Why is ignore DVCC charge limit when is enable DC Feed In?
asked
DVCC - FeedIn
It is clearly explained in the DVCC section of the Cerbo/GX manual, footnote 6:
6) DVCC charge current limits are not applied to DC MPPTs when ESS is enabled with Allow DC MPPT to export. This is to get maximum output from the solar panels for export.
I read manual, but I dont understand why victron support team cant change configuration or update FW when fix this option?
Likely because it is more complex than you think it is. Everything cannot be fixed with firmware, sometimes there are more moving parts involved that it appears on face value.
If it was that simple, it would have been done already.
Can be. But if that's the case, it was good to pay attention to it. If it is a hybrid system, then this should be resolved. I can't imagine that someone has 20kW solar panels and a 5kW battery pack. Due to this missing function, the batteries cannot handle only a few charging cycles because it will be destroyed by the high charging current. The solution would be for the converter to limit the charging current if there is no connection to the BMS of the battery, even if h FeedIn is turned on.
with correct battery sizing, this should not be an issue.
But i agree in some way.
There should be an additional parameter:
if selecting DC-feed-in ON, there should pop up an additional parameter, asking:
ignore CCL from BMS: yes/no
I hope Victron will implement this in future.
Why would you set a current limit with a smart battery? Mostly irrelevant in that use case.
Main problem here would be, for example, that the DC from the mppt needs to be changed to AC. It passes over the terminals where also the battery is attached.
If the battery is the easiest path they go there, if the AC is the easiest path that's where they go.
The battery itself would need a way to refuse charge without disconnecting.
You can also cap voltage so the battery does not actually get full and can take overshoots.
Most efficient way to feedback is still AC PV on the input/grid side of the inverter.
Its not that complicated.
I know of applications, where an external control tweaks CVL down via Modbus, until the BMS-CCL is met.
simple as that. And it works well.
This reduces feed-in power, but that is clear. But there are installation that need this feature to protect their batteries.
Victron could easily do, if they would like do
Ignoring feed-in. Smart batteries wouldn’t usually have a charge limit set in DVCC, and that same energy is passing the battery to serve loads on AC out. The physics doesn’t change much because of feeding-in..
not really sure, what you mean?
For my understanding:
If a BMS sends out a charge current limit (CCL), it does not want to see higher current flow into the battery than this limit. Why do you want to ignore that?
If DC-feed-in is OFF, Victron respects this CCL from the BMS.
It looks at CCL from DVCC and CCL from BMS and uses whichever is lower.
If DC-Feed-in is ON, the Multis still respect the CCL from DVCC and BMS, but the MPPT´s does not. They can produce as much as they are capable of.
In my opinion it should be configurable, if the MPPT´s also respect this limit or not.
It is still OK if the MPPT´s provide more current, nobody has any problem with that. But anything higher than BMS-CCL, should then be fed into grid or serve AC-loads, but not flow into the battery.
If the Multis have not enough inverting power to accomplish that, Voltage needs to be lowerd.
I don´t see anything wrong with that.
Important would be, to have it configurable.
But sadly Victron does not offers us this option
CCL isn’t ignored. Only the manually set dvcc charge limit is ignored. Something that isn’t normally set for a managed battery anyway.
oh, you are wrong. Also CCL from BMS IS IGNORED by MPPT´s if "DC-Feed-in" is ON
Nonsense. Usually a dvcc limit isn’t set, yet mppts produce full power so they can service loads AND meet charging needs.
I have no charge current limit set in dvcc (as should be the case) and with ccl=0 the mppts pump power into grid and loads with nothing going to battery.
have really tried this?
it is NOT the way you are saying!!!
I do tune this every day, so i know very, very well:
if you set in DVCC CCL to 0A
-> then the Multis charge nothing into the battery, correct
-> but Smartsolar MPPTs charge all they can into the Battery!!
(if DC-Feed-in is ON)
but if DC-Feed-in is OFF, then also Smartsolar MPPTs charge nothing into the Battery!
CCL of 0A = do not produce.
So saying feedback yes, then don't ignore the battery means the battery stops production. If you want to feedback this is a conflict.
