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gcrank1
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# Posted: 25 Apr 2025 06:03pm
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12v, 100ah x2, I swap out as needed (no charging thus far on site).
I charged it up from the winter lay-up in home basement, let the Meanwell power supply run at 14.2 for more hours than I have before (Ive been just 'topping up' at 13.8). My thinking was that even though Ive used these for a couple seasons (fairly light use) that they maybe could use a good balancing charge.
I put that battery in service maybe early March? for our occasional day trips. We run the 1 ceiling fan on low to mix the air from the heater throughout the space. After each visit when I shut things down I take a look at the bat voltmeter. As of yesterday I figure we've run the fan (nothing else) for about 10hrs total and that bat still is reading 13.3v before actually having a rest!
This is better than Ive seen before 
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paulz
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# Posted: 25 Apr 2025 06:21pm - Edited by: paulz
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Nice! Yeah my Lfp bank has been doing great too. I’m on solar though, and the increased April sun has kept me at 13.3. Great to forget about battery and worry about other things.
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gcrank1
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# Posted: 26 Apr 2025 01:30pm
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Ive been reading up this winter about 'top balancing' (mostly over at DIYSolar forum) and it sounds like some (most?) BMS's dont start balancing until 13.8ish (for a 12v bat). The 14.2 I set the Meanwell at wont hurt an LFP though I do monitor the charging pretty close. Iirc it got up there and the amps had fallen way off but I still let it run for about another hour.
I brought it up so anybody that thinks their bank maybe isn't as strong as they think it should be might consider this.
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paulz
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# Posted: 26 Apr 2025 04:55pm
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Quoting: gcrank1 I brought it up so anybody that thinks their bank maybe isn't as strong as they think it should be might consider this.
Yes, good info. My bank never gets past 13.8 on the solar. On the charger it will get over 14 if I run the genny long enough, but it’s been about 2 months since I last did that, probably wouldn’t hurt to do it again.
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MtnDon
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# Posted: 26 Apr 2025 08:59pm - Edited by: MtnDon
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Quoting: paulz My bank never gets past 13.8 on the solar.
I have no idea what your solar setup is, so this may be a dumb question; what is the solar charge controller absorb voltage setting?
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paulz
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# Posted: 26 Apr 2025 09:51pm - Edited by: paulz
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Ha, glad you asked. Just checked my notes (I’m at the house until tomorrow), I have it set at 13.8. Used to be higher but after a long thread here on ‘Li Battery Charging’ I cut it down. May have been thinking that 3.5 volts per cell was the practical limit, or there may have been something else said.
13.8 is what it’s been at when I arrive lately, before any output. It likely sits at that for several days I’m not there.
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MtnDon
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# Posted: 27 Apr 2025 12:00pm - Edited by: MtnDon
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I guess if it works, it is good. Charging to 13.8 goes against what I have been told and what I do, but like I said, if it works, I guess it is OK.
With help from two engineer friends, John & Dave, we built several 24 volt 200 amp LFP batteries about 9 years ago. CALB cells and a BMS. They have cabins nearby and work for a global electronics firm and have contacts in China. I built the containment boxes and they supplied the technical expertise and sourced the parts direct from China.
We use an absorb of 28.8 volts (equiv to 14.4 on a 12 volt system). Float at 27.6 (13.8). If we did not charge at the higher voltage the BMS cell balancing would not kick in. The BMS has a display and lists each cell separately.
That battery still works great and has run nearly constantly since summer 2016. I can't be hurting it too badly. It powers the security cameras and Verizon data link 24/7 all year, plus the weather station.
So, as the subject line states, I too am "Feeling Good about my LFP"
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Steve_S
Member
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# Posted: 27 Apr 2025 12:38pm - Edited by: Steve_S
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Below is my recommended Solar Controller / Charging settings for LFP.
Steve's Recommended SCC settings
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gcrank1
Member
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# Posted: 27 Apr 2025 05:13pm
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I should mention that my Meanwell setting is at the power supply terminals, Not at the battery. The bat wont read the set voltage until it is charged up to that point.
