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?

[wintersun]

Electricity is not a good source for heating anything. I got by for weeks with a single 100AH AGM battery and two 100W solar panels by using the battery to power the propane fridge controller and the fan for the propane furnace. We made coffee in a drip percolator on one of the cooktop burners. If we had needed to heat food it was with the propane cooktop and this would apply to baby formula as well.

If you don't want to change our camping lifestyle then the option is to add a generator to your rig and run it in the morning to recharge your battery and at night to heat the RV or stay in parks with shore power (best option overall).

We survived in comfort with temperatures in the teens and with our propane furnace as the heat source which was fine as the cubic feet of air to heat was half that of a bedroom and that was with an uninsulated camper. Better to warm the living space then to use electric blankets.

With the exception of a special low temp Relion battery the lithium batteries will not charge at temperatures below freezing or 32 degrees. You could add a 12v warming pad around the battery but I would put this at the bottom of the list of changes to make.

[StirCrazy]

phemens wrote:



Every wire gauge calculator I've tried recommended 4/0 cable for my setup, and my lengths are nowhere near 30ft. From the battery bank to the bus bars is 3ft, and from the bus bars to the 3000 W inverter is 5ft. At 300 amps for a couple of minutes (say running the microwave), those wires heat up fast. I'm not going to gamble an expensive set of batteries for a couple of bucks.

no harm in going bigger but for a money vs preformance issue (for some one that dosent have 4/0 laying around to use( I would have just used 0 gauge to the bussbar then at 5 feet 2 gage would be more than enough for the 5 feet. for some one buying the wire they will probaby save 70% with out sacarficing any preformance.

Steve

[c_traveler2]

RickLight wrote:
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.

I have a dual Lithium (Battle Born 100Ah) set and they are separated by about 6 feet. I have run 4guage wire so there not a problem with voltage dropped (I checked it). I also have 320 watts of solar that is managed by a single combi unit...Renogy DC50s DC-DC MPPT charger/controller, it's been very reliable...Renogy

[c_traveler2]

Bert the Welder wrote:
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.....

You lose about 20% of you power when that heater kicks in for the battery...check Battle Born website.

[otrfun]

Grit dog wrote:
My mistake, by much smaller, I meant couple sizes (which is considerably smaller diameter and cost).
A 2000W inverter will draw approx 200A at full load.
I also assumed a relatively short wire run, under 10’. With that 1/0 would be more than sufficient and 2/0 would be conservative.
No harm in overkill on wire size. ( Just like pickup trucks, right? Lol). Just not necessary for the load from a 2000W inverter unless it’s a long run. Which would make no sense as it’s far more efficient to have the DC load close to the power source and distribute with AC current to AC loads.

IMO one should strive for =<2% of voltage drop (while under maximum load) to get maximum productivity from the inverter and battery. Higher voltage drops reduce the number of AH you can access from the battery, and thus the inverter's runtime.

If you used 4/0 cable for a 2000w inverter (while under a maximum load of ~200a), the longest cable run you could use and still maintain a 2% voltage drop would be 12 ft. This would drop to 8 ft. with 2/0 cable and 6 ft. with 1/0.

[phemens]

StirCrazy wrote:

Grit dog wrote:
^Like I said, no harm, no foul. I’m sue your setup works great.
It’s just not necessary to use wire that size.
Starter motor on a diesel pickup pulls 450+ amps through 2/0 wire, for comparison.

More so posted for others who don’t have the knowledge, that they do not think 4/0 welding cable is required for this setup.
Cheers
Happy New Years !

wow, I dont know if I would use 4/0 for anything but welding haha. I dont have a situation where I have to carry 400plus amps up to 30 feet away. but ya if you got it use it.


Every wire gauge calculator I've tried recommended 4/0 cable for my setup, and my lengths are nowhere near 30ft. From the battery bank to the bus bars is 3ft, and from the bus bars to the 3000 W inverter is 5ft. At 300 amps for a couple of minutes (say running the microwave), those wires heat up fast. I'm not going to gamble an expensive set of batteries for a couple of bucks.

[Camp_woof]

I have a Bigfoot 10.4 with 2 Lifeblue lithiums. Just stuffing a small blanket inside the door takes care of most of my issues. Started to use that blankie for the dog, so now will use facon heating pads, only if I need to charge and the batts are 40 or below. With blanket and cabinet doors open, will have to be quite cold outside air. Been down to teens at night and daytime high of 33, but moved after 1 day!

[StirCrazy]

Grit dog wrote:
^Like I said, no harm, no foul. I’m sue your setup works great.
It’s just not necessary to use wire that size.
Starter motor on a diesel pickup pulls 450+ amps through 2/0 wire, for comparison.

More so posted for others who don’t have the knowledge, that they do not think 4/0 welding cable is required for this setup.
Cheers
Happy New Years !

wow, I dont know if I would use 4/0 for anything but welding haha. I dont have a situation where I have to carry 400plus amps up to 30 feet away. but ya if you got it use it...


Steve

[Grit_dog]

^Like I said, no harm, no foul. I’m sue your setup works great.
It’s just not necessary to use wire that size.
Starter motor on a diesel pickup pulls 450+ amps through 2/0 wire, for comparison.

More so posted for others who don’t have the knowledge, that they do not think 4/0 welding cable is required for this setup.
Cheers
Happy New Years !

[PastorCharlie]

Grit dog wrote:

PastorCharlie wrote:
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.

4/0? OMG, why?
Presume you had it laying around and then thus more economical than buying adequate but much smaller cable?

Less resistance and will deliver whatever ah I need and is available to use. No hot wires. I called local welding supply and they delivered. Adequate is like operating a truck at its max....its adequate.

My philosophy is, if I go cheap doing for myself I cannot complain because I know who stuck it to me.

[Grit_dog]

My mistake, by much smaller, I meant couple sizes (which is considerably smaller diameter and cost).
A 2000W inverter will draw approx 200A at full load.
I also assumed a relatively short wire run, under 10’. With that 1/0 would be more than sufficient and 2/0 would be conservative.
No harm in overkill on wire size. ( Just like pickup trucks, right? Lol). Just not necessary for the load from a 2000W inverter unless it’s a long run. Which would make no sense as it’s far more efficient to have the DC load close to the power source and distribute with AC current to AC loads.

[phemens]

Grit dog wrote:

PastorCharlie wrote:
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.

4/0? OMG, why?
Presume you had it laying around and then thus more economical than buying adequate but much smaller cable?

Mine is wired the same way, and nope, didn't have 4/0 just lying around. Depending on the draw (microwave, etc), you can pull several hundred amps off the batteries in short bursts - I've seen in excess of 300. Much smaller wire will not be up to the task.

[StirCrazy]

I would move your battery inside and add another. double your AH availble. even next year when your not doing bottles that would still let you go longer between generator use, and even though your not going to be warming bottles you'll probably be still running the furnace more than you did.

if it was me I would get up to about 650 watts of solar also, if you have the room to do it. this might eliminate your need to even use the gen. but you would still have it if there was a week of overcast or somthing like that.

Steve

[Grit_dog]

PastorCharlie wrote:
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.

4/0? OMG, why?
Presume you had it laying around and then thus more economical than buying adequate but much smaller cable?