LiFePo4 battery users

[Ticklebelly]

...a BMS in a lithium battery is for everyone that uses them.

When BMS is used as a generic term, I agree. The trouble with the generic use of BMS is the same one we see when people talk about cycles. The term covers a range of descriptions and definitions and nuance. A BMS can be such as installed in commercial offerings of the so called Drop In products. The BMS in those products use hardware and AI oversight to control software to manage charge, discharge, and cell balance. At the other end of range of descriptions of what is a BMS, a DIY Lithium installation can use dumb devices at the front and back end and user uses wetware to decide things like charge and discharge stop points and capacity to be used as well as checking if the cells need a manual balance.

A BMS in a lithium system needs to be a bit more sophisticated than the older tech multi-stage chargers for AGM technology.   Low voltage stop points in AGM systems are often as simple as the integral low voltage protection in the fridge

[tx2sturgis]

Well, sure, it could have a very broad definition, but my reference is to the typical drop-in RV style LiFePo4 batteries, such as Battle Born, Bioeno, SmartBattery, Trojan Trilliums, etc. 

Those are the style and type that are more likely to be bought by van dwellers and RVers, and they generally include a built-in battery management system. 

DIY lithium systems with no BMS or a DIY BMS, are subject to a variety of solutions, and/or issues, so they are hard to generalize about.

[justjim]

I have been in the process of installing three 100 Ah lifeblue batteries. The reason I suggested them is that they have blue tooth. Each battery can come on the app and show exactly how much capacity each has. No more useless amp counters.

[tx2sturgis]

Each battery can come on the app and show exactly how much capacity each has. No more useless amp counters.

That sounds like a good idea...one of the issues I have with my BattleBorn is that it's a guessing game as to how much capacity is left after using it for awhile. I have seen some large LFP batteries that have a small LED 'gas gauge' built-in.

[Wayne49]

LifeBlue BT app looks cool. Useful tech.
https://www.lifebluebattery.com/smart-co...index.html
Bookmarking LifeBlue.

[sternwake]

I kind of decided years ago to wait on the fence and see how the Lifepo4 knowledge and lifetime expectations played out. Did the same for Carbon Foam AGM. The research I did back then on Lifepo4 was kind of limited and much forgotten, so this thread has been helpful.

One of the reasons I have not pursued lithium further, is I have LEad acid down pat, and can achieve excellent longevity. I'd have no problems getting another NorthStar AGM and living from 90 to 100Ah of total battery capacity when my existing battery is too compromised to keep using, whenever that will be.

But I also think of 100Ah of prisimatic Lifepo4 cells. I manually control the voltage of each of my charging sources and have nothing to yell at me if I overcharge or overdeplete now. But then again lead acid is forgiving of a few aim at foot and shoot incidents regarding overcharging or overdepleting. Overdepletion has pretty much never happened unintentionally. The times I was sub 11 volts were intentional and monitored closely. Unintentional Overnights all night at 14.7v have been frequent though.

I think I would be OK being a human BMS with lithium, the main issue would be to lose the' get it full quick, keep it full often ' mentality I developed with lead acid. if i were going lithium i would probably intentionally use more KWH just to insure I ws not in danger of overcharging.

Anyway, I appreciate those with experience with these batteries sharing their knowledge.
Keep this thread going.

How about some bottom balancing talk.

I imagine each cell having its own 3 decimal voltmeter. What process is used to bottom balance manually?

[RoamingKat]

Sternwake....I have discovered that I am so anal that I know the state of my battery every moment.
I know a couple of lithium users that choose battle born because they never pay attention to the battery and they do not want to ever be bothered. (They run the electric heat all night and just let the BMS shut it down whenever it is drawn down so far the system has to protect the battery.)

So, the battery chargers that I have (solar and other) have limits set to prevent over charging. So that is not an issue. I am so intune with the draw on my batteries that I usually never have let it get down past about 50%. (I tried to charge an electric car with my house battery one time...dropped to about 40% and almost melted a cable besides).

Temp is set on two relays. They turn on heat or fan. Plus ring an alarm. Mostly that is for overnight protection. I have never set off the alarms yet. If it ever came to it, I can shut off everything with a master switch on the positive side of the battery. Since I do not have to,be concerned about out-gassing....The batteries are inside with me. So heating and A/C to suit me also is good for them.

