Flexnet DC shunt connections and accurate SOC

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wodiwodi
Forum Member
Posts: 11
Joined: Wed Jul 22, 2020 6:31 pm
My RE system: 3kW PV primary array
1kW PV secondary array
24 Volt 1320 Ah Lead Acid battery set. Yuasu Enersun SSL consisting of 6 x 4volt units.
2 x FlexMax 80 MPPT controllers for primary array,
1 x Plasmatronics PWM Regulator, PL60, for secondary array
OB Hub4,
OB Mate2 (not currently used),
OB FLEXnet DC
OB AXS_PORT with OpticsRE
The Inverter is a 4KVA Latronics LS 4024 (it is the newer model which is actually 4.5KVA).

Flexnet DC shunt connections and accurate SOC

Post by wodiwodi »

Sorry, a long post but I try to give a detailed picture of my predicament and what I am learning from these forums. Thank you to all the knowledgable and patient people out there.

I am trying to reconcile the information I am getting from the Flexnet DC via OPTICSRE regarding charge levels of the batteries with readings of specific gravity which suggest a much lower level of charge.

I have set out below three dilemmas I have regarding my system. I would like to get the system up to speed because in the next month I am going to double the battery capacity and reset it as a 48 volt system and get a new 48volt inverter. It seems to me to be important that the new batteries are not degraded by the older ones (only two years old) in a less than fully charged state.

I have been reading lots of partly related posts and responses in the Forums and found them very informative but I remain unconvinced that I understand what is happening.

I am certain that I have connected the shunts correctly, in terms of polarity, however I am not sure of how the input from the shunts is used (combined) in the FNDC to calculate the SOC.

The situation is compounded by the last 6 months of wet and cloudy weather I have experienced here on the south east coast of NSW, Australia. We have had 124 rainy days in the last 6 months with many of the non rainy days being cloudy. There have been few occasions where I have had 4 or 5 bright and sunny days in a row to really ensure full charging of the batteries.
I have read about how the FNDC readings can "drift" from the true values over time and also about calibrating the FNDC. I have not had a chance to reset the FNDC at 100% as I have not been assured of a true 100% level of charge and I have no generator/battery charger at my disposal. I have also read many knowledgable contributions about tweaking the FNDC charge parameters and understand much more about their role - thank you.

In my setup I have 3kw of panels connected through 2 FM80 regulators into a 1320Ah 24Volt lead acid battery bank. The input from the FM80s is measured via one of my shunts, call it Shunt A. The FNDC measures this current reasonably accurately.
I also have about 1kw of panels configured as 24volts connected via a Plasmatronics regulator. These input charge to the batteries via a relay which the FNDC shuts off when the batteries are at about 97% so that the FM80s can do the absorption and equilisation stages without getting into a battle with the Plasmatronics regulator.

The system has worked very well, thanks to help from this Forum about programming the FNDC. The 1kw of panels allow me to maximise input in the morning before the 3kw really cut in due to the need to orientate the two sets differently.

The 1kw set inputs via a second shunt, say shunt B.

My inverter is connected via shunt C.

I have attached a typical graph for a 24 hour period. The green represents the input from the CCs, the dark blue seems to represent the whole of the input from all sources, although at the end of the day the green is higher than the dark blue??? The light blue represents the current going to the inverter.

Dilemma 1:
I find it interesting that the dark blue column can ever be lower than the green column and it is this fact that makes me question what the FNDC is doing with the inputs from shunts A and B. Apart from early in the morning before then 3kw array cuts in, the dark blue is always much more than the 1kw panels are generating, which has always seemed to me to suggest that the FNDC is combining the inputs and on the spot readings seem to verify that. How then can the green column (input from the FM80s) be greater than the total??

Dilemma 2:
How can I change the charge parameters on either the FM80s or the FNDC to bypass the triggers in the system that stop the charging because of an incorrect assessment of the SOC.

Dilemma 3:
I have purposely not designed a generator/charger into my system because I always been able to manage usage to match weather conditions and have never had the system shut down because of low battery charge. Should I borrow a generator and spend a day charging the batteries to get the Specific Gravity levels to where they should be, independently of the FNDC, the input from the PV and the CCs control?

