Batteries not reaching float

2twisty

OK, in continuation of my other battery woes (very low SG), I am now no longer reaching float.  I can run my generator all day, and I never get there.  Always a few volts below.

Quick version of my setup:

9 250w panels in 3x3 arrangement to make just over 100V.
Classic 150
16 GC2 batteries wired as 48V bank(2 strings of 8)
Outback 3648 inverter/charger
7000/8500W electric start generator

If I run the generator, the outback will charge at its max (2400W charging) for quite a while then slowly taper off and stop charging.  I assume that this means that the Outback thinks that I'm at float, yet I am a couple volts shy of my 54.4V float setpoint.  After turning the generator off, even in strong sun, the classic never gets to float (stays in bulk, no absorb either).  WBJr reports that I'm still putting 20A into the batteries, which is about all my panels can make.  

WBJr reports that SOC is 100%.

I thought perhaps I had a bad cell causing my nominal voltage to drop.  I went out this morning before the batteries were fully charged.  My older string of 8 batteries all measured about 6.2x volts when completely disconnected from each other.  The newer string all measured 6.5x.

The 2 strings measured differently, but each battery in a given string measured within a few hundredths of a volt of each other.  So much for a bad battery or bad cell.

This is in addition to the fact that I have extremely low SG, and even running an EQ on the batteries for several hours on the generator, the batteries never rose to the EQ voltage of 61.2.  The best I saw was 58.8V.  After EQ for 9 hours, They levelled off at 56.4V for the entire back as measured by the MATE on my outback.

All that EQ ( and $15 in fuel! ) had no appreciable effect on the SG.  After running that long EQ, that's when my batteries started refusing to hit float.

What should I check now?  I know this likely means that my batteries are on the way out, so Im starting to figure out how to replace them.  But what can I do to make them last as long as possible?  Finances are tight for us, so $1600 in replacement batts isn't something I can just pull out of the bank in the next week.

Please advise.

Dave Angelini

If you can't get to 59V for 5 hours or so you will probably find that your batteries are shot.
 Maybe, with SG readings you can build a good string and use that with the hope of charging the bad string to close to normal as time permits. You will need a battery disconnect switch between the strings. 

Photowhit

Sounds like you added new batteries to old? Not something that is advised unless the batteries are very close to new.

How old are your old batteries?

Are the batteries the same Make model, size?

It sounds as if your old batteries are shot, have minimal capacity left. I think I would first remove that string and see if you can get the new batteries to come up and equalize. If you have no budget to replace, I would look to reduce loads to use just the newer string of batteries. You may find you have as much or even more capacity, than you currently have as the old string won't draw energy off the new string.

Photowhit

Batteries in parallel strings will try to maintain the same voltage. current will run from the higher voltage batteries to the lower voltage batteries. You may find that after they sit for a while some batteries in the old string will continue to drop voltage.

2twisty

String #1 is 2.5 yrs.  String #2 is 1.5 yrs.  

Interesting tidbit:  After going out and disconnecting all those batteries to check their voltages, I went ahead and cleaned all my terminals.  I filled the batteries, too.

I came back in and the system went to float, according to the Classic.

All my SGs are low because I allowed the batteries to overflow and lose acid.  I am contemplating correcting the acid concentration, since the lower SG is (IMO) more likely related to the loss of acid.

I know that parallel strings are frowned upon.  That's why I only have 2.  Sadly, reducing my loads isn't really an option -- I could reduce them some, but not enough to remove the need for the extra string.

All the batteries are GC2s.  They all have similar capacity.  I think the old ones are 220aH and the new ones are 208aH.  I couldn't get identical ones when I went to buy the second string.

So, here's my thinking on correcting the SG:  if I'm wrong, please explain why -- don't just call me a dummy for thinking it.

Batteries raise SG as they increase their charge level (and therefore voltage).  I KNOW I have lost acid to boil-over since I have seen the greasy liquid that is acidic on top of the batteries many times.  I keep adding water only -- this results in a slow dilution of the electrolyte, causing the batteries to never be able to get to full capacity.

