Inverter/Batteries in compartment

[Jack Mayer]

If you have a battery compartment that is vented you will not overheat a flooded cell or AGM battery. You might "bother" a LFP and shorten its capacity over time with summer desert ambient temps in a compartment. But we are not talking LFP here - that is my assumption. For LFP to optimize capacity think of the battery as "you" - if you are not comfortable the battery is not.

 

A cooler with venting is not going to overheat unless the charger is not any good. That is what heats up a( battery - overcharging continuously. In normal charging, you are not going to achieve the temps that would damage a battery.

 

I think my website still shows a plastic container used as a battery box. That is a good way to do it. A hole in the bottom on one side and a vent hole at the top with a hose leading to the outside works for a regular battery. AGM does not really need that. Just some convection vent holes for the AGM is fine,just in case.

[mocroc]

Sealed AGM or Lithium batteries can be used anywhere. The are even shipped via FedEx or UPS as they are deemed as non-toxic.

 

rocmoc n AZ/Mexico

[oldjohnt]

THANKS FOR YOUR INFORMATION JACK "A cooler with venting is not going to overheat unless the charger is not any good"

 

I didn't really want to dig out my old Thermo books and run all those complex calculations anyway lol

 

Of course the "venting" you spoke of obviously needs to be sufficient and with adequate CFM to prevent the cooler from overheating and depends on ambient temperature, external air flow, R value, and the charging watts dissipated in the cooler. Glad to hear its NOT going to overheat, whewwwwwwwwwwwwwwww lol

 

 

PS there are 3.41 BTU of heat energy created per Watt. If batteries were to draw say 30 amps of charging current at say 14 volts, that would generate 420 watts or 1432 BTU of heat inside the cooler (quite a bit for such a small volume). Of course, if the cooler wasnt sufficiently ventilated to remove the hot air, inside temperature would rise significantly. Regardless how well the cooler was insulated or its volume, if the venting process were to allow enough cooler air to enter and exhausts it and the generated heat out at sufficient CFM, the temperature inside the cooler wouldn't rise YAYYYYYYYYYYYYYYYYYYYY lol it would not overheat as you stated

 

John T

[Ronbo]

If you have an inverter/charger or a solar controller it should monitor the battery temp and adjust charge accordingly

[KodiakJack]

John T you got me to thinking. I have an 80 amp charger and no temp sensor so at full tilt it could warm things up in short order. So Plan B is to install a small 12 volt fan to the cooler inlet. Original though is say a 80/100 mm type fan typically used for computer case for cooling (but this could and likely will change if there is a possibility of a spark). Haven't crunched any numbers yet but figure I'll be shooting for 10 ACH or so unless the numbers say more.

Later,

J

[JCTex]

I think this is related enough to this thread. What's a good source to find thermocouple, heat-sensing switches that can automatically turn on our computer fans?

 

Three years ago I built a portable electrical system with a fan in the box for the inverter and charger. One day I forgot to turn the fan on. When I woke up and saw the temp in that box on my remote thermostat, I jumped up and went to open the box. It must have been over 120* in there. When I put my 2 Lifeline 6 volts in a box in the back of my Jeep, I'm going to be sure it's not near the inverter.

 

Jerry

[oldjohnt]

Kodiak Jack,

 

Glad to hear I'm NOT the only one concerned about the possibility of a well insulated "cooler" possibly heating up due to the charging of enclosed batteries. HOWEVER I haven't crunched the numbers and Jack (who has a ton of knowledge and experience in my opinion which I respect and appreciate) claims it wouldn't overheat, and I don't have all the numbers and formulas to perform an accurate heat calculation, so I cant say YES the cooler will overheat, I just don't have all the necessary specs and data. I can, however, raise a legitimate concern based on good old physics and heat transfer.

 

That being said and similar to my concerns above, if you were supplying say 70 amps of charging current at 14 volts, that's 840 watts which corresponds to (840 x 3.41) 2864 BTU of heat generated inside an "insulated cooler", which, if not vented, will cause a temperature rise inside the cooler. If you generate heat inside the insulated cooler which isn't totally removed THE LAWS OF THERMODYNAMICS TELL US TEMPERATURE MUST RISE. Of course, all this depends on R value, cooler volume, heat generated inside (2864 BTU) and most important CFM OF VENTING be it natural or fan forced.

