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]

About a week ago I heard a report relating to certain parts of southern Calif, where some folks with plug-in hybrids are no longer plugging them in because it was actually cheaper to buy gas which seems a very disturbing trend - is ‘California Dreaming’??

https://www.eenews.net/articles/surging-electric-bills-threaten-calif-climate-goals/

3 tons

[pianotuna]

time2roll,

If one is returning home--the charging would certainly allow maximum range to be used, as that's where the majority of charging happens. So the majority of the time nearly 100% range is quite possible.

The ionic 5 now can do 100 k (60 miles) of charging in 5 minutes, assuming the "right" charging station is available.

[time2roll]

I see this like an electric vehicle. Almost impossible to get maximum range as it would require a charging station right as the battery is fully depleted. So while it is perfectly fine to go to zero it becomes rather inconvenient. If cutting it so close just run the generator already.

Very different from lead-acid as the user knows there is a significant toll for going down well below 50%. The only real issue with LFP it the full loss of power to go 100% discharge.

[BFL13]

Good info by itenerant1 and implied advice to other LFPers. Stay far enough above the lower knee and never mind about not using 100% capacity. Monitor!

[Itinerant1]

BFL13 wrote:
StirCrazy note that more solar will not save you if sky is overcast. LFP does not change need for gen as back up. Portable gen but not built in is also recovery method for LVD

So true all the extra solar does is allow you to run more items from it and give the batteries a break on the side line waiting for the coach to call them into play when needed while possible still being charged to some degree or after being charged and floating the solar is running the loads if you have enough solar to cover the loads. But when there are multiple days of poor solar or just use alot of power like I do it helps to have a backup plan for charging.

[Itinerant1]

BFL13 wrote:

time2roll wrote:

BFL13 wrote:
Some think it is ok to zero% and experience shut off--except this LFP brand's BMS cuts off higher than that at 5%. There is a lot of confusion over how far down is zero!

The prismatic LFP cells are 2.5 volts minimum x4 = 10 volts. However the cut-off is at the cell level so it would be incredibly rare to get all to 2.5 at the same time. Some might be 2.7 -2.9 but the low cell calls it done.

Scroll down a bit for the general specs. Bulk cells on Alibaba

A pre-made battery may allow cells a little beyond the range or a little inside. That is a warranty call made by the builder.

OK, so the monitor measures SOC based on total voltage of the cells, but BMS uses lowest cell.

If not been to 100% and balanced for a while like itinerant1 operates, what is the risk the monitor will not warn in time before BMS LVD?

And that is top balancing

The risk is dependent on the quality and the cells being equal or matched to each other. When charging and nearing full or discharging nearing the bottom of capacity of cells you could possibly have a "runner" meaning one can start to climb or dive in voltage, this is were the bms comes into play protecting the cells or battery. Also, if the cells weren't properly top balanced you could have a runner in a lower state of charge compared to the other cells in the group. Some folks are anal about having every cell equal in voltage at x.xxxv level I can say since day 1 mine have been with x.04 of each other and never worried about because it's close enough for me and doesn't trip the high/ low voltage at any time even when drawing high amp current items in a low soc. I can view every cell live time while they are all in constant flux of each other.

It sounds more confusing than it is. If you were to have one of these batteries and had the proper charging device/ safe guards in place they truly are a set and forget battery/ system or atleast mine has been.

[BFL13]

StirCrazy note that more solar will not save you if sky is overcast. LFP does not change need for gen as back up. Portable gen but not built in is also recovery method for LVD

[3_tons]

Jaycocreek said, “3 tons..Sorry for sounding snarky...I'm one of those guys that can't walk and chew gum at the same time..Being pushed on this end to go out out and bring in wood and posting here..Not well thought it out..lol”

No worries, in fact you may have even noticed, that I tend ‘to thrive’ on abuse anyways - lol…

FWIW, I think you’re strategy is definitely right on track :)…I would say that it’s kinda interesting how in-spite of the occasional ‘techno-wizard’ distraction, ‘these threads’ routinely end up revealing or expanding upon even more the attributes of LFP (though no perfect battery technology exist), Gotta give thanks to the OP !!

