Moving LiFePo4, Rewire or run Long Extensions?

[adamis]

On my Bigfoot Camper my battery compartment is on the outside compartment of the camper. The door is just a lightweight metal door with vents in it (no insulation). There are no heater vents to the compartment either. On a recent camping trip in early Fall we were up near Lake Tahoe at high elevation. The temps at night got into the low 30s / high 20s. We had to run the heat all night to keep our twin babies warm (can't smother then in blankets) and my 100ah Battle Born LiFePo4 couldn't make it through the night running the furnace (another upgrade project). We had to run the truck in the early morning to start charging the battery and I noticed that it was charging really slowly at about 3 amps (I have a 20 amp DC to DC Renogy charger installed). It took me a while to realize the slow charging was because the BMS was likely limiting the current while the battery was so cold. Later it charged around 15 amps. Although we don't camp in the off season often, it is something I would like to be prepared for. Moving the battery to keep the temperature maintained better seems like a worthwhile endeavor.

I'm considering moving the battery inside the camper, under the dinette seat right next to the onboard charger / inverter. The conundrum I face is, I currently have appropriately sized wire for a 2000w inverter, my 20 amp charge controller, 200w (soon to be 400w) of solar plus my genset all wired to the current battery compartment. I can rerun all of these to the new compartment at extensive time and effort. It would shorten the run for the solar but lengthen the run for the inverter / genset.

The alternative is to just run some heavy gauge wire to bridge between the old compartment and the new compartment. Less work overall but running thicker cable (thing 4awg or suggestions...) can be more difficult in the tight spaces. I will do the work if it really is necessary but I'm thinking about taking the easy route on this one.

Thoughts?

[Bradymydog]

Hello Adamis,

I also have a Bigfoot Camper 25c 9.4 and am going through the process of gathering all the information I can regarding Lithium Batteries. On my camper the "Battery Box" enclosure is a plastic box with a vented metal door on the outside of the camper. The BB is located directly under and behind the sink cabinet with an open (at the top) partition separating the two.

Here are my suggestions for your situations.

1. Insulate the access metal door with poly iso foam board - cheap at R 6.5-7/in. fit it very tight. Now it will be inside you conditioned space.

2. Keep cabinet doors open during the night to allow heat to circulate into the cabinet area. If your set up Is similar, remove the partition to allow more air to circulate around the BB.

3. Only use the inverter portion of the inverter/charger during times you need to warm baby bottles or make coffee, avoid using the converter for convince i.e., microwave, AC outlets, etc. Note: baby bottles have been warmed on the (propane) stove in water and tested on the wrist for decades, use an accurate digital thermometer if you want to go hi-tech.

With the above low cost measures, you should be able to: have more usable Ah in the battery and keep the Battery warm for very little time and expense.

Congrats on the baby girls. Enjoy and safe travels.

[phemens]

adamis wrote:
Thanks for the comments and suggestions. I think I need to clarify a few things as a few of the suggestions seemed to focus on the wrong issue in my opinion. What is unique about this camping experience is our twin baby girls that required us to heat their bottles multiple times a day and to keep the furnace running at night because at their age you can't cover them in blankets.

The bottle warmer pulls ~300w for 10 minutes 4 times a day. The wife's coffee was ~700w for about 4 minutes each morning. Finally, we have running the furnace in the evening which was ~100w for about 5 minutes but cycling probably one to two times an hour from midnight till 6am. The 200w of solar is usually fine for our "pre-baby" camping needs during the summer but with these new needs and less sunlight in the winter months, just was not enough to get the battery topped off each day.

Next year we won't be doing bottles or need to run the furnace as aggressively so those factors will go away. The coffee pot we can run the genset for if really necessary though I think without the other two factors, the coffee pot isn't going to be an issue.

The point of my post however is that what I did discover is that the LiFiPo4 battery when it gets cold will limit it's charge rate. This was a bit of a head scratcher the one morning when we ended up with a dead battery so I started the truck around 6am (~20 degrees outside) in order to be able to run the furnace and put some charge back into the battery. I found the battery was only charging around 3 amps when I have a 20amp DC to DC charger. It took me a while to realize it was the BMS on the battery limiting the charge because of the temperature.

Moving the battery inside is just a project I am considering because I have a pretty optimal location for it that would eliminate the cold factor. In normal use I don't think I really need to add more battery capacity but will eventually add another 200w (for 400w) total of solar power. I might also replace the furnace with a more efficient two speed unit as well.

Just FYI, there's an active thread on heating pads for LiFePO2 batteries to keep them in the 'green' zone for cold weather charging. This presumes you might consider keeping your batteries 'outside'.

[PastorCharlie]

When installing my system I used 4/0 welding cable with equal runs connecting 4 batteries ( 450 ah ) and a 2,000 watt Magnum inverter. Fuse the + at battery. All terminals are both crimped and soldered. Estimate your needed run and buy the cable in one piece and cut to desired lengths. Simple and minimizes loss.

[Grit_dog]

Except your battery will only stay warm if the furnace is running....

[BFL13]

In the OP, the object was to do more "off-season" camping. So adding more solar won't do any good in the dark half of the year.

You need more AH for the "off season". IMO your calculations of needing fewer AH next year will only help in the sunny, warmer half of the year.

