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tverweij avatar image
tverweij asked

MPPT Max Charge current not using BMV Battery current

I have a BVM712 Smart, that is transmitting Battery Voltage and Current sense. And I have a Smart Solar MPPT 150/85 that is receiving Battery Voltage and Current. The are in the same VE.Smart network. Firmware of the BVM is 4.12 and the firmware of the MPPT is 1.61

I have set the Max Charge Current in the MPPT (settings menu: Battery) to 26 A to make sure my battery is charged at 1C (my battery bank is 260 Ah).

When I look what happens now, is that when I have a load of 10A, the battery wont charge higher than 16A. With a load of 20A, only 6 A is charged into the battery.

This means that this setting is limiting the charger output instead of the battery input as provided by the BVM712.

I think this is a bug in the MPPT firmware.

As the setting clearly says "Max CHARGE current", and the charge current is provided by the BVM - the current measured by the MPPT itself is the charge current + load, so it should use the BVM value instead.



bug reportcharge current limit
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
26A is only 0.1C for a 260Ah battery.

1C would be 260A

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kevgermany avatar image
kevgermany answered ·

@tverweij

To be clear. The BMV cannot control the MPPT in your current installation. It simply reports what it measures.

So MPPT output is permanently limited to 26A by your settings. As you're seeing, current to the battery will always be MPPT output - loads.

As @snoobler said, you must add a GX device to gain the control you expect. This will control the MPPT and allow battery charging at 26A. But if there's insufficient solar, load will take priority.


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mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi all,

I never looked at it this way, but I can see how the label "charge current" of that setting can be confusing, especially when having paired the solar chargers with a BMV via VE.Smart Networking.


The reason that it doesn't work like that is that the update rate of the Current Sense coming from the BMV is slow; and unreliable: Bluetooth packets get lost now and then. To make a stable current control loop on that is not straightforward.


I'll take the comments both on the name of the setting as well as this potential improvement and see what we can do on that in the future.


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tverweij avatar image tverweij commented ·
Thank you for this answer.


For the slow update from the BVM - something is beter than none; there will be some peaks but the BVM measurements will keep the peaks short instead of the continuous high charge that I have now when the load is switched off.

Some more on the situation: I live offgrid, running on Solar only, depending on the batteries for my complete household (Tropical, so always enough sun). This story was about my first array that is now 4 years old and the batteries starting to ware. I am building the second array now (twice as big) and I want to apply what I learned in the last 4 years, hoping that this array will last longer. Therefore I made this request.

And about the resistence I have against computer - its not only the cost. Its about a lot of other equipment (including cars) that failed miserably because of computer failures. So I try to keep the amount of computers I have to depend on as low as possible.


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snoobler avatar image
snoobler answered ·

The MPPT is a charger, and it can work independently with no other devices connected, so this value is intended to set the maximum output of the MPPT. Since it's a charger, it's called "charge" current. You are extrapolating additional desired function. If this value didn't behave as you observe, there would be no way to limit total output from the MPPT.


You want features not available at this hardware level.


The function you seek is available with the addition of a GX device and the DVCC feature. The DVCC can manage ALL connected chargers to limit CHARGE current to what is specified in DVCC while allowing all sources to provide additional current as loads require.


For the above DVCC function to work, you would need to set the MPPT to 85A. If you left it at 26A, the MPPT would continue to limit output to 26A.





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tverweij avatar image tverweij commented ·

"If this value didn't behave as you observe, there would be no way to limit total output from the MPPT.

Why should you want to limit the output of the MPPT instead of the battery charge current (that is known)?

I can not think of a reason to want that,

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snoobler avatar image snoobler tverweij commented ·
MPPT can function with no other devices. Flooded Lead Acid batteries may not be able to handle the full array output, so one would need to restrict current via this setting.


Again, to get the function you want, you need a GX device and DVCC enabled.

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tverweij avatar image
tverweij answered ·

You both say that the BVM cannot control the MPPT and that may be true.

But the MPPT is already measuring the tail current using the BVM information and correcting its output accordingly. So, it is already taking the current measurements of the BVM in account at that stage - and that is why I think it is a bug that it is not taking it in account for the maximum charge current; it is clearly able to do that, it just won't as this is not programmed into it.

