll look harder for proper deep cycle that will fit.

    Where would you put the golf cart batteries?  I definitely don't want a battery inside the van, and I can't imagine where else I'd put them.  There's some space in the engine compartment, but I'd need a mount (which I imagine would have to be fabricated).
    Loads aren't well defined, and it would seem odd that you will mainly have daytime loads? No lights at night? No music/phone charging etc at night... With a cheap square wave inverter a 8x80= 640 watt load will quickly become 800+ watt load. at 12 volts that's 800/12= 67 amps, a higher regular drain that we would normally recommend for a pair of 6 volt golf cart batteries in series with a storage capacity of 215 amps...

    At night I'll use a headlamp running off AAA batteries (this is my norm for camping, and even at home at times).  I don't often listen to music at night, but I'll have the phone if I have an urge for music. If the phone (or system) doesn't have enough juice, then I'll abstain from music...  The phone won't normally need to charge at night, b/c I plan to charge it during the day and turn it off whenever I need to conserve it.

    Lvd are generally not recommended to use in conjunction with an inverter are your loads all 12 volt?

    Yeah, I expect my typical load to be all DC.  So, no plans to use an inverter at night, and rarely during the day.  

    I have a basic 120W inverter that I think would cover my occasional need.  The LVD circuit on the controller I mentioned claims to have over-current protection, but I'd also have a 15A fuse on it.

    However, if you do run the battery "dead" (or it fails in 1-2 years do to deep cycling) and the vehicle won't start--Does that leave in in a bad/dangerous situation? Or just call a  friend/autoclub for a jump start and buy a new battery at the autoparts store?

    Yeah, I'd have a backup plan and not bet my life on the battery.  Even now, I don't expect my auto to be 100% reliable and do my best to include a safety net in my plans.

    But I also didn't realize that these dual-purpose batteries are so "delicate".  Why do they advertise them as good for use with trolling motors?

    The LVD value is generally set to protect the controller, not the battery. Running the battery down to LVD (~10.5v?) will be hard on it, and prevent starting the engine to charge or move. You may want to consider getting a lithium booster pack to enable starting in case this happens.

    This controller has a settable LVD, so I can set it at 11.7V or higher.  But either way, I plan to monitor the DOD (if necessary, with a battery monitor).

    I've definitely considered a lithium jump starter.  If only lithium batteries didn't have that nasty spontaneous explosion (thermal runaway) potential...

  • mcgivormcgivor Posts: 1,900Solar Expert ✭✭✭✭
    edited July 9 #7
    To me, your plan is pretty well thought out, the battery would merely be a buffer for a passing cloud for example, the loads would be powered by the array as long as it's large enough, remembering a 100W module will not give you 100w, more like 80W, for this reason I would suggest your 200W option. By description the battery would never/rarely  be used so keeping the existing starting  battery would be fine as long as diligence is practiced, during cloudy/overcast would be when the battery may be called upon, but the vehicle could always be started to provide charge.

    The only thing missing is the 6 to 8 hours, not many locations will provide useful sunlight for that many hours, you may get away with it nonetheless if, repositioning or tracking is used, try and see how it goes no experiment is without risk 

    With regards to the lithium jump start, there are different chemistries with lithium batteries, LiPo4 are safe, some others not so, but they all get painted with the same brush.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

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