Battery issue

[choob]

I have two 200ah 12v batteries in series. They are connected to the inverter via a battery protect which cuts them off at 24v. They're 2 years old.

The only time the battery cuts off is during the rainy season if we get multiple overcast days.

We had this situation last week, and the power would cut off at around midnight. The next sunny day, when I would have expected a return to all night power, they cut at 6pm. Strange, i thought.

Next morning I went out at 8am to reset the breaker and voltage on the battery was 28.9v. Its not usually possible to see it above 25.5v at 8am when charging normally after a cutout.

Are my batteries toast? How could this happen so suddenly? My previous set of cheaper, worse quality FLA batteries died a long slow death and I was running them with no protection.

[Mike90250]

Whenever a inverter shuts down from low battery voltage, the batteries are often in danger from being in a low state of charge, If they are not recharged soon, they will begin to sulfate, and as they sulphate, they loose capacity. My guess is they batteries did not get recharged as soon as possible, and the sulfate hardened and is not likely reversible, it's tough luck, bbut that's what happens. The older a battery gets, the more susceptible they are to sulfation.

[choob]

Thanks. Is 24v too low for a cut out voltage? I had assumed this was 50% and therefore a safe cut off

[Mike90250]

here's a chart for voltage/state of charge & for depth of cycles and life cycles. Up to you to find where you have been operating.


battery-state-of-charge LeadAcid.jpg




DoD_vs_CycleLife.gif

[choob]

So at max 50% DOD and over 700 days battery life it looks like my average DOD (if that's a thing) is betweent 35-40% so actually not too bad but nowhere near the 3-5 years promised by the supplier. sigh.

[Mike90250]

Keep in mind, my charts are not "your" charts, but the basics are the same. Deeper discharges = fewer cycles, and time below 80% full counts toward sulfation

[choob]

I've got new batteries on offer but this is still bothering me. I've had batteries for a slow painful death while being abused (80% dod) but I babied these ones and they died a sudden death.


My previous batteries became very slow to charge at they died, these ones hit 28+V at 9am. They ate sealed so I can't check inside. How do batteries behave is fluid Levels get too low?

The room they're in is pretty hot but they're indian made and Indian summer gets to 50c+... They have a 3 Yr warranty in India but local supplier gives only 1.

I don't expect to save them, just wondering if it could be a manufacturers fault?

[Chip]

I have a similar issue. I have a solar powered cabin used intermittently on weekends. 500 watt array and a 2200wt inverter fed by 4 golf cart batteries. When I get to the cabin the batteries are usually fully charged. I use a countdown timer to shut off the inverter in case I forget to turn off something. (I also use timers on some of the individual circuits.) I am considering installing small 12V refrigerator or cooler connected in a new circuit on the battery bank. I would connect it through a low voltage cutout switch set at 12.5 or so volts. This theoretically utilize my excess energy and keep a few beers cold for my arrival! Question: Is this a good idea and what would be a good cutout voltage for the relay.?

[choob]

My low voltage cutoff using a victron battery protect is at 24 v which would be 12v for you
.


Turns out my batteries were almost empty! They're sealed but when I got my new ones I opened them up and they were almost dry. Miracle they worked as long as they did.

I have serviced them and will use them to run things at the farm during the day. In the future ill stick with tubular batteries just because they're serviceable

[Chip]

From what I am reading it would seem that 12 or 24 volts would be a little low for lead acid batteries. I am looking for some leads on small compressor refrigerators that operate on 12volts, although I could connect through a separate small inverter for that purpose. The solid state (Peltier?) coolers are not efficient at all and would not serve my purposes.