22 Charge controllers & 1 battery bank

mike760

I have my two inverter systems connected to a common battery bank.  The charge controllers are split between the two systems as far as xanbus goes but connected to a common bus as far as output goes.  I am having trouble with the two separate banks of charge controllers staying in matching modes (bulk/absorb/float) even through the parameters match.  I was thinking they would be much better if they were all controlled by one inverter system but then I exceed the maximum number of devices on the xanbus network.  Theoretically the bus should support than number of devices but SE does not recommend that many for traffic reasons.  Has anyone ever exceeded the 18 device max recommendation?  Is there a better design opinion?  Any suggestions or ideas?  

System A:
6 @ XW6848 Pro

8 @ MPPT 60/150

6 @ MPPT 100/600

1 @ SCP

1 @ Gateway

System B:
4 @ XW6848 Pro

8 @ MPPT 100/600

1 @ SCP

1 @ Gateway

2 @ Battmon

1 @ AGS

48V Battery Bank:
48 @ Rolls Surrette 2YS 31P (2VDC 2527AH)

Generator:
1 @ Volvo 100KVA Diesel

PV Panels:

488 @ 250W

BB.

In general, I thought that there is not really a "need" to have paralleled charge controllers always being "in sync" (bulk, absorb, float, etc.)... If one controller is "ahead" of another controller--It really does not matter much.

The controller that tripped "first" (if programmed correctly) things that battery bank is "full". The second controller is going to add a bit more charge before it also goes into the next mode.

As long as the battery bank is "hitting" the appropriate "marks", it does not matter if it happened with two controller going to "float" or if one goes to float first, then the second.

If you have "issues" with battery voltages/current/state of charge--You may have some programming issues with one or the other controller (i.e., if battery bank is over charging--One controller is over charging while the other is in "float").

There was one report (years ago here) where charge controllers behaved "differently" during charging (different hardware and/or software levels). When the bank was running with a "battery desulftator" (which sends "impulses to break up hard sulfate deposits on "problem" lead acid batteries). When the desulfator was on, one of the paralleled charge controllers shutdown long before the second. With the D.S. off, the chargers tracked each other fairly closely.

-Bill

mike760

I guess I forgot to mention that this is an off-grid system if that makes any difference in your analysis. 

There are several scenarios that I believe are related to a lack of common control.  One example being that the inverters on system B might start to draw down on the batteries around 3pm and the charge controllers on that system appear to be putting out maximum wattage given the amount of sunlight (let's say 10KW).  When you look at system A, the charge controllers on that system  will not be putting out much if any wattage (<1KW).  So this creates a scenario where the batteries end up supplying the difference instead of the other charge controllers using the available PV to make up the difference to maintain the AC load.

It is also prolonging the absorption stage.  Actually, I don't believe I even have enough time to properly complete the absorption stage when half of my charge controllers are actually "sleeping."  I'm almost at 4pm and my bank is still taking in >150A when the absorption timer is expended.

On another note, I noticed that the 60/150 charge controllers have 4 charge modes available which are stand alone, primary, secondary and echo.  Anyone know what echo is?  I looked for documentation and came up empty.  I also noticed that this charge mode selection is not even available in the configuration of the 100/600 chargers.

mike760

This is an earlier picture during installation so it does not show all of the equipment listed.  Both walls are packed so it's hard to get everything in one picture.

BB.

Impressive system.

I would suggest using a higher resolution DC volt meter (I.e., XX.XX to XX.XXX whereas a XX.X meter may not have enough digits) and measure the voltage on the output of each charge controller (I.e., solar when charging with sun, and hybrid AC systems when/if charging from gensets), and measure the charger(s) terminal voltages.

My first guess is that under heavy loads/current, your terminal voltages are significantly different between the chargers--The chargers with the lowest DC output terminal voltages may be doing most of your charging (due to voltage drop of the various cable lengths and possibly unmatched battery bus voltages.

Also, double check the voltages across each battery (or cell) and see if they voltages match (under load, under charging, etc.). If there are any "unbalanced" voltages, check cell Specific Gravities, look for voltage drop across terminals (I.e., between lead battery terminal and battery wire terminal/copper, even end to end drop on cable to bus bar connections, etc.). You can even check temperature of connections/cables under heavy load.

Looking for anything that could indicate poor electrical connections (loose/dirty/corroded terminals/etc.). Basically--Looking that everything "matches" voltages under heavy current (during loads and currents).

