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Wet Cell Lead Acid Battery Venting

Feb 17, 2006
4,874
Lancer 27PS MCB Camp Pendleton KF6BL
Is there any cause for concern if the batteries are located in the cabin of the boat?
 
Jan 18, 2016
528
Catalina 30 Dana Point
No. Unless they're being massively overcharged, what comes out is pretty much pure hydrogen that'll rise and dissapate. They don't gas much if the charge profile is good.
 
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Likes: Brian D
Jan 11, 2014
5,753
Sabre 362 113 Fair Haven, NY
We just had this discussion on a Sabre email group.

The issue is twofold, off gassing of hydrogen and sometimes the sulfur components from the sulfuric acid and the dangers posed by these 2 gasses.

It is not too difficult to get an explosive level of hydrogen to build up inside a poorly ventilated battery box and if there is an ignition source there will be a big boom and the lid will fly off. The ignition source would likely be a loose connection. The lower explosion limit (LEL) of hydrogen is surprisingly high, at 4%, higher than propane, natural gas, and ethanol vapors. In the confines of a battery box, the volume of air is pretty small so it doesn't take much to reach the LEL. If the hydrogen is allowed to escape, it will rise and dissipate into the next larger enclosure because it is lighter than air. If that volume is large enough and ventilated well, there is little explosion hazard.

The battery box needs to have ventilation at the top of the box. Some old style boxes are ventilated by loose fitting covers and cut outs for cables. If the hydrogen doesn't have a way out, it will build up to explosive levels. So, make sure the box is ventilated at the top.

The other gas is the sulfur component of the sulfuric acid. The issue here is corrosion when the vapors condense on something. Locating the battery box under a stove or under sensitive electronics or wiring might lead to their early corrosive demise.

Here's an interesting chart that shows the upper and lower explosive limits of various gases. https://www2.mathesongas.com/pdfs/products/Lower-(LEL)-&-Upper-(UEL)-Explosive-Limits-.pdf

And just because we like to see things blow up, here's a link to exploding hydrogen:
(this is just one of several videos he has on hydrogen).
 
Apr 14, 2009
713
Sabre 28 NH
I saw this product being used on one of the U Tube electric boat videos.
Person claimed he only needed to add very little water twice in the course of year & there's no outgassing.
https://www.thermoil.com/
Does it work, I don't know.
Is it worth doing, I don't know.
Snake oil or a very well kept secret? I don't know.

Bob
 
Sep 20, 2006
2,713
Hunter 33 Georgian Bay, Ontario, Canada
Mine has 5 batteries under the settee. Battery charger is mounted in there and there are slotted vents through the walls into the cabin. The newer Hunters all have them in the cabin somewhere.
 
Jan 11, 2014
5,753
Sabre 362 113 Fair Haven, NY
I saw this product being used on one of the U Tube electric boat videos.
Person claimed he only needed to add very little water twice in the course of year & there's no outgassing.
https://www.thermoil.com/
Does it work, I don't know.
Is it worth doing, I don't know.
Snake oil or a very well kept secret? I don't know.

Bob
Snake oil, or perhaps battery oil? If this was really a viable method there would be competition. I'd be interested in a deconstruction of the video by Maine Sail.
 
Apr 14, 2009
713
Sabre 28 NH
There's nothing to deconstruct regarding the video. The guy was just showing his 48 volt Interstate fla battery bank & mentioned he used this product. Does it make any difference, to him it did.
 
Feb 17, 2006
4,874
Lancer 27PS MCB Camp Pendleton KF6BL
So the key is good ventilation. That should be a no brainer, but sometime the brain gets left at the dock. LOL

Thanks again for the replies.
 
Dec 19, 2006
5,649
Hunter 36 Punta Gorda
I have had my 4-6 volt batteries under the sette seats at the table in the main cabin since 2010 and have had no problems and really have not added any ventilation.
The first year I had batteries that did go bad and were gasing really bad,went to the boat one day and was gasing really bad and did at that time just replace with all new batteries and did have solar vents in the front hatch.
I have my solar do all my charging at the dock.
 
Oct 30, 2011
542
klidescope 30t norfolk
So factory bmw battery and most European battery come with a vent hose attachment ( 1/4 tube ) because battery is in trunk to vent gas or acid out of car thinking about running tube to mason jar to catch acid then running tube to intake manifold of engine because when engine running is when I get most of my charging. Do you think the hydrogen will burn in little diesel maybe give More hp
 
Jan 11, 2014
5,753
Sabre 362 113 Fair Haven, NY
So factory bmw battery and most European battery come with a vent hose attachment ( 1/4 tube ) because battery is in trunk to vent gas or acid out of car thinking about running tube to mason jar to catch acid then running tube to intake manifold of engine because when engine running is when I get most of my charging. Do you think the hydrogen will burn in little diesel maybe give More hp
There will not be enough hydrogen to make a difference in a diesel engine. Some aspiring chemist could actually calculate how much hydrogen could be released from a battery and what volume is the critical volume to reach the LEL and when I was an aspiring chemist, I could do the math, but that was 45 years ago. :(

As for the acid, I think most of it will condense on the top of the battery compartment and drip back down on the battery. Again, the amount is mostly inconsequential, however, things that are sensitive to acid, like battery chargers, electronics, etc would be better placed in a separate compartment from the batteries.

