One funky cell in one battery...

[plongson]

Hi all...

I have not been around for a while but do log in periodically to see waass' up. We are nearing 4 years off grid and all has been (mostly) well! Very good times!

I do have a question though. I have one cell in one battery that decided to be a bad player. I first noticed it about two months ago and it went from normal to funky in about two weeks. The tip off was very low water use. SG on all the cells mostly top out at around 1.265 but never higher. The cell in question will not rise much above 1.230 no matter how much I charge or EQ. It's other two partners are 1.265.

I think it is starting to crap the bed. What do you do in this case? Watch it close? Live with it? Like I said, the Surette 48v 800Ah /2 string bank is almost 4 years old.

What say you?

THANKS!! Paul

[Vic]

Hi Paul,

It is nice to hear from you -- had wondered how you were doing.  Sorry to read of the reason for this post,  however.

How do you terminate Absorb?  If EA,  what is that value,  and if by time how long is Absorb time setting?
What is your Absorb voltage?
What is your EQ voltage,   and how often do you EQ?  Is EQ temp compensated?
Roughly how deeply is this battery cycled every day?
How much water does this bank use?

You could try a Corrective EQ,  perhaps only on the string with this lazy cell.   This would not be great for the rest of the batteries in the string or the bank (if this one string is not separated for the EQ),  but  short of making a single battery Charger,  and EQing this one battery with that,   seems little that you can do.

EDIT:  OH,  and should have asked you if you have and use a Clamp-On  DC ammeter to monitor string current balance and take corrective action if significant imbalance is noticed.

Thanks,    Vic

[Westbranch]

Hi Paul, LTNS...  Just wondering:  Do you have  a WBjr on that Classic?

[plongson]

Hey Guys, Hi Vic!
Thanks for the reply.

Here are some stats...

1.) I'm running a Classic 250
2.) Terminate absorb at 8 amps. I've tried to set it at 14 or so but it always ends up going back to 8amp. Seems like a bug?
3.) Absorb voltage 59.5
4.) EQ voltage 64 and it is set to auto EQ once every 10 days for 3 hours with 1 retry
5.) DOD this time of year is about 88% and in the winter low 80's%
6.) Water use is about 2 gallons/month
7.) I have a good AC/DC clamp-on ammeter and checking each leg from the two strings they are usually within 2 amps. Connections from battery to battery are very close to the same value but change as you go up or down the string kind'a equaling the 2a difference between strings. It seems to me the system is in good balance but please give me your opinion...
8.) It seems like these Surrette's need to be charged hard to get the SG up to a decent value.

ALSO...on the Midnite status panel, the BASIC-ABSORB-TIME is 8 digits:2 digits, whats with that? It's always been that way too.

Firmware
Classic Rev:1849
Network Rev: 1839

THANKS for the help!

Paul

[Vic]

Hi Paul,

Thanks for all of the detail.

Seems that your charge and EQ parameters SHOULD get the batteries charged and EQ as well as one can.

The EA at 8 Amps should be fine if those are Shunt Amps from the WbJr.

Think that the 2 A string imbalance should be OK.  Having one lagging cell will probably make the imbalance worse.

2 gals per month of water use is quite a lot,  but  that is probably just due to the fairly high Vabs and the frequent EQ and relatively high Veq.

Looks to me that you are certainly not undercharging your batteries.

What is your Absorb time setting?  EA  will be the thing that ends Absorb,  unless the Absorb timer times-out first.

Also,  when you are EQing,  do you know the battery current when the target EQ voltage is just reached,  and also what is the battery current at the end of the EQ period?  Just curious.

Thanks again.   Later,   Vic

[plongson]

Vic,
Not sure of answers to your last EQ questions. I use to EQ manually but got kinda lazy and set the EQ to auto. During the winter when the days were short, cloudy and snowy, I was hitting the EQ maybe too hard to get the SG up without running the genset. Once every three days, and in retro, that might not have been a good idea. Anyway, that's water under the bridge now.

I had an entire battery completely go dead about a year ago and got Surette to replace it under warranty. It went in and it is playing well withe the others.

After 4 years with these batteries, I can say I'm not a big fan of Surette's...JMHO.

[Vic]

Hi Paul,

Thanks for the reply.

Well the EQ every 10 days for three hours at 64 V ** ( was this voltage Temp Compensated ) **,   in your previous post seems very aggressive.    But,  if that was the only way to get the bank fully charged (at least a couple times per week),  then that was what was needed.

EQing every three days sure seems like a lot.
Believe that your batteries/power electronics are in your garage,  which should moderate temp swings quite a bit ...

Do you have the EQ voltage set to temp compensated??

Cannot see your Signature,  but believe that you have 12 ea  235-ish watt PVs (?).  This is a reasonable amount of PV  --  should give you about 50-ish Amps from the Classic,  less any system loads.

Are you using Shunt Amps to end Absorb (via the WBjr)?

What is the Absorb time set to?

