RV holding tank heaters to keep lifepo4 batteries warm?

[XERTYX]

I didnt want to hijack the thread on the renogy self heating batteries to ask this question. 

I know that people have been using similar heating pads for some time to keep their lithium batteries from dipping below freezing while charging and I have a few questions that I cant seem to find answers to online. 

If you have used a heating pad for this purpose OR perhaps their designed purpose of keeping a holding tank from freezing what kind of power usage can you expect?

I know the size of the item being heated, insulation, and temperature have a huge impact but.... if you google RV holding tank heater watt draw or something along those lines it will link to an amazon heater. 65w. 

Well that's useful but it has a thermostat, so 65w wont be constant. I'm looking for a real world figure here. Just a ballpark obviously as every setup would be different. 

Also kinda a side note, as these batteries can be discharged below freezing but not charged would it be a good idea to put them on a timer? That way the batteries arent nice and toasty at night and completely dead in the morning?

My 27DC battery has had a hard year and I need to replace it. I'd like to go with a 50ah lifepo4 battery. But I wanna figure out how to keep it warm if I do go that route. Also with any luck this winter or early spring I'll be buying an off grid home base so I want to be able to setup a 4 season solar option there as well, preferably using lithium.

 

[gizmotron]

I'm in the middle of a van build and actually considered this approach. I mentioned it to a rep at Ampere Time that I was going to do this that way. And I discovered that the heaters use as much watts as my fridge when on.

While completing my side walls in the shower areas I discovered blank spaces too small to be useful for storage. So I decided to use them as air ducts for air flow. I purchased two 5 inch dc powered computer fans, 5 watts each. I have a warm air feed duct and a cool air return that dumps to a simi outside location just outside my false wall where the RV door is located. In the back section's mechanical room space will be where all my electronics, plumbing, and lifepo4 batteries are located. That is also the space where my 5 gallon propane tank is located. So I get to keep warm my plumbing, the water holding tank, the blackwater holding tank shutoff valve, the batteries, and the electronics. I also keep my Ninja Foodi back there. Any leakage from the propane tank is sent out from there too.

So the warm air in the living room space is sent to the mechanical room and then out the side through the tilt out window on the side van cargo door. I changed my mind because of the wattage. And I'm repurposing the warm air. Not only that but it solves the condensation problem too.

 

[StarryNights]

I live in NH where winter temps are often well below freezing and have a DIY 100 amp 24v LiFeP04 battery in a box insulated with 1/2" foam board. At the bottom of the box I have a 3" x 11" 12v 7 watt RV elbow pipe heater attached to a piece of 3/16" aluminum which serves as a heat spreader. This heater has no thermostat so I kept it on 24/7 in winter months but by-passed it in warmer months. The low 7 watt draw seemed to have little impact on the battery.

Battery temp would rise during the warmer daytime, and slowly drop at night. All worked fine unless outside temps went below 10F (rare) when the little elbow heater could not keep up. To handle this, I installed a thermostat programmed to disconnect the solar input to the charge controller to prevent charging if battery went below 34F and resume charging at 36F. Kept battery on all winter and all worked flawless.

Parts are inexpensive on Amazon:

RV elbow heaters come in different sizes, see https://www.amazon.com/s?k=rv+elbow...x=rv+elbow+,aps,181&ref=nb_sb_ss_ts-doa-p_6_9

There are many inexpensive 12V thermostat switches: https://www.amazon.com/s?k=12v+thermostat+switch&ref=nb_sb_noss_1

A Caution: The inexpensive switches have a 10 or 20 amp capacity; when above freezing relay closes (on), below freezing it opens (off). My thermostat has a 20amp relay so I am OK with my 24V system. (I have 400 Watts of solar but rarely see output above 275 Watts in winter months.) 12V systems with over 250 watts of panels should probably have the thermostat activate a 40 amp or larger automotive relay to switch the solar input.

 

[tx2sturgis]

Also with any luck this winter or early spring I'll be buying an off grid home base so I want to be able to setup a 4 season solar option there as well, preferably using lithium.

I want to suggest that, all other factors being equal, for a fixed operation, that you should choose AGM over lithium.

For mobile operation (vans, trailers, RVs, etc) LiFePo4 batteries have a lot of advantages. But, for standby or primary operation in a fixed location, off-grid, cabin, etc, they lose most of the advantages that they have when used in a mobile setting.