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paulz
Member
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# Posted: 27 Apr 2025 07:00pm
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Thanks Steve! Glad you’re still checking in.
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paulz
Member
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# Posted: 27 Apr 2025 10:13pm
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Quoting: gcrank1 I should mention that my Meanwell setting is at the power supply terminals
My Meanwells are also set above 14. There output amperage seems to be less the lower the voltage setting. With solar no problem, peace and quiet, but genny makes a rackey, not to mention fuel use.
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Brettny
Member
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# Posted: 28 Apr 2025 07:19am
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You cant go by voltage for SOC on a lithium battery. It's really a bad way to get SOC for a flood cell battery also. I thought it was a decent way until I got a battery shunt meter.
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gcrank1
Member
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# Posted: 28 Apr 2025 08:19am
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Doesn't the shunt meter only show you amps/watts in and out? I think I can see how that's useful if you have all balanced cells in the bat and have it start at a full charge then cycle regularly so you get a feel for it.
In my case I dont think I ever really got the bat up to a full charge, perhaps a runner cell hit the HVD in the BMS and stopped the charging? After using/cycling the bat the past couple seasons I think the cells may have balanced pretty well on their own and this 'top balance' Ive done seems to have really topped up well.
IF I put on a meter now and tracked capacity, from say 98%, it would be meaningful but not if the bat only ever got to 80%.
I dont know how I could get a bat to full charge without using voltage.
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Steve_S
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# Posted: 28 Apr 2025 08:49am
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Not all "Smart Shunts" are the same, it all depends on their resolution and what they can read. Some will not read anything below 0.5A, while most others may do 0.3A and the best doing about 0.1A (bigger bux there) and what corrections / offsets they can handle. Shunt placement is also a factor, because it needs to be able to ready "everything in/out" and account for device losses & inefficiencies. The way the majority of SmartShunts handle this is by resetting when attaining true 100% (determined by Volts & Amps taken by batt) which can remain valid for typically 2 cycles if 100% is not reached, after which the cumulative losses skew the SOC readings.
Lithium Based batteries cannot really be compared to FLA or other chemistries (not even Sodium) as each chemistry family has it's own personality you might say.
A Quick View at Pack Voltage will give you the "standing SOC" at that moment, which will be affected IF there is charge incoming or discharge going on.
As you all know, I run a respectable bank of LFP. Over Winter they rarely hit 100% and only if I run the genset to top them off but will hit 80% or so just on solar without huge problems. Come spring when Sunhours go up the Solar can bring them to 100% and into Float allowing the packs to internally balance the cells & cross balance between the packs in the bank.
The first few times they hit 100% & goto Float, most packs will be imbalanced internally by about 0.100-0.150mv which is fine and totally expected. Now after 3-5 times of doing so (pends on pack), by the time they reach Float they are typically at 0.010-0.015mv difference and the active balancer levels them all to 0.005mv internally and across the packs as well. After a month of reaching "natural" 100% & Float they all hit 100% & enter into float with only 0.007-0.005mv difference. THIS IS CONSISTENT !
My Smartshunt (WizBangJr from Midnite Solar) is quite accurate once the cells & packs are reaching full & proper 100% after March but in winter from end of Nov to end of Feb it's a "good close guess".
SOC from Voltage works and is accurate IF the cells have been charged to the set 100% Voltage and the amperage taken by pack has dropped to 5% of rated AH Capacity, because at that point the cells are properly saturated.
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gcrank1
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# Posted: 28 Apr 2025 09:09am - Edited by: gcrank1
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This bat was resting at 13.4v since the charging, I take it as a good sign as close enough to 100% for me
Ive been swapping the bats out at about 12.8ish as it keeps me in the good operational 'juice' for whatever we do.
