5 months old Lead-Acid batteries already worn out? - Page 1
Forum section: electronics / projects

author: mrflux
author_rank: Contributor
timestamp: December 19, 2016, 10:26:35 pm
content: I bought three cheap solar batteries on Amazon.de: generic brand, 100Ah(C100) / 80Ah(C20), approx 100 EUR.They've been working fine during the summer, but suddenly a month ago, the voltage dropped quickly after just half a day's load, seeming to have approximately 100Ah effective capacity at 5-10A discharge rate (as opposed to 200Ah effective) before reaching 12.0V (open circuit reading after 5h).I've been careful not to discharge them beyond 12.2 V, and they are typically charged with solar panels daily (some days with gray weather, but most days give approx 80-100Ah).I've measured the specific gravity after several days without load and being fully charged with float. The reading is only 1.18 at 5c, but I'm reading on the internet that it should be 1.28 at that temperature, and that 1.18 at full charge would mean 50% effective capacity remaining.I've occasionally discharged with 20-30A per battery for 10-20min, and charged them at max 20A for 10min and then 10-15A (per battery) for 2 hours for fast charging.The batteries have never needed to be refilled.As far as I can tell, they don't look sulphated.Any ideas what might have happened?Are they just shitty batteries?Can I add any chemical to improve the specific gravity? (I realize I won't get back the capacity, but if the liquid has the wrong density, perhaps it will function better?)Anything I can do to restore them?I'll do a load test one of these days: 10A, voltage over time for 5h + resting for 5h

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 20, 2016, 04:03:58 am
content: I suspect that your specific gravity measurements are accurately reporting the state of charge of the battery - not fully charged, as at your 5C temperature you should be getting at least 1.28.If your charging circuit is based on voltage, as most lead acid charging circuits are, it is cutting out too soon at low temp. Making the reduction in AH that occurs at low temp even worse.The following excerpt fromhttp://pssurvival.com/PS/Batteries/Lead_Acid/Lead-Acid_Battery_State_Of_Charge_Vs_Voltage_1993.pdfdescribes this.Temperature and BatteriesThe lead acid reaction is temperature sensitive. Cooling the cell changes its voltage vs. SOC profile. As the lead-acid battery cools, its internal resistance increases. This means that voltage elevation under recharging is increased in cold cells. The same internal resistance increase produces increased voltage depression in cold cells when discharged.At 32°F (0°C), the effect of temperature becomes pronounced enough to distinctly change not only the battery voltage vs. SOC profile, but also its useful Ampere-hour capacity. The discharge voltage curves may be depressed by as much as 0.5 VDC from those shown on the graph. Charge voltages will be elevated by as much as 0.5 VDC for a cold 12 Volt lead-acid battery.Your batteries should work just fine again next summer. If you need better performance during the winter, you need to modify the charging circuitry to be temperature dependent. Or you need to arrange some heat for your battery compartment. Heating the compartment should get all the performance back, while changing the charging circuit looks like it might buy you half or less of the lost capacity.

author: mtdoc
author_rank: Super Contributor
timestamp: December 21, 2016, 02:26:15 am
content: Sounds like chronic undercharging and sulphation (you cannot tell this by looking at them).Are you using a proper 3 stage charge controller? with temperature compensation?Are your batteries outside or are they in a temperature controlled environment?What are you using for your bulk, absorb and float voltages? What are the battery manufacturer recommended voltages?How are you ending your absorb stage? by end amps? by time in absorb? (usually CC dependent).Have you tried equalizing them?I assume you have the 3 batteries connected in parallel, is that correct?What is the output of your solar array?Can't help without answers to these questions....

