Sunday, Apr 17, 2011 at 17:16
Hi Sand Man and sorry but again another myth.
There is the reverse mentality that if you use flooded wet cell batteries inside the cab of a car, 4x4 or under the bed or seats of a caravan, that they need to be vented.
NOT SO.
The minimum ratio of hydrogen to atmosphere that is needed to make the hydrogen/air mix explosive is 4.1% hydrogen.
The IEEE has set a maximum safe hydrogen to atmosphere ratio of 2% and there is only so much hydrogen a lead acid battery can produce based on the amount of electrolyte in a lead acid battery.
There is a calculation put out by the IEEE that gives the minimum amount atmosphere needed to make it impossible to get a hydrogen to atmosphere ratio of 2% and this is formulated based on the VOLUME amount of electrolyte not exceeding 0.28% of the surrounding atmosphere.
Now as no battery manufacturer lists the volume of the electrolyte in their batteries ( and they don’t need to ) so unless you are prepared to empty a flooded wet cell battery and measure the volume of the electrolyte, you won’t really know the volume of the electrolyte is.
I use a VERY rough way of calculating to determine the minimum atmosphere in a vehicle or caravan or storage shed or what ever needed to be safe for a given battery ( or batteries ).
I measure the total volume area of a battery by measuring the length, width and height ( over the battery housing not over the terminals ) then I measure the volume area of the place the battery is going to be mounted/stored.
I then multi the battery’s volume by 200 and if this figure is less than the volume of the area where I intend to place the battery then, even in a worst case scenario of a total overcharging of the battery, the amount of hydrogen that battery can produce, can not exceed 2% of the surrounding atmosphere.
This calculation has a very large margin of error factored in to make the calculation safe.
This equates to the average 4x4 being able to have 3 x 100 Ah batteries in the cab and even if all 3 were cooked dry, there still would not be enough hydrogen in the cab to cause an explosion.
As long as the area around a battery is open, then ALL batteries, no matter what type they are, are actually much safer than they would be if in a battery box.
This is fact not fiction.
One more point, when mounting a battery inside a vehicle or caravan, say under the bed or seats, while you do not need to vent the battery because there is a sufficient volume of atmosphere, you still need to mount the battery in a secured plastic battery box, even when it’s a sealed battery like an AGM.
Again, all batteries will spew electrolyte if they are over charged for what ever reason, so ALL batteries should be in a plastic battery box when mounted inside a vehicle or van.
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