I have been rather unhappy with my battery performance and have felt the charge seems to spend a LOT of time in the 80/90% SOC even when charging at 6kW. Further, I am getting low battery alarms when I have 75% SOC or more.
My system is a 6kWPV with 400Ah LiPO4, Cerbo and a Quattro 10kVA.
I aspire to running mostly off-grid.
Quattro settings snippet:
Summary
TAB: Assistant Configuration
ESS (Energy Storage System) (size:1044)
*) System uses LiFePo4 batteries with a VE.Bus BMS
*) The battery capacity of the system is 400 Ah.
*) Sustain voltage 50.00 V.
*) Cut off voltage for a discharge current of:
0.005 C= 52.00 V
0.25 C= 50.00 V
0.7 C= 49.20 V
2 C= 48.00 V
*) Inverting is allowed again when voltage rises 1.20 V above cut-off(0).
*) Relevant VEConfigure settings:
- Battery capacity 400 Ah.
- PowerAssist unchecked
- Lithium batteries checked
- Dynamic current limiter unchecked
- Storage mode unchecked
See the above image of a recent period of charging.
1_ Note the SOC% by battery voltage (64%) profoundly disagrees with SOC% from Cerbo (87.5%)
2) We now go through a charge to 100%.
Thw graph gives charging power approx as 5510W (avg) tot with consumption at circa 800W [part charger losses part own consumption] so net to battery about 4700W.
3) Over the 3h7m charge time approx 14kWh of net to charging. (!)
4) As specified the total battery (400Ah@53V = 21kWh) this should be about a 75% charge. Iff (not impossible) victron rate real world usage so say a quoted 400Ah is actually from 15% to 95% to give an absolute of 400Ah for 80% or 500@53 ~ 26kWh abs max.
5) Taking (4) into account and allowing some leeway on the ~14kWh of input charge and the Vbatt assessment at 65% SOC looks much more reasonable than the 87.5% SOC from the cerbo. Ex Vbatt the 65% SOC= 35% charge = 9kWh vs ex cerbo 87.5% SOC = 12.5% charge = 3.3kWh which is clearly total nonsense.
6) Neither are very convincing though suggesting something is not right with the sensors as well as the software.
7) Currently my system seems to report an overall efficiency of <80%, I would have hoped for nearer 90%.
In conclusion there is a software problem with the carbo measurement of SOC%.
A rather big one in fact.
I think you have a 16S System ?
Check your Sustain / cut-off voltages and adjust them according to the Victron specifications with an 15S or 16S System …
What is entered in the system as the battery monitor? Your BMS or the Quattro
Does the BMS communicate properly with the GX and is it just one BMS or possibly several?
What is a 16S system?
I have a 6kW PV inverter, 4x 27V 200Ah LiPO4 batteries and a quattro 10kWh charger/inverted. All victron.
I do not think the cutoff voltages are relevant, I set them high because I wanted the system to stop discharging the batteries at 40% (rather than the 25% - from memory, default) charge to reduce chance of damage.
I have a v ictron Energy VE.Bus BMS V2, Quattro has been chosen by the system/cerbo as the battery monitor. The quattro sees the BMS, always has (once a faulty NMS was replaced). Single BMS.
Originally the cerbo simply said nothing about the BMS, but later updates seemed to have fixed this and it now shows Quattro in control (which is not unreasonable).
But it would and should definitely be the BMS system …
If you don’t write anything about your battery then I can only assume a 15S or 16S battery at this voltage, but now we know that you have 2x2 Victron …
It was not possible to set the BMS into the cerbo when the original install went in. I did raise a bug query at the time.
I don’t see what the BMS has to do with the SOC% problem.
The Quattro is perfectly able to protect my batteries, it has tripped off die to Vbatt<52V on several occasions (SOC% on cerbo being ~70% at the time which was ‘annoying’).
I said in my first para I have 400Ah LiPO3 batteries.
Hope this is helpful, but I cannot see the relevance to my query.
The Cerbo does not do anything to calculate the SOC, it repeats what it sees from the chosen battery monitor. The Quattro can calculate SOC, but it is not as accurate as a shunt especially if you have DC solar power because the Quattro is not measuring anything on the DC system apart from its own consumption. If you do not have a SmartShunt in your system connected to the Cerbo then I suggest that you think about purchasing one because this will give you accurate SOC readings.
No it will not, the VE Bus BMS is a simple low cost BMS that only provides the protection functions shutting down equipment on low voltage or high voltage etc. It does not include any measurement or control of charging. When using a VE bus BMS a shunt is always best.
Thank you kindly for your reply,
I am not sure if that is correct because the PV inverter definitely and without doubt DOES alter the SOC%. Its been doing that here for two years.
So it seems to me that the cerbo is getting I/O information from the quattro and the Victron Inverter RS 48/6000 and using it.
Indeed it has all the information and even in today’s gloomy sunlight you can see some PV improving (slightly) the SOC% (to the right of info line). In fact, it is the only device with all the information to integrate the various devices into a SOC.
Below older data where I was running completely (almost) off grid. It’s very clear the PV inverter is taken into account when calculating the SOC%.
