Sulfur dioxide fumes from batteries

Saipro · January 2016

A little chemistry help needed. So charging an RE battery to full capacity ends with a bout of electrolysis (courtesy of holding the absorb voltage for a variable period). Water is broken down giving off oxygen and hydrogen as gas. No problems there. Production of sulfur dioxide fumes however indicate electrolytic breakdown of the acid itself.

I swapped out my Midnite Classic 150 on my of my setups to enable further data collection on an iTracer IT6415ND. I set absorb to 56.8V (that's what my Classic restricts it to when I set absorb to 57.6V). The Classic more or less fixes it at 56.8V and can register it as absorb at values as low as 56.4V. All the while, no smelly sulfur. On the iTracer, the 56.8V actually fluctuates between 56.72V (early in absorb) and 57.16V (random spikes late in absorb). I use Trojan T105-RE (FLA) batteries.

Here's the issue: once at absorb, I start smelling sulfur. Opening the cell vaps, I notice pretty cheerful bubbling (kinda like effervescence from Epsom salts in water). I don't mind too much because that kind of thing is a given when charging via my inverter (something I rarely do anymore). The Classic never did that yet I had happy batteries. I've reduced absorb to 56.0V for now. SG appears normal at the end of each day and bubbling is less vigorous.

The questions:
1. Asides from during equalization cycles, are sulfur fumes acceptable at any other time?
2. Is this gassing off of sulfur going to hurt my batteries (if it continues unchecked)? The smell isn't as bad as when I set my inverter to 57.6V (hence the eventual reduction to 56.4V) but still noticeable.

BB. · January 2016

Bubbling flooded cell batteries is part of charging--But you do not want to do too much of that as "equalization" charging is hard on the battery plates (drives oxygen into positive plate and grid, causing corrosion, erosion of plates, battery heating, driving off water, etc.). Generally equalization is only done once a month (or less), and for 1/2 an hour to a couple of hours (depends on how "unbalanced" your specific gravity between cells is).

Use a descent quality volt meter to make sure your batteries are charging a the correct voltage.

What you are probably smelling is actually "misting" of the electrolyte. Besides the smell, it can also cause corrosion on nearby cables, electronics, metal cabinets and such.

Other than reducing the amount of bubbling, there are two types of battery caps intended to reduce gassing/water loss.

The first are Hydrocaps. These are caps with a catalyst inside (something like Palladium or similar). These caps actually recombine oxygen and hydrogen back into water... Same thing as used in Sealed/AGM type batteries. Do not really recommend them. Expensive, sometimes hard to get, and have a limited life.

http://www.hydrocapcorp.com/info.htm

Another type of cap is the Watermiser type. Basically little plastic balls that help scrub the mist (liquid) from the gas as it is vented. There are something like three different height caps. Our host has one of the heights (medium?):

http://www.solar-electric.com/batwatmiscap.html

-Bill

vtmaps · January 2016

As Bill mentioned, it is electrolyte mist... you are spraying sulfuric acid out of your batteries. The mist settles on top of your batteries and becomes conductive... it can become a parasitic load on your batteries. On another forum I read of an interesting investigation... A plywood battery box was found to be charred on the top and upper part of the sides. They tightened battery lugs, used infrared thermometers to look for hot spots, measured voltage drop across cables and lugs... they couldn't find a source of heat. Turns out it was electrolyte mist charring the plywood. Have you ever seen what happens to organic materials in the presence of sulfuric acid? The organic material turns to carbon as the sulfuric acid reacts with the hydrogen and oxygen in the organic matter.

Step 1 (temporary) is aim the vents in your caps away from the battery lugs. Step 2 is replace your caps with the tallest water miser caps (they make 3 heights).

I take my batteries up to 29.4 volts regularly and have vigorous gassing. I haven't smelled sulfur since I put on the water misers.

I do fault Watermiser for their advertising... they put too much emphasis on how the caps save water. They do save a bit of water (electrolyte mist and some of the evaporative loss), but the main loss of water is gassing and they do nothing for that.

There are caps (Bill mentioned) that do recombine oxygen and hydrogen, but you can't use them during equalization (when you need them most) because they will overheat. Also, they don't last long because of the acid mist.

--vtMaps

vtmaps · January 2016

BB. said:
Another type of cap is the Watermiser type. Basically little plastic balls that help scrub the mist (liquid) from the gas as it is vented.

Bill did not explicitly mention that this "scrubbing" of the mist does not trap and sequester the mist like a filter might do... the electrolyte drips back into the battery.

--vtMaps

Dave Angelini · January 2016

What is the battery make? If you are not using their recommendation on set-points are using some weird battery you are on your own.
In a normal large space, you should barely smell the battery near the end of absorb only and only close to the battery.

Saipro · January 2016

vtmaps said:

I take my batteries up to 29.4 volts regularly and have vigorous gassing. I haven't smelled sulfur since I put on the water misers.

Dave Angelini said:
What is the battery make? If you are not using their recommendation on set-points are using some weird battery you are on your own.
In a normal large space, you should barely smell the battery near the end of absorb only and only close to the battery

My batteries are Trojan T105-RE 6V. I can't try 29.4V without the room smelling like a laboratory. I do the equivalent of 28.8V (48V system so it's actually 57.6v). The tropics are pretty warm though. Which make of battery and type are yours?

vtmaps · January 2016

Dave Angelini said:

What is the battery make? If you are not using their recommendation on set-points are using some weird battery you are on your own.

Saipro said:
My batteries are Trojan T105-RE 6V. I can't try 29.4V without the room smelling like a laboratory. I do the equivalent of 28.8V (48V system so it's actually 57.6v). The tropics are pretty warm though. Which make of battery and type are yours?

As per my signature, the batteries are four Interstate L-16. Not the HC (high capacity) model. They are made by US Battery. This is the battery: US L16 XC2, but with an Interstate label. They seem to go 6-10 years in off grid homes.

Interstate battery's tech department and customer service are brain dead as far as understanding the charging requirements of their batteries. I posted Interstate's charging recommendations here.
NOTE: The inline links on that page are broken, but down at the bottom of the first post is a working link to a file, interstate.jpg, that I posted. Notice the typo where the bulk voltage is 14.4 for 12 volts and 28.4 for 24 volts... I spoke on the phone with their tech service department who insisted that the chart is correct and that the voltages at 24 volts are double the voltages at 12 volts. Another thing to notice is the differing voltages for bulk and absorb... That cannot be accomplished with the standard IUoU charging protocol used by the renewable energy industry.

Anyway, I look to US Battery for guidance.

--vtMaps

Dave Angelini · January 2016

How big is the room? When I lived in the tropics I did not have a temperature sense device on the battery. They just were not around then and in the tropics the temperature in the shade is around 80F most of the time. You should have one these days!

If you are not using the recommended set-points I would hope you are using a hydrometer to determine if you are charging properly. The other problem I can think of that causes this to be an issue is not a large enough charging source to get through the charge in the minimum time without over amping the batteries. Usually 10% max amps of the 20 hour AH capacity of the bank.

I use L16 batteries from the usual sources in the US. I mainly do large homes for my 80+ clients. Good Luck

Sulfur dioxide fumes from batteries

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