Another battery question - deeply sorry.

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mick

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First off, thanks to all who replied to my earlier battery question.
My boat has two batteries in a space under the quarter berth bunk. The boat was obviously designed to use wet batteries without provision for venting to the outside. Now, the boat has survived for 24 years with this arrangement, so I'm not terrified of explosion. Question is, what are the risks involved in such a set-up? I suppose I could arrange some plastic tubing to vent to the outside, but I'd rather not if the risks are minimal.
 
I agree, there are plenty of Sadlers around and I've never heard of their batteries exploding. What I have heard of, and experienced myself, is that they can get extremely hot, being completely surrounded by insulation. I assume that this can occur on 26 and 29, as well as my 34.

My solution is this:
Batteryboxfan.jpg

Cooling fan blows air from the bottom of the battery compartment into the engine compartment via four drilled holes. Has improved the overheating situation greatly and also disperses any gases.
 
Cooling fan blows air from the bottom of the battery compartment into the engine compartment via four drilled holes. Has improved the overheating situation greatly and also disperses any gases.

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Thanks for reply. I didn't realise overheating could be a problem. However I'm a bit concerned about volatile gases being pushed into the engine bay. Possibility of sparks?
 
I had always understood that the lack of specific arrangements for venting batteries on boats is that the hydrogen escapes upwards and out of the hatches and other ventilation, unlike butane or propane which sinks into the bilge and hides there until it's ready to explode. I can see that if batteries are enclosed in a compartment there could be an accumulation of potentially explosive gas but I've never heard of this as a cause of fire or explosion.
 
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I agree, there are plenty of Sadlers around and I've never heard of their batteries exploding. ............

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I had a 29 and the batts did explode! Had left them on charge all night, with the batt compartment covered by its lid and the bunk cushion. Pressed the starter button next morning, BANG!, frightened the life out of me - both batts split, so expensive!
 
Highly unlikely that enough hydrogen will evolve to still be in the flammable range by the time it has been blown in to the engine bay. It a different matter in the small space over teh batteries themselves.
 
Yes, batteries heating when charging is a problem that my cooling fan doesn't solve. They can get very warm if the battery charger is left on for a long time. Whenever I do this now I remove the cushions and lift the wooden lid.

I am guessing that maybe a loose connection in your case caused explosion of hydrogen/oxygen mixture in the small volume of the battery compartment. My thinking with the forced venting is that gases blown into the much bigger engine compartment would be well below the explosive limit.
 
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...The explosion would happen when the Hydrogen concentratio is twice the Oxygen content (H2O). As the atmospheric oxygen concentration is about 20% this makes the required Hydrogen concentration 40% which, as James says is pretty high.

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Nope.

The lower explosive limit for hydrogen (i.e. the concentration at which an explosion becomes possible) is about 4% by volume.

I still don't think it's a problem as long as the gas is free to rise and disperse, rather than being concentrated into a space, waiting for a spark.

Hydrogen is very mobile, so doesn't need much of an excuse to escape.

Andy
 
when i was in the forces, we had a venting pipe from the equipment batteries which went into a bottle with some white powder in it, to absorb the fumes. a simple solution to venting it, but i don't know what the powder was, maybe someone on here would know what it was...
 
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My thinking with the forced venting is that gases blown into the much bigger engine compartment would be well below the explosive limit.

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Would it be acceptable, then, to use plastic tubing to vent gases to the quarter berth area?
 
I think the key is hydrogen very definitely wants to go up unlike LPG, on submarines we had battery ventilation when charging and catalitic burners but our battery banks were b****y big especially when compared to a boats few hundred ampere hours at 12 volts. There is a risk but more from blocked vents than general hydrogen build up. Just look at the design of the standard battery box, no ventilation and a lid.
 
In principle, yes I'm sure it would, if the hydrogen could vent straight up. In practice, this means your plastic tube will go right through the berth cushion? Personally I wouldn't worry, I think it's a non-problem so long as all your battery connections are good.
 
I don't think that it is a matter of hydrogen going up as if contained in a balloon, rather of its molecules being so small that they diffuse very rapidly in all directions. This will allow them to form an explosive mixture with air very rapidly, but also to disperse out of this rapidly and eventually escape from the Earth's atmosphere entirely (unless a lightning strike or being sucked into an aircraft engine combines them with oxygen on the way.). More practically, I agree with leaving the battery compartment lid open and the boat ventilated during charging.
 
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rather of its molecules being so small that they diffuse very rapidly in all directions

[/ QUOTE ] And escape very quickly though very small holes!
 
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More practically, I agree with leaving the battery compartment lid open and the boat ventilated during charging.

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Do you mean only while using a dedicated shore charger or also while charging through the alternator?
 
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