LiFePO4 and freezing temps

**creativepart** · 12-31-2022, 05:12 PM

I installed 2-200Ah Renogy LiFePO4 "lithium" batteries last April. These batteries have a low temp cutoff to protect them from freezing temps. The BMS stops charging at 39F and stops all output at -10F (4C/-25C).

My RV came with AGM batteries, so the basement battery compartment is open to the outside on two sides and the rear.

But this Christmas week in Texas brought 36 hours between 15F and 27F followed by 3 nights below 20 degrees. That got my attention. I brought the RV to the house stuffed reflectix in the openings around the batteries and put a small ceramic 110v heater in the battery bay.

That worked great but I decided I needed to be more prepared. So, I spent the last 3-days enclosing my battery compartment and adding heaters to my batteries. Winnebago didn't make this an easy job - the battery tray is not a compartment floor. It's a separate shelf about 2 1/2" lower than all the other compartments. So, I couldn't just fashion a new floor to span the battery openings below.

I did get some thin sheet metal and sealed in the biggest opening on one side but I could see that doing this on all sides and the back would be difficult. So, I built a "battery box" inside my battery compartment. Again not super easy... but working down low in a tight space is never super easy for my XXL 72-year 6'1" old frame.

A post like this without a photo is worthless. So, here it is. It's all done save for wiring in the battery heater switches - oh, yes, the heaters... they are Facon Tank Heaters.

Here's a before and after photo:

Marine359 · 12-31-2022, 05:17 PM

Nice Job.
Methinks many of us ordered Facon heating pads after this recent spat of very cold weather. Now you can sleep well without worrying about your new Renogies.

**creativepart** · 12-31-2022, 05:24 PM

I didn't want to stick the tank heaters directly to the batteries - the heater has super strong adhesive and I wanted to be able to remove the heater if necessary. So, I put aluminum foil on that sticky backing and taped the heater to the battery with Gorilla Tape.

Marine359 · 12-31-2022, 05:54 PM

Quote:

Originally Posted by creativepart

I didn't want to stick the tank heaters directly to the batteries - the heater has super strong adhesive and I wanted to be able to remove the heater if necessary. So, I put aluminum foil on that sticky backing and taped the heater to the battery with Gorilla Tape.

Thanks,
My heater arrives next week. I was planning to go with the Will Prowse method of using bent aluminum sheet, but I suppose foil works just as well. That’ll save some time and money.

Forgot to ask, did you use an inline fuse?

**creativepart** · 12-31-2022, 07:00 PM

I saw someone else use aluminum foil and thought that would be simple and easy and eliminate any metal binding.

That sticky side is VERY VERY sticky.

I have two inline fuses - each 10 amp for each 12v line. They only sent one fuse pigtail, for two heaters and a 2-button switch.

And, the switch wiring diagram doesn't make any sense to me. It shows no main negative/chassis ground. Just positives and grounds from the heaters back to the switch. It shows a 12v positive to the switch... but no negative. That can't work. The switch bodies are plastic, so it's not grounded by the mounting plate.

I pretty much know what I'll do - but I can't find any details of others using the Facon heaters and the Facon switch. So, I'm guessing as I go.

Marine359 · 12-31-2022, 07:31 PM

I think I’ll wire mine to my fuse block using a 10amp blade fuse. I’ll be curious to hear from you about the switch when you get it untangled. Thanks again.

Redd22 · 12-31-2022, 08:27 PM

Great job!

I put two of the Renogy 100 amps in my View. Was thinking about the tank heating pads, now that I know they work well it will be my next project.

Marine359 · 12-31-2022, 08:45 PM

Just taking a swing at it,,
If it’s a lighted switch, the switch positive needs to be between the mat positive and the 12v power source positive. The switch negative isn’t that important. On a 3 pole switch, I’ll wire mat negative to fuse block negative directly without using the switch negative wire. Without a fuse block, you can still wire mat neg to 12v source neg, or use the switch neg wire to gnd. I’m just gonna buy a 3 prong lighted rocker switch.

**creativepart** · 12-31-2022, 10:16 PM

My plan is to wire it as shown and then add a 12v neg from the switch negative to the shunt. This load, like all others must go through the shunt.

What I don’t understand is why this wiring diagram simply ignores 12v negative entirely??? Wired like the diagram you don’t have any power to the heater pads.

And, yes it’s a lighted switch, one for each pad, also from Facon.

Marine359 · 01-01-2023, 08:24 AM

Yeah,
What I didn’t understand about those switch instructions is how neg made its way to gnd or neg to complete the circuit. With just one neg wire to mat, the circuit would be open. My Facon didn’t come with a switch, but I think I can get a lighted switch from an auto supply store.

TravatoJohn · 01-01-2023, 08:41 AM

Great job. Have you determined the amperage draw. Would suspect at least 10 amps. Probably requires being plugged in?? Travato john

Marine359 · 01-01-2023, 09:47 AM

Search Facon heating mats on Amazon. There are amperage specs there for all their mats. My 11”x18” draws 4.8 amps constant when it’s on.

Morich · 01-01-2023, 10:28 AM

There are times when items made for a specific purpose are great, so no disagreement from me on the heat pads but maybe let me throw in some different thinking for those still choosing how to go on battery heat.

It may also apply to freezing pipes?

As an alternate idea, rather than pads, industry often needs things that can be changed out quick and easy and batteries in remote sites are one of those, so having battery heat without needing to deal with extra attachments directly on the batteries is a big item at times. There are often other factors or items in the same space which also need protection. That makes heating the space rather than the battery a better way to go.

Many things that are critical require speedy fixes, even if the initial cost is a problem but both are considered if you have a bunch of the same site spread out over hundreds of miles to service.