 

HOWEVER OF COURSE if your vent (be it convection or forced) draws in outside air and exhausts it plus the generated heat AT ADEQUATE CFM the temp inside the cooler WILL NOT rise above the outside ambient temperature. If ALL the 2864 BTU of heat generated inside the cooler is exhausted TEMP INSIDE WILL REMAIN SAME AS THE AMBIENT (pretty sure that's right lol)

 

If normal convection venting where air flows in from bottom open vents and flows out top vents or tubes etc AT SUFFICIENT CFM you're good to go and as Jack notes it wont overheat. I WOULD SAY THE SIZE OF THE VENT HOLES AND/OR VENT TUBES IS CRITICAL if you go with passive natural convection. Id bet a few 1/2" holes and a 1 or 2 inch vent tube would NOT adequately vent all the heat generated meaning temp inside the cooler MUST RISE.

 

FAN FORCED VENTING The problem with that could/might/maybe be the risk of spark introduction. Therefore, if I researched and went that route, Id (assuming the battery gas is lighter then air) place the fan OUTSIDE the cooler,,,,,,,,,,,Blow fresh non toxic outside air INTO the cooler at the bottom creating positive air pressure,,,,,,,,Have the vent holes at the TOP opposite where the fan is so any hazardous gasses are as far away from and higher then the fan as possible. OF COURSE THE CFM OF THE FAN IS CRITICAL to vent the generated heat so there's NOT a temperature rise inside the insulated cooler which has a 2845 BTU heater inside it. That much heat being generated inside such a small insulated cooler would, in my unresearched no warranty opinion, have to cause the temperature to rise UNLESS THE GENERATED HEAT IS ADEQUATELY VENTED.

 

BEST YET USE ONE OF THOSE MARINE FANS POSTED ABOVE WHICH ARE FAR LESS HAZARDOUS!!!!!!!!!!!!!!!!!!!!!!!!! THAT HAS TO BE MUCH SAFER!!!!!!!!!!!!!!!!!!!!

 

DISCLAIMER; Absent all the specs and data especially the venting CFM and all the heat transfer calculations, I am NOT saying temp inside the cooler will rise or not rise !!!!!!!!!!!!!! IM ONLY SAYING ITS POSSIBLE but I have no proof or calculations whatsoever. I AM SAYING IF HEAT GENERATED INSIDE THAT SMALL VOLUME INSULATED COOLER IS NOT ALL VENTED (enough venting CFM) TEMPERATURE INSIDE THE COOLER MUST RISE ACCORDING TO THE LAWS OF THERMODYNAMICS. I cant say if natural venting subject to size of air inlet and outlet holes supplies adequate venting????????? I don't have the data to compute how many CFM of venting is required, does anyone?????? If so please enlighten us.

 

BOTTOM LINE vent or not vent at your own risk and choice. If you vent use natural or forced air and if forced how may CFM??? DO NOT DO AS I SAY IM AN ELECTRICAL NOT A MECHANICAL ENGINEER. My battery compartment is NOT an insulated cooler,,,,,,,,,has all kinds of ambient air flow all around outslde it,,,,,,,,,,,,has bottom fresh air intake and higher exhaust vent outlets,,,,,,,,,,is natural vented,,,,,,,,,,,BUT IM STILL CONSIDERING MORE AIR HOLES AND//OR FAN FORCED VENTING but if it were a small insulated cooler THEN I WOULD BE EVEN MORE CONCERNED ABOUT TEMPERATURE RISE AND VENTING which, if adequate, will be fine (but whats adequate?????????? I sure don't know until I had the data and performed the heat calculations, but if people by experience can say its not a problem, I certainly respect their opinion )

 

NOTE PS: One of those typical 120 volt electric 1320 watt space heaters might operate at say 660 watts on the Low setting, that's 660 x 3.41 = 2250 BTU of heat versus 2864 BTU of heat generated by a 70 amp charger operating at 14 volts as noted above. NOW DONT TELL ME IF YOU STICK THAT HEATER ON LOW INSIDE A SMALL INSULATED COOLER THE TEMPERATURE ISNT GOING TO RISE!!!!!!!!!!!!!!! That's why its my unresearched uncalculated concern if you stick batteries under charge inside an insulated cooler and its not extremely well ventilated, it will get fairly hot inside. That's my story and I'ma stickin to it lol