Ventilation is the key. Hydrogen wants to go up, not down or sideways, give it a path and it will leave.
 
Mar 26, 2011
2,611
Corsair F-24 MK I Deale, MD
There will not be enough hydrogen to make a difference in a diesel engine. Some aspiring chemist could actually calculate how much hydrogen could be released from a battery and what volume is the critical volume to reach the LEL and when I was an aspiring chemist, I could do the math, but that was 45 years ago. :(

As for the acid, I think most of it will condense on the top of the battery compartment and drip back down on the battery. Again, the amount is mostly inconsequential, however, things that are sensitive to acid, like battery chargers, electronics, etc would be better placed in a separate compartment from the batteries.

Ventilation is the key. Hydrogen wants to go up, not down or sideways, give it a path and it will leave.
Basically, it will depend on how much water your batteries are using. For each pound (pint) of water you will evolve 1/18 pound-mole of H2, which will occupy 20 ft^3 at standard conditions. At 4% LEL, that's 500ft^3. However, given that H2 goes up and diffuses very fast, and that this will tank 6 months, any reasonable amount of ventilation results in very low risk. As others have said, eliminate all chances of spark, make certain there are vent openings, and the risk is trivial.

The acid gas damage threat is more serious. As others have said, keep sensitive things away, and apply heavy grease to the rest. Grease Grease (Omni) and Lanicote are both well proven for anti-corrosion in testing (Practical Sailor).
 
Jan 11, 2014
5,753
Sabre 362 113 Fair Haven, NY
Basically, it will depend on how much water your batteries are using. For each pound (pint) of water you will evolve 1/18 pound-mole of H2, which will occupy 20 ft^3 at standard conditions. At 4% LEL, that's 500ft^3. However, given that H2 goes up and diffuses very fast, and that this will tank 6 months, any reasonable amount of ventilation results in very low risk. As others have said, eliminate all chances of spark, make certain there are vent openings, and the risk is trivial.

The acid gas damage threat is more serious. As others have said, keep sensitive things away, and apply heavy grease to the rest. Grease Grease (Omni) and Lanicote are both well proven for anti-corrosion in testing (Practical Sailor).
Drew, thanks for the math. Always good to have a real chemist around.

A pound of water is about a pint, which is less than the amount of water my 4 GCs take in a season.
 
Oct 22, 2014
12,566
CAL 35 Cruiser Portland OR, moored EVERETT WA
OK who remembers the HS Science teacher with a beaker of Hydrogen adding oxygen to the beaker till there was an explosion that caused the class to jump?
 
Jan 11, 2014
5,753
Sabre 362 113 Fair Haven, NY
OK who remembers the HS Science teacher with a beaker of Hydrogen adding oxygen to the beaker till there was an explosion that caused the class to jump?
The old electrolysis experiment. Collect the gas in a beaker, stick a smoldering wood splint into the Oxygen side and like magic it ignited. Stick it in the hydrogen side and POP! I still like the hydrogen balloons from the youtube videos. If my college chem professors had let us blow things up, I might have become a chemist.

Electrolysis_Apparatus.png
Image from Wikipedia (https://en.wikipedia.org/wiki/Electrolysis)
 
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Likes: jssailem
Feb 14, 2014
4,723
Hunter 430 Waveland, MS
Basically, it will depend on how much water your batteries are using.
This is the key... How much!
I use about a pint of water every 6 months. So the hydrogen rate of production is so small that the finger hole in my deck panel is sufficient to vent the hold.

Last point...
When is the Hydrogen being produced?
Charging... and when it is in a state of "overcharge".

It is the excess current that makes the free Hydrogen.
_______
I am not trying to lessen the precaution, since the big unknown is the conditions of your battery and what the battery thinks is Overcharge. Old batteries can overcharge at 11vdc.:yikes: for example.

So add battery condition and life to your Hydrogen reduction plan.
Jim...
 

Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
A gassing FLA battery is spewing H2 SO4 vapor (sulphuric acid) while it is producing H2 on recharge. Any battery in a living space should be vented, have battery caps that capture acid vapor and the batts should be in a box to contain said acid spew. I am currently sitting on a Jeanneau sloop equipped with a house 4D FLA battery, not boxed but the owner can deal with the corrosion I suppose...FLA batts are dirty batteries.
 
Nov 26, 2008
1,910
Endeavour 42 Cruisin
My boat is 30 years old and has had FLA batteries under the aft berth. There is no sign of any kind of damage from 30 years of gassing
 
Jan 11, 2014
5,753
Sabre 362 113 Fair Haven, NY
My boat is 30 years old and has had FLA batteries under the aft berth. There is no sign of any kind of damage from 30 years of gassing
If the batteries are in a covered box, most of the acid vapors will condense in the box and show up as moisture on the surface of the battery. If there is nothing near the batteries that would be sensitive to acid vapors, then there would be no apparent damage.