3 tons

[StirCrazy]

BFL13 wrote:

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

think for emergency reserve. when I did my Camper I set it up to normaly only use about 10% of the capacity per day. my reason for this is I am usaly using it around now and into november where I need my furnace and cloudy days are quite common. so in the event of crappy weather or a issue with my solar I could go aproximatly 10 days with out worring about it and with my solar I can regain about 4 days worth of power in 1 good day (well 3 days capacity at the end of that day. so if I ever got down to close to 0% SOC it would take me 3 days for the solare to bring me back up. when I add a microwave or what ever maybe Ill change things up and add another solar panel but for now this works for extended off season trips.

Steve

[BFL13]

time2roll wrote:

BFL13 wrote:
Some think it is ok to zero% and experience shut off--except this LFP brand's BMS cuts off higher than that at 5%. There is a lot of confusion over how far down is zero!

The prismatic LFP cells are 2.5 volts minimum x4 = 10 volts. However the cut-off is at the cell level so it would be incredibly rare to get all to 2.5 at the same time. Some might be 2.7 -2.9 but the low cell calls it done.

Scroll down a bit for the general specs. Bulk cells on Alibaba

A pre-made battery may allow cells a little beyond the range or a little inside. That is a warranty call made by the builder.

OK, so the monitor measures SOC based on total voltage of the cells, but BMS uses lowest cell.

If not been to 100% and balanced for a while like itinerant1 operates, what is the risk the monitor will not warn in time before BMS LVD?

And that is top balancing

[jaycocreek]

Another factor in cycle life is charge and discharge c rate. Go high, cycle life goes down. Go low, cycle life goes up.

Exposing the battery/cells to excessively cold or hot temperatures while operating at higher c rates will also reduce cycle life. Ideal temp is 75-77f.

Using a lifepo4 battery/cell, in any way, reduces its cycle life.

Pick your poison--lol!

Pretty much...It will take a 100amp charge but we recommend 20..lol..Anything to sell a battery..

3 tons..Sorry for sounding snarky...I'm one of those guys that can't walk and chew gum at the same time..Being pushed on this end to go out out and bring in wood and posting here..Not well thought it out..lol

[otrfun]

jaycocreek wrote:
When I first posted on this thread it was all 80/20 or 90/10 talk compared too...I simply mentioned why not use 100% as most manufacturer batteries have a cycle count for..Some people may choose to use it all or very close to it without harm...If a user needs 102ah,it's there for use without worry whether he trips the LVD or not... . . . .

These numbers are loosely based on a lifepo4 cell manufacturer's spec sheet I saw a few weeks ago. More to show cause and effect relationships than anything else.

Cycle life defined as number of xx - xx% SOC cycles a cell/battery can sustain before the ah capacity drops to 80% of its original rated capacity.

30-50% = 10,000 cycle life
20-80% = 5,000 cycle life
10-90% = 4,000 cycle life
0-100% = 3,000 cycle life

Another factor in cycle life is charge and discharge c rate. Go high, cycle life goes down. Go low, cycle life goes up.

Exposing the battery/cells to excessively cold or hot temperatures while operating at higher c rates will also reduce cycle life. Ideal temp is 75-77f.

Using a lifepo4 battery/cell, in any way, reduces its cycle life.

Pick your poison--lol!

[3_tons]

jaycocreek wrote:

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

When I first posted on this thread it was all 80/20 or 90/10 talk compared too...I simply mentioned why not use 100% as most manufacturer batteries have a cycle count for..Some people may choose to use it all or very close to it without harm...If a user needs 102ah,it's there for use without worry whether he trips the LVD or not..If I didn't put it on paper right,oops..lol

Not really into nit picking word games...

Thanks for the added clarity and for stating your worthy objective - seems then a load test may be in order (though it’s not clear to me how a follow-up enquiry constitutes word games, but that’s just me…)

3 tons

[jaycocreek]

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

When I first posted on this thread it was all 80/20 or 90/10 talk compared too...I simply mentioned why not use 100% as most manufacturer batteries have a cycle count for..Some people may choose to use it all or very close to it without harm...If a user needs 102ah,it's there for use without worry whether he trips the LVD or not..If I didn't put it on paper right,oops..lol

Not really into nit picking word games...

[BFL13]

time2roll wrote:

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.

Voltage at inverter lower than at batt posts, but idle thought was whether BMS voltage is too. Monitor reads batt posts. Trimetric lets you tune its voltage reading to match DVM reading at batt posts

Not a concern to be so accurate if staying well above lower knee but then you are not using full capacity.

Seems it is more about steering clear of LVD than longer batt life.