This doesn't mean don't use it if you already have it, (or a bank or lithiums is donated to you!) but I'm just saying that for a new purchase in fixed operation that a large heavy, inexpensive bank of lead acid batteries (flooded or especially AGM) still have a a couple of real advantages (including AH bang for your buck and high-low temperature tolerance) over lithium.

I know this is not your main focus, more of a sidebar, but I'm just tossing this in the mix so you can focus more on the mobile use of the LI battery and not be as concerned with accommodating it's 'quirks' when installing in a cabin or other fixed location.

 

[XERTYX]

Thanks for the replies. I'm thinking of going with an ampere time 50ah battery to replace the 109ah (I think.....) group 27 deep cycle from Wally world. That will run everything I run now just fine and give me the flexibility to run my rice cooker from my inverter. The rice cooker seemed to REALLY impact my battery the only time I used it. Just a standard ass basic bitch 300 watt rice cooker. But I think the battery had suffered some serious damage already. I had left my fridge on for about a month and I assumed the battery was getting a full charge from solar every day. :/

One reason I wanna go with lithium at the off grid is so that I wont have to run a generator on rainy days. I had thought of building a massive 29DC or even golf cart or AGM batteries but I think I'd still rather the lithium. Santan solar is now open in Savannah Ga so I may head that way and see what they have on their grand opening event Nov 6th I believe...

But the off grid is definitely gonna have an obscene amount of panels. Lately I have been using around 120-300 watt hours a day and that does everything I need BUT I want to be able to use some nifty gadgets when I get the property. Who knows? I might even go nuts and buy a microwave for the cabin I plan to build.

 

[gizmotron]

I'm no expert, far from it, but that 50ah battery sounds like it's not enough. I have a 200ah from them and it's the "Plus" model that allows 200 amps all at once. It won't shut off at 100 amps like the basic 200 ah battery from them does. And I don't think it is enough. I only have 400 watts of solar panels.  Someone here might point out this and why 50ah might not be enough.

 

[XERTYX]

Well a 50ah lifepo4 is 640 watt hours. In the dead of summer with the fridge running I was using around 500 watt hours total for the day. My inverter is an 800 watt surge but only 400 running watts so my inverter should discharge from the battery just fine. Even while I'm running my DC fridge. The fridge pulls around 40w and around 10-15ish watt hours every hour in the Ga heat in my experience.

So IF I have the inverter on with a 400 watt load AND the fridge AND my 12 watt USB ports all at the same time it shouldn't be a problem for the BMS if in fact it's a 50A BMS.

I've learned to scale my electric usage down QUITE a bit over what I was accustomed to in a house.

 

[gizmotron]

That's great. I like seeing someone run by the numbers and make it work at the top end of capacity.

 

[XERTYX]

Haha. Thanks. That is still theoretical of course. I've never ran lifepo4. Also cheapo chinese lifepo4s dont always run at their advertised ratings, but based on my usage with lead acid it's a solid replacement for my walmart battery based on my needs.

I just worry about it getting too cold and crapping out. 200 bucks for a cheap 50ah is pretty cheap. BUT so was $80 for a walmart battery that has noticeably less capacity after 8 months or so....

 

[XERTYX]

As I have re read my post. (Do people not really re read their posts like I do?! Haha)

I've noticed some confusing points.

Using the 50ah ampere time or similar battery would be for the van. With a heater ideally. To replace my existing 27DC battery.

It would be designed to run a 300w rice cooker as well as my USB chargers.

12v fridge switched off during lulls like it is now.

If I use seriously high drain devices (like at the off grid) those would be sized accordingly. Like microwave ovens.

In the van I've mostly used my inverters AC power to charge a chromebook computer, run a soldering iron, or to run 12v lead acid chargers. Other than the 300 watt rice cooker load ran once that taxed my damaged 27DC battery.

I'm fairly minimalist as far as electricity goes. That's kinda why I'm trying to find numbers on holding tank heaters as battery warmers.

 

[XERTYX]

So... I've been thinking of ways to mitigate the risks of charging a lithium battery without low temp disconnect.

My EPEVER charge controller has a temp probe port.