Balancing is done...first the bottom cell balancing is done internal by the type of battery I purchased. (I would guess that most people are not going to assemble the individual cells themselves). The balancing between the batteries is done by 4 external balancers that are wired to each battery and then wired together. I have 16 batteries....3.1V X 100 AH. Wired to create first 12v X 100ah battery...then in parallel. This makes up 12v x 400ah. Only time I use much of that is running A/C. Which I can do for about and hour and half at night when it is really too hot to sleep. Even the electric heat doesn’t use that much....mostly because I am not in freezing temps so I don’t need to run heat much in the morning

So, that leaves the only unanswered question. How much is too much when talking about the batteries being full over time. Right now, I turn off the solar panels for a day every other day. I do not know if that is enough. When I run the AC I have all my solar panels deployed, so I do not worry about that because of the large draw down....but the rest of the time I feels like my batteries are full almost always if I don’t disconnect charging. A chart with time on one axis and degree of full on the other would be a awesome diagram to have! Right now it is a guessing game.

[sternwake]

Thanks. I had not thought about temperature alarms.

I've little interest in drop in/ plug and play/automatic anything, as that seems to take all the need to learn anything , from the system.

i can see the appeal for those who do not want to think about such things, but that is not what I want, nor do I want to spend extra for it.

If my electrical needs stay the same, then if I can expect 5.5 years from another 350 dollar lead acid AGM and not have to change anything, well thats fine too. But then I gain no experience with Lifepo4.

[Ticklebelly]

I started playing with LiFePo4 when I bought A VW van to convert to a campervan. Serious interest in weight minimisation and flexibility in charging arrangements pointed me towards small, and light, and quick charging, batteries. My Pb stuff is still working in a Caravan and an off-grid arrangement in a shed. I expect to be able to donate the Pb batteries to a deserving cause long before they run out of life.

Staying active mentally and especially learning and retaining new information, is one strategy I have in place to stave off cognitive decline and possible descent into dementia.

[sternwake]

Ok for discussion purposes, how fast can Lifepo4 be fully charged, even though it need not be fully charged?

My AGM I can get to 80% (from just about any % under that) charged in under an hour, it is just that 80 to 100% which took about 3.5 hours when new, is now around 5.5 to 6 hours now at close to 5.5 years old and 1000+ deep cycles. I've no fear of taking my AGm down to 20% SOC and have done so over a hundred times, and it has still been able to start my engine when that low.

I think the whole lead acid 50% rule is a bit whack with people believing that deflation below that level is instant or near instant death. As long as it is promptly and fully recharged afterwards i have seen no degradation by drawing down to 20% vs 60% and the total lifetime KWH hours the battery provided are likely little different, they are just accumulated in fewer total cycles

Regarding weight, in my own system, I have no additional battery. The one group 27 AGM does both engine starting and house duty, Although i could fit three group 27's total, I just do not need that much capacity at present and it would be a waste of fuel to carry around another 120 Lbs of battery. The original starter battery is supposed to be a group 27 with no less than 550 CCA. These can weigh as little as 52Lbs. My AGm-27 is 68Lbs.

I guess I could eliminate 35 to 40Lbs of weight with 100Ahof Lifepo4 compared to a single LEad acid AGM 27. 100Ah of Lifepo4 must have pretty incredible CCA figures, if they were ever tested for that. When new my 930CCA AGM spun the starter motor scary fast.

One of the data points I use to judge Lead acid battery health is how low the voltage falls when cranking the engine when overnight cold both when i've been floating all night or dischared the regular 25 to 45AH each night.

Anybody ever use Lifepo4 for engine starting. Does the voltage still stay flat even under the ~140 to 180 amp load?

When new my Agm was staying over 12v during cranking, now if fully charged it stays over 11.0v, but I've seen it go into the high 8's when 65Ah from full. It does not sound like the starter is struggling when it falls into the 8's.

Makes me wonder just how bad regular starting batteries are in daily drivers are when their owners hear the dreaded click click. So many of those daily driver owners a month earlier would likely say the battery is 'still going strong'!!

I have the 18Ah mightymax '600 watt' stereo battery (ub12180) for jumpstarting when that becomes necessary. That battery alone can just barely start my engine in 80F ambients. I estimate it has 170 CCA.