You could also use a DC Current Clamp meter and insure that current in "identical cables" is being shared equally (I.e., suggest that within 10% current sharing is probably "ideal". Where as >50% differences in sharing is not good).

Looking for "higher" voltage drop and lower current flow in specific locations and see if you can find a reason for the differences (I.e., bad connections, different cable lengths--I.e., longer cable runs have higher voltage drop and lower "share of current").

With physically large systems, it is going to be difficult to have "equal" cable lengths between everything for matched resistances.

Ideally this is the choice between Star and Daisy Chain wiring for battery banks (generic wiring--AKA sub battery for encoder):

The problem with Daisy Chain is the battery(ies) closest to the source will tend to absorb/source the most current. While the ones at the "end of the ladder" will tend to participate less (due to increased wiring resistance). (in the above star configuration, ideally looking for equal wiring lengths for source to each battery--equal wiring resistance.

In the above STAR wiring, the source could/would be a common bus bar connections--All batteries connect to common point, all chargers connect to same common point, all loads connect to same common point --This way all devices "see same DC Bus voltages".

There are lots of variations to "balance" battery wiring/voltage drops with multiple series batteries. Example of matching total battery bus length--Splitting + and - wiring destinations to end up with identical total path lengths:

I am sorry, I don't have the knowledge to discuss the different controller setups (alone, primary, secondary, echo). One of those modes may offer better overall charging performance (I.e., Master makes the "decisions" and the slaves simply follow).

I am no expert in these systems--Just my overall experiences in other power systems over the years and how I would start some debugging/thinking of system issues.

Best wishes,
-Bill

Dave Angelini

Which model Gateway?     Insight home, Insight Facility, or the original gateway?

mike760

Insight Facility information

Insight Facility name
Model designation	865-0335
Application version	v1.18
Application build number	41
Application build date	2023-07-25_20-09-43

mike760

And BB, thanks for all of the information.  I'm trying to make sure I have the Schneider equipment connected in the best way possible given the higher number of devices and then move on to troubleshooting if necessary.  And there are some things that you touched on that I am struggling with but I don't want to open that can of worms in this thread.      

Not sure If I'm going in the right order but I want to make sure any communication/synchronization, or whatever that is necessary for the charge controllers to operate optimally, has been setup properly.  My first concern is the proper xanbus setup for two separate systems of inverters, gateways and charge controllers operating independently but sharing a common DC bus / battery bank.  

BB.

No problem. Just take one step at a time

Good luck,

Bill

Dave Angelini

Draw out how you have wired the 2 xanbus networks?

 Or, you are reading the XWP multiunit design guide? If so you are past the max devices on the network and will have some issues that may be acceptable for Offgrid.

Good Luck!

mike760

I have the charge controllers on Xanbus 2 and then the balance on Xanbus 1.  I did both systems like this.  

I'm thinking of just going for it and putting the charge controllers all on the same gateway.  It's not like there is any significant life altering danger like blowing my berries off or something.  Worst case I move the cable back to where I started.

It doesn't seem as if anyone has actually done this to see if there are in fact any traffic issues that the documentation cautions about.  There are enough addresses available (32) on each network so that is not an issue.  Looks like I will still have to keep all of the chargers on the same chain because xanbus 1 cannot communicate with xanbus two according to docs.  Although this is interesting as I wonder how the controllers obtain SOC information held by the battmon which is on the other bus.

mike760

Got to throw in a pic to break up all of this boring txt 

Dave Angelini

You are in commercial power range, for offgrid??? I have seen some very large systems and built a few but it always has ended up the designer did not use power saving thinking in the beginning!

There are parts of the 2 networks that can communicate and there are parts that can't! That is the beauty of facility in that you get real time data for a very large canbus system. Your 60a mppts also have the problem that they do not supply network power as the 100A mppts do. So, there is that issue that may be here also. Not even mentioning the wiring and using the raceways as designed.

Below is from my training back in the day when there was training. I think I would get the system working correctly and have some of the mppt 100a's off the 2 networks and just use them for bulk charging on their 3rd network.  Good Luck!

mike760

Yes it is off-grid and I am using the system to supply 120/240 split phase, 3-phase 208Y and 3-phase 480 delta.  I have machines that have various requirements.  And I might eventually drop the split phase.  Almost any equipment that needs 240VAC these days will also run on 208VAC.  You are not picking up any amperage per leg on split vs. 3 and you lower your supporting equipment costs per system like only having to buy 1 SCP or 1 gateway per 6 inverters (not to mention load centers, breakers, disconnects, etc.).

