I've found the Zephyr Power vents to be a little undersized in larger
batteries with arrays over 1000 watts. Still get that smell in the room
outside of the battery box, though its not explosive. That was with the
12 v model. I wouldn't mind seeing someone make a similar vent plumbed
to larger pipe with about double the flow rate.
Ray
On 1/16/2012 11:59 AM, Kent Osterberg wrote:
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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