But its tricky to even set these up for lithium, they dont use the same wifi/bluetooth app as they do for SLA/FLA/AGM type batteries for 1. So maybe it wouldn't even shut it off.

I could buy a victron controller and the nifty little low temp disconnect gizmo they sell like Will Prowse showed in his ampere time battery video. Spending a couple hundred bucks to make a bank of cheap batteries work is a smart idea. Not so much a single cheap battery.

I could use a $60 thermo statically controlled holding tank heater that draws 65 watts and would kill the battery overnight potentially.

I could combine the heater with a mechanical 12v timer. (~$25 on amazon) Just like the ones from back in the day with the little pins to set on/off cycles like youd connect to a lamp when you're on vacation so thieves thought you were home. That would switch the heater on before sunup and off after sundown.

I could buy a 12v 3d printer heating pad and a 12v thermostat AND the 12v timer.

I also happen to have a knockoff "hotlogic" lunch box. It was like $14 on amazon and it only heats to 120-130 degrees. So it's pretty much useless for cooking food like the hotlogic does.

Maybe I could reverse engineer the heating pad from it with a thermostat to keep it around 60 degrees AND the 12v timer.

I think I'm just gonna replace the 27DC battery with another one and wait on going lithium. It's doing my head in to try and redesign the good battery with crap temp controls to suit my needs.

I also thought of tearing open the case like will prowse did in his ampere time video and just replacing the stupid high temp probe for a low temp one but again. I feel like im trying to put lipstick on a pig here.

 

[datac]

>>>>>> So... I've been thinking of ways to mitigate the risks of charging a lithium battery without low temp disconnect.

>>>>>>>My EPEVER charge controller has a temp probe port.

I have a 40A Mppt Triron EPEVER as well. They do have a low temp disconnect. If you have not found it, I remember it being in one of the main toolbar drop downs in the PC software, just not anywhere you would expect it.

That said, I set mine to 41F, then I took one of those cold compress packs from the freezer and put it on top of the temp sensor which is on top of the battery.

I went inside to watch the display show the battery temp dropping. When it hit 41F, the EPEVER started flashing a RED LED and there was no more current coming into the battery, even though it was a bright sunny day. I forget, but I think it pulled the source power as well, at least the display was not showing any incoming power.

I removed the ice pack and watch the temp climb. As I recall, it went quite a ways higher than the 41F... maybe up as high as 46F before it kicked back into charge mode. This amount of spread is a good thing... probably would make me put the setting at 35F perhaps. Not sure yet.

Now the question is do I really trust it ?  We know what it means if it fails. I'd like to find time to install a second tier of protection. There certainly are many ways to do it externally. Had my battery have a disconnect built in (ampereTime), combined with the charge controller, I probably would trust it.

For this year however, I will remove the battery and put a Lead Acid back in which will work fine for what I need to accomplish over the winter season. That wont work for everyone.....

 

[datac]

Let me add that my battery is fully outside any heated area.... If I had it inside where I was attempting to LIVE, I would just set the charge controller accordingly and watch it until I felt a little more confident. On nights when I was really worried, I would just pull the fuse from the panels. Charge controller temp sensor will tell me what and when I can re-apply power.

Going to a Lithium has been a big eye opener for me though.... Night and day difference in everything.

 

[XERTYX]

I have a 40A Mppt Triron EPEVER as well. They do have a low temp disconnect. If you have not found it, I remember it being in one of the main toolbar drop downs in the PC software, just not anywhere you would expect it.

That is actually REALLY helpful feedback. I appreciate that. Maybe I'll give that some more thought. 

My epever CC is a 20a model. I think yours is the "headless" model?? Mine has a display. And my computer is a chromebook so I cant run the "PC" software but I may download the "lithium" app apk software and take a look in there.

I have poked around a little bit in the lead acid app for android but mostly I use it to monitor watt hours in from the solar etc.

Im in a dodge caravan and the "stow n go" cubby in the second row where the seat used to be is where my battery lives. So its IN the living space but under the floor. I'm going to be heating my living space with a 12v diesel heater but under that cubby it's like ¼" of steel plate away from the outside so I worry about how cold it would get down there.

I doubt I'll be buying a lithium battery in the coming month or so as the 12v diesel heater is barely in the budget. Also I have to figure out where in the heck I plan to saw holes in the floor to mount the heaters fresh air in and exhaust. 