My planned procedure:  Charge the batteries until the voltage won't go up anymore and the SG peaks.  Then, using 98% pure H2SO4, slowly add small amounts of the concentrated acid until the SG gets to about 1.260 or so.  Then charge the batteries again and observe the results in both voltage and SG readings.  If my batteries are toast, Im not sure I have anything to lose in trying this.  

Yes, I know that acid is dangerous, etc.  I am smart enough to know how to be careful with caustic and acidic substances.  I routinely work with pure lye when making soap.  If I'm wrong, please explain how the chemistry is wrong.  If it's worth trying, I'll order the acid from a supply house and start the experiment.

Estragon

IIRC you should never add acid to water. Adding acid to diluted acid may not be as bad, but probably still risks pretty violent action.

Seems to me there was a thread a while back about recovering batteries along the lines you're suggesting as an experiment -last ditch effort. Might have been @mcgivor

I'll see if I can find it.

Estragon

The thread is Water treatment in old battery tech. In that case he was trying to recover a sulfated battery.

He lowered SG by taking acid out and adding water in stages and charged with the progressively diluted acid, then brought the SG back up by reversing the process. Apparently it worked out ok and @mcgivor is still with us ☺.

It sounds like what you have in mind is the second part of the process so maybe worth a (very careful) shot?

Photowhit

Batteries out gas, some of it will be acidic, If you only had out gassing and didn't have a battery filler system in place that some how continued to force water into the bank or some other catastrophe, batteries knocked over, I would not add acid.

I don't know how Outbacks do equalizing, but I don know, in general, equalizing doesn't require a lot of energy. I would thing you would be better served to charge the batteries in the morning with the generator and then let the charge controller equalize the batteries.

There are other reasons for batteries going bad other than age! I suspect you may have been working the original set very hard before adding the 2nd set of batteries. Without them being the same make, model and age, they will have different internal resistance and one string will do more work than the other.

Measuring the voltage when just pulled off of the system will not tell you anything, they should be very close in voltage. If you can, take the whole system off line for a few hours, then you will find it easier to see what batteries you are having problems with. If you compare measurements just after and 4 hours later you may find cells that have enough sulfates collected in the bottom to create minor shorting across the plates.

Again, removing one set may increase your systems capacity. Try charging then equalizing, just the new set of batteries! I didn't go back to the old thread, but I believe the new batteries have a SG indicating they are at 75-80% of capacity and the old set, 60%. Both of these would indicate major sulfating on the plates. It's likely adding acid will just create higher density of acid in the electrolyte and there will be no place for the sulfate to go if you can get it to recombine.

I think one person here equalized for several days to recover some Rolls batteries that had been chronically under charged. Batteries must first be completely charged. Are you using end amps for your charging profile? I think the Classic's basic charging is just to maintain a timed set voltage for an hour, with diminished capacity will allow that to happen very quickly, you might set absorb to 3 hours and then manually equalize. Also check your equalizing voltage, No reason to not push it up if you have a Temperature sensor, 62 volts (or even a bit more) have lots of distilled water on hand and really push them around, you are intentionally over charging the batteries!

I hope I wasn't derogatory, we all are learning. I have a bad cell in my battery bank, I suspect it was poisoned (I worked security in a community I lived in). One of my cells had the electrolyte that was very dark, from a couple months after the battery arrived. It lived outside, unlocked... Well end of last summer the cell cleared up, I didn't think much about it, and had skipped that months SG measuring. When I did the following month that cell was around 1.20! I worked on it equalizing often through the cloudy fall, by January, it was 1.265 and guess what? The cell had gone back to being very dark. When this thing dies, I'm going to pull the electrolyte from that cell and see if someone can tell me what's in there that shouldn't be...

