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Old 18-08-2009, 03:58   #16
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During normal battery charging, between 10 - 20 cm³ (cubic centimeters) per hour, per battery, may be released. To achieve a 1% hydrogen concentration, this must be mixed with 99 times its volume of air, or 1,980 cm³/hour/battery.

Since 1980 cm³ = 120.827 in³, and 1 Ft³ = 1,728 in³; this must be mixed with 0.069923 Ft³ per hour/per battery.

Assuming 4 batteries, equalizing for 8 hours; we require 38.6646 in³ (2.2375 Ft³) of free air (to ensure < 1% hydrogen concentration)*.

* Assuming 4 batteries, for 8 hours equalization; the battery compartment must have a minimum free-air volume of at least (4 x 8 x 0.069923) 2.237536 Ft³ to ensure < a 1% hydrogen concentration.
Free air volume is that which is only occupied by air, and not by other equipment (batteries, engine, & etc) in the subject space.

Further assuming the 4 batteries are 10 3/8" L (264mm) x 7 1/8" W (181mm) x 10 7/8" H (276mm); we can see that they occupy a volume of (10.375 x 7.125 x 10.875) 803.9 in³/Each (49.057 cm³ or 0.46522 Ft³), or a total of 3,215.6 in³.
Lets also assume that cables, fuses & etc occupy an additional 184.4 in³ of volume.

It’s apparent that the above equipment occupies about 3,400 in³ of battery compartment volume.

Hence, the battery compartment must be at least (38.6646 in³ Free Air + 3,400 in³ Equipment Occupied) 3,438.66 in³ Total Internal Volume. Let’s call it 3,450 in³.

An arbitrary Battery Compartment of 24" Long x 16" Wide x 14" High (internal measurements) will have a total volume of 5,376 in³, more than sufficient to maintain LESS than a 1% hydrogen concentration.

As someone else said elsewhere, “the devil is in the details”, and so each case must be examined under it’s own specific parameters.

Since 1 cm³ = 0.061023 in³ , and 1 in³ = 16.3870 cm³
10 cm³ = 0.610237 in³ , hence 20 cm³ = 1.22047 in³
1 Ft³ = 1,728 in³
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Old 18-08-2009, 06:49   #17
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Returning to the original question:
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Originally Posted by unbusted67 View Post
I am wondering if any one has had any really dicey situations with equalizing their batteries ? The warning on my inverter charger sounds pretty scary. Exactly how well Ventilated does the area need to be when I Start the process? They say it takes eight hours, am I going to need to not cook down below while I do this?
Given a moderately sized battery bank, and an adequately sized battery compartment; I wouldn’t be too concerned about accumulating an explosive level of Hydrogen gas when equalizing. (see the arbitrary example in my previous post)

Notwithstanding, and remembering that any risk assessment should evaluate both the likelihood of an untoward event occurring (quite low, in this case), and the severity of it’s consequences (unfortunately very high, possibly fatal); it behoves the analyst to do his own due diligence.

All bets are off, if you should inadvertently drive the batteries into thermal runaway!

Calculate the total gas generated, over the anticipated charging/equalizing duration.
Calculate the free-air (unoccupied) volume in the compartment.
Divide the Gas Generated by the unoccupied volume = the % gas by volume.
4% Hydrogen b.v. is the Lower Explosive Limit (LEL) - you want to be well under this percentage.
The commonest recommendations are to remain below 1% or 2%.
Ventilation is always a good idea.

BTW: Because the battery vent caps aid in the internal recombination of gasses produced, reducing the amount vented to the atmosphere; I DON’T generally RECOMMEND REMOVING THE CAPS, during charging & equalization.
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Old 18-08-2009, 11:02   #18
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Nick-
All risk is relative. Charging batteries is generally "safe". Lawyers Weekly for one summary of an industrial accident from a battery explosion. IIRC there are something like 40 similar incidents in the US every year simply from jump-starting cars. (You & Gord can probably pull up correct numbers form the web.)

Statisticians would disagree, but the risk of your battery exploding can be seen as 50-50. Either it will, or it won't. More conventional odds might be one in one hundred million, but who really cares about longer odds if yours is that one that does?

Every year a couple of service stations in the US explode while cars are fueling. Some from static discharge at the fuel nozzle, more from folks conveniently buying and lighting cigarettes at the same time they filled up. Still, we accept the odds are still go to gas stations.

Every year a couple of homes, businesses, and the occassional shopping center or mall blow up from propane or piped natural gas leaks, but again, we tend to ignore those and keep using gas heat. Most of us would also exit and call the gas company if we smelled a leak, and wouldn't do our own gas plumbing even though we could--because it just doesn't pay to take the chance of becoming that one in a hundred million.

Equalizing batteries? Almost perfectly safe even without any safety measures. Almost.

But personally, I'm one of those guys who sets an extinguisher with the safety pin already pulled conveniently at hand whenever I'm using a torch or welding. You know, just in case I'm the hundred-millionth-customer and the lucky winner of the "whoosh!flash!boom!" lottery. After all, someone's gotta win it.
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Old 18-08-2009, 13:56   #19
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FWIW: 51:49

Like Hellosailoir’s “it will or it won’t” scenario (an excercise in illogic), each flip of a coin has a 50/50 chance of landing on heads or tails.
However, as the sequence continues toward infinity, the chances become lower that the sequence will continue, thus the odds decrease and the chances increase that the sequence ends.