 

UNLESS OF COURSE ITS ADEQUATELY VENTILATED, AND IF FULLY (ALL generated heat is vented and removed) TEMP WILL NOT RISE

 

 

 

Keep your batteries and their enclosure "COOL" yall

 

John T NOT a Mechanical or Thermodynamics engineer, so NO WARRANTY vent or not vent as yall please, but if you choose fan forced venting, look at those Marine fans is my advice. If you believe or know natural venting will suffice, that's great and easier, cheaper and simpler. As of now that's what I have, HOWEVER, my batteries aren't enclosed in a small insulated cooler!!!!

[Jack Mayer]

John, what I said was a properly vented cooler would not overheat if the battery charger was operating properly. I've built and used enclosed battery boxes in large RV electrical systems for years. I have never seen one heat up to any real temperature, and I have checked them. I'm NOT talking about an inverter in the box. A battery is what I'm talking about. As I said, a convection flow will be sufficient for venting fumes. Use a 2" hole in the lower-side on one side and a 1.25 or 2" vacuum cleaner hose coming out the upper-side on the opposite side of the box. Vented to the outside. You will not heat the box to any significant temperature. Certainly not enough to damage a battery. Again - PROPER battery charger, which is a three stage temperature compensated charger.

[oldjohnt]

Thanks Jack. I agree given adequate venting (enough CFM) there wouldn't be a temperature rise inside a battery box BUT IF NOT ADEQUATELY VENTED YIKES

 

If an external charger (I dont mean inside the box either) is pumping 70 amps through the batteries at 14 volts, that's 840 watts or 2864 BTU of heat generated inside the cooler, but I sure agree if there's adequate venting (even if natural) THERES NOT A PROBLEM and if your experience indicates the same then Kodiak Jack has no worries. I just don't have the CFM or volume or the coolers R value or ambient temperature to calculate the venting required to extract 2864 BTU of heat, so not having built boxes like you I just cant be certain of what the temperature might reach inside grrrrrrrrrrrrrrrrrrrr That's NOT to doubt your experience, ONLY that I don't have the data to perform the necessary calculations.

 

Nothing like experience, that's how I learned over the years, but as an ever curious engineer I'm more comfortable if I knew the coolers volume and R value and ambient temperature and watts and BTU of heat generated (likely in the vicinity of 70 amps x 14 volts = 2864 BTU) so I can calculate the necessary venting CFM. In the meantime based on your knowledge and experience I dont feel bad or worry about my batteries inside a non insulated larger box (NOT an insulated cooler) with natural venting whewwwwwwwwwwwwwwww lol

 

PS yes Im aware the charger wont be pumping a full 70 amps long long periods and if the boxes temperature is monitored and charging is compensated that also reduces heat generated, but still when the batteries see 70 amps that's 2864 BTU of heat which needs vented and as long as the venting you described removes that heat????????????????????????????? THERES NOT A PROBLEM.

 

 

Great chat and info, thanks Jack and others

 

Keep your battery boxes cool now

 

John T

[mscans]

^{Once again, one of the problems being overlooked is the acid mist sometimes generated by batteries that are overcharged. The mist is not good for any electronics. I believe the original question referenced inverters and batteries in the same compartment. NOT GOOD!}

[Lou Schneider]

 

If an external charger (I dont mean inside the box either) is pumping 70 amps through the batteries at 14 volts, that's 840 watts or 2864 BTU of heat generated inside the cooler ...

 

Wouldn't the heat generation be limited to the percentage of input power that's NOT reforming the plates? If the battery's storing 80% of the input power it would seem that only 20% of the input is going out as heat, otherwise you'd violate the principle of conservation of energy.

 

Hmmm, put the battery in an insulated enclosure, add some thermocouples and feed the resulting electricity back into the batteries - perpetual motion?

[Yarome]

- perpetual motion?

 

Thats a good'n right there...

