My AGM to Lithium conversion

[Rbertalotto]

Here is a quick article I wrote on my adventure going from AGM batteries to Lithium.

http://rvbprecision.com/rv-projects/rv-lead-acid-agm-to-lithium.html

http://rvbprecision.com/rv-projects/rv-lead-acid-agm-to-lithium.html

[3_tons]

jaycocreek wrote:
0% state of charge or LVD..I have not taken a 100ah LFP to shutdown,I have taken a power station with LFP cylindrical cell to shut down to calibrate the screen..I have only read that taking a normal 100ah or whatever LFP battery down to BMS shut down,requires some TLC to get it back running like a charger that does that or jumping it off another 12V battery,even a car battery..I have been in the 10+ volt range and shut it down myself,checking on battery capacity..


I have no idea what the manufacturers call 0-100% and the 2-3000 cycles doing so..My last battery came with a voltage chart for it(yes we all luv the charts..LOL) but it shows 10.8 as 1%(9.5V 0%) and the recommended shut off..Do they mean let the BMS shut it down for the 0-100% or really close too?..Seems letting the BMS shut it down could be a pain..

Is this merely a hypothetical exercise (pondering the outer batt limits?), or are you in someway concerned about exceeding it’s limits and activating the LVD??…Maybe I’m confused, but IF it’s the latter (though, as with FLA’s I don’t know why one might purposefully do so??), since you already have a competent shunt-based Victron, why not just do an actual load test? This would also inform you as to your actual a/hr capacity upon disconnect, and (assuming you have an inverter…) of potential low voltage alarms…Just saying…

3 tons

[time2roll]

BFL13 wrote:
Another thought- the LFP is seeing a loaded voltage at its posts Does the BMS with its wiring see the same loaded V?

The BMS has sensing wires direct on each of the individual cell terminals. That is all it knows or cares about. If there is undersize wire to the inverter the voltage could be significantly different. BMS does not care if the inverter shuts down for low voltage.

[jaycocreek]

0% state of charge or LVD..I have not taken a 100ah LFP to shutdown,I have taken a power station with LFP cylindrical cell to shut down to calibrate the screen..I have only read that taking a normal 100ah or whatever LFP battery down to BMS shut down,requires some TLC to get it back running like a charger that does that or jumping it off another 12V battery,even a car battery..I have been in the 10+ volt range and shut it down myself,checking on battery capacity..


I have no idea what the manufacturers call 0-100% and the 2-3000 cycles doing so..My last battery came with a voltage chart for it(yes we all luv the charts..LOL) but it shows 10.8 as 1%(9.5V 0%) and the recommended shut off..Do they mean let the BMS shut it down for the 0-100% or really close too?..Seems letting the BMS shut it down could be a pain..

[Itinerant1]

Not sure. Maybe typing in thought and something got left out at the fingers. I do that sometimes.

[BFL13]

Itinerant1 wrote:

BFL13 wrote:
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....

What are you calling zero? SOC zero% = what ever the bms is set for whether 2.8vpc or 11.2v battery pack? If you mean zero voltage... well good chance it's a cooked battery.

You will have to ask jaycocreek what he means by zero for any clarification on that

jaycocreek wrote:

Never quite understood the need to only use 80%of lifepo4 batteries when there advertised to get 2-3000 cycles at 100% discharge and 10 years service life then you still have 80%capacity after that.,0..That's 5X the average flooded battery and under $400 in some cases....

If I was back full timing, I wouldn't hesitate to use 100% of my lifepo4 batteries..But I'm pretty careful now not to go below 50% on my remaing AGM..lol

[3_tons]

“Caution, Now Entering the Minutia Zone”….lol

3 tons

[Itinerant1]

BFL13 wrote:
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.

What are you calling zero? SOC zero% = what ever the bms is set for whether 2.8vpc or 11.2v battery pack? If you mean zero voltage... well good chance it's a cooked battery.

[3_tons]

“ 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.”

As previously stated, this is why a ‘person of interest’ might be inclined to perform a simple load test…Either way, I suspect (admittedly, based on my own example…) that the typical drop-in LFP’s actual capacity (whether parsing w/hrs or a/hrs - most know that V varies…) may be somewhat greater than it’s advertised capacity…Just my guess, but in practical application (for the non-nerdy types) from my perspective, I see this of little concern..

3 tons

[BFL13]

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.

[Itinerant1]

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

[jaycocreek]

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

[3_tons]

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

[pianotuna]

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.

[3_tons]

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]

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.