I look forward to some clarification.
Kindest regards,
Howard Jones
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raysun
Forum Emperor
Posts: 7743
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A-01, (2) FM80, MATE3s, FlexNetDC
6 SimpliPhi 3.8-48 (48v @ 75AH. 450AH total)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Flexnet DC shunt connections and accurate SOC

Post by raysun »

Hello Howard,

Welcome to the forum.

There's lots to address in your post. To start, it would be most helpful to make some additions to the equipment list in your profile: exact battery brand and model; inverter brand and model.

At its simplest, the FNDC is a "current counter". It tracks the flow of current through up to 3 shunts, and integrates the values to derive totals. Properly connected to a battery, the totals represent current flowing into the battery (charge) and current flowing out of the battery (discharge). The FNDC can monitor current flow from any compatible device. The current flow through a shunt can be bi-directional, though the "directionality" is dictated by the connected equipment. Charge controllers are typically "charge only" devices. Inverters are typically "discharge only" devices. Inverters with built-in battery charging function are both discharge and charge devices.

In OpticsRE, the representation of current flow is shown in three categories: Solar, To Battery, From Battery.
Solar represents the output from the FM80s. The FlexMax/AXS/FNDC have enough smarts to recognize each other and categorize the charge controllers as the source of "Solar".
To Battery is the aggregated value from all charging sources. In this case, it should represent the total solar harvest of all 3 charge controllers.
From Battery is the measure of discharge current. In the configuration described, it should represent the current flowing to the inverter.
I find it interesting that the dark blue column can ever be lower than the green column and it is this fact that makes me question what the FNDC is doing with the inputs from shunts A and B.
In the example, I assume the PWM controller may be contributing little or no charge current in the 15:00 hour where the apparent disparity between Solar and To Battery is depicted. In this case, the values would be exclusively from the FlexMax units. I commonly see this disparity. Many years ago, an Outback engineer explained it to me as a difference in the resolution between the FlexMax and FNDC metering. Between the two, the FNDC is higher resolution. In absolute terms, To Battery is preferred over Solar when evaluating how much current is flowing into the battery.
How can I change the charge parameters on either the FM80s or the FNDC to bypass the triggers in the system that stop the charging because of an incorrect assessment of the SOC.
The FNDC, in and of itself, doesn't control charging in any way. If Automatic Charge Termination Control is enabled in the AXS port, that device can instruct the FlexMax devices to end Absorb charging. Otherwise, the FMs operate autonomously, and charging is in accordance to the parameters set in each controller.

I am going to reserve comment on #3 awaiting more detail on the battery (and inverter.)

Cheers!
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EA6LE-ONE
Forum Czar
Posts: 788
Joined: Tue May 05, 2020 7:51 am
My RE system: System 1:
MATE3s, 3 x Radian GS8048A,
6 x FLEXmax 100, HUB10,
2 x EnergyCell 48V 2700RE,
1 x FLEXnet DC, 6 x FLEXware ICS Plus,
78 x PANASONIC VBHN325SA17 325W

System 2:
MATE3s, Radian GS8048A,
2 x FLEXmax 100, HUB10
1 x EnergyCell 48V 2700RE,
1 x FLEXnet DC, 2 x FLEXware ICS
21 x PANASONIC VBHN325SA17 325W
Location: Providenciales, Turks & Caicos Isl.

Re: Flexnet DC shunt connections and accurate SOC

Post by EA6LE-ONE »

Howard,

For my system I am using only one shunt which can help eliminate your confusion to an extent.
You count only what is going in and out to the battery. the disadvantage is that you will not have counting what is coming from CCs and what is going to inverter. it will relay on the metering from CCs and inverter that can be a little bit off. the FNDC supposed to be more accurate.

This is how graphs are looking:
01.jpg
02.jpg
wodiwodi
Forum Member
Posts: 11
Joined: Wed Jul 22, 2020 6:31 pm
My RE system: 3kW PV primary array
1kW PV secondary array
24 Volt 1320 Ah Lead Acid battery set. Yuasu Enersun SSL consisting of 6 x 4volt units.
2 x FlexMax 80 MPPT controllers for primary array,
1 x Plasmatronics PWM Regulator, PL60, for secondary array
OB Hub4,
OB Mate2 (not currently used),
OB FLEXnet DC
OB AXS_PORT with OpticsRE
The Inverter is a 4KVA Latronics LS 4024 (it is the newer model which is actually 4.5KVA).