You can add more batteries or charge what you have more often, twice a day even - most likely need to do both. Alternative is to wait for the "season" to use the TC. Just how it is. You are not the first to wake up to a dead battery at night when first trying to RV in the "off-season". So it is "go big or go home" basically. 🙂

[RickLight]

Yeah we can get off track easily.

Sounds like the big question is how much better will the solar be with shorter wires? Longer 120 is not a factor under 50'.

Plan exclusively for the future 400W system. Then do your voltage drop calculations for both ways. https://www.southwire.com/calculator-vdrop At 10' 6AWG is probably good, but 4 will be half the loss. What can't be calculated is the value of your cash and sweat.

Moving LI batteries inside is a no brainer for me, if you plan on any cool temps. I've been snowed on in mid summer! There are heaters for batteries but that takes time with the truck noise, fuel and fuss.

[adamis]

Thanks for the comments and suggestions. I think I need to clarify a few things as a few of the suggestions seemed to focus on the wrong issue in my opinion. What is unique about this camping experience is our twin baby girls that required us to heat their bottles multiple times a day and to keep the furnace running at night because at their age you can't cover them in blankets.

The bottle warmer pulls ~300w for 10 minutes 4 times a day. The wife's coffee was ~700w for about 4 minutes each morning. Finally, we have running the furnace in the evening which was ~100w for about 5 minutes but cycling probably one to two times an hour from midnight till 6am. The 200w of solar is usually fine for our "pre-baby" camping needs during the summer but with these new needs and less sunlight in the winter months, just was not enough to get the battery topped off each day.

Next year we won't be doing bottles or need to run the furnace as aggressively so those factors will go away. The coffee pot we can run the genset for if really necessary though I think without the other two factors, the coffee pot isn't going to be an issue.

The point of my post however is that what I did discover is that the LiFiPo4 battery when it gets cold will limit it's charge rate. This was a bit of a head scratcher the one morning when we ended up with a dead battery so I started the truck around 6am (~20 degrees outside) in order to be able to run the furnace and put some charge back into the battery. I found the battery was only charging around 3 amps when I have a 20amp DC to DC charger. It took me a while to realize it was the BMS on the battery limiting the charge because of the temperature.

Moving the battery inside is just a project I am considering because I have a pretty optimal location for it that would eliminate the cold factor. In normal use I don't think I really need to add more battery capacity but will eventually add another 200w (for 400w) total of solar power. I might also replace the furnace with a more efficient two speed unit as well.

[BFL13]

I had a similar problem in the TC but with a different set of circumstances. What is the same is that the single (SiO2 instead of Li in my case) 100AH battery was good for running the inverter, but not enough AH to run the rest of the 12v normal RV loads for a couple of days as well.

I split the two jobs into two separate battery banks, which solved the problem. You have to decide which bank to use for which job depending on ease of wiring and what the batteries can do.

To solve your problem IMO, move the Li batt inside and also get a couple of Wet batts for the outside compartment--whatever will fit. A pair of 6s would be ideal. Whatever gets you the most AHs that will fit and that you can get at to check with an hydrometer and do all that usual battery care stuff.

You then can run the rig including the furnace off the Wets in the outside compartment and not have any serious wiring to do. Use the Li inside as your inverter's battery, move the inverter if need be to get the wiring right.

You might have to do something with the 120v side of the inverter if you move it, but a 120v extension cord can be as long as needed without a voltage drop problem.

Now you just have to figure out how to charge the two different battery banks. I used the OEM converter on one and a portable charger on the other. I only had truck to camper alternator charging on one bank and the solar was on one bank too. Your genset can do both at once by running the converter on one and the portable on the other though.

[Kayteg1]

I read it that main problem in the situation was that adamis learned about new technology limits the hard way.
Common experience says that would he put 2 wet batteries - he would never have the problem, while he would save tons of money with some weigh addition.
Talking about inverter use - they sure beat starting generator or truck engine for making cup of coffee. Even my coffee mug is 1 liter size.
Having trucks with dual batteries under the hood, I was considering using them for overnight camper use and have 20 lb generator as a backup for recharging.
But I camp in warm climates, so that never become big issue.

[jaycocreek]

noteven wrote:
Why do we the truck camper boondockers generate and store electrical energy at 12v then use 20% of said energy to invert it to 110ac before it does any work again?

Inverters have there place like the op and coffee for momma..My 5 cup Mr Coffee takes six minutes from start to finish and doesn't use that much battery...Very few items get used on an inverter in my TC,just special stuff that keeps the wife happy and well worth that 20%..

Using them lightens the load on the generator..

[noteven]

Why do we the truck camper boondockers generate and store electrical energy at 12v then use 20% of said energy to invert it to 110ac before it does any work again?

[Bert_the_Welder]

Just saw a LiFePo battery that has a warmer built in. It seems to kick on first, before putting the juice to the cells. Once warm, the BMS lets the charge go through. CanBat was the company. Canadian, eh.....

[Bert_the_Welder]

cavie wrote:
Do not put wet cell batteries inside the camper.

?????

[cavie]

Leave the battery where it is. Insulate the compartment with some spray foam insulation. Run a small heat duct to the area. Do not put wet cell batteries inside the camper.

[Bert_the_Welder]

Any chance of getting The Boss to give up the power hog coffee pot and going for pour over? You could try and sell it as the hip way to brew.... LOL
(And it does make awesome coffee once you dial in the water to grounds to soak time.)