I don't understand these low device limits.  How is anyone supposed to supply a 6 inverter system consuming a max of 40KW with 6 chargers supplying 6KW MAXIMUM each?  My controllers are overbuilt to 7KW and I can hit 5.5KW+ on good days but it's not all day.  And then what is left to charge the batteries?  My batteries are taking in about 45KW by 10AM.  The 100A chargers only came out not too long ago.  I actually started with the 60A and good luck with them supplying anywhere near 3.5KW.  There's not many options for building them out with panels to where you get anymore than maybe 2.3KW out of each one.  They are really a waste of time and money.

As long as I am ranting.....  What's with the PDP only having three 250A breaker mounts?  Why not drop one or two of the smaller ones and add another 250A?  I mean apparently no one needs more than one or two charge controllers per 6 inverters anyhow.

Dave Angelini

Mike, you are at the end of my general info.

 Become a client and I will dedicate the time and with a guarantee. You can email me below for more.
 Good Luck

mike760

Thanks for the offer Dave but I'm fairly experienced with this installation.  I was just curious if anyone had ever put that many chargers on one bus.

So for anyone wondering, I just connected all 22 chargers on one bus.  The Insight gateway recognized all the them and I successfully updated some of the settings on the chargers and everything performed normally.  Hopefully the equipment functions correctly in the morning when the sun comes up.  I'll post some updates with the results as soon as I can incase anyone else out there ends up with a similar system.

t00ls

mike760 said:

"I have my two inverter systems connected to a common battery bank."

are you saying all these inverters are working off 1 48 volt battery bank

t00ls

from the picture above though....it looks as if there are 2 battery banks of 48v

why not split the panels and CCs for 2 separate systems

JRHill

Something for nothing.

"You are in commercial power range, for offgrid???

Classic

Dave Angelini

I have done quite a few of offgrid machine shops, so yea commercial for sure! But, it is funny still...

JRHill

For me the power to run the big machines comes from a Miller Bobcat. With the exhaust piped out a side wall it heats the shop in the winter pretty quickly.

Dave Angelini

Nice old Bobcat !   

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mike760

t00ls said:

mike760 said:

"I have my two inverter systems connected to a common battery bank."

are you saying all these inverters are working off 1 48 volt battery bank

Yes.  One system consists of four inverters for split phase and the other consists of six inverters for 3 phase.  I have machines that require 208VAC and 480VAC.  I am able to run my 3 phase welders as well throughout the night without the generator starting up.

mike760

t00ls said:

from the picture above though....it looks as if there are 2 battery banks of 48v

why not split the panels and CCs for 2 separate systems

There are two sets of batteries but they are paralleled.  Splitting panels and CCs didn't make efficient use of the power.  The demand on each inverter system is never going to be the same, at least for my usage.  I would run into a situation where the generator would start up if one bank got low but the other one is sitting there almost fully charged.  It is better to draw them both down evenly and use as much of the stored energy as possible before burning diesel.  Otherwise, I could also be increasing the number of cycles on one bank which would reduce overall life.  Another consideration is that the draw on a paralleled set is halved between them which effectively doubles the hour rate thereby increasing the overall amp hours available.

A similar situation applies to the CCs as well.  If one system depletes its batteries overnight and the other system does not, half of the CCs and panels will be sitting almost idle in the morning instead of helping to charge the other bank.  A certain usage pattern could occur, for example, where one system has very low demand and the other has high demand.  Now lets say this is happening in the morning and the batteries need to be charged.  The output from the CCs for that high demand system will be used to support the load first and then the charging with the balance.  It could be 9am and actually drawing on the batteries instead of charging them because of insufficient pv generation while 50% of your equipment is relaxing on the other inverter/battery system because it has little demand and light battery depletion from the night.  If the banks were paralleled, you would have all resources available to give you the extra power needed to maximize your current charge cycle in addition to the load.  

The charging details can also become problematic.  First, the charge cycle might not complete due to insufficient power as described above.  Second, the batteries need to be hit with a fairly good amount of power for them to heat up sufficiently and prevent sulfating on the plates.  This happens during the bulk charging phase which is the first one and that obviously happens in the morning so having good PV generation early is important for me.  I try to stay around 800-900 amps on my bank during the bulk phase.  I also like having the bulk of my info combined on a single insight gateway.

So basically, these are some of the problems that I resolved by configuring things this way.