What is going on with battery banks?

softdown said:

There are two 12 volt battery banks yielding 48 volts per bank. Each battery in the lower bank shows at least 12.1 volts. Each battery in the upper bank shows 11.6 or 11.7 volts.

Does this voltage discrepancy occur while the two battery strings are connected to each other in parallel?  If so, you have a wiring problem.

--vtMaps

Maybe you could post a pic of your battery bank and buss bars.

softdown said:

Sometimes I confuse series and parallel. There are two 48 volt banks. Each bank has four 12 volt batteries. Every connection is done with 4/0 copper. I keep the connections pretty clean with baking soda.

First,  try thinking of Series connections as being serial (one is after another).

Second,  you DO NOT want to have Baking Soda on any connections.  Clean connections,  and sand lightly with very fine sand paper,  clean again,  and then coat all connections lightly with Petroleum Jelly (even coating the mating surfaces of the lugs and battery terminals).

A dilute Baking Soda solution can help keep the battery surfaces clean,  and after using it,  clean again with a clean cloth,  wetted with clean water.

Third,  it is best to add water during the Absorb stage,  OR,  add water when the battery is fully-charged,  and do a short high-ish voltage Absorb.  Or,  perhaps add water just before your periodic EQ charge.

It is not clear what you are saying when you note,  "One battery does have SG averaging 1.12....lower than the rest".   You cannot be saying that one string might be 1.265,  and the other is 0.065!!

At some point,  a number of us do wish that you can buy some new batteries,  so you will have a better chance of learning on a set of batteries that have a known past,  and will not have been damaged/ruined by others.

Good Luck,   Vic

softdown said:

I've been using 8Ds since late 2010....they simply are not as evil as some would have you believe. Not going to replace them until it makes sense.

Why do Americans seem to often think that everybody can buy anything when things may be inconvenient?

Some people trip over dollars to pick up dimes.
If you are really looking for help-advise, list your batteries 1 through 8 and the specific gravity for each cell of each battery. It's really not a good idea to take 12V off one battery in a string, but I think you already know that.

Soft, low voltage events are a big wake up call, that things are really wrong.

Batteries, series and or parallel, doenst matter which, as soon as you combine more than one battery or cell, you have to take special care to ensure that each sub battery and cell are intially and at all times subsequently maintained balanced at more or less exactly the same terminal voltage, SOC and SG.

Why? because, charge setpoints apply to the whole bank and thus individual cells and batteries will only be properly charged if all the sub batteries are in a similar state. Sub batteries that are not charged properly... sulphate and die rapdily. And, on the discharge side of it, the weak cells will hit zero SOC earlier than the stronger cells. If you are lucky, enough sub batteries will hit zero at the same time and the overall terminal voltage will drop enough to hit the LVD and the system shuts down to (maybe) try to protect your setup ((however note that inverter LVD rarely and tend not to be designed to protect the bank, just the inverter, so by the time the inverter shuts down the damage is already done.)). If you are unlucky the one weak cell will then reverse charge, causing profound chemical damage to that cell or cells.

So.. What do do? Simple, you need to test all your batteries to determine which ones are similar, and group the like ones together into usable banks. Say you have half of your 8 batteries with similar capacity, then make a bank of them, and use them alone, or using a battery switch or similar. And, if you still have some variance, then you need to cycle the bank in a safe SOC band. For most people that will be in the upper realm, because lead tolerates overcharge (way) better then undercharge. Then, youll need to do ongoing testing, and stand ready with a steady supply of spare cells. With the aim of maintaining a group of similar health batteries in your bank. Or you can do what most do, and buy a matched set of new cells

To repeat , you cant series or parallel batterys that are in quite different states of health, or charge, or internal resistance. Doing that you will be recycing that lead very very soon.

Then, on the load front. If your night time loads are such that your SOC goes to 75% overnight everyday, then it stands to reason, or at least is pretty likely that protracted less than perfect weather, you are going to have to be ready with the genset. Keeping the SOC above 50% is really important for the long term health of the batterries.

And lastly BTW, with that eratic bank of yours the last thing id be doing is relying on the FNDC's idea of SOC. So be careful how you estimate SOC.

softdown said:

Though still a bit mystified by an inverter shutdown at a "78% SOC". One bank was about 78%. The other bank? Lower....

It is curious to see people howl when voltages drop below 12 overnight. It happens.

Your the only one I see posting with a problem. Every night before I go to bed I check my system's soc and do whats necessary to make sure I have enough power to make it through the night. If you want to go below 50%, then go for it. It's your credit card.

I assume you have a FNdc, without proper calibration it'll never be accurate, even then things change, batteries age and the temperature changes. The first thing you have to do is get your batteries to 100% charge based on the SG readings from your hydrometer. The charge efficiency setting of FLA batteries is between 82 - 88% ( that you have to set and adjust until you know the setting, it may take 10 or more cycles of adjusting it based on the hydrometer readings and the amp hrs returned, if your showing 100% before you really are you lower it, if your showing 100% and accumulating amp hrs, you raise it ) Once you get to 100% then pull the cat5 cable on the hub and reset it.

It ain't easy and it ain't bean bag.

>It is curious to see people howl when voltages drop below 12 overnight. It happens.

Not in my world it doesnt. Or at least not more than a half dozen times a year.

Did you read my post? All your answers are in there, and what others are telling you.

Why don;t you try some $29 battery HA01  balancers from ebay, you will need 3 per 48 volt string, you can;t make things worse at this point I am battling the same issue, undercharged and overcharged batteries in the string. I will be testing the results of these units shortly.
http://www.ebay.com/itm/251906187493?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Dave, if you and i lived on the same planet, i suspect we'd get along just fine.

I don't clean using baking soda. I keep 2 boxes right handy to the batteries in case of an emergency such as a spill on my body. Call me paranoid but FLA's have vent holes. Even small amounts of baking soda getting inside a cell will neutralize a small amount of acid. I use small wire brushes and scrapers to clean the terminals and the copper straps I use as interconnects. Then I use red lacquer to coat the terminals. I find that works great as a preventative measure and is less messy than petroleum jelly.

Mountain Don said:

I don't clean using baking soda. I keep 2 boxes right handy to the batteries in case of an emergency such as a spill on my body. Call me paranoid but FLA's have vent holes. Even small amounts of baking soda getting inside a cell will neutralize a small amount of acid. I use small wire brushes and scrapers to clean the terminals and the copper straps I use as interconnects. Then I use red lacquer to coat the terminals. I find that works great as a preventative measure and is less messy than petroleum jelly.

yes same here, never have used anything since the late 70's working in remote Telcom at HP up in the Big Basin area (Silicon valley) where the earth station was.
An old guy taught me then to not put anything but clean shiny metal in all battery connections. Wipe them down with clean rags and water every other month and there should never be  a need for anything else on a battery. I think many people mess up there batteries by overfilling them and then doing an EQ.  Once you start the corrosion process you are screwed until you replace it all.

Vic said:

And,  regarding the Petroleum Jelly,  on clean terminals and lugs,  BEFORE mating them,  have always done this,  and the terminal protection seems to just last forever.   AND,  there appears to be NO ill effect from this compound between mating contacts.  In all probability,  the micro-rough contact areas simply displace the jelly as the connections are torqued.   This treatment literally seems to last forever,  without any corrosion.

+1

There are all sorts of commercial products for the terminals, but petroleum jelly works so well that I don't see what a commercial product could do better.

Vic, that's interesting about the shop towels... I will try to find some.... where do you get yours?

--vtMaps