[oldjohnt]

^{Good morning Lou Schneider, Good questions, here are my thoughts (NO WARRANTY Im NOT a Mechanical or Thermodynamics Engineer).}

 

^{You ask "Wouldn't the heat generation be limited to the percentage of input power that's NOT reforming the plates? If the battery's storing 80% of the input power it would seem that only 20% of the input is going out as heat, otherwise you'd violate the principle of conservation of energy."}

 

^{To start with just because you have a 50 or 60 or 70 amp charger that don't mean its pumping full amps hours on end. An automatic smart charger may indeed deliver max amps for some time (depends on battery state) and then back off. However, during the time its pumping the full 70 amps at 14 volts, that's 840 watts or 2864 BTU of heat (subject to how much heat and how much to battery energy increase) being generated which MUST be extracted or else box temp must rise.}

 

^{PHYSICS AND CONSERVCATION OF ENERGY}

 

^{The batteries have a resistance to current flow like any other load and when the charger is pumping 70 amps through them at 14 volts that's 840 Watts of power. Nowwwwwwwww you cant create or destroy energy so alllllllllllllllllll that gets transformed someway, somehow, somewhere. True some goes to replenish the batterys total stored energy (since it was depleted when dry camping) while the rest goes to heat and inefficiency. REGARDLESS the total energy in is Volts x Amps (840 watts) and it allllllllllllllllllll gets converted inside the box either to heat or gets stored as electrochemical energy in the batteries.}

 

^{SO I TEND TO AGREE YOU HAVE A VALID POINT. Not all 840 watts in gets converted to heat, but a fair amount is my best guess. That's whY I cant give an accurate answer without all the specs and data and the insulated coolers volume and its R value and the CFM of venting.}

 

^{Way back up above somewhere, I was addressing the issue where an insulated "cooler" was used as a battery storage box NOT a big more open NON insulated battery box. Even if not alllllllllllllll the watts in is converted to heat, I still cant calculate the insulated coolers temp rise without all the data, but still believe a 2864 BTU heater (even if less depends on battery state etc) placed inside an insulated cooler might not suffer a significant temp rise UNLESS THE HEAT IS ADEQUATELY VENTED WITH SUFFICIENT CFM.}

 

^{It doesn't appear the battery storage boxes Jack built are INSULATED COOLERS (where Im most concerned and I was addressing) in which case less venting can be required.}

 

^{THANKS, I AGREE NOT ALL 840 WATTS CONVERTS TO BTU OF HEAT and it depends on the batterys state of charge. Energy in = energy out be it heat or stored electrochemical battery energy. The box does NOT create or store energy. I still fear an insulated cooler IF NOT ADEQUATELY VENTED may suffer a significant temp rise but again I cant calculate it absent the volume and R value and ambient temp and CFM}

 

^{Thanks again Lou, good discussion on conservation of energy. How much venting is required depends on so many factors. Volume, R Value, Watts in, how much to battery versus to heat (AS YOU SO WELL POINTED OUT, THANKS), ambient temperature.}

 

^{John T}

[KodiakJack]

Here is what I plan to do. Find a low tech thermometer that will register high and low temps. I figured one of the electronic type thermometers will either corrode or blow the rig up...hence low tech. Install inside cooler battery box. Head north for Alaska next week and look to see what the thermometer says after we get there. I will post here when I get the data.

Later,

J

[oldjohnt]

Kodiak Jack, "NORTH TO ALASKA"

 

I like your idea of a t stat, that way you will see your low and high temps inside the cooler and perhaps natural convection cooling/venting will suffice??? Of course, the worst case scenario is if your batteries are low and you have a charger running full blast and the ambient temp is fairly warm THATS WHEN COOLING AND VENTING IS MOST NEEDED and when you need max CFM.

 

Keep us posted

 

John T

[KodiakJack]

Kodiak Jack, "NORTH TO ALASKA"

 

I like your idea of a t stat, that way you will see your low and high temps inside the cooler and perhaps natural convection cooling/venting will suffice??? Of course, the worst case scenario is if your batteries are low and you have a charger running full blast and the ambient temp is fairly warm THATS WHEN COOLING AND VENTING IS MOST NEEDED and when you need max CFM.

 

Keep us posted

 

John T

Here is the thermometer I ordered. Not quite low tech but the range is good and only thing that will go in the box is the sensor in its little holder. I will keep the remote where I can read it daily or more often and can compare to the ambient temperature. Not sure this will provide most folks a lot of information but it will be a fun project.

