Infrequent battery use

System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
I have a solar PV system for my mountain cabin. It consists of a 700W array, Outback MPPT charge controller, Trace (Xantrex) inverter, and a 24v, 400Ah AGM battery bank. We use our cabin very little in the winter and there are no loads connected when we are not there. I am concerned that the batteries may degrade if they are not cycled during these periods. I have read that battery life may be reduced if they are not frequently cycled by at least 10% due to the build-up of lead dioxide in "clumps" (rather than an even film) on the plates.

I am considering connecting a small load (a light, or some small appliance) to the system to help "exercise" the batteries during these long periods of non-occupancy. Do any you have experience with this and can offer some advice?

Thanks,
Greg
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Infrequent battery use

    This is going to sound like "non-advice" but ... I wouldn't worry about it.
    I leave my FLA's "to chance" over winter and every spring come back to fully charged batteries (except next year; it's replacement time). AGM's are even less prone to "chemical troubles" than FLA's.

    Someone else may have a different opinion/advice.
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  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    #3
    Re: Infrequent battery use

    Large industrial battery applications, like telecom sites use agm batteries and they let them float for years at a time without cycling them. Some of the larger battery mfg advertize a 20 year float life. So as the coot says "don't worry about it" Just make sure you have remote temp sensing and adequet amps availabe to keep them fully charged.
    Larry
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Infrequent battery use

    i think what greg is worried about is cycling through bulk and absorb daily and that could cause some undue stresses to the batteries without loads on them. do what i did under that type of circumstance and reprogram bulk and absorb for a much lower voltage. maybe put it about say .1v or .2v or so above the normal float voltage leaving the float setting as is. this, of course, means leave it connected all winter and be sure you have the bts to compensate for temperature variations.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Infrequent battery use
    niel wrote: »
    i think what greg is worried about is cycling through bulk and absorb daily and that could cause some undue stresses to the batteries without loads on them. do what i did under that type of circumstance and reprogram bulk and absorb for a much lower voltage. maybe put it about say .1v or .2v or so above the normal float voltage leaving the float setting as is. this, of course, means leave it connected all winter and be sure you have the bts to compensate for temperature variations.

    No worries there as the Outback controller adjusts the Absorb time according to the Bulk time. When the batteries are not significantly depleted (no loads) Bulk time and thus Absorb time will be quite short. You can also set Absorb End Amps to decrease that cycle even further.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
    Re: Infrequent battery use
    Cariboocoot wrote: »
    No worries there as the Outback controller adjusts the Absorb time according to the Bulk time. When the batteries are not significantly depleted (no loads) Bulk time and thus Absorb time will be quite short. .

    That's the beauty that I've found of the MX-60, if come morning the batteries are still up on charge, unlike many other charge controllers, it recognizes that the batteries are "full" and either goes to sleep again, or goes very quickly to float.
    A non-outback controller I have, insists on a two hour absorb no matter if the batteries are already fully charged, which I don't like, but in "normal" use, it has other advantages over the MX-60, like extremely fast sweep times.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Infrequent battery use

    i agree coot that changing the time is a very good solution too. i was just in a mode of thought to just keep it close to being on float all of the time by lower voltages.

    actually the classic is somewhat programmable too, but i am somewhat unsure of it as there is a minimum and a maximum. mine is sitting at 30min minimum and 2hrs max and i believe that was default settings, but don't quote me as it has been awhile since delving into the setup. i need to read a bit on it and maybe in the meantime halfcrazy or boB could elaborate on this aspect further?
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #8
    Re: Infrequent battery use

    The Classic has a Minimum and a Maximum Absorb time so in Niel's case his Classic would never spend more than 2 hours in absorb and if the Classic went from bulk to absorb really quick it would only spend 30 minutes in absorb. The Classic will start a timer when it starts its bulk charge then it will stay in absorb for this same amount of time unless it is outside the Min/Max window.

    Ryan
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
    Re: Infrequent battery use

    great, i see you found the thread i mentioned to you.

    that is an interesting thing as it is not only programmable, but programmable to be somewhat automatic too based on bulk times.8)
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