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Inverter/Batteries in compartment


4x4ff

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I know it is NOT recommended to put the inverter in the same compartment as the batteries due to explosion hazards but was curious if the batteries are in a vented battery box if it was ok? In other words my batteries are in a vented to the outside Noco battery box in the front compartment of my 5er and would like to mount an inverter on the back wall of this compartment. If I can do this it will help free some room in my 'basement' compartment.

 

Steve

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A lot of factors there... is it actively or passively vented (ie, motorized exhaust fan, separate air intake and exhaust vents)? Will you be partitioning the batteries from the rest of the storage area? How far away would the inverter be from the batteries?

 

It's certainly possible with a partitioned, well ventilated battery bank. Even then, just to be safe, I would want to mount an inverter flat on the floor of the storage area.. or at least as low on the wall as possible (H rises). Even an 1/8" plywood partition with foam weatherstrip to seal up against the door would work.

 

9 times out of 10 you're just fine, but in the unlikely event that your batteries are overcharging and boiling off H in higher concentrations, it "could" become an issue.

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If these are wet cell batteries, there is a greater chance of off-gassing. It would have to be accumulated to a degree that some induced or static spark could set it off. IMO, I would erect partitions and seal them off to the degree their gassing could not contact electricity. Other than their own. Second, the gas must be managed, which you've done.

 

Absorbed Glass Mat (AGM) batteries, under normal conditions, do not off-gas. "Abnormal" usually occurs from something having to do with the batteries' current, usually too little voltage. You can find many places on the net discussing the care and feeding of AGM's.

 

I personally believe sleeping in the same cabin as AGM's are mounted is safe. I have read many van and truck ca,per owners who feel the same; but many of them run hoses from the box to screened vents outside. I have cut and attached 2 cents in the top of my box. I. Any hose the, outside but currently have no plan to do so.

 

Jerry

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If I had my "druthers" I would NOT have an Inverter (a device that creates a spark) in the same air space as flooded lead acid batteries. HOWEVER (must confess) mine are currently but the compartment is well vented above the batteries and to one side as well as the bottom, plus the Inverter is on the floor at a lower level. (I think the gas is slightly lighter then air right???). The obvious hazard is if the batteries are outgassing explosive vapors which get trapped and aren't vented to the exterior and can accumulate, then say the fan on the Inverter kicks in that can create a spark YIKES. On mine I'm thinking about adding a small 12 VDC muffin vent fan to create forced air ventilation out the box because my relatively small RV (29ft Class C) lacks room for all my accessories. Although I was already aware of this issue and am normally very safety minded, this post got me thinking so I am going to get that small fan installed, its a cheap and easy fix which I will install on the opposite and lower side from where the batteries are.

 

 

INSTALLATION CONCERNS: I guess?? I will mount it (can yield sparks ya know) outside the box up against it to blow air INTO the box creating a slight POSITIVE PRESURE so any gasses get pushed out the boxes existing vent holes. The alternative would be pulling air INTO the box (via its vent holes) then venting that air plus any gasses out via the fan. I THINK I LIKE THE FIRST METHOD (blow air in creating a positive pressure so air and gas vents out the holes versus the fan)

 

Very interesting and safety related post, thanks

 

John T

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I don't think a fan is really necessary... and probably not very desirable since it introduces a potential spark source and adds an additional parasitic load to your rig.

 

One of the quick, cheap, and easy mods I've seen just uses a 2" flexible hose mounted through the top of the battery box/boxes, give it a good 6" rise, and attach it to an outdoor vent. H rises so there is almost no risk of it spilling down and out the top overhang lip of the battery box.

 

For some reason I had the impression that the OP was talking about "open" batteries (not in battery boxes), so that is why I suggested at least partitioning them off. Basically creating a battery box effect. You would still want to vent to the outside though.

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Thank you guys for all of your input. The batteries will be in a Noco battery box http://www.allbatterysalesandservice.com/browse.cfm/4,9098.html with a lid THAT I AM GOING TO MODIFY to have the standard 1-1/2" or 2" (Cant remember exactly right now) hose that runs up a good 18"-24" to the outside. The Noco box doesn't come with a vent standard but I am going to modify it to include one. In a nutshell yess...It will have a passive vent to the outside as well as a 'makeup air' vent on the bottom and of course a lid.

 

 

Steve

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Convection will vent the sealed battery box just fine. As WDR says, a fan is not a good idea unless it is properly designed for that application.

 

If the battery box is SEALED....well, there is your answer. It is essentially as separate compartment and you can safely mount your inverter outside of it.

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Inverters can also have a vent fan that cycles upon temperature and there is yet another potential spark producing device which maybe isn't a good thing to have near the batteries???

 

If a small 12 VDC Muffin Fan were installed, I think it would be safer to mount it OUTSIDE THE BOX with its bladé and shield assembly up against and blowing air INTO the box to create a positive pressure forcing any possible combustible gasses out the safe vent holes rather then pulling them past the electric fan.

 

I'm glad to hear how convection alone can vent the gas, whewwwwwwwww I already have enough of that (I think) so will study and consider all the factors if I really even need to add a small external muffin vent fan configured OUTSIDE THE BOX as described above as I believe its MUCH safer (via positive box pressure) to force gasses through the vent holes rather then draw them past the possibly sparking fan. I may well leave things as is, but the thread has sure provided food for thought THANKS GUYS. You REPORT, now its up to me to DECIDE....

 

PS I like that marine device, sounds much safer !!!!!!!!!!!!!!!!!! no reason I couldn't use something like that

 

John T

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Convection will vent the sealed battery box just fine. As WDR says, a fan is not a good idea unless it is properly designed for that application.