Re: Flexnet DC shunt connections and accurate SOC

Post by wodiwodi »

Thanks to raysun and EAGLE-ONE for quick replies. I have gleaned information from both replies that helps me understand the limitations and meaning of the GUI components.

I have added information on my system to the profile.

I realise that a system like mine which is made up of a number of different brands is going to have compatibility problems and as the Inverter I have does not "talk" to the other components and the input is from different charge controllers, there is a bit of fuzziness in the way that things should be interpreted.

Nevertheless the FM80s basically do their job and the FNDC and the ASX_PORT provide me with visual feedback.

The most important issue for me is to ensure that the FM80s keep my batteries in good health. In general terms I only use between 10% and 15% of the battery capacity on any one day and under normal circumstances I would not be confronted with the high percentage of rainy days. As I mentioned originally, I am looking for ways to ensure that the batteries are returned to the high level of charge that they originally had (based on specific gravity) and that the settings can be tweaked for a while to reverse any period of undercharging that may have occurred over the last 6 months.
EA6LE-ONE wrote: Tue May 10, 2022 6:23 am For my system I am using only one shunt which can help eliminate your confusion to an extent.
I get the impression that I don't really need to have the current from the FM80s going through a separate shunt as that current is automatically added to the current from the PL60 anyway.

That might resolve the graphical issue however more importantly I need to resolve the charging problem.

Thanks
Howard
raysun
Forum Emperor
Posts: 7743
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A-01, (2) FM80, MATE3s, FlexNetDC
6 SimpliPhi 3.8-48 (48v @ 75AH. 450AH total)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Flexnet DC shunt connections and accurate SOC

Post by raysun »

The 3 shunt setup is fine. The difference in measurement between the FMs and the FNDC does not affect battery charging in any way. If it is visually distracting, simply click the radio button next to Solar and Optics will stop displaying the value. The 1 shunt setup 'resolves' the issue by ignoring it entirely, showing only net current flow to and from the battery, as measured across the shunt.

A chronically undercharged state will impact battery health. Ideally, a lead acid battery should be restored to a full state of charge daily. At the very outside, it should be fully charged weekly. Six months at partial state of charge has likely impacted capacity to some degree. That it is lightly used is not necessarily a "saving grace". Very large capacity batteries that are lightly discharged and subsequently lightly charged (or left at partial charge) tend to experience electrolyte stratification and the effects of sulphate buildup. This battery needs to be fully charged ASAP. After reaching full charge, its likely to benefit from an Equalization charge to help bring all the cells to the same Specific Gravity. The EQ charge can be an hours-long cycle. The challenge will be to find a 24V programmable battery charger that will do the job.

The FNDC is a monitoring device and has no direct effect on charging. It simply reports the state of the battery according to the set parameters. When a battery is fresh from the factory and fully charged, the parameters set in the FNDC should be those values supplied by the maker. As the battery ages, Amp Hour Capacity and Charge Efficiency decline. These values may need to be established by testing and the FNDC parameters changed accordingly.
wodiwodi
Forum Member
Posts: 11
Joined: Wed Jul 22, 2020 6:31 pm
My RE system: 3kW PV primary array
1kW PV secondary array
24 Volt 1320 Ah Lead Acid battery set. Yuasu Enersun SSL consisting of 6 x 4volt units.
2 x FlexMax 80 MPPT controllers for primary array,
1 x Plasmatronics PWM Regulator, PL60, for secondary array
OB Hub4,
OB Mate2 (not currently used),
OB FLEXnet DC
OB AXS_PORT with OpticsRE
The Inverter is a 4KVA Latronics LS 4024 (it is the newer model which is actually 4.5KVA).

Re: Flexnet DC shunt connections and accurate SOC

Post by wodiwodi »

Thanks again for the further clarification. Thought provoking indeed.
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