The Smartshunt synchronizes to 100% state of charge based on voltage, time, and tail current. In a real world solar system, synchronization can be triggered early or not at all due to changes in solar output, changing loads, etc.
VE.smart networking seems to currently support only one-way data between a Smartshunt and SmartSolar - the Smartsolar receives battery voltage and temperature from the SmartShunt.
It seems to me that synchronization could be made more accurate if the SmartSolar were to inform the SmartShunt when it is switching to float mode, which is a better indication of a full charge than what the SmartShunt can determine on its own. Correct me if Iām wrong, and consider this an enhancement request if Iām correct.
The key is to set the charged voltage in the shunt to 0.1-0.2V lower than the MPPT absorption voltage so you avoid premature synchronisation to 100%, the battery is then fully charged because it has got close to absorption voltage and to a low tail current. The charged detection time avoids cloud cover triggering the sync as it give time for the voltage to decay. The other important thing is to make the end of absorption settings harder to achieve so float always occurs after synchronisation. I have seen plenty of cases of wrong MPPT settings causing premature float so that is no better.
Which requires something more intelligent than volts, amps and temperature information. āIntelligenceā requires a processor which is where a GX comes in.
But i think in your case it is likely settings as @pwfarnell has mentioned. You need to tailor them a bit more for your set up.
I am aware of the recommendations for settings given in the SmartShunt manual.
But the manual does not do a good job of explanation, and gives this example:
In the case of a 12V battery, the battery monitor will reset the batteryās state of charge to 100% when all these parameters have
been met:
ā¢ The voltage exceeds 13.2V,
ā¢ the charge current is less than 4.0% of the total battery capacity (e.g. 8A for a 200Ah battery) and,
ā¢ 3 minutes have passed while both the voltage and current conditions are met.
It sounds like the voltage and current have to be continuously maintained to keep the timer running. Does the countdown reset if the voltage falls below the threshold, or does it continue to accumulate during periods the voltage is maintained? Itās certainly possible, in the real world, that the voltage drops due to loads going on/off or a drop in solar production (e.g. clouds).
Similarly for tail current. A load can draw from solar (or solar production drops) and reduce the tail current, making it an unreliable measure of how much charge the battery will accept. This can result in a premature sync.
The absorption stage may last several hours to achieve a full charge, but the SmartSolar charged detection time tops out at 100 minutes. So a sync may occur hours prematurely. But a load may also briefly lower the voltage and reset that timer, so it may never go off. The SmartSolar controller may also have issues when loads are present, but it seems that between the two, the SmartSolar switching to float is the best indication of 100% SOC available. But again, that manualās description is unclear, do voltages need to be constant or are they triggers; do timers get reset or are they cumulative?
The charged voltage and tail current must be maintained for the whole charged detection time. I have no idea if the charged detection time is reset or if it is cumulative. However, that has never been a problem in 5 years of operation on my boat. The reset or cumulative is a secondary issue, if I was to guess based on my experience the timer is reset. The manual says to set the charged voltage just below float, that does not work for solar, hence my putting absorption in bold, do that and you avoid nearly all early synchronisations. The absorption time on the SmartSolar can be set to many hours, the charged detection time on the SmartShunt not so, but you do not want to setbit top high, the most I have seen people use is 10-15 mins. You have to remember that SOC is an approximation anyway, you are after a repeatable synchronisation to stop drift in the SOC.
My feeling is you are over thinking this, get the system running and tune the parameters to suit.
I understand what youāre saying, but better is better.
Another useful enhancement would be for the SmartSolar to learn the amount of charge going into the battery from the SmartShunt. For lead acid batteries, thereās a recommended maximum charge current (e.g. Trojan says 10-13% of C20). The SmartSolar can be programmed with a maximum output current. But, that limits the total output of the charge controller, not just what goes to the battery. If it knew what was going into the battery, it could limit that but at the same time provide additional current to power loads.
Say I limit the SmartSolar to 20 A of output, because thatās the maximum recommended charge current for my batteries. If I also have 20 A of load, it could put out 40 A without exceeding the maximum charge current. As it is, all the current would go to power the loads, and none to the battery, because it has no idea of how much of its output is going to charging.
Thanks. Looked at it and it doesnāt seem to do that:
the total charge current of the inverter/chargers and all MPPT solar chargers will be controlled, nothing else. Any other sources will be extra charge current, unaccounted for. Even when installing a BMV or other battery monitor.
DC Loads may not be accounted for, unless a SmartShunt or BMV-712 is installed and correctly configured as a DC meter. For example, without the DC load monitor a configured maximum charge current of 50A and DC Loads drawing 20A, the battery will be charged with 30A, not with the full allowed 50A.
My takeaway is that DVCC controls charge current, not based on the SmartShunt current (which makes the most sense to me, since itās directly measuring the charge current), but by measuring load current (which requires a 2nd SmartShunt configured as a DC meter), adding desired charge current, then telling the SmartSolar it can produce that much. Seems bass-ackwards to me. Simply using the SmartShunt battery current would avoid all the issues with other sources and loads.
Yes, DVCC just limits the total charge current, it does not measure it. It will take into account all the loads it can measure, so if you want to take DC loads into account you have to have a way of measuring them (like a 2nd smartshunt).
What issues? in my experience the systems works fine. In all likelihood measuring the charge current at the shunt and then trying to react to that will introduce new issues.
As for the first post, is this something you have issues with in your system or is this purely hypothetical?
Purchasing less components is always nice but i donāt agree this is an issue. The system works as designed and described in the manual.
Donāt know, i donāt write software. I can only imagine rewriting the control loop will introduce issues that need to be worked out.
I also donāt see what the advantage would be except sometimes not having to buy a shunt for DC loads. Most small installations donāt use a cerbo and most big installations donāt have a DC load.
For users with a GX, DVCC is not just about control, it also has functions to share battery voltage, current and temperature (SVS, SCS & STS(share current sense) from a BMV, SmartShunt or BMS with the MPPT so the tail current is the true tail current. It would be good if the VE Smart Network did the same, as it does not I assume some form of limitation but do not know any details.
So hereās a serious limitation due to how they implemented this. In order for DVCC to work, you need a sensor (SmartShunt) on the battery negative lead, and another configured as a DC meter on the negative lead going to all the loads (the charge controller would be in the middle). On most RVs, thatās impossible, since many loads tie into the frame, the same as the battery negative lead. There is no single lead going to all the loads, except the one from battery negative via the SmartShunt. So thereās no way to actually measure the total load current directly. Perhaps by tying into the positive lead going to the loads and then powering a SmartShunt with 24 V (on a 12 V system).
So, so, much simpler if DVCC simply controlled charging current based on the battery current (which is reported by the SmartShunt via both Bluetooth and VE.Direct) instead of trying to calculate it from controller output current minus load current.