And as that is illogical, I call this a functional bug as a programmer.

Hoping for an answer of someone at Victron itself - not from resellers or hobbyists.


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snoobler avatar image snoobler commented ·
You may see it as a functional bug, but you're not acknowledging that you want a feature for which a solution already exists, yet you don't want to spend the money necessary to get it.


Not all options are available on all products.

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kevgermany avatar image kevgermany ♦♦ commented ·
No. The MPPT is not measuring tail current. This is controlled by the battery alone.


The MPPT simply works on voltage. NOT current.
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snoobler avatar image snoobler kevgermany ♦♦ commented ·

I think they're referring to this:


https://www.victronenergy.com/media/pg/VE.Smart_Networking/en/voltage,-temperature-and-current-sense---further-details.html


The MPPT uses the shunt current for tail current instead of the MPPT measured current.

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tverweij avatar image tverweij snoobler commented ·
Correct - If it can do it for the tail current, it can do it for the Charge current.


I am just asking for something that Chinese Junk can easily do and is missing on the state of the art, expensive Victron equipment, that can only do it when you spend even more money.

Not a really important request, only needed to extend the lifetime of the batteries (also Victron), so nothing serious at all.


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snoobler avatar image snoobler tverweij commented ·
Problem:

You want a feature not available at this price point.


Solution:

Get a GX device or RPi running VenusOS, connect MPPT and BMV, enable DVCC and SVS/SCS. Set desired charge limit. Gain functionality you seek.


Alternative:

Scream into the void because you think it should already be available.

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tverweij avatar image
tverweij answered ·

Well, let me say - I learned a lot from this topic.

When I started it - I did not expect to get so much hate. How did I dare even suggesting that the current behavior could be a (functional) bug? It looks like I am touching someones earning model.

But for sure, as Victron itself did not intervene, from the answers I have to conclude that - when you buy Victron equipment for several thousandth of Euro's (one Phoenix, one Quattro, two Skyllas, two SmartSolars, one BVM, nine battery balancers) you can not expect that this equipment will charge your battery in the correct way in the pricerange I bought.

I have now limited the charger to 0.2C (52A) to create an acceptable max charging and also an acceptable range for the load. But it is strange that such expensive equipment can not do it right,

As you see on top, this thread has been reported to Victron. I was the one who did that to inform them about this thread.

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falkon avatar image
falkon answered ·

Hello, I have found this topic because I am wondering about the same question as OP did one year ago.

I would really like to see, that the SMART MPPT charger will take into account the battery current (Isense) to adjust produced current for charging and load.

While the answer like "This is unsupported feature for now" is somehow valid, it is also very legitimate to suggest new features to Victron, so that they can potentialluy add new features into the new firmware versions.

The SmartSolar MPPT chargers do have SMART in their name. The VE.Smart is fully supported in the recent models. SmartShunt (and all other BMV-like devices) are VE.Smart compatible, and are offering the Isense.

So why not to implement a simle logic, that would adjust Output Current based on the Isense?


This irequest is definitely NOT against its stand-alone working capabilities - if the MPPT charger does NOT receive "Battery Current" values, it will work as previously: OUTPUT current = Max Charge Current.

BUT, if the Battery Current IS available, it will be SMART enough to take them into acount, so: OUTPUT current = Max Charge Current + Load


And while GX devices implement these capabilities, it always adds some complexity to the system,so.need not to be preferred by all users.

I believe that the suggested improvement deserves to be part of the Smart MPPT product ranges, because it is the way how many users will expect it to work when they connect SmartShunt/BMV with MPPT charger (like me).

Many thanks to Victron for their awesome products and I hope they may consider this feature request.

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Justin Cook avatar image Justin Cook ♦♦ commented ·

"Smart" indicates only the presence of Bluetooth comms, there is no other meaning. The capability of each Victron "Smart" device to communicate with other components via bluetooth is device-specific, and generally laid out in the device's user manual.

Note mvader's response above, as to why the requested functionality is not currently available, the issue with making it available, and the extent to which such functionality will be considered both in feature naming as well as possible future product development.

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