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Marco57
Member
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# Posted: 24 Nov 2010 11:26am
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New Member,
5 years ago i purchased a complete solar system for my cabin in the woods since there is no hydro service available in the area.
The system includes 5 solar panels (100W/each), a 2500 Watt Inverter (Xantrex), and 8 (6 volt) batteries wired for 12 Volt.
In spring 2009, i had to return all 8 batteries to their manufacturer to be recharged, because the batteries were high in voltage but very weak in amperage (strength). All normal battery chargers were not able to bring them up in amperage.
This fall i have the same problem. I get to the cottage and the batteries are fully charged, but as soon as i start using a few lights, they drop down below 12 Volts. I've been so careful with my usage in the past year, and yet, i still have the same problem. I've been equalizing the system monthly as recommended by manufacturer.
My supplier always has an excuse. I use the system too little, or too many batteries, should go down to 4 instead of 8 etc...
It's been a 5 year trial and error situation. I'm tired of dealing with it.
Do any of you have any idea on why the batteries always get so weak?
Thanking everyone in advance for your answers!
Mark
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Rob_O
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# Posted: 24 Nov 2010 12:54pm
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So your batteries are now 5 years old?
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Marco57
Member
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# Posted: 24 Nov 2010 01:49pm
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Yes, the batteries are now 5 years old ... my supplier has informed me that they need to be replaced after 8 years of usage.
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MikeOnBike
Member
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# Posted: 24 Nov 2010 02:01pm
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Perhaps they are badly sulfated.
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Marco57
Member
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# Posted: 24 Nov 2010 02:27pm
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If they are badly sulfated, how do i fix this problem?
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Rob_O
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# Posted: 24 Nov 2010 02:41pm
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Reviving a sulfated battery
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MikeOnBike
Member
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# Posted: 24 Nov 2010 02:50pm
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First of all I'm not an expert.
You can use EDTA to chemically break down sulfation.
There are some pulse chargers that pulse a high voltage charge to break down the sulfation.
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MtnDon
Member
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# Posted: 24 Nov 2010 02:57pm - Edited by: MtnDon
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Thanks for that Mike.
Does the system get used a lot? In the past, how much are the batteries depleted on average? Fifty % of depth of discharge, or DOD, or greater? Do you use a hydrometer to check charge level? Do all cells have hydrometer readings that are very closely matched?
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It sounds like you have golf cart batteries. Or maybe L16 types. If you have golf cart batteries my guess is they have reached the end of their useful life. While it is possible to get 7 to 8 years out of a golf cart battery, in the real world most people don't make it that far. Four to five years is more like the longest most golf cart batteries will last, and that is with keeping the DOD to 25%. I've managed to eek out a not so satisfactory 6th year on a pair in the RV. L16's will make it to 7 or 8 years in many cases, if cared for.
When one has so many parallel strings (you have 4 ) it can help extend the life if the batteries are rotated in the pack.
How is the inverter connected to the battery bank? Do the positive and negative to the inverter connect to the same series pair at one end of the pack? Or does the positive connect to the first series pair and the negative to the furthest series pair? The second method is better.
When a battery bank gets to more than three parallel strings it is definitely better to use larger batteries and fewer in parallel. That's one reason I believe 12 volt systems are only suited for the very smallest of systems.
Sulfated cells? Could be and if so most likely the easiest and most satisfactory solution is new batteries. There are desulfaters available and I know someone who has managed to squeeze out some more use from a set that had been declared dead. A good desulfater costs a lot... hundreds of dollars.
One other thing, batteries should not need equalizing monthly. Too much equalizing not only increases the water use but may damage plates. The necessity to equalize is best determined by our friend the hydrometer. Equalization is required when the cell specific gravities vary from highest to lowest by +/- 0.015 (1.245 - 1.260 at full charge). I do twice a year, spring and fall, "just because".
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MtnDon
Member
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# Posted: 24 Nov 2010 05:13pm
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I realized I made an assumption; I assumed you had flooded wet cell batteries, not AGM or other sealed type. Quoting: Marco57 Do any of you have any idea on why the batteries always get so weak?
In the preceding years what has the average discharge rate been, in percentage terms, what's known as depth of discharge. IE, if half the rated capacity was used the DOD is 50%. The greater the discharge, the shorter the battery life.
If a battery is discharged to 50% on average, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%.
Is the charge fully maintained by the PV modules and charge controller when the cabin is left vacant? They should be as they will self discharge if left offline.
Has the water level dropped below the plate tops frequently and left that way for prolonged periods?
Are the batteries used / stored in a very warm place, above 75 degrees F? Here in the SW desert batteries can have years shaved from their expected life when subjected to prolonged elevated temperatures. On the other hand batteries used in colder places can have their life extended.
Have the batteries been subjected to frequent overcharging with the resultant overly high battery temperatures. Good charge controllers have battery temperature sensors to prevent that.
? That can also shorten life.
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Marco57
Member
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# Posted: 24 Nov 2010 05:25pm
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I only use the system on weekends ... i use aprox. 100 amps daily
Yes, i've checked the system with a hydrometer, it's been stuck in the middle of white area for two months now. Yes, all cells have identical readings.
No, they're not golf cart batteries, they're 1/3 taller, must be L16.
They we're rotated 1 1/2 ago.
Yes, the positive is on the 1st series pair, and the negative on the furthest.
How can i test my batteries for sulfated cells?
I never used to equalize monthly, till i sent the batteries back to the manufacturer. My solar system provider, along with engineers from Xantrex, and the battery manufacturer informed me to start equalizing monthly. It's apparently the newest recommendation for solar systems with batteries.
Thanks again everyone for all your help so far!
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Marco57
Member
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# Posted: 24 Nov 2010 05:48pm
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We had a problem the first few months after initial installation of the system. They changed the inverter from a 2000W Xantrex to a Trace Engineering SW series 2500 watt inverter/charger with "synewave" option. It alawys worked since then.
My main consumption is from a 3/4HP-220Volt water centifuge well pump. It's peak is 3000 watts for a few seconds and then stablizes at 1200 ... to fill up my tank, it takes aprox. 30 seconds and consumes 3 amps.
I don't believe that i ever used the batteries more than 30-40%
Yes, the system is fully maintained when i'm gone. It was designed for 3 day usage & 4 day charge.
No, the water level has never been below the plates.
I've always left the batteries in a warm place between 41 F in winter, and a maximum of 68 F in summer.
No, the batteries have never been overcharged, my Trace SW inverter/charger always protects the batteries from overcharging.
In case you're interested, here are the specs of the Trace Sw inverter:
www.kyocerasolar.com/pdf/specsheets/sw2_user.pdf
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MtnDon
Member
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# Posted: 24 Nov 2010 06:03pm
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Yes, sounds like L-16's. About 110-120 lbs?
Article on sulfated batteries here...
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Youngster
Member
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# Posted: 25 Feb 2011 04:46pm
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Quoting: MtnDon ...He tells me the biggest problems people have with off grid systems is overdrawing the batteries...
Although my knowledge regarding solar-power setups is very limited, wouldn't the Low Volt Disconnect (LVD) on a charge controller safe guard against this happening?
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MtnDon
Member
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# Posted: 25 Feb 2011 06:09pm
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Well, from my perspective, if the low voltage cutoff on an inverter is called into action, the system has failed.
No power right when it might be needed is a failure in my book. Drawing the batteries down to that low a voltage shortens their life, another sort of premature failure. Every inverter with a LVD has it set very low, down in the acid turns to water region. Freezes too and that is complete failure.
That's my opinion, anyone can have a different view.
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