How to build a LiFePo4 battery bank.

[StirCrazy]

A lot of people dont have any idea how easy it is to build a DIY LiFePo4 12V battery so I'll post a deicent video of how to do it so people can decide for themselves if it is in there capability.

this video is pretty decient on how to do it, what is missing is some sort of case. the Prismatic cells like to be clamped togeather slightly if you going to be running high currents. I have seen cases made out of wood with threaded rod providing the pressure, and several other ways also.

also I am not a fan of the BMS he uses, there are lot better ones, but he explains he needed the high capacity one to do a torture test on the cells.

so he builds a 280Ah 12V battery in this video, if you need more you could build 2 and then just tereat them like two 12V batterys and run them in parralell, or just build it all in series and do a 24V set up if you want to do the higher voltage systems.

280Ah LFP build

Steve

[StirCrazy]

time2roll wrote:


Not really an expedition vehicle. Not likely to be in Canada in winter.

dont lump all of canada into thoes cold winters haha. my normal day time high in the winter is 32 degrees but I onlu have to drive a short distance to drop that significantly. on the island if you around victoria the normal day time high is 42 in the winter, but if we go to winnipeg then it could be -40

Steve

[Itinerant1]

Time2roll glad everything is working out. Give it a little more time and you'll really stop paying attention to the batteries because they just there in the background working effortlessly with solar at all the tasks within reason. Me personally lfp is the only way now. Until you actually get them and use them, some of the lfp stories sound to good to be true. I know with mine now after 5.5 years and the paces they've been put through it's just amazing at times....no more dead lead. 😉

[time2roll]

No. The heaters did not come on. Set to on 40, off 45. I did test the system with an ice cube before attaching the sensor to the battery. Collectively just under 6 amps was moving evenly through the heaters giving about 60 watts of heat. No power source at that point so no temperature rise verification or performance was measured.

I assume it is good to 20f, maybe lower, and covers about the worst I would see. Could be they never activate. Glad to know they are there to buy some time so as not to create an immediate panic to roll out.

Not really an expedition vehicle. Not likely to be in Canada in winter.

[BFL13]

time2roll wrote:
Currently I have it set for 35F on, 45F off. Will see how it goes. Thinking about going 38 to 42 or similar.
Not sure it is a huge deal to be exactly something to be perfect.

With ambient to 37F, What were the settings for on and off when you saw the 44F low at the battery? Did the heaters come on at all?

Good that it all worked.

[time2roll]

IIRC coldest was 37f, daytime was 50s, battery coldest 44f. Not exactly severe conditions.

[pianotuna]

time2roll,

Any idea how cold it got and what the high temperatures were during the day time? I'm glad it has worked out so well.

[time2roll]

After a week in chilly Yosemite.... LFP is really game over for lead-acid. For me anyway.
Absolutely no issues. Could have completely ignored any battery or power related activity and just focus on everything else.

[Itinerant1]

Freezing temperatures with lfp is certainly something to think about and have some sort of plan "but" from my experience over the past years unless you will be in below freezing temps both during the day and night your cells should stay above freezing without issue.

I've posted before that all my cells (20) have a temp readings, I can see compartment temp and know what outside ambient temp is, even when I was in a strech of nighttime temps of 13-17f, daytime temps 37-45f none of the cells ever dropped below 40f by morning and during the day would warm up to low 50f. Even having a small load 7-9a on the pack all the time will not warm the pack.

I would let the batteries charge at what ever the solar would produce and being winter that's not awhole bunch till 9-10 when the sun would get some height and be able to hit the front panels along with the panels down the door side of the 5th wheel.

If needed and throwing a hold over charge of 100ah (.2c charge rate) from the inverter/ charger & generator with the cell temps at 45-50f seems not to effect the batteries performance yet after 1,800 partial cycles.

[BFL13]

Yes, it shouldn't matter most scenarios. Just thinking about how heating takes time and how it would all operate.

I don't know if the -10C stop discharging is a good idea. What if some unusual night the heat pads can't keep up and the batts get to -12C? If the cells can take -20C, and the BMS can be set there why not use that? What does it do for you not to use all the margin it could have?

Worst thing is no 12v all of a sudden. Now the heaters won't work except from the truck's starting batt, or the gen (night time event) -20C setting would give you more margin to still have 12v.

[time2roll]

Currently I have it set for 35F on, 45F off. Will see how it goes. Thinking about going 38 to 42 or similar.
Not sure it is a huge deal to be exactly something to be perfect.

[BFL13]

time2roll wrote:

StirCrazy wrote:
I was thinking about this at work, and I may be wrong... it all depends on the BMS and how it is configured for the internal pass through of power. if it is just one line then the cold weather will kill the whole battery, but if they spent some money and used diods and did two internal paths then you could controle charging and discharge independently. I guess we would have to dig into the BMS construction to know for sure...

Steve

My BMS cuts charging at 1C and discharge at -10C.

What would you set the Tstat relay temp at to turn on the heat pads so there is time as the temp drops to arrest the fall in batt temp before it gets down to -10C and turn it around to climb back to the Tstat set temp?

You need to know how long it takes for the heat pads to have enough effect so they get turned on in time. If you leave them on at some "low" then you need to learn how much they can do vs ambient to keep above -10C or 1C as needed.

Thinking of a desert scenario down that way where it might get cold at night but you want the batts at 1C or better at sunrise so the solar can start its work.

-10C isn't all that cold so not much margin if the temp drops fast in the night. Can the heat pads counter a fast temp drop like that? Guess you will find out and adjust as required.

[time2roll]

StirCrazy wrote:
I was thinking about this at work, and I may be wrong... it all depends on the BMS and how it is configured for the internal pass through of power. if it is just one line then the cold weather will kill the whole battery, but if they spent some money and used diods and did two internal paths then you could controle charging and discharge independently. I guess we would have to dig into the BMS construction to know for sure...

Steve

My BMS cuts charging at 1C and discharge at -10C.

[Ivylog]

time2roll wrote:

Ivylog wrote:
I just paid $350 for 8-280AH cells and $370 for 8-310AH cells.

Almost too good of a price. Please update when you get them.

I agree but I’ve gotten confirmation of them being shipped.

[StirCrazy]

StirCrazy wrote:

time2roll wrote:

Itinerant1 wrote:
If the heating pads are wired directly to the batteries terminal and if needing them because the actual cells are below 32f and not the ambient temp how would a generator help unless you have a heater cube plugged into it throwing heat to the compartment.

Are you going to add extra insulation on the walls/ floor to help keep heat in and cold out during the colder months if using them during that period?

Heaters will be wired on the load side of the BMS. If the load side is powered by generator, solar or vehicle, the power will go to the battery heater.

Insulation will not be added unless it seems to be needed. Most camping is in fair weather. Not intended to be a north pole expedition vehicle. Just some minimal protection for a mild cold snap.

I think everyone is going on about a mute issue, unless the batteries are totaly dead then just the charging is going to be cut off at 32 degree ish, the discharge will still be available so the heating pads will work untill it gets down to a heck of a lot colder. if you insulate good around the batteries you may never come to this as the discharge from using/charging the batteries will create there own internal heat and with the right insulation it might be enough to keep them above zero down to a pretty cold temp, but that just theory...

Steve

I was thinking about this at work, and I may be wrong... it all depends on the BMS and how it is configured for the internal pass through of power. if it is just one line then the cold weather will kill the whole battery, but if they spent some money and used diods and did two internal paths then you could controle charging and discharge independently. I guess we would have to dig into the BMS construction to know for sure...

Steve