Auxilliary Battery in tub

[G-Dubya]

I have had an auxiliary battery in the tub of my D22 for the last 2 years or so. It is a Century 100ah deep cycle lead acid battery (not AGM). I intend on changing the battery to AGM when this one fails but don't know when that will be.

This aux battery is being charged by a Ctek D250s Dual and both are installed inside a ply box along with associated wiring, anderson plugs, volt meter and switch panel.

I have read that when lead acid batteries charge they release gas that can cause an explosion.

With the battery being inside a ply box approx. 55cm (w) x 38cm (h) and 22cm (d) is there a chance of gasses building up inside the box? I have number of holes in the top of the box and down the side to allow wiring in/out, access for Anderson plugs and approx. 1mm gap around the door for the box.

So questions I have are as follows:
1. Is there a possibility of gas build up inside the box or is there enough ventilation with the holes and gaps already there?

2. If more ventilation is required will fitting a vent panel in the lower part of the box suffice or do I need to consider some sort of small fan to assist with venting any gas (much like the fan used in the ARK Powerpack Battery Box which is always on when the charger is connected)?

3. If a fan is recommended what would be the best way to connect it?

Cheers.

 

[Old.Tony]

Batteries can release hydrogen gas when being charged. It's much lighter than air, so vents/openings near the top are required.

Generally (assuming a reasonably competent charger which the D250S certainly is) the batteries won't release much at all and it's nothing to worry about. However the risk is still present and because it's a "flooded cell" battery, it will have small vents in the caps to allow that gas to escape. AGM and gel batteries are called "VRLA" (valve regulated lead acid) batteries or sealed batteries - they will vent gas, but only in extreme conditions. Usually, the charger has to break for that to happen.

Overcharging the battery will increase the amount of gas released. By using the D250S, you're on pretty safe ground to start with. A small vent near the top would suffice. Open the lid when you're manually doing a 'refresh' charge (usually with a mains charger).

To answer your specific questions:

1) You would have enough already. You don't need much of a gap or large hole at all to be safe.

2) No need for a fan.

3) It's not so much the way it's connected, it's the type of fan - it MUST be 'brushless'. A brushed fan could emit a spark and the very tool you're using to make the equipment safer will be the cause of its destruction. However, it's not needed. If you were going to put one in, I'd connect it to the input side of the D250S, so that it's powered by the car and running when the charger is charging (which is the only time the battery could emit much hydrogen anyway).

 

[G-Dubya]

Sounds like it's nothing to worry about. I will get a vent into the top of the box. Thanks for the info Old.Tony.