author: mrflux
author_rank: Contributor
timestamp: December 22, 2016, 02:54:41 pm
content: Today I've tried an equalization/intentional overcharge:The batteries were resting at 12.62V for 12h. The specific gravity was 1.18.I pre-heated the batteries with a heater, to about 20c. Then turned it off, to more accurately monitor for over-temperature.I used a car battery charger to apply a charge. It started at 15-20A (for three batteries) and rose to 14V within 5 minutes. After 15 minutes it was at approx 15.15V, which is probably the maximum for the car battery charger.In the beginning the liquid was very clear.After 2 hours, the liquid became completely cloudy like mud and I was unable to see the plates.The temperature remains steady at about 20c-25c. This is possibly due to an ambient temperature of about 10-15c.The specific gravity is now approx 1.23. But can this be due to a surface charge? e.g. that the specific gravity might return to 1.18 after a resting period?The strange thing is that despite being at 15.15V for 4-5 hours now, they don't seem to have lost any liquid, although they do bubble (3-5 bubbles per second). I have distilled water ready, but haven't needed it.About the installation:3 batteries in parallel, 100Ah eachThe charger is a Victron 100V/30A MPPT charger. It charges at 14.4V for a few hours, then goes to float at 13.8V. It monitors charge current, but also seems to have a time limit as well, I guess since load during charging could otherwise be misinterpreted as charge current.I'm considering manually setting a charge until 15.5V, then float at 14.0V during winter.The solar panels are 440w. The MPPT charger reports a daily charge of 800w, or approximately 60Ah into the batteries.The MPPT charger is seperate, but has an option for remote sensing, e.g. that I can program my microcontroller to tell it what the real temperature is. I'll do that soon.Recommended charging voltages are standard 14.4V, 13.8V.

author: madires
author_rank: Super Contributor
timestamp: December 22, 2016, 03:47:59 pm
content: Based on the price they seem to be cheap car batteries. A proper battery for solar applications would be twice as much. Just saying...

author: mrflux
author_rank: Contributor
timestamp: December 22, 2016, 04:04:56 pm
content: I did a test on a different battery, and it went up to 15.80V.Now the batteries are at 15.39V.Perhaps they really were sulphated and under-charged, and basically refusing to accept charge at lower voltage.I'll leave it running for another 5 hours or until it starts losing liquid.But any ideas why the liquid doesn't evaporate / turn into hydrogen.The other battery I tried caused my CO-alarm to beep after just 5-10minutes of charging. Whereas these batteries have not set it off for 5 hours, suggesting that they are not off-gassing at all.

author: rstofer
author_rank: Super Contributor
timestamp: December 22, 2016, 04:05:48 pm
content: There is a huge difference between storage batteries and engine start batteries. Start batteries don't contain nearly as much lead and aren't designed for cycling. You can get an idea of the cost difference when looking at Marine storage batteries.http://www.westmarine.com/WestAdvisor/Selecting-a-Marine-Storage-BatteryStorage batteries are expensive!

author: mrflux
author_rank: Contributor
timestamp: December 22, 2016, 05:05:54 pm
content: They say "solar battery" on the packaging, but I agree that they're probably of poor quality.I've been considering to buy 2pcs VARTA LAD 150 instead. But I have a few hesitations:- I've read that AGM can be fast charged with currents like 50-100A per battery. And that they provide better discharge rates at higher current. But I also read that AGM batteries should be charged slowly. So I'm not sure which one is correct.- I'm worried that I'll overcharge an AGM battery and won't be able to see the overcharge, nor replenish itNevertheless, 800 cycles at 50% sounds pretty good. That's 1850 Wh per day, which far exceeds my typical use, e.g. should last 3-4 years.