Estragon

I think the outback is time based absorb and eq. Don't think I've ever used it for absorb though, so might have an end amps but I don't think so. Is the 54.4 in your OP a typo? I would set Vabs using the generator to bulk to at least 58.4 (temp compensated), maybe a bit higher. I don't know what quite a while is, or the initial SOC, but I would expect ~1-1.5hrs of bulk for each 10% below 80%. If batteries were at 50%SOC that would be 3-4hrs bulk.

If not a typo, the Outback is going to absorb at 54ish volts and holding there while current tapers. When you charge with Classic it has to to a proper bulk to 58ish volts so maybe runs out of sun before it can absorb?

@Photowhit - If the batteries were heavily sulfated, wouldn't the voltage come up much more quickly?

Photowhit

Estragon said:

@Photowhit - If the batteries were heavily sulfated, wouldn't the voltage come up much more quickly?

It will for a while, I suspect he is getting past that point where sulfates have accumulated in the bottom of the first set of batteries and they are near dead. Then they won't hold voltage.

Perhaps he will take them off line for a while and check them after a few hours.

Estragon

I've probably never had batteries get that far. They just seem to charge (and discharge) faster as they get worse until I get fed up enough to replace them.

Wouldn't voltage still come up fast (or even short) with sulfate sitting on the bottom?

Estragon

Thinking about it, the "even short" part would be like turning the battery into a water heater, with the sulfate short as the "element".

Most of the current would be going into heating the element. This could continue until the earlier of; a weak part of the element acting like a fuse and opening the short, turning off the power, or the battery boiling dry. If the concentration of hydrogen was right in the dry contained cell, it could turn a bad day into a really bad day quite suddenly.

A load test on individual batteries is likely the best way to tell if any can be salvaged then. If there's enough sulfate on the bottom to short, even the water treatment thing would be a waste of time.

mcgivor

Estragon said:

The thread is Water treatment in old battery tech. In that case he was trying to recover a sulfated battery.

He lowered SG by taking acid out and adding water in stages and charged with the progressively diluted acid, then brought the SG back up by reversing the process. Apparently it worked out ok and @mcgivor is still with us ☺.

It sounds like what you have in mind is the second part of the process so maybe worth a (very careful) shot?

The link is to where treatment process, the Pdf in the first post also contains information regarding correcting SG by adding acid, electrolyte, read the instructions carefully. For what it's worth my attempt at restoring a bad cell was successful, what I noticed was that when I attempted to EQ  parallel strings the voltage was not ballanced, favoring one, dragging the voltage down, seperation gave better results, the voltage required for EQ was met, it struggled with both strings. Had to live for a week on economy mode whilst separate, half capacity, if you have two sources for charging the process will be easier, but I would highly recommend seperation and treat each string individually. Using an infa red themometer for detecting hot spots, internal shorts, is also  a useful tool to have.
Good luck.
 
http://forum.solar-electric.com/discussion/351467/water-treatment-for-over-sulfation#latest

2twisty

OK. I will go get some new voltage measurements tomorrow.  I will charge for a while in the AM and then disconnect the older string and let them rest for 4 hours and then measure voltages.

What I find strange is that about 20 minutes after making my original post, the Classic dropped into float.  Not sure what that means. 

My settings in the classic:  I do use End Amps.  Bank total Ah is about 400ish.  So I have the End Amps set to 3.7.

Absorb voltage is: 59.2
Float voltage is: 54.4
Absorb time is 2 hrs

mcgivor

You may want to extend the absorb to 3 hours, the end amps will /should terminate absorb if the setpoint is met, from my experience, although all systems vary depending on discharge etcetera, that 2 hours is not long enough, YMMV.

Photowhit

2twisty said:

OK. I will go get some new voltage measurements tomorrow.  I will charge for a while in the AM and then disconnect the older string and let them rest for 4 hours and then measure voltages.

What I find strange is that about 20 minutes after making my original post, the Classic dropped into float.  Not sure what that means. 

My settings in the classic:  I do use End Amps.  Bank total Ah is about 400ish.  So I have the End Amps set to 3.7.

