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Small Cabin Forum / Off-Grid Living / Lovin my LFP
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gcrank1
Member
# Posted: 25 May 2022 12:45 - Edited by: gcrank1
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Wow!
These 100Ah LFP bats have sooo much power to use and sooo user friendly. I still have not hooked up my solar, just hooked up a bat in-cabin, clipped on the psw inverter and have 120vac every time I want it.
Too Easy!
All that futzin with Lead Acid bats is NOT missed.
These are the 3rd best thing after getting the Champion 1700/2000W inv/gen and the PSW inverter for the bat-bank.
Seriously, anybody considering getting solar for small-scale I suggest getting an LFP battery first, using it for a while while you sort out what else you 'might' want to do. So much on tap and light enough to haul home to recharge.

SCSJeff
Member
# Posted: 25 May 2022 14:55
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Agreed!

I just replaced my (2) 205AH Costco Golf Cart Batteries w/ a DIY 170ah LFP. Oh my, how much faster it charges

Will have to see this winter if I need to do anything about keeping them warm enough to charge. But, for the most part, if I'm at the cabin when it is that cold, I'm either out hunting all day or doing work and would be using the generator anyway...

Nobadays
Member
# Posted: 25 May 2022 15:22
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Been happy with my Chins LiFePo4 batteries I got to replace the Chevy Volt modules that went south last winter.

Bought 4 x 24v, 200ah and wired to 48v, 400ah. We are using right at 30% per day (should say evening/night) so theoretically we would have 2 maybe 3 days reserve.... more likely 2 days. We go to bed around 9pm and the batteries read 53.0v (55.2v is Float according to Chins parameters... a little low I think) and reads, often 53.0v in the morning.... sometimes 52.9v. That's with the satellite internet on all night! Impressed!

May add 2 more, when the budget will allow, to get 600ah and another day or two reserve.

Yes it's a lot of ah but we live here.... we jokingly refer to our place on a cul-de-sac in AZ as the "cabin" because we haven't spent more than 2.5 months there per year in the last 3 years. Here at this "cabin" we have an electric fridge, freezer, 40" TV, and satellite internet. Obviously lights, charging, etc.

paulz
Member
# Posted: 25 May 2022 18:18
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Yep a big improvement, especially if you are hauling them back and forth. Besides the weight savings, when I was hauling FLAs back and forth all my jeans had acid holes where they rubbed on my legs. I still have 10 pairs of jean cutoffs.

Brettny
Member
# Posted: 26 May 2022 09:29
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Lithium is a definite if your hauling them. Granted I left my FLA all winter and came back to full batteries.

gcrank1
Member
# Posted: 28 May 2022 21:31
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We spent the past two days at the cabin with a movie on the old tube tv c/w vcr (kind of an energy hog) before bed. We ran everything we wanted off the LFP with the low draw 300W psw inverter.
The bat integral dig voltmeter read 13.3v when we got there (that bat has been there for 3 or 4 day trips before) and when running stuff went down to 13.1v under load but was at 13.3 after resting today before we left.
Yeah, voltage is not the best way to evaluate an LFP, but bouncing back up to 13.3v sure shows Im not down at 13.0 or less.
Id run the water pump but the bucket works fine.
Fridge? Another hog; we use a Yeti clone icebox. My home-froze ice bottles last and last.
Enough beans to run a microwave? No, I start the little Champ gen for the few minutes IF we want/need to use it (700W unit) or any other high-draw, short use device; no big deal.
Wife is good with all of this too

gcrank1
Member
# Posted: 28 May 2022 21:34
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SCSJeff, how about keeping an inexpensive 'marine/leisure' battery around to stick on there for the winter?

SCSJeff
Member
# Posted: 31 May 2022 09:32
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Quoting: gcrank1
SCSJeff, how about keeping an inexpensive 'marine/leisure' battery around to stick on there for the winter?


Maybe... But, I have the battery inside a dead chest freezer inside my shed. I'm thinking I can setup a 12v heater on a temp controller inside there and that will be enough. But, I'm going to wait and see just how cold it gets in there once the battery is being used.

Worst case, I'll bring the battery home (or even inside the cabin in a pinch) to charge

gcrank1
Member
# Posted: 18 Oct 2022 20:04 - Edited by: gcrank1
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Looks like winter is setting in early here.....I was so hoping for a long, pleasant fall but we are 'unseasonable cold'. And my wife is recovering from a total knee replacement so we arent making cabin trips, thus my 'cabin year in review'.
This past year I never did re-hook up any of the 6x102W panels in any config; discon'ed it all about a year ago, got the LFP's around the 1st of the new year and put into service asap last spring. Our winter afternoon trips were few. Rotating the 2 bats with home charging worked a treat. I think their internal BMS shuts each down well before the LVD of the inverter. The clue is typically when an led light shuts off for a bit (actually the inverter), rests, then comes back on. If I discon the bat then there is no trouble re-starting the BMS and the recharge. Iirc that all happens about a 12.8/12.9 volts under the load. Let the bat rest and the voltage rises a bit.
If I just swap bats at 13.0-13.1v it is seamless. There isnt a lot of Ah's under 13.0 anyway, unlike the Ah's per 'tenth of a volt' above that.
Im pretty much shooting for about an 80% use, not going below the bottom 10% or trying to even recharge the top 10%. (though it may be more like the bottom and top 5%?). The learning curve wasnt steep with the help of those with experience here and over at diysolarforum.com, especially Steve_S.
I doubt the BMS is even registering a total 'cycle' the way I use them; they should outlive me (headin toward 70).
Getting rid of the pain and suffering of LA was a good thing for me! And if starting anew I would seriously consider going 24v right off; the downside is you have to get more expensive 24v bats and a low-freq 24v inverter. Many/most? 12v LFP cannot just be hooked up in series like LA to make 24, the BMS's cant take it (think feeding your computer with dbl its design voltage). LA's are Dumb, LFP's are Smart, some smarter than others though.
Not a deal breaker for me as is because I can/do put the LFP right in the living quarters with the PSW inverter feeding currently to the outlet and lights circuit.
KISS Principle. No need to have them remote, close to array and SCC, as with LA, inverted to 120vac there to be able to make the long 100ish' run to the cabin.
As the commercial used to say (havent seen it in a good while),"Just Do It".

