Do I have battery sulphation?

Back41

Greetings, I am new to this forum. I live off grid with a 4.8k solar array and a 840 amp hour FLA battery bank @ 24 volts nominal. I use a Trimetric battery monitor. We only use 12% of our battery bank's capacity on a daily basis. The Specific Gravity is uniform across all the cells. I use a calibrated refractometer. The specific gravity at the end of the charge cycle and tested when in float is 1.290
The batteries are behaving normally. However I can see something growing on the plates. It is grey in color and looks like fuzz. When I probe it with a stir stick the grey fuzz breaks up and goes back into the electrolyte and turns the electrolyte a cloudy grey color. All the sulphation I have seen in the past was white. How could this grey stuff be sulphation if the specific gravity is 1.290? I have really babied these batteries and have come to a full charge within 3 days and never lower that 85% SOC.  The batteries are 4 years and  2 months old. There are eight UL 16HC interstate batteries. Any insight on this mystery would be very appreciated.

Vic

Hi back..,

Generally this grey material is, plate material that is shed during charging.   Thee are very small particles, which are suspended in the electrolyte during charge (particularly during Gassing).

This debris  is deposited after Gassing charge stages,   and can be seen,  deposited on the Moss Guard on the top of the plates,   or on the separators and plates,   depending upon the construction of the FLAs.

IMO,   this is normal,   especially,   as the batteries age.

FWIW,   Vic

mcgivor

I agree with with@Vic this is a normal phenomenon associated with age, especially in a stationary application. In a mobile application, such a a forklift, the electrolyte is sloshed around allowing particles to settle in the well below the plates.

Back41

That is great news. Will this grey material ever cause bridging across the plates or will it eventually fall to the bottom of the case? Also do you think I should cycle a little deeper now and then? Or is my game plan of babying them the right thing. I have a friend who had his battery bank last 18 years doing it this way. I live in the Pacific North Wet where we get 50 plus days in a row every winter with no appreciable solar gain. During that time I run the diesel for a couple hours and then let the solar finish the absorb mode. Last year we only burned 25 gallons for the whole year. Not a big deal in cost but if cycling a little deeper like to 80% SOC rather than 88% would help the batteries in some way I would be willing to do it. Thanks for your input.

Estragon

IMHO, it should shed naturally. Going to a deeper DOD may not make much difference, but getting some vigorous bubbling in late absorb or EQ might help get the stuff to the bottom where it's designed to accumulate.

mcgivor

Using such a shallow discharge will extend the life expectancy at the cost of getting value for money, actually using the capacity to say 60-70% to  state of charge may be the compromise point. These are arbitrary numbers but the point is, money was spent to purchase the batteries, if they are essentially left in float for the majority of their life, then either the bank is oversized for the loads, or there are times when the reserve capacity is needed. Always remember batteries will die of old age even if never cycled, so to answer your question I would say use a little more of the capacity.

Vic

High quality Deep Cycle batteries often have enveloped (usually only the positive) plates.   This is a micro-porous plastic envelope  that surrounds the plate and is usually heat-sealed shut.   This does help reduce the effects of shed plate material causing  discharge paths,  either at the bottom of the cells,   or,   at the top.

Some batteries have a plastic plate,  with some holes in it (often called the Moss Guard),   which should also help reduce the chance of debris causing discharge paths between the plates.

The more time spent in Gassing stages the more plate material that will be shed (generally).

Also,  there is still some plate erosion during Float.   SO,   IMO,  it is best to try to set a Float voltage what will just barely keep a fully-charged battery,   fully charged,   at least on FLAs.

Just more opinions,   FWIW,   Vic

Back41

Thanks for the information I really appreciate it. I had the hardest time getting information from Interstate battery Co. I could not get a strait answer on the charge recommendations. I finally found a distributor that would give Interstates  charge recommendations in writing. My particular batteries call for 2.58 volts per cell. For me that 31 volts in absorb mode. I was 1 volt short of this for 4 years and had a hard time getting the SG up even with 3 1/2 hours of absorb time. Now that I have it set at 31 volts in absorb the time is down to 2 hours 15 minuets. I may shave a little off of this as the SG is 1.290 and spec is 1.288
The batteries are running cooler and I am using less water. It seems the space between shedding plate material and sulfation is very small.
I heard one say its like dancing on the head of a pin. 

mcgivor

Interstate is not a manufacturer of batteries but rather marketers of other companies products, this may be why charging information is somewhat difficult to extract from them. Johnson Controls is the latest supplier from what I understand but that could change https://en.m.wikipedia.org/wiki/Interstate_Batteries

Back41

Thank you so much. That helps a lot.