battery gas in lockers

[clyst]

Hi All
My house batteries are under a false floor in a large cockpit locker . Although there is a built in vent at the top of the locker just wondering how dangerous is the hydrogen gas given off when charging since there is also leccy boxes and switches in there .

cheers

 

[simonfraser]

How long has it been there for ?

No guarantees in life ...

 

[bedouin]

IMHO not at all.

Hydrogen is the smallest, lightest (therefore fastest) molecule there is. No way is it going to hang around in a cockpit locker waiting to go bang.

 

[Rigger Mortice]

Just make sure that the vent has a clear run to fresh air. Then go sailing.

 

[clyst]

Thanks chaps the boat is near 40 year old and we have had her for many of those years and it hasn't gone bang but whilst ferreting in the locker it just crossed my mind

 

[sarabande]

you need to know about stoichiometric mixture

A 2 : 1 hydrogen : oxygen mixture, at standard atmospheric pressure, can self-ignite with a small spark. Once ignited, hydrogen will burn when it is mixed at between 5 and 95% with oxygen (not air).

So, basically you have to have quite a lot of hydrogen, and some form of spark to set it off.

Assuming that your electrical kit is properly installed and operating, you will not get much in the way of sparks.

Added to that, hydrogen has a density of 0.09 kg per mcube, (approx 10 mcube to have a mass of 1kg)and so will float upwards very strongly, and through any air gap in the cockpit locker. If the locker is sealed or the lid held down against a neoprene strip, then if you were being ultra-cautious, you might look at a way to let the hydrogen (IF it is produced) have free access to atmosphere.

In normal use, unless there is something quite severely wrong with your battery charging system, you should have no concerns. BTW, hydrogen does not smell.

You can buy gas detectors specifically for hydrogen, but like all clever gadgets, they can be costly.
http://www.sbsbattery.com/products-...nt-1/battery-monitoring-equipment/sbs-h2.html

 

[ProDave]

My BIL was charging is tractor battery in his garage. And decided to do some welding.

There was a big bang and a flash. Left his ears ringing for a while and singed his hair. Lucky it was not more serious.

Ventilation IS important (i'll bet the garage doors were closed)

 

[Mistroma]

Lower explosive limit (LEL) is more relevant than stoichiometry. I did the calcs. a while ago when installing ventilation for new battery box and the LEL is around 4% in air.

Other factors are:
1) How quickly will you be generating Hydrogen. This varies greatly but I seem to remember that a 100Ah flooded battery charging at ~14.8V produced around 10cc per hour. Hydrogen production will obviously be a lot worse with an equalisation charge and negligible on float charge.

2) Volume of air in battery box. I remember it being around 2000cc per 40mm spare height above a 100Ah battery (rest of space obviously taken up by the battery).

This means you'll get to about 0.5% in an hour and 4% in 8 hours (assuming the box is well sealed). These are only very rough estimates, just to give some ball park figures.

The old battery box lid was becoming discoloured with fumes from the batteries and so ventilation was worthwhile on my setup even if I ignored Hydrogen removal.

 

[KellysEye]

Since batteries are generally sealed can somebody please explain how hydrogen can escape?

 

[ProDave]

Since batteries are generally sealed can somebody please explain how hydrogen can escape?

Not sure if thus link will work

 

[Rigger Mortice]

Since batteries are generally sealed can somebody please explain how hydrogen can escape?

My understanding is that they are sealed to reduce the amount of water loss but that gas is allowed to "blow off" to prevent a build up of pressure.

 

[clyst]

seems all a bit doom and gloom now so where are your batteries fitted chaps and how do you ensure good ventilation ?

 

[sarabande]

" how do you ensure good ventilation"


I have a 40 yr old wooden boat with lots of tiny gaps round cockpit locker lids and up into the winch boxes. So air can get in and any mixtures get out.

 

[clyst]

Having more than doubled the battery compacity since build maybe i should fit a small FD blower similar that those fitted in MOBO engine comps.

 

[sarabande]

in which case, perhaps make sure it is classed as an "explosion-proof" or "non-sparking" fan


http://www.halifax-fan.co.uk/component/content/article/7-applications/138-explosion-proof

 

[lw395]

Lower explosive limit (LEL) is more relevant than stoichiometry. I did the calcs. a while ago when installing ventilation for new battery box and the LEL is around 4% in air.

Other factors are:
1) How quickly will you be generating Hydrogen. This varies greatly but I seem to remember that a 100Ah flooded battery charging at ~14.8V produced around 10cc per hour. Hydrogen production will obviously be a lot worse with an equalisation charge and negligible on float charge.

2) Volume of air in battery box. I remember it being around 2000cc per 40mm spare height above a 100Ah battery (rest of space obviously taken up by the battery).

This means you'll get to about 0.5% in an hour and 4% in 8 hours (assuming the box is well sealed). These are only very rough estimates, just to give some ball park figures.

The old battery box lid was becoming discoloured with fumes from the batteries and so ventilation was worthwhile on my setup even if I ignored Hydrogen removal.

A mol of electrons = 96500 C,
so 1 amp produces 1/(96500*2) mol of H2 per second
That's 22.4/(96500*2) litres per second or 0.4 litres per hour.
That's for each lead acid cell, so times six.
That's assuming all the electricity goes into gassing the water, i.e. the battery is already charged.
(it also assumes my fingers are not too fat for this comedy keyboard, which is tenuous...)
So if I'm right, whacking 10A in for a couple of hours could give you 50l of pure H2 which could be explosive in a fair sized space

 

[clyst]

Im beginning to wish I never started this thread . It seems we are all doomed !

 

[sarabande]

on the other hand, generating all that hydrogen...
Being positive about this .


You could place the batteries in a sealed compartment, extract the hydrogen and compress it in a steel cylinder, and then feed it into the motor, thus providing free, clean fuel for the engine which charges the batteries even more, so you have more hydrogen, so...


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