Do remember that you had one battery go dead previously,  and that you were disappointed with the Warranty procedure that Surrette forced on you.

I am still very happy with the Surrettes here,  they are 10 years old,   and probably would buy Surrettes again.  These batteries do like to be cycled,  with an occasional discharge to about 50% SOC,   IMO.  With a larger battery bank,  recharging from this DOD can take quite a bit of time.

Keep an eye on the SGs of the entire bank,  and the current balance  between the two strings.  A lagging cell should affect the balance,  which could diverge over a period of time.

Seems unlikely that with all of the EQing that you have been doing that any cell would be sulphated.

If you are not using the WBjr,  with a good Shunt,  it would be a great addition to your system,  IMO.   Back to work,   here,  but will ponder this some more.

FWIW,   Thanks,   Vic

[plongson]

Vic,

The EQ is temp compensated.
I've used the EA seting at 8 for so long, I'm embarrassed to confess I'm not sure how to set the EA for TIME. I do have the setting on the status panel that does not seem to respond (see attached photo). But what are the guidelines for setting EA time or amps? I seem to recall it's 1% of bank capacity +4...but guessing here.

Other than a perfect balance between strings (+/- 0a) what is generally acceptable in the real world?

No wizzbang but have the shunt from Magnum installed.

I must admit, when I commissioning this system, it got my FULL attention. I gradually got in a routine where everything seems to be in harmony and I've just let it perk along...and it DOES perform VERY well. I'm treating it like a work truck and not a classic car where you are constantly tinkering.

I guess back to my original question though. With one goofy cell, is there really anything I can do different than what I have been doing or is it eventually doomed to fail and require a battery replacement? That would really suck...

I'm assuming here that as long as it's lazy I'll live with it but if it totally goes south, it'll be replacement time.

Here is a piece of information too...There are about 9 solar plants going in here in So. Utah and they need to feed to a Rocky Mountain Power sub station not too far from our "ranch". They have been in contact with us and need to cross the tip of out property with a transmission line. Well...not without dropping a stepdown transformer and pulling power to my doorstep. There is a very good chance we'll get power and net meter back. It sure would make life a bit easier and not agonize over these dang batteries all the time. LOL

[Vic]

Hi Paul,  thanks for the additional info.

Have only used CC EA to end Absorb.  For the banks here,  use about 1% or 20 hour C.  Since the introduction of the WBjr,  have used real battery charge current to end Absorb.  This works very well.

For CC (only) EA,  there usually will need to be some added amount of current for average loads.  This is probably where your 1% + 4 A came from.  With Flooded batteries it is fairly easy to monitor the SGs and dial-in the CC EA value.

Have you measured the string current balance since you discovered this lazy cell?  It might be a very good idea to watch for any real divergence from your previous measurements.   I would think that a balance of +/-- a few percent is good,  although,  this could change fairly quickly.   So watching for differences in SGs in one string vs the other is also a good indication of balance.  If your strings have SGs that are very close,  then your balance is probably good enough (disregarding the one lagging cell).

On what to do about the battery with the lagging cell,  it is always difficult to know that to do ...  it this one cell just an early indicator of where the entire bank is,  or is it an outlier?

A new battery for this one laggard will also have its own imbalance contribution,  most likely.

Perhaps your battery Dealer might have a Surrette S-530 (or whatever is your model #)  that is used,  but in good condition ...  hard to know just what to do.

On the TIME setting.  In the Charge menu,  under Time (IIRC),  there should be an Absorb time value.  When using EA,  this Time setting will be the absolute maximum time that the Absorb will run,  regardless of the actual CC output current at that time.  It is an OR function -- either the CC EA,  OR the Absorb Time will end Absorb,  whichever occurs first.

I do not use the LA,  so have no experience with it.

Back to work.    More later.  FWIW,  since you already have the Shunt,  the WBjr would be a nice addition to your system.  It is about $55.00 delivered from Wind-Sun,  and  will allow ending Absorb from actual battery current.

Thanks,  Vic

[Westbranch]

I just had a 'gotcha' moment,  Paul  have you updated the Local App recently? 

There is a button in the LA to do that....had to do mine over  the weekend.

[plongson]

Huh...Actually I had a computer issue last week and had to reload the Local App from the Midnite website. I need to update my classic though, it's been about 4 months.

Where is the button/link on the Local App though, I didn't see it.

Paul

[Westbranch]

it's in Settings / Config   page 6 of the manual
http://www.midnitesolar.com/pdfs/Local_App_manual.pdf

hth

[plongson]

Duh...Sorry, I've seen that and ya, I'm updated.

As for the goofy huge number in the screen shot I posted, do you see that too, or is it just me?

Paul

[Westbranch]

That is a first for me, I would suspect a faulty install if that just showed up. 

Have you deleted it and reinstalled, or just updated recently?

[plongson]

I uninstalled the app and reinstalled it fresh. Still the same...

Ryan, what do you make of it? Here it is again...Hope this tread isn't being side-railed with this question.