I might have no choice but to go with 1 more lead acid battery until cold weather passes at which point I should have the funds for the off grid property which will include an upgrade to the caravan as well.

Thank you so much for that clarification though that the epever model you have DOES have at least that fail safe.

 

[jasper]

I have a similar situation.  Five year old 100 AH AGM house battery charged by alternator and solar.  12v refrigerator behind van passenger's seat. Diesel Air Heater to the left of side door. 

Two years ago I bought a 30AH Ecoworthy Lifepo4 to keep the fridge alive during low sun days and to try lithium.  It's mounted on the side door step panel at the front below the fridge.  The battery has a BMS that limits charging and output current to 30 amps.  It has no cold shutoff.

My 2KW diesel heater is three feet away from the Lifepo4.  My wife has been using a piece of flex duct on the diesel heater's outlet as a hair dryer for a few years.  So far not needed, but I plan to direct the heat with the flex duct if need be.

I'm happy enough with the lithium battery that I plan to get a 50AH version.  My reasoning for the smaller batteries is the demand from the alternator.  Mine can handle 50 amps.  Also, with multiple batteries, if one fails, there is backup.

My 100 AH AGM is in the engine compartment.  To avoid the heat would require running larger charging wires to the new lithium location. Has anyone had a Lifepo4 in a high heat area?

 

[XERTYX]

Well I googled the temperature range for lithiums as I didnt know the upper limit. Their operating range is generally between -4℉ to 140℉. They shouldn't be charged at or below 32°F and shouldnt be discharged below -4°F. Idk if it will get above 140°F in the engine bay but it will definitely get too cold in there in the winter depending on the climate.

Also you mentioned alternator charging with lithium. It's my understanding that it's best to use a DC to DC charger like the ones that renogy sells to alternator charge a lithium battery. Some say yes some say no but it makes sense to me, even if your alternator can handle 50 amps like you say that's still a huge tax on the alternator in my opinion.

If you're not familiar with them the way I understand it it will connect to your starter battery and then to the lithium battery. It only runs when the engine is running and it's less of a strain on the alternator as the starter battery helps to buffer that high drain load.

 

[datac]

[quote pid='553448' dateline='1635282783']
>>> My epever CC is a 20a model. I think yours is the "headless" model?? Mine has a display.

https://www.amazon.com/EPEVER-Contr...1&keywords=epever&qid=1635353201&sr=8-19&th=1

>>> And my computer is a chromebook so I cant run the "PC" software but I may download the "lithium" app apk software and take a look in there.

H'mmm..... Borrow a windows PC to get it set ? If you do some research, youll find that the lithium APK worked like garbage... at least that was last spring when I was playing with it.

I was only successful with the APK when others mentioned they just used the Lead Acid version, then set each and every setting manually. AmpereTime gave me a really good book with those details.

>> Im in a dodge caravan and the "stow n go" cubby in the second row where the seat used to be is where my battery lives.

Gosh.. I tow my 6x12 with a 2016 T&C... I have to hold myself back from converting it into a semi livable space BECAUSE of those awesome large storage "holes" in the floor.

>>>So its IN the living space but under the floor. I'm going to be heating my living space with a 12v diesel heater but under that cubby it's like ¼" of steel plate away from the outside so I worry about how cold it would get down there.

I think you could very easily insulate that hole first, set the battery in, and use a very, very small PC type fan just to push air into the area. If you can keep the Van above 60 degrees, and you can insulate that cubby, there is no reason it could not be kept above 40 degrees down there. Just go overboard on the insulation the first season to see how it works. Dont forget that in a crisis, you could run a 2" flex hose up to the ceiling level to pull the warmest air from if you run into trouble.

>>> I doubt I'll be buying a lithium battery in the coming month or so as the 12v diesel heater is barely in the budget. Also I have to figure out where in the heck I plan to saw holes in the floor to mount the heaters fresh air in and exhaust. 

I usually SIT on a plan for a few days when it comes to hacking holes. I always make sure I am choosing the best possible option at the time of the need. I dont always get it right... down the road one does another step and wonders how much better it "would have been" to do theat first thing different, but you have to move forward.

>>> I might have no choice but to go with 1 more lead acid battery until cold weather passes at which point I should have the funds for the off grid property which will include an upgrade to the caravan as well.

