[RE-wrenches] battery venting; Corrosion

[Kent Osterberg]

John,

Thanks for the follow-up on this subject. I'd like to change the example 
to show the ventilation required rather than the hydrogen liberated.

Consider a 48-volt bank of L16RE-B batteries: that's 24 cells of 370 
amphours. Using the 14 cc/hr/Ah/cell H2 rate for equalizing gives a 
total hydrogen of 124320 cc/hr or 124.32 liter/hr. To keep the hydrogen 
concentration down to 1% would require that the total ventilation is is 
12432 liter/hr or 12.432 cubic meters per hour or 7.3 CFM. A 12-volt 
Zephyr battery vent will move about 6 CFM, that enough to keep the H2 
concentration down to 1.2%. Zephyr Industries claims the vent is 
suitable for 2200-amphour (12-volt) battery banks which is six 
370-amphour batteries. I've seen too many battery boxes with no 
ventilation or with a single Zephyr vent for 16 or 24 batteries.

There is a DIN standard (EN 50272) for ventilating battery rooms. The 
calculations for it are based on an assumed (electrolyzing) current for 
various charging voltages. The main reason it is interesting is that the 
ventilation requirements come out about to be twice as much as when 
using the H2 rates you provided. I suspect that is partly because it is 
intended to to cover all batteries and it is intentionally conservative.

Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
t: 541-568-4882


On 1/6/2012 5:53 PM, John DeBoever wrote:
>
> Wrenches,
>
> Thank you for your patience (as I was busy all day).  I appreciate the 
> valid issues raised and good perspectives provided so far by the 
> Wrenches. I will try my best to clarify the hydrogen production issues 
> as follow.
>
> ·All lead acid batteries, flooded and VRLA require ventilation. 
> Flooded lead acid generate much more hydrogen by design and require 
> watering maintenance. VRLA AGM, per design, have up to 99% hydrogen 
> recombination, so production of hydrogen is much smaller, yet still 
> release hydrogen and require ventilation to keep the hydrogen content 
> between 1% to 2%. Sealed enclosure is no go in term of safety, as 4% 
> hydrogen content is highly explosive.
>
> ·Here are the (approximation) ranges for Hydrogen gassing rates of 
> Trojan deep-cycle flooded batteries for:
>
> üFloat Charging (2.20 VPC @ 25^o C)                     1.0 to *2.5 
> *cc/hr/Ah/cell
>
> üAbsorption Charging (2,47VPC @ 25^o C)         2.5 to *4.5* 
>     cc/hr/Ah/cell
>
> üEqualize Charging (2.58VPC @ 25^o C)               4.5 to *14.0*   
> cc/hr/Ah/cell
>
> Please be advised that a range is given since Hydrogen production vary 
> with the battery voltage during the said charge mode duration, quality 
> of charge algorithm to tapper the current vs. voltage and total 
> duration, and, vary over the life of the battery, ageing of the 
> battery and application specifics. To be on safe side, I recommend to 
> consider the *higher* approximate figure for conservative Hydrogen 
> production value. Please note these are given at 77F (25C). Higher 
> temperature will generate higher current levels and hopefully a 
> temperature compensation feature of the voltage settings will take 
> place to mitigate the impact.
>
> Example: Trojan Signature T-105: 225 Ah @ 6V @ C/20: 225 Ah x 3 cells 
> x 4.5 cc/hr/Ah/cell = 3,040 cc/hr during the absorption charge, @ 25C. 
> During equalization @ 25C, production of hydrogen is intense: 225 x 3 
> x 14 =  9,450 cc/hr.  Use these values as inputs for further 
> calculations for ventilation requirements per applicable standards.
>
> ·The "float charging" mentioned above is kind of confusing to many. 
> Indeed, there should be no mention of gassing during "float" charge 
> mode, since we are below gassing voltage. It is mentioned for info 
> here although not typical for deep-cycle products: the Hydrogen 
> production is only a concern for UPS type of applications, where the 
> battery stays at float charge for several days /months. Float charge 
> mode is actually meant in "float" applications to mitigate the 
> self-discharge of the battery due to its natural self-discharge. 
> Indeed, even the very small float charge current build up hydrogen 
> over time. Note: VRLA technology will generate less Hydrogen than 
> flooded since the required float current will be less for VRLA 
> technology (0.2 to 0.5% of C/20). Sorry for the confusion to cyclic 
> applications minded Wrenches.
>
> ·Here are the (approximation) range for Hydrogen gassing rates of 
> Trojan VRLA AGM batteries for:
>
> üFloat Charging (2.25 VPC @25^o C)                     0.01 to 
> 0.019     cc/hr/Ah/cell
>
> üAbsorption Charging (2.45VPC@ 25^o C)         0.019 to 0.025    
> cc/hr/Ah/cell
>
> üBoost Charging (2.39 VPC @25^o C)                    0.013 to 0.015  
>  cc/hr/Ah/cell
>
> Please be advised the "boost" charging is only acceptable on VRLA AGM, 
> not VRLA GEL. It has the same role as the regular equalization event: 
> to equalize the cells, although for a much lower voltage and very 
> limited time. The "boost" charging is often not activated as a safety 
> precaution on poor charge algorithms.
>
> Please keep in mind that the above are approximations, as, when lead 
> acid batteries issues are involved, "it depends" is the first words 
> you hear from battery OEM's.  Hope this is helps.
>
> Good evening,
>
> John
>
>
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