 

If the battery box is SEALED....well, there is your answer. It is essentially as separate compartment and you can safely mount your inverter outside of it.

It is 'sealed' to the extent of a formed plastic lid that is held on with 2 screws.

 

Steve

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It is 'sealed' to the extent of a formed plastic lid that is held on with 2 screws.

 

That'll do. A "make-up vent" on the bottom isn't really necessary. If there were any leakage, you probably don't want that running into your storage area. 18"-24" rise is more than adequate. Sounds like you're golden. Enjoy!

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Have LFP and supposedly there is no venting of explosive gases under other than extraordinary circumstances.

 

Unfortunately I work every day in a world filled with 'extraordinary circumstances' for someone.....lol. What does LFP stand for?

 

Steve

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OK, let me be more specific. If you have a quality battery box that is mostly sealed, AND a vent system that is properly constructed then you won't have an issue. IMO.

 

I build battery boxes with an intake in the bottom and exit higher than the box and taken from the top of the box someplace. Typically the side, near the top. With that setup, and reasonable sealing of the lid (no it does not have to be air tight) you can safely place an inverter into the same space.

 

The devil is in the details, as usual. Someone can construct something based on the above words that will not provide a safe environment under some peculiar set of circumstances, I suppose.

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Another detail not mentioned is the CORROSIVE vapors generated by the batteries. Charging batteries generate a mist of sulfuric acid under bulk and sometimes normal charge conditions. Not a friendly environment for electronics and/or electrical connections on the inverter.

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The battery box I am going to use is actually a marine rated box that is Coast Guard Approved (whatever that means) and also certified for golf cart use (really....whatever that means). Surprisingly there is no built in vent so I am going to add one nor is their a true seal but the lid attaches with 2 screw/knobs. I saw a post on another forum where a guy used the very same box and his turned out pretty slick.

NOCO-HM426_zpspk2w5iug.jpg

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I used a cooler for a battery box because it best fit the space I had available. Installed a louvered vent opening at one end as close to the bottom as I could get and used 2" vacuum hose to vented out the top at the other end. Box hold 4 CG batteries and seems to be working so far. No signs of corrosion in the area.

Later,

J

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I, too, have a really good battery box with a footprint big enough; but it's a little short for the 2 Lifeline 6CT's I want to use. I plan to add something around the top of the box to make it work. HOWEVER, it has molded protrusions in the lid for cables to exit. Those are going to be hard to seal. I thought about using a cooler but I became very worried about heat gain and dissipation.

 

Jack, et al, in whatever container we put our house batts in, what degrees inside it are TOO hot. I can install a remote thermometer, even one with a set point alarm; what what degree should I be worried about. Then, there's this: what if I'm off galivatin' and am not around to monitor overheating and do something about it. It's my training that these good AGM's almost never off-gas, but that overheating IS one of the things that can cause it. Yes/No?

 

Jerry

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Jerry, isn't your battery compartment already enclosed? Is there a specific reason you want them boxed? Typically, those cable exits are fairly well covered to direct elements and not necessary to completely seal them. It actually wouldn't be desireable to have an air tight battery box as your batteries need to be able to dissipate heat generated during a charge cycle. While it is true that AGM's are more suseptable to thermal runaway, it takes a pretty extreme set of circumstances to occur.

 

Others may have more ideas, but to me, the best defense against that is using a temperature compensated charger to begin with, provide adequate air flow, and don't store/charge your batteries in direct sunlight.

 

I could be wrong, but I don't know if it's so much a matter of a set temperature that thermal runaway can occur so much as the rate of thermal increase. I believe catostrophic failure for most of lifelines AGM's occur around 320 degrees, but I have no idea of a specific temperature that would indicate onset of a thermal runaway. It seems like you would have to consider rate/duration of charge, artificial ambient temperature, internal heat generation, rate of temperature increase, rate of heat disipation.... it boggles my mind to try to pin a specific temp range, but there are smarter folk than I around here. :P

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With respect to using a cooler (an insulated fairly tight enclosure) as a battery box;

 

To give an accurate engineering answer I would have to know the volume,,, and R value,,, and ambient temperature,,,and air flow around the cooler,,,and venting CFM,,,, and then the watts,,,, in order to calculate the temperature rise or temperature inside the box during charging. That takes some work and dusting off the old thermodynamics books YUKKKKKKKK lol

 

That being said, Id venture a "pure guess and speculate" using a cooler as a battery box may yield some temperature issues. Sure I like the idea of adequate venting explosive gasses and am considering ways to improve my own situation.

 

So before anyone has a calf IM ONLY SAYING charging batteries inside a cooler could/might/perhaps cause some problems as far as the temperature inside the box. However as I noted, it would take the cooler volume and R factor and ambient temperature and air flow and venting CFM, and watts to accurately compute the temperature rise, and unless and until all those calculations were complete I don't see how an opinion of the outcome could be very credible. Of course, the net CFM which takes place in the venting is critical to the temperature calculation. If venting of the box is exchanging inside and outside air at a sufficient rate, there would be little temperature rise, but I dont envision natural convection venting as that many CFM, in which case when the batteries are undergoing a high charge the temperature inside the cooler might rise significantly (ONLY a guess not having performed all the necessary calculations)

 

AS ALWAYS people are free to use or do as they please, its their money, their RV, their risk, their choice NOT MINE and I wouldn't be surprised if folks say "Ive done it for years never a problem" Its just the way my old brain works to always consider these type of engineering questions, being both an engineer and attorney is a curse, Im always thinking and wondering about things and alternatives and issues most people never have to consider grrrrrrrrrrrr I cant help myself lol

 

Take care and keep safe everyone

 

John T

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