What to do with the lazy cell in FLA batteries

mcgivor · October 2016

Been off grid for little over a year and so far so good except for a lazy cell which showed up a few days ago during a regular SG test, equalization is sorting the problem out but it's a wait and see process.

During my career in late 1970's as a signals and telecommunications tech we serviced standby batteries, as failure was not an option, any weak cell was replaced (depending on age or battery)and sent to a service center where it would be replated or if Ni Cd, flushed and new electrolyte installed. Backup to the backup were Leclanche type safricial cells, just add ware to activate. Of course our option to simply remove and replace comes with financial considerations so we have to improvise.

Personally I'm not a fan of monoblock, if you lose a cell it takes the others with it, will go to individual cells next time. The experience I gained was with float not cyclical but we checked SG and voltage biweekly at remote sites so a little different to off grid but I habitually test the SG on a weekly basis to keep my finger on the pulse, so to spesk.

Would be great to hear what you seasoned off gridders do, think or suggest.

BB. · October 2016

Assuming that this cell/battery is part of series string (i.e., 2x 6 volt for 12 volts, 2x 12 volt for 24 volt, etc.)...

If you want to try it--An isolated 6 volt (or whatever your battery voltage with the lazy cell is)--recharge/equalize just that battery--At least you avoid stressing the rest of the batteries.

Another suggestion would be would be to, on the "good batteries" connect a 6 volt to 12 volt brake light bulb across them. This will "bypass" a couple of amps around the good batteries and force it through the battery/lazy cell--Again without stressing the rest of the battery bank with lots of equalization.

In the end, if that cell/battery block is running low voltage (under loads or under charging)--There is probably not much you can do. Other than try any product with "magic" in the title (magic battery restoration additives; or a desulfator). The additives and desulfator may not help and in some cases may cause other issues (a desulfator has been known to create electrical interference that cause at least one Outback MPPT charge controller to have reduced output).

-Bill

Vic · October 2016

Hi mcgivor,

Since you are able to measure SGs, your batteries must be Flooded.

It is not clear just how lazy is that one cell is, but since you are doing such a good job taking SG measurements, it is probably not too far from the SGs of the other cells in the bank. What is the range in SG readings that you are seeing?

EQing a battery is intended help remedy just what you are seeing with that one cell. Periodic EQs can actually be helpful to Flooded batteries.

How much Distilled Water are you adding to the batteries per month, or perhaps two?
What brand and model battery?
Does this battery bank have parallel strings, if so, how many parallel strings?
Do you use a Remote Temperature Sensor (RTS/BTS) on all charge sources?
How is the Absorb stage ended -- fixed time, End Amps, etc?

Thanks for the added info, Vic

mcgivor · October 2016

Hi Vic

Will answer the last questions first.
Watering is required about every 2 months 1/4" to each cell, even usage.
Battery is Yuassa EB 130 × 4 two strings of 2 in parallel, 24v
No RTS, Morningstar has internal temperature sensor everything in same concrete room stable temp., battery and controller same temperature as tested with IR themometer.
Absorbtion PWM, reduces current and percentage at 28.8v, never goes into float as there are intermittent loads, checked with Morningstar tech support, they said it was normal as there is a time factor which prevents it going into float when loads are present.

The SG of the lazy cell is at 1.080, the cell was the first on the positive side of one string, now is in the middle. All other cells are around 1.280. Have removed that string and currently in equalization, I'm not discharge it at all. The EQ voltage is 30.2v current is around 6A ,the cell is beginning to gas and SG climbing, now in second 3 hour EQ cycle but still too early and of course the sun is not cooperating, need to get to 30.2v then it can be overcast but there have been brief spells of full sun today.

Will conserve again tonight, my only constant load is refrigerator and a very efficient inverter model. So it is a wait and see process
Thanks to all who repond.
mcgivor

Vic · October 2016

Hi mchivor,

Thanks for the additional info.

That one cell is much lower than I had expected. Good that you are EQing.

As you probably know, parallel battery strings can have current sharing issues, which can cause one string to not be well charged, and so on.

If you have access to a Clamp DC Ammeter, you can see how well the two battery strings share charge and discharge currents.

Am familiar with Yausa batteries, when they were made in Japan, and they were known as a quality manufacturer.

If this battery bank has been very deeply-discharged, one, or a few cells can become damaged, by becoming completely discharged, and at times, even charged in reverse, which usually means that that cell will never really recover. Am not saying that this is what has occurred with that one cell.

Am not familiar with the model battery that you have. But, from the nominal SG readings of most of the other cells, would seem to me, that your Absorb voltage is a bit on the low side, and the EQ voltage seems low. But, these voltage values may well have been provided by the manufacturer, or the Distributor/Dealer.

More later, Good Luck, Vic

mcgivor · October 2016

Thanks for your input Vic and Bill, will follow Vic's suggestions and up the absorption and equalization to 29.2v and 30.6v respectively, initially I chose the lowest settings as the temperature was in the 30 deg.C plus range, now it is 24 to 27 deg. ambient. That is the mid setting of 3 for FLA, the highest only changes the absorption to 29.6v, EQ voltage remains the same. The sun as mentioned didn't last today and had to charge the good string for the remainder of the day. The SG has increased so will try again tomorrow. And thanks again to to Bill but I'm not much of a believer in anything magic although I'm sure he meant it as a last resort but your other suggestions are great, appreciate the input.

Have a good one today.

westbranch · October 2016

since Absorb and EQ do not make full use of the available power you could do a gen charge for a couple of hours and let the solar do the rest... puts an honest load on the gen and the PV will do the inefficient part...

BB. · October 2016

Yes, "magic battery savers" as a last resort.

Mostly, because you would have nothing to lose if they don't work.

I do not suggest counting on magic as a design tool.

-Bill

mcgivor · December 2016

Well it's been a few months now and after doing much research came up with a plan. The plan was to do an EQ for one hour @ 30.6v for 15 days in order not to raise the temperature, rather than 15 hours straight which is impractical as I do not use grid or generator.
The "lazy" cell has shown improvement and the SG is now at 1.225 but that is where it wants to be, saw no reason to continue for the sake of the the ballance of cells. Put the battery back into the bank and have run for 2 weeks and with daily DOD of around 20% the battery as a whole is doing fine but I am very well aware that the other cells are working harder to support the "welfare case" if you like, and the taxation on the remainder will in no doubt result in an earlier than planned demise of the battery as a whole, but so be it, education doesn't come cheap.
The whole exercise has taught me a thing or two that I wasn't aware of, going into the whole off grid experience, and with the help and guidance of valuable people here along with information from manufacturer's sites, have discovered some fundemental mistakes I've made, not big mistakes, but mistakes none the less. Now I feel more confident in resolving the minor issues and have learned that just because one is an electrican doesn't mean you are a solar electrican, there are many differences, thanks for the input.

Dave Angelini · December 2016

You may do all the right things and still have problems with any battery make offgrid. It is right up there with going to space or on the ocean, just a bit safer

Good luck!

What to do with the lazy cell in FLA batteries

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