Later,

J

http://www.amazon.com/gp/product/B00DTPHNV2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

[Lou Schneider]

JohnT -

 

I'm not a thermodynamics engineer either, the reason I brought up storage vs. heat is from observation.

 

If you put a recording amp-hour meter on a battery bank, the difference between amp-hours taken out of a battery bank versus the amp-hours needed to recharge it is just a few percent.

 

This doesn't mean the battery is > 95% efficient, since you're charging at about 10 - 15% more voltage than the battery delivers.

 

But even at 80 - 85% efficiency, the amount of heat generated during charging is significantly lower than your estimates.

 

Further observation shows most of the heat generation occurs during the latter portion of the charging cycle, when the plates are more fully reformed and the charging current has dipped significantly below the bulk rate.

 

Again, I'm not an engineer, just someone sharing practical observations.

 

And yes, putting batteries inside a sealed, insulated enclosure is a bad idea unless you're using them in sub-freezing temperatures where the higher operating temperatures are desirable. If so, they'd better be an AGM or other non-outgassing type. But you don't need a hurricane flowing through the box to carry away the waste heat, either.

[oldjohnt]

Thanks Lou, Like I said many many times I just don't have enough data like volume and R value and ambient temperature and CFM of venting plus now, heat versus electrochemical energy conversion, to accurately compute the temp rise inside an insulated cooler used as a battery enclosure grrrrrrrrrrrrrr

 

So if you are charging the batteries at say 70 amps and 14 volts, I cant say how much of that 840 watts converts to heat and how much converts to other energy.

 

I still fear placing the batteries inside an insulated relatively small volume and putting 840 watts into the enclosure might cause the cooler to overheat UNLESS THERES ENOUGH CFM OF VENTING,,,, BUT THATS SOMETHING I DONT HAVE THE DATA TO CALCULATE??????

 

Perhaps a Thermo or Mechanical Engineer can compute the temperature rise for us???????????????????

 

Thanks Lou, very fun discussion for techy and engineering types even if we bore the others, sorry lol

[Ray,IN]

All my lead-acid batteries are on the bottom of one compartment, it has a shelf above the batteries that contains the inverter. That shelf has a rubber gasket seal on the lip that contacts the compartment door when closed. The shelf does have a hole for wiring from the inverter to the batteries. That is the Winnebago design for Ultimates. IMO, if that was of any concern about sparks and fires, their engineering dept. would have scraped that idea immediately. This picture is not of my MH, but same configuration.

 

[oldjohnt]

Thanks Ray, a picture is worth a thousand words!!!!!!!! It appears they have a potential spark producing device (such as say a cooling fan or relays etc. in an inverter or charger) separated by how ever well those gaskets and seals work??? I cant see how and where the battery compartment is vented (maybe the door or in the rear or elsewhere not shown, maybe the back is somewhat open???). I thought the gas out the top of charging lead acid batteries is slightly lighter then air?? If that's the case and if I were the designer, I would have put the inverter and charger in the bottom and batteries in the top??? There's also the concern of acidic fumes corroding electronics which is another reason my personal preference (electrical not thermo or mechanical engineer) would be for an inverter or charger to NOT be where such fumes might be present !!!!!

 

Id guess surely they have mechanical and thermodynamic engineers who (unlike me) had all the specs and data and volumes and air flow around the boxes and R values and they know how many CFM of venting was required.

 

The picture makes me feel better regarding how much battery compartment venting I currently have, even though I'm adding yet more, better safe then sorry and cant get too much venting for safety in my engineers opinion.

 

Id also guess that battery compartment does NOT have the thermal characteristics one gets by placing the batteries inside an insulated cooler???

 

I just don't see any way to gather up all the specific data necessary for adequate venting and cooling calculations, but as long as the batteries aren't in an insulated cooler your picture sure makes me feel safer. But as always, both people and designers and Winnebago are free to do as they please.

 

THANKS RAY

 

Yall keep safe now

 

John T

[mscans]

All my lead-acid batteries are on the bottom of one compartment, it has a shelf above the batteries that contains the inverter. That shelf has a rubber gasket seal on the lip that contacts the compartment door when closed. The shelf does have a hole for wiring from the inverter to the batteries. That is the Winnebago design for Ultimates. IMO, if that was of any concern about sparks and fires, their engineering dept. would have scraped that idea immediately. This picture is not of my MH, but same configuration.

