Winterizing off grid solar for summer cabin.

[Basketcase]

Just to give an update, I opened the house this weekend and everything was perfect. Batteries were charged up and had lost very little water. Plates very much still covered. To fill all cells, I used maybe 1 cup of distilled water. (2, 6v batteries) . I set the charge controller back over to the regular setting for the summer. Thanks for the advice everyone. I think we have a system now.

[littleharbor]

What I read about AGM, actually steered me away from them. Higher price, lower life span. I thought the major advantage of AGM was higher charge rate in cases where you need to take advantage of a shorter harvest time? I'm just going off fuzzy memory of when I looked into this months ago. Am I confusing AGM with something else?

+Just a suggestion. AGM aren't for everybody and you need to weigh their benefits and drawbacks. I personally feel they are the right battery for my situation. As my off grid system has to sit unattended through three months of Summertime Baja heat. Your situation is different but still you may benefit from very low discharge, complete system shutdown and not having to maintain electrolyte levels.

[Basketcase]

IS it possible for you to just haul the batteries back with you when you winterize the cabin? Set the batteries in a garage with a trickle charger for the winter?

Possible, but not practical. Its on an island in a bay in Rhode Island. No easy way to get them to mainland. Honestly, for the price of these batteries, I'll be happy with the 6 years I got on the old 12v ones. From the research I've done, I should get more. I wont cry if I dont, but I'd like to do what ever is reasonable for me to do that will extend their life.

[Basketcase]

For your next set of batteries you might consider AGM . They have much lower self discharge rates. They can be left fully charged, and disconnected, for many months with little SOC loss, especially when cold. You could also hang a solar panel vertically connected to a small controller to "maintain" your batteries if you feel the need.

What I read about AGM, actually steered me away from them. Higher price, lower life span. I thought the major advantage of AGM was higher charge rate in cases where you need to take advantage of a shorter harvest time? I'm just going off fuzzy memory of when I looked into this months ago. Am I confusing AGM with something else?

[Basketcase]

What causes a battery to BBQ (from EQ) is that the controller forces a full BULK and ABSORB cycle. THEN it starts the EQ. EQ can only start after Absorb.. But the BBQ part comes along when the sun sets in the winter, and the EQ has not completed (from not enough sun hours in winter days) - So it tries all over again the next day. And the next. All the cycles bubble some electrolyte away daily and pretty soon you need to water the batteries, but you are not there, and so water level falls further and the the exposed plates dry and are ruined. Maybe there will be a couple sunny days and the EQ can finish., and start counting the next 30 day cycle.
So for winter, when you are not cycling the batteries, set absorb = Standby Float voltage and no EQ

That makes perfect sense. Thanks. That's pretty much what I figured.

[citabria]

IS it possible for you to just haul the batteries back with you when you winterize the cabin? Set the batteries in a garage with a trickle charger for the winter?

[littleharbor]

For your next set of batteries you might consider AGM . They have much lower self discharge rates. They can be left fully charged, and disconnected, for many months with little SOC loss, especially when cold. You could also hang a solar panel vertically connected to a small controller to "maintain" your batteries if you feel the need.

[Mike90250]

What causes a battery to BBQ (from EQ) is that the controller forces a full BULK and ABSORB cycle. THEN it starts the EQ. EQ can only start after Absorb.. But the BBQ part comes along when the sun sets in the winter, and the EQ has not completed (from not enough sun hours in winter days) - So it tries all over again the next day. And the next. All the cycles bubble some electrolyte away daily and pretty soon you need to water the batteries, but you are not there, and so water level falls further and the the exposed plates dry and are ruined. Maybe there will be a couple sunny days and the EQ can finish., and start counting the next 30 day cycle.
So for winter, when you are not cycling the batteries, set absorb = Standby Float voltage and no EQ

[Basketcase]

IMO it would be better to just bring home the batteries instead of trying to keep them warm and charged through the winter. It might be more work but at least you won't freeze or boil them batteries.

Its easy enough to disable the EQ setting, and I was planning to. I would like to know what will cause it to BBQ the batteries. Is it the lack of available PV power?

I agree that taking them home and tucking them into bed would be an ideal situation, but I have zero intention of dragging them out of the loft, down the trail to the dock, onto the boat, across the bay and then home to my house. My father (who was the caretaker before me) got 6 years out of 12v marine batts in parallel just by disconnecting them and leaving them with whatever charge they had when it was time to leave. When I took over, I began leaving them charging (with the old pwm charge controller from the 90s) for the last 2 years of their life. I have to assume that I can expect similar, if not better performance from 6v batteries in series and a charger that I have some control over. Its a good suggestion to bring them home, and if it were just a camp I drive my truck to, I probably would. In this case its just not practical and hopefully not absolutely necessary.

To recap, it seems like the best practical choice is to set all the voltages (bulk, float, etc) to 2.30-2.35 volts per cell (per Deka) and disable the EQ charge. This is AFTER I make sure they are fully charged and filled.

[SunEagle]

you need to be sure you can DISABLE the automatic EQ for the winter, or it will BBQ your batteries when it tries and fails, and retries the next day and the next and the next

IMO it would be better to just bring home the batteries instead of trying to keep them warm and charged through the winter. It might be more work but at least you won't freeze or boil them batteries.

[Mike90250]

you need to be sure you can DISABLE the automatic EQ for the winter, or it will BBQ your batteries when it tries and fails, and retries the next day and the next and the next

[Basketcase]

each battery is made of individual cells, inside 1 larger case (cells = number of water refill caps) Over time, they become slightly unbalanced, and need to be Equalized. Or maybe one cell is a bit undercharged, and after 6 months of no charge, it becomes low enough to freeze, or begins to sulfate, thus ruining the entire battery.

That makes sense, and I understand what an equalize charge does. In this case, I will have the charge controller connected all winter, but at float only. I'll have to see if I can figure out how to force this controller to do an EQ charge. I know it is set to do one automatically every X amount of time, but I'll have to see if I can force it. Worst case, I can connect the generator to them, but that is a PITA because of location.

[Mike90250]

each battery is made of individual cells, inside 1 larger case (cells = number of water refill caps) Over time, they become slightly unbalanced, and need to be Equalized. Or maybe one cell is a bit undercharged, and after 6 months of no charge, it becomes low enough to freeze, or begins to sulfate, thus ruining the entire battery.

[Basketcase]

Basketcase

Step #1
======
Charge ( Bulk & Absorb ) the batteries until 100% SOC.
Continue charging until they BUBBLE.

Step #2
======
Start an EQUALIZE charge.
Equalize until the SG reading stops rising for two consecutive readings, one hour apart.

Step #3
======
Set the Charge Controller to FLOAT.


Do you understand why you cannot skip steps #1 & #2, before you leave for 6 months?

I understand why the batteries want to be fully charged, but I do not know the science behind what you are suggesting. I would like to know. I'm not sure I have the kind of control over my charge controller that you are talking about. Maybe I do and I just don't know it.

[NEOH]

Basketcase

Step #1
======
Charge ( Bulk & Absorb ) the batteries until 100% SOC.
Continue charging until they BUBBLE.

Step #2
======
Start an EQUALIZE charge.
Equalize until the SG reading stops rising for two consecutive readings, one hour apart.

Step #3
======
Set the Charge Controller to FLOAT.


Do you understand why you cannot skip steps #1 & #2, before you leave for 6 months?