Schneider 6848pro..Voltage difference in SCP and lifepo4 battery JK bms

rroman1159

Greetings to everyone in the group...I want to learn about my renewable energy system...I have been monitoring my Schneider 6848 system because it has a lifepo4 battery pack and my JK bms installed. I have noticed that the voltage indicated by the SCP (54.4v) is not the same as that given by the JK bms (53.7v)..in the JK bms it never reaches 54.4v or 3.4v or battery..I wanted to know if there were some setting, through insight home, so that these voltages were similar. I measured the battery at its ends and the voltage it gave me was 53.7v, in the same way I measured the battery connection to the inverter at the end and it gave me 53.7v...thanks

Dave Angelini

It would be very hard (need Config tool and the talent to use it)  for you to get into XWP and change the DC calibration. Also the V cal is based on low, medium, and high power averages I seem to remember.

All that matters is your open loop BMS V set-points are correct.  Live with the SCP reading.

rroman1159

 Ok..thanks...zero what would be the most correct thing...

Dave Angelini

I do not use that battery and that is up to you to get it set right with open loop.  

hogback

You could fudge it too and calibrate the jk.  Of course it's wrong, but it would at least match!

twistedtree

I was never able to get this working satisfactorily when I had XW equipment.  You mention an XW6848.  Is that the only charging source, or do you have any solar charge controllers?  I had the same inverter plus two MPPT60s.  The first issues is that it was unclear which device's metering the SCP was reporting.  The 6848?  MPPT #1?  MPPT #2?  Nobody seems to know.  Also, it's unclear which device's metering is used to control charging.  Is the SCP voltage used, if we even knew what it represents?  Does the 6848 use it's metered voltage, and if so how does that compare to the SCP?  The MPPTs work in concert, but based on what metering?  All this makes it really hard to program any given device because you have no idea what offset is needed.

Oh, then throw in an AGS.  Who's reported voltage is it using?

Then of course there is the lack of remote voltage sense, so whatever each device is metering is impacted by cable voltage drop, and also (seemingly more significantly) by voltage drop internal to the device up to the metering point.

None of this mattered with lead batteries, but now with LFP it does matter, and I would argue that these devices just aren't up to the job.  I was never able to get mine programmed optimally, just close enough to live with.

Dave Angelini

The system voltage on these older XW inverters is what is used. It could be calibrated back in the day with the configuration tool that very few people ever bought to do the Calibration. The tool is also used to calibrate AC voltage which is critical to get the multiple XW's outputting the same power on each inverter.

One of the reasons XW pro was built was to not depend on voltage and use State of charge from a lithium battery BMS. Any BMS for that matter.
XW pro also added the needed memory that the old XW+ and greaybox XW needed to be future ready.  

The problem the OP has is that his battery company has not done the legwork (software RS 485) to get it's BMS data into the Schneider gateway for bi-directional control of 2 system networks. I think if you asked him is he happy, he would say mostly. Closing the loop would get real time voltage, Soc, temperature, and hours left at current rate into both networks. Gateway below on Insight Cloud.

hogback

I don't know if the current measuring devices in many of these bmss compare too well with a proper shunt like from schneider or victron.  I also never understood why a good tier 1 inverter/charger like the xwpro would not include a decent shunt built in, especially if the purpose of the pro was to allow soc control.  At the end of the day, the soc is reliant on the V to reset at 100%.  

hogback

My mppt60150s and the xw(+ in this case) are off by about 200mV. 

Dave Angelini

hogback said:

I don't know if the current measuring devices in many of these bmss compare too well with a proper shunt like from schneider or victron.  I also never understood why a good tier 1 inverter/charger like the xwpro would not include a decent shunt built in, especially if the purpose of the pro was to allow soc control.  At the end of the day, the soc is reliant on the V to reset at 100%.  

You have some problems in this post. I think you are mixing up open and closed loop.  In Closed loop with Schneider and others, there is no external shunt or bat mon. This circuitry is all internal to the battery internal BMS. 

 The reason the bat mon has never been built in is it requires proper calibration at the site and has been shown to be notoriously inaccurate over time. Also it would be a waste of money and another $500+ down the drain.

 More battery banks have been killed by  (any manufacturer)  a bat mon and it's shunt than is worth saying.   Probably 100's on this forum alone.

hogback

I understand.  I was just trying to point out that there is current measurement built in to the xw, and that I presumed that the reason one can't use this for soc control (not mentioning closed loop) is that the measurement isn't as accurate as one could get from the battery monitor shunt.  I use xw+ without any battery monitor (for the simpliphi 3.5s that are its dc source) as I think V control is fine in my off grid case.  I know full, and I know 'mostly' empty, just from V, which any shunt uses as well to reset to on the top end.  I've been playing with some jk bms with some other 'project' cells, and their soc resets to 100% at the top end from single cell V, and is user configurable.  As far as I know, the insight home/facility closed loop bms control has, until very recently, only used this bms-calculated soc as part of its 'closed loop' name.  mppt 'smarts' is only in the last firmware release, and I've not seen anyone demonstrate that this works for throttling charging as a function of bms information, which would be a good chunk of the benefit.  Throw in temperature information too.  So, if historically with schneider 'closed-loop' the primary information was the 100% soc reset plus coulomb counting, are the components in a particular bms better than, or even good enough, compared to a decent shunt?  

WaterWheel

Dave Angelini said:

 More battery banks have been killed by  (any manufacturer)  a bat mon and it's shunt than is worth saying.   Probably 100's on this forum alone.

That's why I pull the SG meter out and verify the SCP reading is accurate about once a month on my FLAs.        Using the SG meter I adjust my charging parameters slightly 3-4 times a year. 
      
If I had lithium I'm not sure what I'd do to verify charge except possibly unhook the batteries for a while and check resting voltage I guess.
Someday I'll move to lithium and then I'd have to learn a different way to verify battery charge.

Dave Angelini

You are a rare bird WaterWheel.  Many never do the initial calibration let alone the required re-cal over time with LA batteries. Once a year cal minimum.

Really great companies that make hi quality LFP have a USB output or a means for you to check every cell for quality and overall health.
Replaceable BMS and meet the simplicity requirements that are worth the cost when the lower cost batteries are long out of business.