Probably a good move, and I would suggest putting together a really, really detailed power usage plan and just double its size for headroom. That plan does have to include how much battery you can actually charge effectively though by whatever means you hope to do so. In other words, if your only plan would be 100 watts on the roof, a 200ah battery might be a little too big... you know what I mean.

>>> Thank you so much for that clarification though that the epever model you have DOES have at least that fail safe.

It does, and it does work. Like I said though, I dont know if I can just trust it with my first Lithium battery and it's cost. It's NOT in a spot where I will be daily over the winter. If I was though, I would trust it by watching closely. Remember, for most people, your charge cycle starts in the morning. SO, you can easily just pull the incoming charge fuse and manually plug it in or turn on a breaker IF you are sure the battery is above the safe temp.
[/quote]

 

[XERTYX]

I've thought about the fan idea. Actually originally I was planning to go with 2 walmart 29DCs in parallel then my local walmart got in a pallet of 29DCs and 27DCs (near the lake lots of boats) the 29DCs I held off on buying because I didnt have the CC or panels yet and then there was a run on batteries. They sold all the 29s and only had a few 27s left so i bought 1 27DC to tide me over and a 1 amp trickle charger to keep it topped off until i started building.

I had hoped to use 2 250 watt santan panels but shipping to the east coast was cost prohibitive so i went with 2 rich solar 100 watt panels.

The battery would still be fine to this day I'm sure but there was a death in the family and i left my van parked for a while and just assumed that my setup was fully charging EVERY day with the fridge on. I'd check it from time to time and even on rainy days it was getting charged. But now i know probably not EVERY rainy day. My bad.

Long story short I'm fine for power at the moment. Maybe I will also be fine for power when I add the 12v diesel heater... maybe not though. I watched a series of reviews this spring when I was still designing my build and found that those heaters pull around 20-25 amp hours a day on continuous use. Much more potentially if you switch it off and on as the glow plug has to warm up via the battery every subsequent burn.

I've been kicking around a few ideas to upgrade my capacity to offset winter time charging and adding a power hog of a heater to the mix. I'll keep brainstorming I suppose. AND possibly make sure I still have my receipt and exchange my battery before its 1 year warranty expires.

Then when the will is probated I'll have some more flexibility to upgrade the van after I buy my property and see how much I can afford to spend on the van. For right now though the lights are still on and I can charge my phone and hotspot. The computer as well, which I dont use very often. So life is good.

 

[datac]

I use the Rich solar panels too. Been very happy with them. 90% of the time, I have been able to get by with just (2) 100 watt panels on the roof of the trailer charging my 200aH battery. If there is little or no sun, I've plugged in two additional 100 watt panels that I turned into a set of folding portables. I already have yet two more panels, making a total of six Rich Solars, and next spring, there will be four permanently on the roof. The portables will be important if I need to locate them in sun if I am parked in the shade.

Another thing I splurged on was a decent 12v compressor fridge rather than the 120v Dorm unit I started with. I started with an ICECO Go20. I love it so much I ordered their VL45 shortly thereafter. Because I do not have to also run the Inverter and suffer additional power losses, the Iceco just sips power. And, I don't need to worry about battery run down with their built in battery cut-out settings.

Regards your Diesel heater, I am in a similar situation, not yet knowing exactly what the drain from that will look like because I have not yet installed it. It is an inexpensive Chinese unit, and sadly, I have been spoiled by having once had an Eberspacher in my last build. Those are more efficient... probably far more efficient than these knock-offs. For one, they actually run via thermostat, always variably controlling blower and flame level depending on room temp, even to the point of shutting completely down and starting up from scratch when temps drop enough to do that. I think the glow plug draw was about the same, but the running amp draw was quite a bit less.

Too, my unit is an 5K, and I know it is going to be way too much heat for a 6x12. I'm actually hoping I stumble into some $$ so I can buy another Eberspacher/Espar to use instead of this one. Somewhere on-line, I saw them for $850 a while back. That's a pretty good price.

One last thought on heat... Check into the 12v electric blankets. I have used one in my last build and it was really pretty nice. It would automatically shut down at some point, and when it got cold enough for me to notice, I'd wake and just switch it back on, to which it would eventually time out and save my battery.... again.