Size the bank correctly and this is not an issue.
Limiting your feedback yourself to within your system capablity is also an option.
Again think about the way the system is physically connected, it means that the DC from MPPTs can not be physically routed up or down since power moves to the path of least resistance. So if that is your battery (with lithium this is usually the case) that is where it goes. It would have to be the battery that has to refuse the charge somehow physically. Disconnecting is not really an option.
i don´t exactly understand what you are talking about?!
sure DC from MPPT´s can be "routed". Why do you think this isn´t possible?
The Multis need to take the DC power available, invert it and use it for AC-grid feed-in or to serve AC-loads.
If the Power from the MPPT´s exceeds the Multis capabilities, the MPPT´s simple must be throttled. Whys should this not be possible?
They can do the very same, if you disable DC-Feed-in
Again:
it would be an easy task for Victron in my opinion, if they would want to support it
You have completely misunderstood how this mechanism works.
If it didn’t work there would be many unhappy users.
I am one of the not happy customer with exactly the problem pedaaa mention. I have sadly bought too many mppt able of charge 200A from my 7.2kWp PV. This is not good for my battery and also not necessary to charge so extreme since most have several hours to charge their home battery of normally 10-15kWh.
It should just charge up to the CCL I set and everything else goes to grid(feedin). I only have one mp2 48/5000, so this also cant deliver all to grid in peak situations, so tjen mppts should lower the charge similar to what it does with feedin deactivated.
I hope Victron solves it, else I need to sell my mppts and buy a Fronius inverter instead.
Also read this in the ess manual for CCL.
why do you say that?!
i assume you are either not familier with that situation/setup ( i assume so, because you didn't know that BMS-CCL is ignored)
This would not be unusual, because you wont see any problems with that, if
- battery set is big enough
- Smartsolar MPPT's are smaller than Multi Inverter power
If all your systems are designed like this... (and they should be), then its most likely no issue at all.
But i know there are installations, that have kind of too small batteries, or too big MPPT's. Then it really could be an issue.
Or we are just talking past each other, and you dont know what i actually want to say?
Could it be possible to by nodered to set mppt max charge to i.e. 35A every night, so this will be the max battery PV charge. And when CVL is reached(charged battery), the mppt were set to full charge capacity to feed in max energy?
The issue of "DVCC charge current limits are not applied to DC MPPTs when ESS is enabled with Allow DC MPPT to export. This is to get maximum output from the solar panels for export." has come up many times! Despite it being "in the manual" I personally think that Victron should address the issue since there are cases where clients are "unknowingly" exposing their battery bank to excessive charge current.
Yes... if you size the battery bank and PV panel array correctly then this problem goes away. But, we all know how expensive batteries are and often we try and get away with the "least" number of batteries to get up and running? Never mind the technical complexity, I would say that this is human nature, despite it sometimes being a false economy!
So, for now we are stuck with either disabling DC feed in so that the DVCC CCL is respected, or sizing the battery bank large enough with respect to the MPTT (s) max charge current output and enabling DC feed in excess. There is another option and that would be disabling DC feed in until the battery bank has reached 100% and then switching feed in ON. This gets over that critical point when the batteries are getting above say 90% (just when they want to start throttling back the MPPT), often late morning when the solar irradiation is getting to its highest!! I have found that with my batteries (Pylon) when they are at 100% I can switch to feed in and the charge/discharge current is minimal even though I may be feeding 2kW to grid. But it is a PITA to have to watch it all the time.
In light of this post I have done a simple test of lowering MPPT max charge current (easy to do in Victron Connect) and with my system it does respect this regardless of DC feed in switch position!
Here's an example of a typical "small" system with Multi-2 48V 3000/35/32/GX, 2x MPPT 150/35, 2x Pylon US2000C. So, at max the 2x MPPT could put out 70A which is greater than the 2x Pylon CCL of 50A. By changing the MPPT max charge limit to 25A they will not produce more than 50A...? This appears to be the case (you could lower it further if desired?). Its not a perfect answer... but I believe it does give a limited safety net. With this system it is not restrictive since the inverter is only rated at 2400W continuous anyway so I am not really exporting less than I want to.