Yet recent research into coin flips has discovered that the laws of mechanics determine the outcome of coin tosses. The startling finding is that they aren't random. Instead, for natural flips, the chance of a coin landing in the same position as it started is about 51 percent. Heads facing up predicts heads; tails up predicts tails.

More ➥
A Reliable Randomizer, Turned on Its Head - washingtonpost.com
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Old 18-08-2009, 20:31   #20
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And then there's that old episode of the Twilight Zone, where the flipped coin lands ON EDGE and remains standing.

Logic, and numbers, can oft mislead.
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Old 18-08-2009, 21:51   #21
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I think you guys are on the wrong track. You watched too many movies with witches and stuff.... we're all doomed!!!....

The only way to look at it is scientifically, not flipping coins! You just make sure the hydrogen concentration stays well below that 4% and you can equalize your batteries all you want for ever without it blowing up. Laws of nature don't flip coins. It's only when you decide you don't care and skip the ventilating that you flip a coin. Or, some are just too messed up to realize that they are close to certain death.

The exploding car batteries while jump-starting cars are caused by hydrogen buildup mostly inside the battery itself. On a boat, when you open the caps while equalizing, the boiling of the electrolyte will quickly expel the gas from the battery and you can help with forced ventilation. Also, you don't introduce sparks like when clipping on a jumper cable.

cheers,
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Old 18-08-2009, 23:55   #22
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Quote:
Originally Posted by GordMay View Post
During normal battery charging, between 10 - 20 cm³ (cubic centimeters) per hour, per battery, may be released. To achieve a 1% hydrogen concentration, this must be mixed with 99 times its volume of air, or 1,980 cm³/hour/battery.

Since 1980 cm³ = 120.827 in³, and 1 Ft³ = 1,728 in³; this must be mixed with 0.069923 Ft³ per hour/per battery.

Assuming 4 batteries, equalizing for 8 hours; we require 38.6646 in³ (2.2375 Ft³) of free air (to ensure < 1% hydrogen concentration)*.

* Assuming 4 batteries, for 8 hours equalization; the battery compartment must have a minimum free-air volume of at least (4 x 8 x 0.069923) 2.237536 Ft³ to ensure < a 1% hydrogen concentration.
Free air volume is that which is only occupied by air, and not by other equipment (batteries, engine, & etc) in the subject space.

Further assuming the 4 batteries are 10 3/8" L (264mm) x 7 1/8" W (181mm) x 10 7/8" H (276mm); we can see that they occupy a volume of (10.375 x 7.125 x 10.875) 803.9 in³/Each (49.057 cm³ or 0.46522 Ft³), or a total of 3,215.6 in³.
Lets also assume that cables, fuses & etc occupy an additional 184.4 in³ of volume.

It’s apparent that the above equipment occupies about 3,400 in³ of battery compartment volume.

Hence, the battery compartment must be at least (38.6646 in³ Free Air + 3,400 in³ Equipment Occupied) 3,438.66 in³ Total Internal Volume. Let’s call it 3,450 in³.

An arbitrary Battery Compartment of 24" Long x 16" Wide x 14" High (internal measurements) will have a total volume of 5,376 in³, more than sufficient to maintain LESS than a 1% hydrogen concentration.

As someone else said elsewhere, “the devil is in the details”, and so each case must be examined under it’s own specific parameters.

Since 1 cm³ = 0.061023 in³ , and 1 in³ = 16.3870 cm³
10 cm³ = 0.610237 in³ , hence 20 cm³ = 1.22047 in³
1 Ft³ = 1,728 in³
I'm sorry whenever you first posted this I was totally lost but after reading over it a few times I am starting to understand. I think that if I leave my battery compartment propped open in the 1/4 birth area then I will definitely be able to keep the H level below 4%, the quarter birth being about 40 cubic ft. Thank you Gord I can equalize in peace now.
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Old 19-08-2009, 00:08   #23
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Quote:
Originally Posted by s/v Jedi View Post
I think you guys are on the wrong track. You watched too many movies with witches and stuff.... we're all doomed!!!....

The exploding car batteries while jump-starting cars are caused by hydrogen buildup mostly inside the battery itself. On a boat, when you open the caps while equalizing, the boiling of the electrolyte will quickly expel the gas from the battery and you can help with forced ventilation. Also, you don't introduce sparks like when clipping on a jumper cable.

cheers,
Nick.

Thats what I say too...but when I talk to 4.00 students none ever hears me..
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Old 19-08-2009, 11:12   #24
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"The only way to look at it is scientifically, not flipping coins!"
So next time some guy is yelling "Cut the blue wire, not the red wire!" I should ask him to cite some sources on that, before I cut the blue wire? (VBG)
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Old 19-08-2009, 11:27   #25
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... So next time some guy is yelling "Cut the blue wire, not the red wire!" I should ask him to cite some sources on that, before I cut the blue wire? (VBG)
1. No, just ignore him; because you don’t ever want to cut the blue wire!!!
2. What’s Venous Blood Gas [VBG] got to do with Battery Gas Emission, or cutting wires, for that matter?
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