Lead Acid Batteries Loud Bubbling While Charging?

st4rgut

I just turned on my 1000W solar system and noticed my two 100Ah marine deep cycle batteries wired in series were bubbling. I understand this is frequently the result of overcharging, but my MakeSkyBlue charge controller showed only 250W produced, which does not seem to be enough to make the batteries bubble. I also lowered the charging voltage from ~27V to ~25.5V, but it didnt solve the issue. For now I'm going to cover the panels so I don't blow up my battery bank. 

UPDATE: The batteries don't hiss, but bubble, which is a result of electroylsis and to be expected from what I read. I guess I just need to place them in a well ventilated space. The voltages of my batteries are about the same, though I haven't checked the water level in one of them for quite a time

My battery is called the Nautilus 31 Deep Cycle Marine Battery. 

The battery specs are as follows: 
Appilcation: Marine
Capacity: 115000
Size: 6-cell
Type: Specialty
Cold Cranking Amps: 650
Canking Amps: 830

ps: Ive also got some sealed lead acid batteries lying around that I can configure as a 100aH pack. Would this be more appropriate than a marine battery for my application?

BB.

Measure the voltage across each battery (is one battery lower than the other, or do they match?).

Measure the SG of each cell... What are the readings? (looking for a cell or two very low SG...).

Typically gassing voltage for a 12 volt battery is around 14.0 volts and above... For a 24 volt bank, then ~28.0+ volts.

Yours should not be gassing unless you have a shorted cell (typically SG of a bad cell is very low compared to the rest)... At least that is my first guess for the vigorous bubbling. (heavy gassing and battery getting very hot are usually not good things).

-Bill

mcgivor

Flooded lead acid batteries need to be charged usually at 28.8V at 25°C, perhaps slightly higher, follow manufacturers recommendations. Reducing to 25.5V will result in undercharging, the most common cause of battery failure. Minor hissing is normal, it's part of the chemical reaction, an indication that charging is occurring, bringing  the sulfate crystals back into solution of the electrolyte. Temperature compensation is required to increase the charging voltage when below 25°C, or decrease when above.

Measure the battery voltage with a meter to confirm the controller is actually regulating the voltage and is the same as the value displayed on the controller. Flooded lead acid batteries are extremely resilient to overcharging, 250W at 27V  the current would be around 9A, which is near 10% charging rate, probably close to recommend for 105 Ah, at full array output 750W, perhaps higher if extremely cold, the charging current nay be a little high at 28A, this would increase the potential of vigorous gassing.

The 27V charging voltage is too low, that is a typical float value, it should be at least 28.8V, use temperature compensation if cold, increase 0.15V for every 5°C below 25°C, unless the controller has a remote temperature sensor to perform this automatically. Charging at a higher rate may be beneficial in winter with limited sun to complete the charging cycle.

Where vigorous gassing may be a problem is if the battery is a maintenance free type without access to the electrolyte, is this the same as what you have? 



  

st4rgut

@mcgivor That looks like what I have. I can routinely top off the battery and now that I recall there was no hissing sound, just bubbling. Is the rule of thumb that the maximum charging rate equals the amp hours of the battery? So my 110 ah battery can sustain a power input of 2640 Watts (24 * 110)? 

mcgivor

No, the charging rate is specified by the manufacturer, each one varies but it will be a percentage of the Ah capacity, usually somewhere in the 10-20% neighborhood so for example 15% of 100 Ah is 15 A,  15A × 28V = 420W. Note this is just an example at a given voltage.

The rated Ah capacity is time based, deep cycle typically refer to a 20 hour rate, marine deep cycle batteries are a compromise between starting and deep cycle typically used on boats, hence  the cranking amp figure. Without doing research on the battery you have, I've no idea which formula was used to determine the capacity listed, nor the recommendations for charging, but the manufacturer should be able to provide this information specific to the model number.

RCinFLA

Bubbling is the fracturing of water in electrolyte into oxygen off the positive plates and hydrogen off the negative plates.  It starts a small amount of gassing at about 13.5v on 12v lead-acid battery and gets more vigorous at higher charge voltage.  Lead-acid batteries should not be charged above about 15% C rate in amps.  At lower state of charge they can take a higher rate but rate should be reduced when they get greater then 85% state of charge.  During charging the electrolyte water near plates surface is reconverted back to sulphuric acid and the electrolyte must have some time to diffuse mix or electrolyte near plate surface will become locally depleted of water reducing charging efficiency.

The greater the charge rate, the greater the battery charging voltage for given state of charge.  Should not let voltage get higher than about 14.5v during absorb as it is hard on battery and creates a lot of gassing that consumes a lot of electrolyte water. 

The bathing of positive plates with oxygen bubbles increases oxidation of positive plates grid support structure which over time increases battery series internal reistance. Sealed lead acid batteries should not be allowed to create too much gassing that can escape via pressure relief vent which is a problem since water cannot be replenished.  

st4rgut

Thanks all. Would I have to worry about overcharging if I always charge my battery in float mode? That way the charge controller regulates the power going into the battery to keep it near 28 volts? This would be perfect for me, because I don't plan to use more power than I make from my solar system. I also only plan on using solar energy during the day.

BB.

You do need to get your bank/charge controller/voltage set points correct and working correctly. You want a system that will not accidentally toast your battery bank if/when the charge controller decides the batteries need charging.

-Bill