Winter charging of batteries

Perch
Perch Registered Users Posts: 11
Here's my situation:

We have a couple boats at a cabin that only gets summer use. The cabin is completely off grid. Those boats have batteries. The nearest boat storage manages to destroy those batteries about every other year, meaning I buy new ones. Bringing the batteries home isn't feasible because we fly.

Question:

What is the best way to keep them charged up at our cabin? We have a small solar system and I leave a 10w panel connected over the winter to keep the batteries topped off. That has worked well for years. However, as I understand it (I'm not super well-educated on solar), if I connect my boat batteries into that system, I'll just bring all the batteries down to the lowest common denominator.

Is thing to replicate that for each boat battery...i.e., 10w panel and small charge controller? That seems excessive but might be the only answer.

Or, is there a 12v to 12v charger that would isolate the solar batteries from the boat batteries and has some kind of low current cutoff so it wouldn't pull power if the solar batteries are low?

Or, something else?

Thanks.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Winter charging of batteries

    Very roughly... a 1% rate of charge is enough to "float" a flooded cell battery in good shape--If the battery is "cold" during the winter--So much the batter, less self discharge at colder temperatures.

    The batteries should be pretty much fully charged (near 100% state of charge) when "put away" for the winter.

    So, if you have a 200 AH @ 12 volt battery -- A 2 amp "12 volt" ~30 watt panel is good enough.

    You could go with a smaller wattage panel--maybe as low as 0.5% and not install a solar charge controller.

    Or you can go with 1% or more and use a solar charge controller (the charge controller will help prevent the battery from over charging/using too much water during float/storage).

    Paralleling batteries--If the batteries are all good--Then floating them at ~13.6 volts or so is great. However, if one battery has a shorted cell--It can take down the rest of them too.

    To float a bunch of batteries, you could always put a diode in series with each battery (and a fuse/breaker too--just for safety in case there is a short circuit somewhere). And a simple charge controller with >1% rate of charge--Will keep all the batteries very happy.

    Another option--If you can keep the batteries cold (near freezing or below)--They should survive the 3-4 month winter without any charging current.

    If the winters are "warm" (70F batteries)--Flooded cell batteries need floating/full charging about once per month to keep them happy.

    The "safest" option--Get a 1% rated panel for each battery and an inexpensive charge controller. That way, if there are any battery failures, it cannot take down any other connected batteries (or your cabin's battery bank). It really depends on how much failure costs/risks you (i.e., if batteries are very expensive/difficult to bring to the cabin--Then you don't want to risk the rest of them to save a boat starting battery).

    wind-sun_2268_7430546.jpg SunGuard 4.5 Amp 12 Volt Solar Charge Controller


    If one "shorted" boat battery "kills" a second battery is not the end of the world--Then just get a larger solar panel and single charge controller and charge the boat batteries in parallel.

    If you have a lot of batteries to keep charged--Then something more complex may be better.

    Other options include just getting a cheap VW type car solar panel or equivalent and wire directly (with fuse) to the battery bank and leave the panel in full sun during the winter and no moving the batteries around. $20-$30 or so per boat/vehicle, and you are done (assuming these are smaller batteries to start/run the engines--Not large house boat battery banks).

    Batteries failing shorted is not common--It is all in your the risk/reward tolerance.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Perch
    Perch Registered Users Posts: 11
    Re: Winter charging of batteries

    That was a comprehensive answer and exactly what I needed.

    Thank you very much.
  • stmar
    stmar Solar Expert Posts: 370 ✭✭✭
    Re: Winter charging of batteries

    I have a Sunforce solar battery charger, mine is 5 watts, that I keep my deep cycle trolling battery hooked to all year round when not in use. I hung the panel in the South facing window of my tool shed to keep it out of the weather and have my battery in a Minn Kota battery box so that I just plug the lighter attachment into the box. Keeps the battery at full charge so far. You can get these panels on sale for around $30, I got mine at Cabela's. That seems like a decent price to solve your problem without risking your battery bank.
  • Perch
    Perch Registered Users Posts: 11
    Re: Winter charging of batteries

    That sounds like the "VW type" of charger BB mentioned. I see that Home Depot has them (Cabela's not showing them online). They say it's $40 for one and $130 for a pair. Mind-boggling to think about how they came up with that pricing!

