__9 December 2013 - The battery manufacturer confirmed the correct calculations. -------- Below calculations highlighted in RED are not correct.__I recently manufactured a couple of battery boxes, each to house a 123 Ah AGM. What I couldn't find was off the shelf was; battery boxes that complied with the Australian Standards in regard to ventilation. There is plenty of information out there offering various calculations to do such, although not to the requirements of Australian Standards. There various international or country specific standards, or industry standards, although it is the Australian Standards of which we must comply with. [Extracts from the Australian Standards are littered all over the net on this topic.]

If you have a

*naturally*ventilated enclosure, (such as a simple battery box that quite a few of us use to house our batteries.) the required opening is rather large in comparison to

*mechanical*exhaust ventilation rate as per the Australian standard, due to the 0.1 m/s ventilation rate used for natural ventilation.

I have several 120Ah AGM batteries - and are an VRLA type even though they commonly referred to as a sealed type. Two in my camper and two in my 4WD in currently inadequately vented boxes.

The batteries are predominately charged from CTeK D250S units whilst driving of which they have a regulated output float voltage of approx 13.6 and a maximum charge current of 20 amps - 14.4V. I charge 2 x 120Ah batteries from this unit at the same time whilst on the go. I also normally set my portable charger at 16Amps although has a range from 8, 16, 35 Amps.

If I calculate an exhaust ventilation rate as per the extract from the Australian Standard AS3011.2 posted in another thread, http://www.myswag.org/index.php?acti...ch=67818;image of which utilises the same calculations in AS4086.2 I get the following.

Calculations below are for one battery only.

Charge Rate

Condition II (i) 0.5 A per 100 A.h at the 3 h rate of discharge of battery capacity of lead - acid batteries;

C 3 rate of discharge. 120Ah Century C12-120DA

123 Ah / 3 = 41 Amps (41/123 = 0.3333 C rate)41 Amps x 0.5 = 20.5Amps C3 (0.16665 C rate)

(20 hr rate @ 1.75 V per cell x 6 cells = 10.5 V: 6.17 Amps x 20 hr = 123.4 A.h)

3 hr rate @ 1.75 V per cell x 6 = 10.5 V: 29.72 Amps x 3 hr = 89.16 A.h (3 hour rate as per battery manufacturers Amp table corresponding to hours.)

89.1 Ah: The charging rate "I" is: 0.5 x (89.1/100) = 0.4455 Amps

Exhaust Ventilation Rate - for one battery

Exhaust rate qv = 0.006

0.006 X 6 cells (one battery consisting of 6 individual cells) X 20.5 Amps = 0.756 l/s

0.006 qv x 1 battery x 6 cells x 0.4455 Amps = 0.016038 l/s

Natural Ventilation Rate

I'm proposing the natural ventilation rate to avoid fitting fans and alert devices. Would the following calculation be correct for the natural ventilation of which is also to be not less than 0.1m/s. opening (X 2) one high & one low)?

A = 100 qv (natural ventilation rate)

where

A = the minimum area of the apertures, in square centimetres

qv = the minimum exhaust rate in l/sec. (With assumed natural ventilation of at least 0.1m/s is assumed through the apertures.)

100 A (qv) X 0.756 l/s = 75.6 cm2 (Minimum open area)

A = 100 x qv 100 x 0.016038 = 1.6038 cm2 (minimum effective cross sectional area for an inlet aperture, or, an outlet aperture)

To qualify; natural ventilation rate

0.016038 l/s X 0.1 m/s X 1000 = 1.6038 cm2.

I'm just not 100% sure if I have got the Natural Ventilation equation is correct for a single battery, consisting of 6 cells.

I have checked on most of the major battery manufacturers sites and they all state that their AGM's are Valve regulated and some of the email advice states I must ventilate and comply with the relevant standards.

Cheers.

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