Calibrating Voltage of your system to ensure Optimal Operations. SCC, Inverter/Charger, voltage matching.

[offgridwelder]

Pretty much all reputable resources and companies for the most part are roughly inline with one another as to the working range and limits for LiFePO4 cells, with some slight variations. There are a couple unique outliers like Winston or Battleborn which have their own quirks due to chemistry or some other factor, but that is the exception to the rule.

Your 'manufacturer' is giving numbers that are extremely out of sync with the rest of the industry (specifically the 51.3V = 100% claim) assuming they are LiFePO4 cells in a typical "48V" 16S configuration. You should ask them for documentation, ideally from the cell manufacturer that confirms the numbers they are telling you.

What @fblevins1 tells you is correct, it all comes down to single cell voltages, everything else is just an extrapolation of those numbers by multiplying by the number of cells in series (x4 for "12V" (12.8V) x8 for "24V" (25.6V) x16 for "48V" (51.2V). Because individual cell specifications are what matters most here, the most authoritative document with respect to proper voltage limits (in my eyes) is the spec sheet from the cell manufacturer. If you buy prebuilt batteries, it may not be possible to get this, but it is worth asking for, or at least asking the CS rep you are speaking with to confirm it themselves on the spec sheet or with an engineer.

Thank you so much for your detailed info. I will go and collect the infos so I can get to the bottom of this

 

[offgridwelder]

Let me see what the vague 3 page owners manual says...

 

[offgridwelder]

View attachment 82194

Thank you all who replied and thank you to the originator of this thread for letting me hijack it momentarily

 

[offgridwelder]

So now that I have that out of the way and we know 51.3 is full what voltage is 20 percent soc?

 

[offgridwelder]

Just a guess but I think BYD might be the MFR of the LifePO4 batteries used in the Rosen Powerwalls as they show BYD as a partner. If that is the case then the specifications for the BYD standard 3.2 volt cell exactly matches the original references given for a LiFePO4 battery, not the values given to him by Rosen Solar. But, since his is a powerwall (a nice one too) then who knows maybe they set some kind of limit (BMS setpoints?, do I even know what I am talking about?) I get confused because I never if the voltage values given are loaded or unloaded, or does floating value mean unloaded and if you do load it...how much of a load to need to give a reasonable state of charge. Ugggg.

Yes Id like to know this too lol

 

[Ampster]

Even if there were 15 cells isnt 3.42 per low ?

I charge my pack to a value of 3.45 per cell for longer life. More importantly the low end of 45 volts is 3 volts per cell which is also consistent to what my low voltage cutoff is set to. I see the manual says there are 15 cell groups in series.

 

[offgridwelder]

I charge my pack to a value of 3.45 per cell for longer life. More importantly the low end of 45 volts is 3 volts per cell which is also consistent to what my low voltage cutoff is set to. I see the manual says there are 15 cell groups in series.

3.45 is going to give increased cycle life?

 

[Ampster]

3.45 is going to give increased cycle life?

Yes, it is my belief that it is better than voltages above that. There is not much capacity above that with my cells. I presume that is a factor in why your cell manufacturer recommended that voltage.

 

[MrM1]

Yes, it is my belief that it is better than voltages above that. There is not much capacity above that with my cells. I presume that is a factor in why your cell manufacturer recommended that voltage.

Is that reaching and immediately stopping at 3.45v, or reaching it and letting it soak there for 45 minutes

 

[Ampster]

Is that reaching and immediately stopping at 3.45v, or reaching it and letting it soak there for 45 minutes

That is point that charging goes from Constant Current (Bulk) to Constant Voltage (Absorb). The charge terminates when current tapers to 25% of the CC setting,

 

[Steve_S]

LETS MINIMIZE HIJACKING !
From the LFP Assembly guide I prepped, located in the resources, link in my signature.

 

[Ampster]

LETS MINIMIZE HIJACKING !

Not sure you are referring to my post but I was responding to @offgridwelder , who had a 15S pack. The manufacturer recommended a charge voltage of 51.3 Volts which is 3.42V per cell. That is a bit more conservative than the 3.5V in your table.
At any rate, the poster's voltages would be different than your traditional chart for a 16S pack.

 

[Daddy Tanuki]

my guess would be either:

1. Something was lost in translation or possibly a misunderstanding by you, them, or both
2. Your battery 'manufacturer', or the specific sales or cs rep you spoke with doesn't have the technical depth of understanding to give correct technical information (bear in mind most brands, even those that imply or claim to be manufacturers don't actually design or manufacturer what they are selling).
3. Maybe these are 15S packs ("48V" for lifepo4 typically = 16S, but its possible they've gone with a 15S config maybe(?) which would make the numbers make slightly more sense)

Do you have a link to what you bought? Or to the documentation or datasheet?

I agree, but every time someone brings up poor translating, or even more so poor business practices on behalf of the Chinese suppliers one gets chastised and banned for two or three months. Makes one ask a lot of questions.