author: mtdoc
author_rank: Super Contributor
timestamp: December 22, 2016, 06:19:12 pm
content: Quote from: mrflux on December 22, 2016, 02:54:41 pmYes - that is good - they were sulphated and a good equalization should help restore some of their capacity. No, the increase in SG does not represent surface charge. Surface charge can affect the voltage measurements but not SG.You have surely done some permanent damage to your batteries but you should still be able to get some life out of them with regular equalization and proper charging.QuoteIdeally you'd want a higher voltage -enough to get them bubbling vigorously. Doesn't your Victron have an equalization setting? A DC power supply could be used.QuoteYou will if you get them bubbling enough.QuoteVictron is a good brand. Those settings should be adjustable. It should also have the ability to use a battery temp monitor to automatically adjust charging voltages to temperature. What is the model number of the Victron?QuoteYes, in order for a CC to use "end amps" to properly end absorb, you need a proper battery monitor with current shunt. Victron makes one.QuoteYes, if your CC cannot do this automatically (with temp probe input) then you need to do it manually. Here is a pretty good article on how best to do this:Understanding and Optimizing Battery Temperature CompensationQuoteIt's not just the total daily AH into the batteries but the charge rate during bulk phase that really matters. Rule of thumb for LA batteries is you want charge current during bulk charging to be about 8-10% of the 20hr AH capacity of the bank. In your case, you have a 300AH battery bank so that means 30A. In normal temps and full sun, your 440w array can be expected to put out about 330 watts or so at the batteries bank (temp, wire and charge efficiency losses = approx .75 de-rating). So 330 watts at 14.4V means 23 amps - a little low. That still could be ok if your getting 4-5 hours of full sun but given you daily 60Ah into the battery then you are not getting that much - at least not this time of year. This is a common problem - most people underestimate the amount of PV they need to keep their batteries properly charged through varying conditions.Depending on your loads, you will probably need to either use a smaller battery bank (use just 2 batteries for 200 AH), get more PV, or supplement charging regularly with grid or generator input.It really is important to define your loads from the outset and design your system around those. For LA batteries you do not want them to ever be discharged below 50% state of charge. (70% cut off even better). Your system (usually the inverter) should have a low voltage cut off setting. Even better a proper battery monitor will track amps in and amps out so be able to use a more accurate measure of SOC.QuoteBatteries markets as "solar batteries" should be proper deep cycle batteries with thick plates.I would not switch to AGMs yet. They are unforgiving of undercharging since there is no way to equalize them. If you can revive your current battery bank with proper equalization then you should be able to get some more life out of them. Consider them your "starter set" and use them to learn and optimize your system before risking loss of more expensive AGMs.BTW - in general AGM's can be charged and discharged at a higher rate than FLAs. But the exact amperage will depend on the size (AH rating) of the battery. Maximimum charge and dishcharge currents will be defined by the manufacturer. That is not generally a big advantage in solar PV systems, though their better charge/discharge efficiency is. Regardless, the general rules I outlined above hold true for all LA batteries - AGM or FLAs.

author: mrflux
author_rank: Contributor
timestamp: December 22, 2016, 06:35:54 pm
content: Hey mtdoc,Thanks for the great input. Very useful stuff. Surprisingly, I've read a ton of articles, but somehow it was never mentioned that the battery bank could be overdimensioned. In fact, most suggest low charge currents, which they argue, will give better health.I've done a few experiments with electrolysis, attempting to manufacture my own PCB by copper-coating an electrified surface. I experienced that high currents would cause a loose bond and burns, while slow currents would cause a strong bond and no burns.Is this related? I imagine that the opposite would be desirable: e.g. high current = loose bond = reduced sulphation.Is it correct to assume that I can basically charge with as high voltage and current as I want, as long as the water level is maintained and that the battery doesn't heat up? (In that respect, I've read about people connecting 120V with current limiting)Is it correct that the main problem with high voltage, is that it can cause draw a huge current, which quickly can increase the internal resistance, which in a matter of seconds or minutes can overheat and therefore become dangerous?Does it make a difference if the battery is charged with 10A of 20V, or the power-equivalent 13A of 15V? E.g. for a de-sulphation / forced-absorbtion charge. I could build such a circuit, but I'm not sure which voltage/current I should choose for.Regarding temperature, CC voltage etc, I'll probably start controlling the charger manually with my microcontroller, since I already have a battery bank shunt, temperature sensor etc.A fun little holiday project

author: mtdoc
author_rank: Super Contributor
timestamp: December 22, 2016, 07:20:28 pm
content: Quote from: mrflux on December 22, 2016, 06:35:54 pmI don't know about that. Equalization is usually done at 15.5 - 16 Volts (for a 12V battery). The better battery manufacturers will specify recommended equalization voltage. I see no advantage of going higher than that. There are numerous "battery desulphators" on the market that use various high frequency schemes. Users vary in their opinion as to whether there is any advantage of these versus just using a constant DC voltage. The experienced off grid users I know say they are all marketing wank and DC is all you need.Battery manufacturer's will also often recommend an interval at which you should do scheduled equalizations. If your's does not specify then I would do it once a month.QuoteThat sound right. You want to keep battery temp below about 115 degrees F during equalization.Basically the idea is to apply the equalization voltage and monitor SG. Once SG is no longer rising, equalization is done. The reason for having a high enough voltage to get vigorous bubbling of the electrolyte is that means better disruption of the sulphate deposits - clearing them off of the battery plates.QuoteAs I mentioned earlier, charge amperage depends on the battery bank capacity. During equalization, amperage drops quickly as resistance rises.QuoteYes, sounds like a good project. A search around the web will yield lots of ideas. 2 online forums with lots of solar PV and battery bank expertise are the Northern Arizona Wind and Sun forum and the Midnite Solar users forum - google will take you there.