    I have two 115 AH boat batteries to deal with at the moment. So, that would be ~$80 for that solution. Alternatively, a Solartech 45 Watt and Sunguard controller from this site would run me about twice the price but give me substantially more charging if I put the two batteries in parallel.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Winter charging of batteries

    If you get lots of snow that sticks--Mount facing south (above drifting snow depth) on a vertical wall to keep them free relatively free of snow.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Perch
    Perch Registered Users Posts: 11
    Re: Winter charging of batteries

    Bill - Will do.

    Here's a question about it. If I do this, I have 45w of panel that would be doing "nothing" during the summer since the batteries would be in the boats.

    Is there a reason why I couldn't mount a marine two-battery switch after that charge controller. In Position A (Winter), it feeds the electricity to the bus bars where my boat batteries would reside; in Position B (Summer), it feeds the electricity to the bus bars of my cabin's solar system along with the existing controller?

    Both of the charge controllers would be Morningstar-brand controllers, if it makes any difference. The one for the cabin is the 30 amp Morningstar PS-30.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Winter charging of batteries

    Regardless of which setup you use, you NEED over current protection it the Pos. line between the CC and the battery/ies to protect your CC.

    Yes your idea of a switch should work, again have the CB/Fuse between the battery and the switch.
     
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  • Perch
    Perch Registered Users Posts: 11
    Re: Winter charging of batteries

    Yes, I thought I'd just put a fuse in the positive line down next to each boat battery. I have a couple of automotive style fuse holders lying around from something else; I could stick a 10a fuse in those and that should handle it since the Sunguard only puts out 4.5a, right?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Winter charging of batteries

    Just remember you fuse for the "wire" capacity. And PWM controllers do not really limit current--It is you cannot install too large of solar panel/array or you will "over current" the 4.5 amp regulator.

    On another note--If your cabin array is not being used during the winter, you could go the other way--Transfer one of the cabin panels to boat battery charging (may need a larger controller).

    And--if you are going to wire in the panel to the cabin--I would think about getting a full size panel that matches the rest of the array. The larger the panels get, the better $$$/Watt the price becomes:

    Solartech 45 Watt 12 volt Multicrystalline Solar Module $137
    www.solar-electric.com/catalog/product/view/id/638/ Kyocera KD140GX-LFBS $275.00
    www.solar-electric.com/catalog/product/view/id/1258/ SolarWorld SW-265 Monocrystalline $272.95

    Of course, the last panel is a Vmp~32 volt panel and would require a MPPT type charge controller for charging 12 volt batteries (optimally--there are other "ugly" options that would work for charging a small battery bank using a PWM controller--Depends on how cost sensitive you are and if the "extra" power is useful or not--etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Perch
    Perch Registered Users Posts: 11
    Re: Winter charging of batteries

    Hi Bill,

    Yep, I know to fuse for the wire. I was just being sloppy in saying that I would just need capacity to handle that particular controller.

    I've thought about transferring one of the existing panels...still thinking about it. The issue is in disconnecting/connecting hard-wired panels...not sure I want to do that.

    About the price/watt getting better. The problem for me is that this is a slippery slope. Even the Kyocera would now be too much for the Sunguard, so the panel becomes cheaper per watt, but now the $30 controller becomes several times that and, all of a sudden, I've spent a lot of money just to keep boat batteries charged.

    Edit: In looking at the various controllers on this site, I see the SunSaver Dual Battery. Am I correctly understanding that this performs the isolation between two battery banks? If so, could this be used (perhaps with that Kyocera *smile*) with the two boat batteries in parallel on one "leg" and the cabin system on the other "leg"? If the boat batteries were connected, they'd get current. If not, everything would go to the cabin. Just a thought.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Winter charging of batteries

    Yes--You got everything correct.

    The fuse thing--Just want to make sure that everything is clear and safe. Does make me sound redundant at times.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Perch
    Perch Registered Users Posts: 11
    Re: Winter charging of batteries
    Just want to make sure that everything is clear and safe. Does make me sound redundant at times.

    I wouldn't have it any other way. I appreciate the help, especially since I am really new to much of this.