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buddhafragt avatar image
buddhafragt asked

MPPT charge current too low

I have a strange problem:
I have 2 MPPT 100/20 in parallel and a Venus/Rasperry firmware 2.94 with a DIYBMS via CANBUS.
If I have now switched on both MPPTs, MPPT1 has e.g. 300W, MPPT2 80W. If I switch MPPT1 off, MPPT2 has 380W.
But this is not always the case. After switching the MPPTs on and off a few times, it works again sporadically.
The maximum charging power is controlled by DVCC and is set to 40A, in the MPPT setup I see 20A in each MPPT. So there should be no power limitation.
It doesn't seem to be a defective MPPT either, I've already replaced it, the Firmware is the actual 1.61
Is this a Venus bug?

MPPT ControllersVenus OSRaspberry Pi
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kevgermany avatar image kevgermany ♦♦ commented ·
What voltage are your batteries?

What is the battery SOC?

What CCL is the BMS setting?

What power are your panels?

Is it winter or summer where you are?


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buddhafragt avatar image buddhafragt kevgermany ♦♦ commented ·
the battery is a 15c with 49.5V - 3.30V/cell, SOC 60%, at this Voltage the current is set to 40A. The panels have 3000W peak. We are in the tropics here, the sun is mostly the same.

I think it is not a setup problem, because after some times switching on and off the inverters and the Venus is it running correctly. But latest next morning the error occur again.


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Alexandra avatar image Alexandra ♦ buddhafragt commented ·

Are all the components programmed correctly and the same? Are you off grid or on grid? What other programming do you have on the inverters?

Unplug the BMS and see if that changes anything.

You can under DVCC remove battery BMS control but some batteries ignore and control it anyway.

It is not a bug, more likely set up related. If it was a big we would see alot more posts about it when the charging is low, are the batteries near full voltage?

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buddhafragt avatar image buddhafragt Alexandra ♦ commented ·

I am off-grid. I think, the BMS take control over the MPPTs, so all the setup in the MPPTs is not working!?

DVCC can not switched off manually, only if the BMS is deatached. If I unplug the BMS the MPPTs stop working, this is normal behavior.

In my post below, you can see, how the MPPTs start working again without any setup change or voltage change at the battery. The question is why??

Maybe the BMS sending something unwanted to the Venus, can I check it somewhere?

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3 Answers
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buddhafragt answered ·

I made some research and see in Node-Red the MPPTs report "1: Voltage or current limited", I would rather expect: "2: MPPT tracker active".

I dont know if it is important, in Victron Connect APP I see 20A max. charge current....

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Alexandra avatar image Alexandra ♦ commented ·

20A is the charge current max (hence the name 100/20 - 100v PV max and 20A charging.)

How much PV do you have attached to each MPPT? What is your battery system voltage?

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buddhafragt answered ·

bildschirmfoto-2024-02-10-um-124458.png

Sometimes it is OK again, in the chart you can see at 10:30 the charge seems to be limited to around 300W, then at 12:30 full power again...


bildschirmfoto-2024-02-10-um-124458.png (34.4 KiB)
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kevgermany answered ·

There's a value, charge current limit (CCL). You see it in the battery monitor(I think) stats in VRM. Should be there in Node-red. Would be good to see that. If that isn't limiting things, perhaps there's an intermittent cable fault.

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buddhafragt avatar image buddhafragt commented ·

all seems OK.... can I monitor the max voltage the BMS is sending?

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Alexandra avatar image Alexandra ♦ buddhafragt commented ·
Yes the CVL. Also sent by the battery.

There is a widget in VRM advanced for batteries.

On the GX itself under the battery in device list is the parameters and details is where you find information.


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buddhafragt avatar image buddhafragt Alexandra ♦ commented ·
thank you, found it!



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