Electrical Bay Layout Safety...

Vikx… thanks for your sage comments.  I don't think the electrician is the one to consult on this issue.  The evidence of what he thought was correct and safe can plainly be seen in the existing electrical bay layout, even despite his excellent design and execution of the system itself.  He opted for a fan instead of a box.  

I had considered building that "wall" you are talking about; seems pretty straight forward.  I would use flexible dryer vent and exhaust to the existing fan opening (not interested in making more holes in the trailer exterior).  But to the left of the batteries is a 110V and 12V outlet mounted on the front face of that dinette bench and I consider this to be the biggest risk to a possible spark discharge when plugging something in etc.  You can see the yellow wire leading to the 110 in the lower left of the photo.  It's all just inches from the battery bank! So the wall would really have to be 2 walls, one right and one left.  I think a container for the batteries, along with the flexible vent to the fan, would be easier to build and install.

So in general, I share your concerns.  Though the likelihood of an event is extremely low in my opinion… a 'perfect storm' of circumstances might blow one of those 6 volts!… that's the definition of an "accident"!

In the box scenario, I think the fan is a necessity even though it will suck up power when boon docking.  Passive venting: for it to be reliable, there should really be a stack straight up out of the top of the battery box (w/ a fresh air source near the bottom).  Obviously, with the batteries under the bench that's not going to happen.  So I will vent from the top of the right side of the box and let the fan pull the hydrogen out and the fresh air in.  My fan, according to specs, consumes 1/3 of an amp… but when off grid, that's 7 Amp Hours in a day.  My 100W of solar panels would need over an hour of direct sun just to make that up.  But the 1/3 amp is rated at 3 to 7V according to the fan's specs.  Of course the fan is connected to a 12V system (which may shorten its lifespan). So would it stand to reason that the amperage would be lower operating at 12V (Watts=Volts X Amps) rather than the 3 to 7V?  My knowledge of electrical physics is a little fuzzy .  

Hmmm… that was an obvious one all along, but I haven't let myself go there  .  The front is so much cleaner without that… But let me actually look at the dimensions etc.  I would only do it, if I could move the tanks forward a minimal amount and slip the box in behind them.  Dropping it as you suggest would also keep it fairly stealth.  There is a nice box for twin 6V golf cart batteries from Century Plastics where the batteries fit in short end to short end: 22" long and only 8-1/2" wide.  It's also of white plastic which might look better on this particular trailer rather than the typical black ones. Century Plastics: White Heavy Duty Battery Box - (part#: GCE-G)

I'll take a look at the tongue and see how that could work a bit later and get back to you, Vikx.  It would make the fan absolutely moot and redirecting some 4 gauge wire would pretty easy; just drill a hole in the floor.  The more difficult tasks would be creating the support structure for the battery box and repositioning the tank platform.  We'll see...

Well drat. There really isn't another place to put the two big batteries. Sounded good, tho...

You may want to consider ditching the charger/converter and switch to a modern controllable charger like one of these:

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Expensive, yes, but they will also greatly increase the life of your batteries. These charge at a slower rate, which true deep cycle batteries prefer, thus minimizing the gassing. The only advantage I can see with the charger/converters is you can have 12V if your batteries are dead. However, in my opinion this is a false security as you should not be discharging batteries more than 50% in the first place. Besides, the charger/converter is useless while boondocking.

A couple more links with more info:

www.pbase.com/mainecruising/installing_a_marine_battery_charger

www.sterling-power-usa.com/marinebatterychargerhome.aspx

One more thing, having the batteries and charger in the same small enclosure is never a good idea as the gasses are not only flammable but also very corrosive to the charger's electronics. Will the batteries fit in the tall closet in front of the wheel well?

Also, there are low amperage solar powered 12v fans with battery power back up.

I'm going to rotate each one 90 degrees so that they are long edge to long edge and box them on the left more or less where they are now.  It will be easier for me to get both the batteries and the box in/out that way.  Right now, the batteries are very difficult to get in and out.  I can also slide the whole thing a few inches to the left (though there is not as much room there as the photo seems to show… to the left is mostly the curve of the front of the trailer and not floor).  I will also run 4 gauge wire out of the box for + & - remote terminal blocks and eliminate the problem of gassing corrosion on the battery lugs which now have lots of connections piled up on them.  As described above, the box will cover the batteries but will have generous perimeter venting at the bottom to draw fresh air in and up… the fan will do the rest and will be ported on the right upper side of the box and go straight to the exhaust fan.  This will keep a constant flow from bottom, to top then outside.  The dinette bench front will also have a low "toe kick" vent to take advantage of the negative air pressure in the electric compartment and provide ready fresh air.  The Tristar solar controller can now be safely mounted to the right of the fan.  The run to the solar panel connection outside will be very short… maybe 2 feet… plus about 10 feet of tether after that.

Right now the fan does have an on/off switch that I can make convenient to reach.  So I can at least do that manually for now.  I'm not sure how I can make it automatically switch with the controller???  But I'm sure someone knows how to do that  .  As you suggest, another $10 12V fan with lower amperage may be in order.

When parked at home, the trailer is almost always hooked up to the house.  It maintains the batteries at only about 13.3V.  If there is no load, it occasionally goes into "boost" mode and runs it up to 14.4, but only briefly.  The 3 modes on the PD4045 are 14.4, 13.7 and 13.3.  They're set and I have no manual control over them.  But with the Tristar and 14.8V solar charging, the batteries will most definitely need to be isolated and vented.  So that's what's going to happen.

The other thing you can't see in the photo is the back side of a 110V and 12V convenience outlets to the left of the batteries.  They are accessed from the front side of that dinette bench.  They're just an inch or two from the batteries and I consider them to be the highest spark risk.  So I would have to build a wall on the  right, one on the left and another on top and make them tight and/or ventilated where need be.  It will actually be easier for me to modify a box and drop it in.  That is, unless you think those outlets are not a spark hazard in such close proximity, let's say during heavy charging.  Certainly the 110 will not be hot unless connected to shore power, but the 12V (which doesn't have to be contained in a metal box like 110) will always be hot.  

Right now the batteries just sit on the floor.  When I do it, they'll sit in a metal pan and the plastic battery box will go over the batteries.  

As you can see, the electrical system was designed precisely and correctly, but from an "RV" use standpoint, many things were not considered regarding battery safety, access and power consumption off grid.  Hence… this thread  .