The BMS is slightly more complex. It has bluetooth and monitors every cell individually. If any one cell goes out of spec, it’s all shut down. It will give battery good status via bluetooth for cell balancing.
But otherwise pretty simple and all you need as a final backdrop, the quattro does the gross stuff and is more adjustable.
You have ac solar power so it will measure that, I said it would not measure DC solar power.
Regardless, the Quattro SOC calculation is not as accurate as a shunt dedicated to the battery. The Quattro relies on seeing a particular trigger condition to reset to a known SOC. I am not sure what it is for lithium, for lead acid it is something like 80% at the end of bulk. If this trigger does not occur then the SOC can gradually drift over time. Additionally if the trigger point is set wrong in the settings it can also cause problems.
No I have DC solar power, via the Victron Inverter RS 48/6000.
The power is read fine by the cerbo (which I’m pretty sure controls the charging levels).
There is no doubt whatsoever that the cerbo is taking both the PV input power (which is to the battery bus at ~53V) and both the quattro output from the battery and into the battery from the grid.
However, one or more or the cerbo software, is making a bit of a hash of it somewhere.
Maybe the measuring of the inputs and outputs is somewhere defective, maybe the software is defective
Addendum.
I cannot see why the measuring system in the quattro is not at least as good as a shunt, indeed probably it IS a shunt. Any el cheapo A-D converter can manage 12 bits of accuracy, so accuracy should not really an issue.
The BMS doesn’t control anything.
It simply provides a “battery in unsafe condition” signal that results in other systems (in this case the quattro) taking steps to protect the battery (in communication with the cerbo).
So the quattro either stops charging or discharging the battery and tells the cerbo what it is doing, which then shuts down the PV charger (as appropriate).
The brains are a little one in the quattro, and a rather bigger (probably a raspberry pi) brain in the cerbo. I have to say that generally, the cerbo software seems pretty smart on charging and discharging methodology.
Ie a bog-standard out-of-the-box victron system: boring.
But it works, EXCEPT FOR THE PROBLEM I AM ASKING ABOUT!"!!!
Which so far nobody seems to grasp but answer something else…
Addendum:
I just checked. There is a connection to the Quattro, and another to the cerbo.
Offhand (since its over two years since installation) I can’t remember what the actual connections are, but available from the manual (various). Its standard. There is a ve bus to Quattro, and a different (more recent) connection from cerbo to the PV-inverter (which is daisy-chainable with terminating plugs) whose name I cannot recall just now.
The answer you’re looking for has already been given. Seems you’ve rejected it.
SOC is a calculated figure, and the sources and algorithms used to determine it are varied. And often adjustable.
You blame the Cerbo, but it’s just passing on the SOC value sourced from somewhere else.
If it is actually a Quattro, then that method emanates from Victron antiquity, when Pb batts reigned and it could give a bit of a guesstimate based on Voltage and charge rates. For Li’s it’s borderline worthless in default form, but you might be able to improve it a little if you try to understand it and use settings more suitable.
Frankly, I’d disable it and get a Victron shunt (and did myself long ago). They’re very popular for good reason.
Indeed I cannot accept your “answer” either for good reason.
SOC is really simple and whilst being calculated it should be correct to a few percent, certainly better than 10%. This one is not even a half decent guess, it’s downright incorrect. An SOC of ~65% reported as 87.5% is totally useless.
Its a Quattro 2.
Its not rocket science.
The PV inveter has an internal shunt. It knows how much DC current it is inputting into the battery. = I1 (in)
The quatter will have a shunt so it knows how much DC current it inputs and discharges from the battery. = I2 (in)
So the battery is getting net (I1 + I2) A in the sampling period - ts (hrs, this will be fractional).
So we have told the system the Ah rating of the battery (400Ah) and all it needs is to do is continually integrate (I1+I2)ts to get the amount discharged/charged and deduct this from 400Ah (the current losses are very small in LiPO4).
I1, I2 & ts should be known to better than 1:1000 (10 bits off 12 bit A-D) so total integrated current should be accurate to roughly this figure.
IFF the battery is taken to full charge weekly (as specs request) any drift will be taken out weekly.
If the gross inaccuracy stated above is the best that can be done, then SOS% AS CURRENTLY ENUMERATED SHOULD NOT BE USED OR DISPLAYED. The battery voltage will be a far better guide to charge levels on LiPO5 batteries because this is (LiPO4 unlike most batteries) a pretty accurate measure of level of charge. This could easily be refined to allow corrections for the current being delivered/accepted, and will certainly be much better than 10%. FURTHER it is not dependent on the size of battery, the % charge is absolute to the battery capacity, so the capacity of the battery is not required to be used.
So I completely reject your “solution” and I do not believe the engineers at Victron (who have proven to be very competent) would be happy with the situation I describe in my original post. I designed similar (not high power) stuff in the distant past, and I would have been horrified if a customer pointed out a glitch such as the one I have illustrated. They are better than I was, I am sure.
Just to save someone coming in and saying the quattro 2 is old and not accurate, 16 bit DAC’s (digital analog to digital converters) came out in bulk as supercheap consumer devices in the early 1980’s. Probably all Victron stuff will have been capable of high accuracy since they started. They are in every computer sound device since then, so ubiquitous. This charger system is Very Slow (50Hz!).