End of last season I messed about with a little 200W pwm pair of semi-portable rigid panels (gifted me by a friend from his RV project), have the correct cords to hook to the big lfp's or my little Ecoflow River2. Maybe this season I'll hook up an lfp after one day/night use and see how much I get for a charge of a good day.
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paulz
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# Posted: 28 Apr 2025 12:06pm
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All this talk got me to plug in my old laptop (windows 7!) and have look at my 4 LFPs, which have been working great. This is what they read, 9am, tv on, inverter, wife peddling away on her stair stepper thingy, fridge on.
Looks ok to my blurry eyes, except one battery shows .01 current and the others .5-.9. Don’t know if that means going out or coming in. Solar monitor says 5 amps coming in.
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gcrank1
Member
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# Posted: 28 Apr 2025 12:43pm
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I think Im glad I dont have all that stuff to look at....
Making sense of solar electricity coming in at the same time as power going out to various devices seems more than a little confusing.
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travellerw
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# Posted: 28 Apr 2025 01:05pm
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Quoting: gcrank1 I think Im glad I dont have all that stuff to look at.... Making sense of solar electricity coming in at the same time as power going out to various devices seems more than a little confusing.
Victron BMV-700. Its a little spendy at $130USD, but well worth it. Its a simple "one pane of glass" interface into your system. I have said it before, but I would not build a system without one.
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paulz
Member
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# Posted: 28 Apr 2025 02:57pm - Edited by: paulz
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Couple of things about my last post/images. First, the bat that showed .01 current again had a loose terminal. I swear, the dog must be going over there at night and messing around. Tightened it up, all currents now close to matching. Then I turned on the microwave oven (some leftover beef stew for lunch but that’s beside the point) and current values went up to 24 per battery, so that is amps out.
This is all 20 year old technology, came with the Valence batteries. Haven’t pulled it up in a long time, usually just read the charge controller panel, but glad I did this time. Darn dog.
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Brettny
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# Posted: 28 Apr 2025 03:37pm
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Quoting: travellerw Victron BMV-700. Its a little spendy at $130USD, but well worth it. Its a simple "one pane of glass" interface into your system. I have said it before, but I would not build a system without on
I have something like it. Just no physical gauge, only the app. It shows 100% full. It can also show Amps, battery voltage coming in/out but more importantly it shows a graph for any of the above for the last 30days. It showed me that at some specific SOC it only takes 2hrs to charge my system.
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travellerw
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# Posted: 28 Apr 2025 05:13pm
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Quoting: Brettny I have something like it. Just no physical gauge, only the app. It shows 100% full. It can also show Amps, battery voltage coming in/out but more importantly it shows a graph for any of the above for the last 30days
With LFP that is all you really need. Just the ability to see the ins/outs.
However with FLA that is where the BMV-700 is king. Victron has worked very hard on the algorithm to ensure accurate charge percentages. FLA is not very efficient and requires complex math to accurately show its charge percentage (you can't just count the ins/outs). If you are bored and want to be confused, lookup Peukert's Exponent sometime.
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jsahara24
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# Posted: 29 Apr 2025 08:12am
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My eco-worthy 12v-160ah LFP comes with an app built in, very nice feature....Can see percentage of charge, watts coming in, watts being used, and how long the battery will last with the current use...
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gcrank1
Member
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# Posted: 29 Apr 2025 08:18am
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Pretty slick J
Paul, I think its a good idea once a year to pull, clean and reinstall all those connections to avoid surprises.
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paulz
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# Posted: 29 Apr 2025 10:39am
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Quoting: gcrank1 Paul, I think its a good idea once a year to pull, clean and reinstall all those connections to avoid surprises.
Right. And my batteries are interconnected by individual short crimp terminal cables. Remember I did this when we were all children. When I bought new bats last year end, a friend gave me enough of this thick bar stock to make bus bars, but with the old bats still hanging in there I not messing with it till I change them. At least your thread here got me to pull up the valence software one more time and discover the loose bolt. To be honest it probably wasn’t the dog, I’m always testing some new 12v gadget by taping into those bolts.
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