My AGM to Lithium conversion

"If" someone is getting lvd from the battery pack while using with an inverter or without what comes to my mind...

1. Why isn't there away to see SOC to know you're getting low?
2. Is the battery pack undersized for the task at hand.
3. Are they using economy lfp dropins with just poor quality cells or components inside.

From my experience when my SOC gets down to 25% (DOD 75%) which is always in the morning if it happens after making a couple pots of coffee, using the microwave for 5 minutes making breakfast the inverter will show 12.2v, I have a decision to make. Will solar be enough to carry my daytime loads and charge the batteries to aleast 65-70% by dinner time or should I throw the eu2200i on for an 1-2 hours for a hold over charge later in the day after solar has done as much as it can. All this is done by the ability to see what the system is doing either on the battery display or the Magnum ME-ARC display. It's not rocket science but a little proper planning in the build or revamping of the batteries will prevent piss poor performance. ;)

I believe BFL13 you're having a hard time wrapping your head around this because you've only experienced dead lead chemistry and it's poor voltage sag and the need to charge them full asap or "lose" life expectations from said batteries and transferring those poor attributes over to lfp chemistry.

3 Tons wrote:
Lots here to do over nothing’ comes to my mind

Pretty much except it appears the ones questioning do not have hands on experience,just reading,which is fine..You have your examples and I have mine and other lifepo4 users have there's,which have been posted time after time,apparently going in one ear and out the other, to some..

I actually found and find actual user reports here very helpful and why I ask questions from time to time...To many conflicting answers on the net, especially in reviews...The few here with lifepo4 actual experience,are very helpful to us newbies without as much experience or hands on...

Itinerant1,

A bit off topic, but how often does the generator get used? Once a month? more? less?

No hard time here. It is from experience with inverters I wonder how it plays near BMS cut off even 10.1 is near inverter 10.5 and those would be as loaded Vs.

Itinerant1 does as expected by staying well above the low knee using his monitor.

I am curious what readings people are seeing who do dance with LVD

Another thought- the LFP is seeing a loaded voltage at its posts Does the BMS with its wiring see the same loaded V?

As for the snide remarks- tasks involving rolling doughnuts come to mind.

More ‘real world’ (to bring from the theoretical, OR to bypass more ‘lead acid-centric’ misnomers…lol!)…

Yesterday, on the Oregon Coast (mid-state, cloud free), the 660w of rooftop solar was harvesting mid-day just over 30amps….So with the higher recovery rate of LFP, and per our typical usage pattern and with heater running at night, this 1 hr of passive charging at 30a generally meets or exceeds our daily power consumption…But we don’t always experience a cloud free day on the OR coast, right??

Here’s a cut & past email I sent to a pal a few days ago upon our arrival:

(Note, that this is shortly after adding another 220w of roof-top solar to the existing 440w, and SOC’s relating to the 400a/h LFP…)

….Left CG this morning about 10 miles south of Grants Pass enroute to coast, about a 2.5 hr drive…Rain and intermittent drizzle with occasional clearing to Low cloud cover, occasional openings of blue sky as we neared coast, typical day in Oregon, not the best time for harvesting…Was between 60-61% SOC upon departure, and upon arrival, but nevertheless, upon our arrival was at a whopping 75%SOC!!…This represents nearly 30a/hrs in just 2 1/2 hrs - 660w is a lot, but Judging by the WX, I would not have thought this result even possible - needless to say, I’m very pleased with this discovery!!

3 tons

BFL13,

The li capacity rating is done by discharging at 0.2 c (20 amps on a one hundred amp-hour battery). The battery management system prevents over discharge by saving a "seed" voltage. BMS also limits demand.

A good BMS monitors each cell of the battery. So what happens at the posts doesn't matter much.

Most folks don't realize the lead acid batteries are only rated at 25 amps draw per 100 amps of storage. Exceeding that creates extra voltage drop. The more one exceeds it the greater the drop.

The microwave draws about 190 amps. So for GREAT service I would need 8 100 amp-hour jars. I got around that by having 7 125 amp-hour batteries, as there was not space for 8.

The exception for lead acid is SiO2 which can do up to 400 amps continuous on a 100 amp-hour jar. I don't have any voltage drop data on them.

As far as LVD’s go, it makes perfect sense that a reputable product might have one, but (now back to ‘real-world’ application), in routine usage it would be kinda difficult for me to imagine (short of an ‘operator error’ caused ‘outlier event’…) the likelihood of a Low Voltage Disconnect - As a former Lead Acid fella myself (having experienced an occasional LV inverter alarm - ugg), I should be a bit more empathetic - Upon reflection, I do now kinda get BFL’s worrisome hand wringing (e.g. a lead-acid user’s paradigm )…

3 tons

It's pretty interesting how sometimes even truly experienced people do things differently like battery reviews,for example...Will Prowse said Chins /Enjoybot and Zooms were clones after his tear downs of all three but this guy tore down the Enjoybot and Zooms to find them quite different and even tore down the BMS..BMS cut off 9.88 volts...

Good video with BMS tear down

pianotuna wrote:
Itinerant1,

A bit off topic, but how often does the generator get used? Once a month? more? less?

It gets used mostly during Nov-Feb, I'll average 12-18 times in a year for 2 hours max run time so 36 hours average +/-.

I do use it at times with the air conditioner for the long hot days and when that happens I'll split the time with batteries/ solar, for instance yesterday it started getting warm in the trailer around 1130am batteries SOC was at 75%+/-, the ac was set at 75f and cycled throughout the day. By 3pm or so the batteries did get charged to 96% soc but it was getting warmer and lowered the ac to 73f which kept it running more constant by 5pm the soc was down into the 70% range so started the generator to carry the air conditioner and let solar throw the balance of the day into the batteries. By 7:30pm I turned generator off reset air conditioner to 75f it cycled a few time till 10pm off batteries and stayed off after that. This morning soc was 55%. Solar production is pretty good and the batteries are showing 70% right now and I have made 2 pot of coffee, made breakfast using the microwave, toaster and have a ice machine going besides the humidifier, laptops recharging small batteries for hand radios, flashlight.

More than you asked just trying to give a real usage of gen/ batteries.

Edit: I should add that I use my batteries in long partial soc ranges and not worry about getting back to 100% soc. 40 days is my longest run before getting back to 100%, 7-14 days is about average during poor solar production months.

Solar production #s

Are those operating from zero to full SOC not hitting LVD at "zero" ? Why not? It is all very strange. What is "zero" is the mystery in that case.

PT- seems LFP rating is done different ways then. I saw where it was done at 1C. The 20 hr rating was then stated as the same given no Peukert

FLAs have various rating by convention for type of battery. Starting vs Golf cart etc. AH and RC. No news there.

LFP capacity is confusing especially when they use watt hours and what is remaining capacity wrt SOC vs using AH and remaining capacity. We did all that in past threads. That engineer's speech that was linked on here explained how they sort of fudged where half way down is between watt hrs and amp hours.

The OP in this thread does have a clue and a monitor, so he might or might not be interested in this other stuff.