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Dave avatar image
Dave asked

Smart Solar MPPT doesn't resume charging after full charge is met

My Smart Solar MPPT 100/50 charges my 4 x 100ah lithium batteries by midday at the moment and solar charging is terminated when the full charge threshold is met.


This is my first season with uprated solar panels (now using 2 x 60 volt 330watt Hitachi panels) and I have never seen full charge characteristics before and I am not sure what the correct behaviour should be, but I am noticing that after several hours, my batteries are discharging and the solar controller doesn't cut back in and resume charging.


If I go into the mppt settings and disable charging and then re-enable it again, I see normal charging resume again.


What is considered normal behaviour once the batteries are starting to become discharged, for example down to 95%?


smart solar charging behaviour
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Mark avatar image
Mark answered ·

Based on the MPPT & BMV plots provided, it seems that you have multiple charge sources.

The MPPT will stop providing charge current once the set absorption voltage is achieved. The other charge source is raising the battery voltage to a higher voltage compared to the MPPT absorption voltage.

Following this the MPPT will likely move into float charge phase, meaning a lower charge voltage setpoint.

So the MPPT will not start charging again until the battery voltage falls below the float voltage setpoint or the charge cycle is restarted.

If you want the MPPT to always 'lead', then you need to set the charge voltage setpoints of the other charge source lower than the MPPT charge voltage setpoints.

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Dave avatar image
Dave answered ·

Thanks for your reply Mark


I am rather embarrassed to say that you are right and on the example that I provided, I chose a day when we cruised the boat and the alternator was charging. Anyway well spotted.

Today however we have had great sunshine and the solar shut off charging as the 14.2 volt upper threshold was passed (with current also below threshold). After boiling the kettle and using other high consumer appliances, the state of charge has dropped to 92% with battery voltage at 13.4v with a current outflow of 5.6amps. The solar panels still have full sunshine yet the MPPT isn't outputting anything and the batteries continue to discharge. I have been into the battery menu in the solar app and disabled and then re-enabled charging and immediately I can see a healthy charge rate again.


I have attached another screenshot to showcase today's events.


What am I missing?

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Mark avatar image Mark ♦♦ commented ·

Hi Dave,

No problem.

Based off your latest VRM data provided - I can see that the solar charger stops charging completely after absorption phase is complete.

My first thought is that you have possibly set your MPPT float charge voltage super low (incorrectly), so the charger wont start charging again until the battery drops to that level- can you please provide some VictronConnect screen images of all your MPPT settings?

Also the VRM graph from the same time period showing MPPT charge state would also be helpful.

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edvanz avatar image
edvanz answered ·

Re-bulk voltage offset Set the voltage offset that will be used over the float voltage setting that will determine the threshold that the charge cycle will restart. E.g.: For a Re-bulk voltage offset off 0.1V and a float voltage setting of 13.8V, the voltage threshold that will be use to restart the charge cycle will be 13.7V. In other words, if the battery voltage drops below 13.7V for one minute, the charge cycle will restart.

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Dave avatar image
Dave answered ·

Still having problems with my solar not picking back up once full charge threshold is met.


Today I happened to look and I was down to 87% with full sun availabile all day.


I have gone with the Victron preset for lithium batteries and I don't understand why I have to manually switch off and then switch back on charging, for normal service to continue.


Here is today's screenshot if anyone can help?......



20200530-172604.jpg (416.0 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

"I have gone with the Victron preset for lithium batteries "

The mppt does not seem to be following that preset. It has not held 14.2v for 2 hours (absorb), and not holding 13,5v at float.

Check the preset again.

Check the mppt firmware version?

What firmware is the venus running?

A screenshot of the [Mppt State] would be informative.

Are you running any assistants or ESS?

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Dave avatar image Dave klim8skeptic ♦ commented ·

Sorry klim8skeptic, I missed your reply.


I am unsure what this comment means sorry.... "Are you running any assistants or ESS?""



Hopefully here are the details you requested.....


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klim8skeptic avatar image klim8skeptic ♦ Dave commented ·

You seem to be running a beta firmware version in your GX device (v2.60~25)??

The mppt seems to be set up correctly, with the current firmware version.

I would not expect ESS to be applicable to a mobile system.

You do seem to be SmartNetworking the bmv with the mppt. Have you also enabled DVCC on your GX device?

Also post a screenshot of your Mppt State, eg

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charger-state.jpg (14.4 KiB)
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Dave avatar image
Dave answered ·

Okay this is still ongoing and I am having to cycle the "enable solar" every day at the moment due to the full charge shutoff being reached before midday. By 15:00 hours I am discharged to 90% soc and the MPPT outputs nothing.


The latest victron connect update introduces a new "reason for solar off" feature which is quite cool, however when I am seeing zero solar output, there is no reason displayed, which suggests to me that the MPPT isn't actually off. Indeed the status displays that it is in bulk mode. (see screenshot)


I wonder if I have a faulty unit.







screenshot-20200624-151408.jpg (280.1 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

2 thoughts.

Unplug the mppt from the gx device (VE Direct cable). To rule out gx/mppt device interference, mppt will then operate in regular stand alone mode, and mppt can still be recorded via Victron Connect.

Reset the mppt to defaults (factory reset?). Just cause a reset might flush bad data out of the mppt. (and it wont hurt any thing to do a full reset/power cycle)

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Dave avatar image Dave klim8skeptic ♦ commented ·

Thanks for the reply


I have done a restore defaults reset and removed the MPPT from the VE bus bluetooth network but I will pull the cable as you suggested and hopefully forcing it to run in standalone mode, it might behave properly.


I will update when I have more information.


Thanks for the continued support.

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redsam avatar image redsam Dave commented ·
hello Dave

just wondering if you still have the problem with you MPPt charger

i have the same problem and i can't find any help around

Thanks

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nuvink avatar image nuvink Dave commented ·
Hello Dave


Thanks to update if you resolved the issue. I am also having this problem on 1 MPPT (out of 2 connected in parallel) not resuming charge after battery drops down from full. A manual reset of the MPTT gets it going, but the issue comes again the next time battery reaches 100% and starts discharging.

I am using a BMS LFP bank and the MPPTs are always showing External Control status, which is normal. What is not normal if that 1 MPPT will resume charging but the other gets stuck.

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