Question about dead deep cycle battery

Ketchikan Bound
Ketchikan Bound Registered Users Posts: 2
in Off Grid Solar & Battery Systems #1
Hello to all, I am not totally new to setting up a solar system but I am always open to suggestiions.

This might seem like a strange question but I hope you will understand why I am asking it.

I am putting together a solar system for a remote cabin I have near Ketchikan, Alaska.

I will only be visiting it 3 -4 times a summer during the next few years.

Since there will be extended periods of time that I will not be there to monitor the batteries it is possible that a battery or the whole group could go bad for cold.. etc.

I will have panels hooked up to keep the batteries on a constant charge while I am not there.

My question is this, if I get to the cabin and all of the batteries did not hold a charge anymore would I be able to run items, minimally, using just the solar panels passing a charge through the batteries then the inverter into the cabin?

I won't be able to get a new battery / batteries for several days.

If you need further clarification please let me know.

I welcome all responses.

Thanks.
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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Question about dead deep cycle battery

    Hi and Welcome!

    There are no inverters other than grid-tie that I know of that will work totally without batteries.

    If you are careful, you may be able to get by by taking along a small AGM battery just to provide the needed energy reservoir to allow you to use the inverter *almost* directly from the solar panels. If you keep a close eye in the state of charge and do not let the CC overcharge the battery (hence the AGM for high current capacity), then it might do what you need.

    PS: If the batteries are kept 100% charged, or even 90%, they will not freeze until -70 F or something like that. So that should not be a worry. Other then freezing, or overcharging or over discharging while cold, there is not much that the cold will do to hurt the batteries.
    Since you are going to be leaving them essentially on Float the whole time, I would make sure that your Charge Controller has temperature compensation on its voltage settings and that it either is in the same space as the batteries or has a remote temperature sensor.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Question about dead deep cycle battery

    A grid-tie inverter doesn't work without grid, so it's irrelevant.

    If the batteries do not have sufficient power to activate the charge controller & inverter (yes it can happen) you have nothing. Without minimum Voltage a charge controller will not function so no power can get through. Even more so, if the battery capacity is diminished then even turning on the inverter can be too much of a load; without the batteries 'in between' there is nothing to stabilize the current & Voltage; panels' output will vary according to insolation and load. Running with dead or severely depleted batteries is like trying to run with no batteries; it doesn't work.

    On the other hand, as long as the batteries are connected to the panels & controller they will stay charged and will not suffer from cold. I leave mine on their own for 6 months at a time in similar climate; no worries. There is a slight concern that if your charging parameters are not correct or if you are away too long flooded cell batteries may lose too much water during your absence, so it is important that this is checked before leaving.

    Have a portable generator on hand just in case.
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  • Ketchikan Bound
    Ketchikan Bound Registered Users Posts: 2
    #4
    Re: Question about dead deep cycle battery

    Thanks for both of the replies, it is as I thought about the batteries.

    I will have a generator to run if needed but then I need to ask Since my generator will be going through the inverter / charger, if I turn it on and the batteries are dead, will the power just flow straight through the inverter and ignore the Batteries?

    Thanks again.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
    Re: Question about dead deep cycle battery
    Ketchikan Bound wrote: »
    Thanks for both of the replies, it is as I thought about the batteries.

    I will have a generator to run if needed but then I need to ask Since my generator will be going through the inverter / charger, if I turn it on and the batteries are dead, will the power just flow straight through the inverter and ignore the Batteries?

    Thanks again.
    Why will your generator be going through the charger and the inverter? Just to avoid using a transfer switch? You will be much better off connecting your loads directly to the generator when you have no batteries. The generator will end up running the same number of hours and delivering roughly the same output power, just less efficiently. It may allow you to supplement the generator/charger output with power from the PV cells though.

    The charger which you use is not likely to be able to deliver the peak current needed by the inverter if you try to run large loads. Especially a problem with motor starting surges, for which the batteries form an essential buffer storage.

    If you are talking about an integrated Inverter Charger with generator support, such as some Xantrex models, then as long as AC is present on the AC input, it will be switched directly through to the AC output, and the inverter/charger will either not be contributing directly or will be trying to charge your batteries or will be trying to add additional power capability (support) to the generator. You have not given us enough information to be more specific.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Question about dead deep cycle battery
    Ketchikan Bound wrote: »
    Thanks for both of the replies, it is as I thought about the batteries.

    I will have a generator to run if needed but then I need to ask Since my generator will be going through the inverter / charger, if I turn it on and the batteries are dead, will the power just flow straight through the inverter and ignore the Batteries?

    Thanks again.

    If you use an inverter-charger and the batteries are too low to activate it, it will not function even as a charger. Nor will the AC loads be passed-through (the default of the relay is 'inverter'). If you use a stand-alone charger the generator can push current to even dead batteries, but that doesn't necessarily mean you can save them. And you should not try to turn on the inverter with dead batteries being charged by a separate charger; wait for them to come up, if they do. Otherwise you are wasting effort.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #7
    Re: Question about dead deep cycle battery

    I'd even be leery about a modern day charger charging a dead battery, most of the newer 3 stage chargers won't if the battery is less than 8-10 volts. Some will with a special procedure. I usually will start a inverter with a good battery and use a set of jumper cables to the bank until I can get up above
    12 volts.
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