Absorb voltage is: 59.2
Float voltage is: 54.4
Absorb time is 2 hrs

Those look like good numbers, I too would extend the absorb time. Even if the voltage doesn't drop a good bit on some of the cells/batteries it will give us more information to work with.


Something to think about is that the system is in use, with the WBjr (I think you said you had one hooked up) the Classic can see how much current the batteries are accepting, the Outback is just aware that the system in total is using 20 amps so it is unaware that the batteries are no longer accepting much current, this might account for longer run times with the generator.

Do you continue with your solar charging when you are running the generator? I don't use a generator, so am unaware if some need the solar charging disconnected.

2twisty

When charging on the generator, I leave the solar connected.  In full sun and generator, I can put about 41A into the batteries.

I'll bump the absorb to 3H.  I have another problem in that I really need more panels.  In the past, I wouldn't usually get to float until early-mid afternoon.  Extending the absorb by another hour means that I will be really pushing it to get to float.

But, if it can extend my batteries' life long enough for me to replace them (I'd LOVE to replace 16 GC2s with 8 L16s) then I'll do what I need to.

2twisty

OK.  I ran the generator and charged the combined bank for 2.25 hours this morning.  WBJr reported SOC=98%.  Classic was in Absorb.

At 9:45am MDT I disconnected the older battery string.  At the time of disconnection, the entire string measured 52.5V.  All 8 batteries measured 6.5V.  I will wait 4 hours and repeat the voltage checks and report back here.

I left the newer string connected to charge.  I may perform the same test on the newer string tomorrow if you guys think it would be diagnostically significant.

Estragon

Just to clarify, extending absorb to some arbitrarily long time on the classic should have no effect on transistion to float. Absorb will end at the earlier of; current dropping to end amps, elapsed time, or voltage dropping to re-bulk because of loads (or dark).

Ideally, you always want to go to float based on end amps. This means the batteries are close to fully charged. Going to float because absorb timed out means batteries are not fully charged.

Estragon

Also, if you can put a known load on the disconnected string for testing you could speed the process up some.

2twisty

I do use End Amps.  It's set to 3.7A.  I don't have a known load for a 48V system that I can use, so I'll just let them sit for the 4 hours that was suggested earlier.  I'm also working on ways to reduce my overnight loads.  I have a couple computers that run 24/7.  I'm pretty confident that I can change one of them to only run as needed.  

Dave Angelini

Why not just make this easy and measure the SG? Look for the low ones. You want to disable the end amps and charge for 5 hours to see if the batteries with the low SG come back. 

2twisty

I didn't check every single cell, but the SGs I measured were the same in every cell I checked. By using my generator which doesn't use End Amps, I have done exactly that; I charged for 9 hours.  SG didn't improve very much.

2twisty

Here's an update:  About 2 hours into the old string's 4-hour rest, voltages read:

String: 51.3
Batts 6.4 (all the same)

So the batts have dropped .1 (or less) V in 2 hours.  Doesn't seem like they are having a high discharge rate.  I wonder if the problem lies in the newer string?  I'll test that one tomorrow, I guess.

westbranch

Recovering old partially over depleted cells is NOT a one time treatment...  it is a long and time consuming event sort of like getting back into top physical condition....
the longer you have not been 'FIT' the longer it takes to recover to where you were,IF  you can ever get back there...
some times it is not possible...  so saying you charged for 9 hrs,earlier, without all the specific details like SG and temperatures/ cell etc etc, is sort of like saying I went to the battery store and looked at a lot of batteries... without telling us the make, model, etc...
For this process DETAILS are what are needed more than ever. hth

ps, the cleaning and retorquing of the connections DID something ... or alternatively removed  a faulty variable from the equation...

2twisty

Well, if we can recover these batteries, I'll be quite happy.  I'll reduce my loads as much as I can to help reduce the daily DOD as well.  Even if they are toast, this alone will extend their life a bit.

But yeah, I need to start assembling the cash for the replacements.  

