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Open Roads Forum  >  Do It Yourself Modifications and Upgrades (DIY)

 > How to build a LiFePo4 battery bank.

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Ivylog

Blairsville, GA and WPB, FL.

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Posted: 10/07/21 06:16pm Link  |  Quote  |  Print  |  Notify Moderator

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.


This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
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time2roll

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Posted: 10/07/21 07:40pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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BFL13

Victoria, BC

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Posted: 10/07/21 08:09pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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time2roll

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Posted: 10/07/21 08:25pm Link  |  Quote  |  Print  |  Notify Moderator

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

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Posted: 10/07/21 09:10pm Link  |  Quote  |  Print  |  Notify Moderator

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.

Itinerant1

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Posted: 10/08/21 07:06am Link  |  Quote  |  Print  |  Notify Moderator

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.


12v 500ah (5,120Wh usable), 20 cells_ 4s5p (GBS LFMP battery system). 8 CTI 160 watt panels (1,280 watts)2s4p,Panels mounted flat. Magnum PT100 SCC, Magnum 3012 hybrid inverter, ME-ARC 50. Installed 4/2016 been on 24/7/365, daily 35-45% DOD 1,800+ cycles.

time2roll

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Posted: 10/25/21 01:59pm Link  |  Quote  |  Print  |  Notify Moderator

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.

pianotuna

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Posted: 10/25/21 04:21pm Link  |  Quote  |  Print  |  Notify Moderator

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.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

time2roll

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Posted: 10/25/21 05:48pm Link  |  Quote  |  Print  |  Notify Moderator

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

BFL13

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Posted: 10/25/21 07:39pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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