 

Can't tell from the picture but is the battery compartment open at the bottom? That would be good ventilation if it was.

[Ray,IN]

Can't tell from the picture but is the battery compartment open at the bottom? That would be good ventilation if it was.

The battery compartment is sealed by the door, just like the top half of that compartment. The floor of the battery compartment is all solid steel, and is a continuation of the steel floor of all the compartments forward of the batteries.(which is immediately in front of the RR duals)

That hole for wiring through the middle partition for battery cables and 2 phone cables is about 2"x4",there is a vent at the top of the battery compartment, that has a water shield to keep it dry, it does allow road dirt into the batteries though; witness the picture.

I sure hope Winnebago knew what they were doing when that design was approved. Perhaps I should seal that wiring access hole between the compartments with something.

[oldjohnt]

Ray,

 

 

Assuming the gas emitted out the top of the batteries under charge is lighter then air (I believe it is) I would NOT want a path from them up above to where sparks (Inverter or charger fan or relays etc) may exist. That's just me, do as the coach maker or you may like. As I said before I would place any potential spark devices (chargers or inverters with fans or relays) BELOW instead of ABOVE the batteries. But do as you wish or the RV maker say NOT me.

 

Instead, I would design a battery compartment such that the gas and heat generated is properly and well vented with sufficient CFM OUTSIDE AND AWAY FROM THE RV to the ambient surroundings and NOT where sparks are or people are present. That will keep the battery compartment from possibly overheating PLUS vent any dangerous gasses to the exterior NOT to where sparks or people are.

 

VENTING AND COOLING This is NOT the same condition above where batteries were placed inside an insulated cooler. If that were the case I would be very concerned there is sufficient CFM of venting and cooling, but a more open NON INSULATED battery box wouldn't cause such concern STILL AS LONG AS ITS ADEQUATELY VENTED WITH ADEQUATE CFM.

 

Im NOT a mechanical or thermodynamics engineer so take the above for what it is NON EDUCATED. That being said and where people may say the RV maker knows whats right and best, I say I (past used RV dealer) have seen situations where the chassis is shipped and then the RV maker has to make accessories fit where they will and perhaps conditions are NOT as safe as they could or should be???? As Ive said before, sure I would likely use the manufacturers specs and directions PROVIDED THEY ARE SAFE AND CORRECT AND CONFORMED TO AT LEAST NEC MINIMUM STANDARDS (may even use bigger wire however). If such is NOT the case I would do whats correct and safe.

 

Feel free to assume if Winnebago or Itasca or whoever built a battery box that way at that location it must be safe?????? (if you're willing to bet your life on that??) its your life and your RV. HOWEVER I WOULD HAVE A BETTER VENTED BATTERY LOCATION AND NOT BELOW POSSIBLE SPARK PRODUCING DEVICES IF I HAD THAT RV...........

 

Call me over safe or over conservative if you like, do as you please and so will I YES IM WELL AWARE PEOPLE CAN SAY I DID IT THAT WAY FOR YEARS (or Winnebago did) NO PROBLEM, but I will still do things even safer thank you.

 

Best wishes Ray, I dont mean to scare you, that's just how I do things and I prefer to err on the side of safety. If you or others like it the way it is I wont argue or try to stop you and expect the same in return. Being both an engineer plus an attorney, I've just seen too many situations where something one person thinks is safe turned out NOT to be.

 

If gas out the top of a lead acid battery under charge is heavier then air THEN I STAND CORRECTED

 

John T

[Jack Mayer]

What I would do is to foam the passageways between the compartments. I assume that the battery compartment is somehow ventilated.

 

You want to prevent air exchange from the lower to the upper compartment.

[skp51443]

Doesn't take much acid mist to ruin an inverter, any time you charge non-sealed batteries hard you are going to get some mist.

 

If you have room adding catalytic sealed caps to your non-sealed batteries can help but you will need to remove them and deal with the mist when equalizing as they can overheat from the large amounts of hydrogen and oxygen to be recombined.