Dave Angelini

New batteries are good for the economy and Westbranch is spot on!
 I wish you did not say that you have not checked all the cells, you lost me there...

2twisty

OK. after a 4 hour rest:

Older String: 51.2
Batts all at 6.4.

I reconnected them and am going to finish charging those with the generator for a while.  I'll do the same test on the newer string tomorrow.

2twisty

westbranch said:

Recovering old partially over depleted cells is NOT a one time treatment...  it is a long and time consuming event sort of like getting back into top physical condition....
the longer you have not been 'FIT' the longer it takes to recover to where you were,IF  you can ever get back there...
some times it is not possible...  so saying you charged for 9 hrs,earlier, without all the specific details like SG and temperatures/ cell etc etc, is sort of like saying I went to the battery store and looked at a lot of batteries... without telling us the make, model, etc...
For this process DETAILS are what are needed more than ever. hth

ps, the cleaning and retorquing of the connections DID something ... or alternatively removed  a faulty variable from the equation...

Hmm..  Based on the fact that the older (and more suspect) string seems to be holding their charge equally after resting for several hours, it seems that perhaps the batteries are just woefully undercharged as you suggest.

I'll reserve that judgement until after I do the same resting test on the other string tomorrow.  Maybe I just need to charge the bejeesus out of them.  If that's the case, how do I know when to stop?  run a stupidly long EQ or temporarily set the absorb voltage higher and the duration longer?

Estragon

What I would do:
- Set Vabs on the outback a bit high - maybe 59v
- Set absorb time to 5hrs on outback and classic
- Start generator charge 2-3 hrs before decent sun
- Check/record voltage and current every 1/2hr or so.
- Stop generator before pv really gets going, check water and sg. Check for battery hotspots. Water should cover plates plus a bit, but not right up to the top.
- Check/record voltage and current until classic finishes absorb and goes to float at end amps.
- Check water/sg/hotspots again
- Assuming sg is still low set classic for 6 hour eq
- Check eq on low pilot cell or two every 1/2hr.
-stop eq when pilot cell reading stop rising or it gets dark.
- If it gets dark while sg still rising, repeat tomorrow.

I would do one string at a time if at all possible. The fact the old string held at 6.4 for 4hrs seems encouraging to me.

Vic

Twisty,

It pretty much has all been said,  but:

What Brand GC2 are  each string?
What is the target SG for the batts in each string?
What is the manufacturer's recommend Vabs and Veq for each string?
What is the recommended Temperature Compensation value for the batts in each string?

Are you using the BTS on the Classic? On the OB inverter?

Would suggest raising the Vabs to at least 60 volts,  or even a bit higher (and using BTS/RTSes and correct Temp Comp value),   and leave the EA where it is,   or,  even set the Classic EA to 0, for now.

YES,  with Lead-Acid batteries,  noting the battery voltages   (as mentioned by Wb),  without noting the battery temperature is not useful to you or those trying to help you,   even if the Temp Comp value is only --3 mV/C.

You may need to charge,  and then EQ for a number of hours.   Be certain to set the Classic Temperature Compensation for EQ to YES.    Probably best to EQ each string individually.   Watch the WBjr Status screen to see the battery current during EQ,   A battery that is not defective (like heavily hard-sulfated)  can require a large current to reach Veq,   but  this current  should diminish,  as the EQ proceeds.   If you are using the OB Inverter to help with the EQ,   you might need to manually adjust the Veq on it,   as the batteries being EQed warm.

YES,  you are correct,   you DO need more PV power.

As Photowhit mentioned,   one of the worst situations when adding batteries after using an original bank for some time,  is that the first battery may well be beaten to death,   before the user decides that more Capacity is needed,   so one can wind up with beaten batts,   and good new ones,   a very bad combination,  usually.

YES,  you DO need a Clamp DC Ammeter,   and,   really an IR Thermometer,   if you do not yet have these.   This helps you monitor battery string balance  and battery temperature differences,   if you are going to continue to run parallel strings.

And so on   ...   FWIW,   Vic