paulz
Member
# Posted: 19 Oct 2022 09:37 - Edited by: paulz
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Quoting: gcrank1
If I discon the bat then there is no trouble re-starting the BMS and the recharge. Iirc that all happens about a 12.8/12.9 volts under the load. Let the bat rest a bit and the voltage rises a bit.
If I just swap bats at 13.0-13.1v it is seamless. There isnt a lot of Ah's under 13.0 anyway, unlike the Ah's per 'tenth of a volt' above that.


This morning mine are at 12.9 with a 5A load, first time I can remember being under 13. I know they are safe all the way down to 12, but as you say not a lot of time left in that range. Going to fire up the genny when it gets light out. They also get down to 12.6 while the 120A coffee maker runs for 15 minutes.

Could be that my 10+ year old Valence batteries are starting to tire, although I checked via the software and all are equal VPC. Sure hope they last awhile longer.

gcrank1
Member
# Posted: 19 Oct 2022 10:23 - Edited by: gcrank1
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During this summer's use I resolved to not use heavier loads after mine hit the 13.0v. The event that caused that was 2/3 way through an evening movie on the old tube tv with integral vhs player (kind of a hog). On that occasion I didnt have my swap battery along even though I knew the cabin bat was 'getting low' (duh). My ancient 'jump-pac' saved the movie, also could have the inv/gen.
Ive since proven to my satisfaction that using that 13.0ish threshold Im still good for led lights and usb charging for a good bit.
Yeah, hammer some amps back in Paul and keep on rockin

Steve_S
Member
# Posted: 19 Oct 2022 11:13
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Just a reminder. There are TWO Voltage ranges for LFP.

The Allowable Voltage Range is 2.500-3.650.
This is the voltage range that the cells can operate in without harm. "The Safe Zone"
For "12V" that is 10.0V-14.6V

The Working Voltage Range is 3.000-3.400.
This is the Voltage Range that delivers the AmpHours the cells are rated for. This is why everyone calculates LFP Battery at a Nominal Voltage of 3.200 Volts per cell (50% SOC)
For "12V" that is 12.0V-13.6V very flat curve

You are quite safe to have a Low Voltage Disconnect @ 2.700 Volts per cell / 10.8V. Note that if a heavy load is applied when the pack is low the voltage sag will be greater than if the pack is full. Most BMS' will allow a certain amount of time before triggering a Low Volt Disconnect (it's in seconds to accommodate surge pulls, like a water pump/fridge/freezer start surge and the like).

Because the BMS in an LFP Battery Pack is millivolt sensitive it's quite accurate to "itself". There is always a voltage difference between what the voltage BMS sees and versus what an Inverter or Charger see at their terminals. Line loss is part of life, every connection, switch, lug etc adds a little loss and it adds up fast... death by a thousand pricks, as it were.

I strongly suggest that you take a Voltage Reading at your battery pack Terminals and then at the Inverter Input Terminals and Solar Charge Controller out terminals to the battery (2 decimal accurate DVOM/DMM strongly suggested). Adjust/Compensate on the Inverter & SCC for the difference, so if the inverter is set to Low Volt Disconnect @ 11.0V (2.750 Volts per cell) that it really is 11.0V @ the battery Terminals.

Gotta say it....
The keep it between 10% - 90% Shtick is more about keeping within the "Working Voltage Range" as the bottom 10% is 2.500-2.800 (short lived cliff fall) and the top 10% is that (cliff climb) from 3.425-3.650

Hope this is helpful and clarifies a few things.

gcrank1
Member
# Posted: 19 Oct 2022 22:41
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Guess I'll just bite the bullet and see how many more hours I can get going down to 12.5v.

Steve_S
Member
# Posted: 20 Oct 2022 18:48
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LOL for me, I've always wanted to know what the "Edge Cases" are so I know what to expect if/When stuff happens.

Like a GAS Car, When I've gotten a new one (for me), I like to top it up and fill a 5 Gallon gas can and chuck that in the trunk, then drive it till it beeps/bleeps and finally runs out of gas to get an idea of just how much mileage I can figure on. But then I have lived in some pretty remote and sparsely populated areas and never wanted to get "stuck".

I even did something similar with my Solar Battery System to know what the real "bottom" is which might spook a few folks but where I am I hafta know ! Luckily I have a couple of generators, so it's a matter of powering one up and push 80A to the batteries... After that I increased my battery bank to give myself elbow room cause winter can be quite hostile at times up here. Like last year, I was Very Sickly and after 3 days of heavy snow, it was piled above my 4x4's bumpers and I could not manage the blower in that mess, a quick call and I had a snowplow arrive to make a path for me and get me dug out.

gcrank1
Member
# Posted: 20 Oct 2022 19:48
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Living into the wilderness certainly underscores the old Boy Scouts motto,"Be Prepared".
Im pretty content to stay off the very edges though I do like to know where the shoulders are and how wide and steep

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