There are really cheap, really handy temperature controllers from a wide variety of places which can be repurposed to fit the speciifc needs we may have.
I have found good value in these really cheap little controllers from E-bay sellers are a good item to build to suit the various places where I need to know the temperature and control the heating so that it turns on only when needed.

https://www.ebay.com/itm/35448251427...579a%7Ciid%3A1

My currrent project is building out a way to protect pipes from freezing at my daughter's house. She is a busy person who really should not have to worry about things like freezing pipes, so I'm working to automate the protection.

If a Battery box was built with the idea of AGM , etc and fully enclosed to cut heat loss, it might make it practical to heat the box rather than each battery. You can get plenty of heat out of a couple rejected 9 watt Christmas lights in a small space. Using several bulbs helps to protect against any single case of a bulb burning out!
Tied to the temp controller, it stays dormant until needed.

Lots of different methods to consider before going with the "normal"!

**creativepart** · 01-01-2023, 02:44 PM

Quote:

Originally Posted by TravatoJohn

Great job. Have you determined the amperage draw. Would suspect at least 10 amps. Probably requires being plugged in?? Travato john

Just under 5amps. They have built in thermostats and turn off and on every 10 mins or so. And, with the switches I'll control when they are going to be active. I have a 10-amp in line fuse for each pad.

I hear you Richard - but these were relatively inexpensive ($33 each pad}, easy as pie to install and, by accounts of others, work well. They aren't as cheap as a string of light bulbs but they run on 12v, don't use a ton of power, are easily removed if necessary plus, they mind the temp all on their own.

Marine359 · 01-06-2023, 08:06 AM

Finished the install of a tank heater on my LiFePo4. It’s a bit sloppy because I didn’t buy the heater with the correct size and aspect ratio. Wish I had taken the time to measure. But it works fine and is heating my battery as I write this, so the battery is accepting a charge at 28F ambient. I also installed a lighted 3-prong switch. I did not use the glued surface of the mat. I wrapped the battery in foil, then placed the mat in its space in the pass thru, sat the battery on top of the mat pushed against wall on one side, and a floor screwed 2x4 on the other to secure. Here’s how I wired the whole thing:

Switch batt prong to fuse block, using 10 amp spade fuse
Switch load to heating mat
Switch neg to gnd/neg bus bar.
Mat neg butt spliced to longer 16 gauge wire to reach fuse block negative

erstanfo · 01-08-2023, 04:36 PM

Looks great!. On my 2012 Journey 36M the AGM's hang out between the frame rails below the slide out tray. When I do LiFePo4 upgrade, I'll have to move them into the compartment between the inverter box and the drivers side. There is just enough room behind the ladder holder.

Four Seasons · 01-08-2023, 05:04 PM

I can definately relate as we, the "Chosen Frozen" can experience overnight winter temps in the -5F to -15F range. Our 2015 Minnie Winnie came with two deep cycle lead-acid batteries in the step well, which were likewise exposed to the exterior. In addition to a drastic reduction in perfomance, the ventilated battery box and everything in it was suffering mostrous corrosion from freeze-thaw cycles and nasty road salts.

To escape the need for ventilation I installed AGM batteries, closed-up and insulated the battery box, and ventilated the box to the interior of the coach. Now the AGMs enjoy indoor temperatures as long as the heat is on.

This wouldn't work in every motorhome, but if your batteries are in the step well or anywhere you can open the battery box to the interior, I find it works very well.

Here's a picture...

https://www.winnieowners.com/forums/...cture1233.html

Shedboy · 01-09-2023, 08:10 AM

Thanks for all the real-life info. I purchased a couple of 100AH Renogys with integrated heater & controller option and the Renogy 110vac charger/maintainer while on sale and haven't installed them yet. Has anyone tried this configuration out? My RV, a Navion has no containment or temperature protection for the batteries, they are exposed to ambient temperature under the entry stairs.

Last two weeks the temperature dipped below -10F twice, w wind chill -30F, didn't get above
freezing (32 F) for 3 days. Original flooded cells seem to be doing OK as is the chassis battery. Renogys are currently stored indoor on charger/maintainer.

Found some definitive LiPO4 low temp info at:
https://diysolarforum.com/threads/re...heating.25782/

**creativepart** · 01-09-2023, 08:26 AM

Shedboy, I know others have posted about having the bottom of the battery compartment extended on each end to close off the bottom. I don’t know if that’s all that is needed.

With temps below zero indoors sounds the best. My Renogy BMS says it will disconnect the battery output at -4. I don’t know if your built in heaters keep the batteries warm enough to stay above that. I guess they do???

**creativepart** · 01-23-2023, 05:29 PM

Circling back to report on adding 12v heaters to my two Renogy 200Ah lithium batteries.

We’ve had 4 or 5 below freezing nights on our current 6-week trip and the heaters have worked as advertised. Right now it is 38 outside and predicted to be 28 tonight. I turned the heaters on earlier (I installed on/off switches even though the heaters have built in thermostats) and right now the batteries are at 48 degrees. The heaters turn on and off pretty quickly using between 3 and 8 amps combined. Overnight they use about 10% of the available amps. Nothing too obsessive.

The internal BMS turns off charging to the battery at 41 degrees and in 20 degree temps the heaters keep the batteries above that temp.

When I bought my batteries I felt that having a low temp cutoff was all that was needed. But when dry camping and relying on solar and a generator to keep batteries charged if your batteries are below 40 degrees you are just plain out of luck. I now think battery heaters, internal or external are a very important feature to have.

Even living in South Texas and traveling to warm locations such as Arizona there are freezing temps you just can’t avoid.