MPPT outputs 16.6v when BMS turns charging off

DIY
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1

Hi.
I’ve got
Victron 100/30 MPPT
Victron Cerbo GX
FogStar Drift Pro 560Ah 12V with BMS
2 x 175w Renogy OCV 21.6V
DVCC turned on and settings checked.

Everything runs fine until the battery decides that it needs to turn off charging as it is full. At that point the voltage creeps up over ~30 seconds and settles at 16.6V

I first spotted the issue as my Truma system started complaining of high voltage.

The MPPT controller is set as a preset of “Smart Lithium (LiFePo4)”
Absorption voltage - 14.2V
Float voltage 13.5V
Equalization voltage disabled.

I’ve spoken with the company that supplied all the Victron kit and also directly to FogStar without success of understanding the issue.

The issue seems to be the signal that the Cerbo receives from the BMS (or doesn’t).
The MPPT works fine when disconnected from the Cerbo or if the BMS is disconnected.

Has anyone come across this issue before?
Any ideas of where to look next?

2

Cap your voltage in DVCC to the 14.2v and see if that helps.

I do find it strange though. I have not seen that.
It may be something to do with the way the bms cvl and cv limits.

3

Cheers. I should have said… I’ve checked that and it’s set to 14.2V

4

Is the bms requesting a higher voltage?

5

Thanks, I’m not sure how I would know.

I’ve got the password for the advanced settings and there isn’t anything obvious.

6

On the gx under the battery parameters it will be visible there.

7

It’s set as 14.7V and charge / discharge limits are 600V.

Is there a way to get at the Cerbo GX logs?

8

600A not volts - fat fingers…

9

Lol. I sometimes cringe at my spelling mistakes.

The logs require either vrm logging you can set up some widgets there.
(or ssh in for deeper stuff. But that is out of my wheelhouse there.)

10

FogStar has some kind of app to allow you to change the requested voltage?

You could ssh root@ip address into the Cerbo and run:

candump -c -a -n40 -e -x can1

to see what the BMS forwards.

11

Hi / thanks, yes it does but… I’ve checked the parameters and nothing looks untoward.
I’ve been speaking with the tech department at FogStar and they don’t believe this is the issue.
Maybe / maybe not.

I’ve ssh’d and run the candump but it’s not overly readable / make sense.

12

Please share the dump so that we can have a look at it. If it is something that the BMS forwards, it will be clearly visible. For trained eyes.

13

Here you are…thanks

image
image463×739 27.5 KB

14

If the BMS is stopping charging by requesting CCL = 0, then this is not an isolated case…

I was/am in a similar situation, on a 48V system where the voltage is jumping to over 60V.

Some experts here will say that’s normal, because in that moment the power has nowhere to go…
If someone could tell me which “power” could be that, when seconds before the event the battery was charging with smaller currents than 50mA, as it was at CVL (which at about 50V means 2.5W !!!) then I can accept it. Otherwise is just BS.
More than this, imagine that Victron, instead of correcting this behavior, has even made a script that follows the voltage and if 3 consecutive readings are over a certain voltage, it simulates a fuse blow… :zany_face:

15

351 [8) 93 00 70 17 70 17 6C 00

Ok. So the charge voltage that the BMS requests is set to 14.7 Volt

16

Parameters from dump are:
CVL = 14.7V
CCL = 600A
DCL = 600A
DVL = 10.8V
But, also according with the dump, those are requested when the SOC is 58%, so not so relevant…

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17

Thanks… Mine settles out at 16.6V so if yours settles out at 66.4V then what you said makes perfect sense.

I suspect that the 16.6V is an upper limit based on configuration of the MPPT.
So if our batteries aren’t sending a ‘clean’ signal then your suggestion about simulating a blown fuse or ensuring the DVCC forces the configured maximum charge voltage sounds like a good call.

18

Not my suggestion… Read carefully, it’s a Victron idea and IMHO, it’s not a solution.

1 Like
19

Thanks.
" those are requested when the SOC is 58%, so not so relevant…"
As it happens my SOC is 58% - therefore is that too much of a coincidence?
ie
But, also according with the dump, those are requested when the SOC is 58%, so not so relevant…

20

Not a coincidence… It’s there in your CAN dump, at line that begins with 355… :slight_smile:
That 3A hex represents 58 in decimal.

You said that the overvoltage happens when the battery is full.
That means that it will be better to make that candump when the SOC is 100% and the voltage is 16V, to see the BMS requested parameters at that moment, not now when SOC is 58%.